Part I
"To illustrate the practical importance of knowing the effects of reiterated heating and cooling on iron plates, one of the most obvious examples is the action of heat upon the plates of boilers which are alternately heated and cooled, as in use or otherwise. When in use, the plates above the fire are subjected to the fierce flame of the furnace on one side, and on the other side to a temperature approximating to that of the steam and water in the boiler. Where the conducting surfaces of the metal are thickened at the riveted seams, a source of danger is frequently revealed in the appearance of what are known as 'seam-rips.'
"The long egg-ended boilers, much used in the North of England, are very subject to this breaking away of the seams. From some tests made by the writer on iron cut from the plates of two different boilers which had ripped at the seams, and one of which seam-rips had led to an explosion resulting in the destruction of much property, though happily of no lives, it was found that the heat acting on the bottom of the boiler had, through time, so affected the iron at the seam as to make it brittle, apparently crystalline in fracture, and of small tensile strength. Farther from the seam the iron appeared in both cases less injuriously affected. But although the alternate heating and cooling of the plates over a long period had produced this change in the molecular condition of the iron, a method of restoration presents itself in the process of annealing. In subjecting the pieces cut from the seam-rips to a dull red heat, and then allowing them to cool slowly in sawdust, the writer found that the fibrous character of the iron appeared again, and renewed testing showed that the ductility and tensile strength were restored.
"The same process of annealing is equally effectual in restoring the tenacity of iron in chains rendered brittle, and apparently crystalline, by long use, and is periodically applied where safety depends upon material in this form. Thus the heating and cooling of iron may be looked upon as the bane or the antidote according to the conditions under which the process is carried out. This affords an example of the importance of the physical effects produced by repeated changes of temperature. The change effected by one heating and cooling is so small that a cumulative method of experiment is the only one by which an observable result can be obtained, and this is the method adopted by the writer in the investigation now to be described.
"It is well known that if a wrought-iron bar be heated to redness, a certain expansion takes place, which is most distinctly observed in the direction of its length. It is also known, although not generally so, that if a bar be thus heated and then suddenly cooled in water, a contraction in length takes place, the amount of this contraction exceeding that of the previous expansion, insomuch that the bar when cooled is permanently shorter than it originally was. If this process of heating and cooling be repeated, a further amount of contraction is found to follow for many successive operations.
"Experiments Nos. 1 and 2 were made to verify this, and to show the increment of contraction after each operation.
"EXPERIMENTS ON WROUGHT-IRON BARS 1-1/8 IN. SQUARE BY 30.05 IN. LONG, HEATED TO A DULL RED, THEN COOLED SUDDENLY IN WATER.
------------------+------------------------+------------------------ | EXPERIMENT NO. 1. | EXPERIMENT NO. 2. | Common Iron. | Best Iron. +------------+-----------+------------+----------- | |Percentage | |Percentage |Contraction.|on original|Contraction.|on original | | length. | | length. ------------------+------------+-----------+------------+----------- | Inches. | | Inches. | After 1st cooling | .04 | .13 | .04 | .13 " 2nd " | .10 | .33 | .10 | .33 " 3rd " | .16 | .53 | .14 | .46 " 4th " | .17 | .56 | .16 | .53 " 5th " | .23 | .76 | .20 | .66 " 6th " | .28 | .93 | .24 | .80 " 7th " | .31 | 1.03 | .27 | .89 " 8th " | .33 | 1.10 | .30 | 1.00 " 9th " | .40 | 1.33 | .33 | 1.10 " 10th " | .47 | 1.56 | .39 | 1.30 " 11th " | .52 | 1.73 | .42 | 1.40 " 12th " | .54 | 1.80 | .47 | 1.56 " 13th " | .58 | 1.93 | .51 | 1.70 " 14th " | .62 | 2.06 | .54 | 1.80 " 15th " | .68 | 2.26 | .56 | 1.86 ------------------+------------+-----------+------------+-----------
"The Table of Experiment No. 5 shows that at the twenty-fifth cooling a contraction of 3.05 per cent. had taken place, or an average of .122 per cent. after each cooling. This is almost identically the same average result as shown in Experiment No. 1 with straight bars.
"The above experiments only having reference to the permanent contraction of the iron in the direction of its length, the author made the following experiments to ascertain the effect in the other dimensions, and to see whether the specific gravity of the iron was affected in the reduction of dimensions.
"Experiment No. 6.--Wrought-iron plate, .74 inch thick, planed on both surfaces and all edges to a form nearly rectangular, and of the dimensions given in Fig. 1429.
"Specific Gravity.--Two small samples were cut out of different parts of the same piece of plate from which the experimental piece was planed, and the specific gravity determined as follows:--
No. 1 piece 7.629 } No. 2 piece 7.651 } Mean, 7.64.
"Quality.--Subjecting a piece to tensile strain in the direction of the grain, it broke at 21.2 tons per square inch of section, the ductility being such that an elongation of 8.3 per cent. occurred before fracture, with a reduction of 9.6 per cent. of the area of fracture. This may be looked upon as representing a fairly good quality of iron.
"A bar of wrought iron, 1-1/8 inches square and 30.00 inches long, was heated to redness, and then allowed to cool gradually in air. Measurements after each of five coolings showed no perceptible change of length.
"Experiment No. 4.--Wrought-iron bar, 1-1/8 inches square by 30 inches long, heated to a white heat and cooling gradually in air.
------------------+------------+----------------+---------------- |Contraction.| Percentage on | Remarks. | |original length.| ------------------+------------+----------------+---------------- | Inches. | | After 1st cooling | No change. | | ---- " 2nd " | " | | ---- " 3rd " | .02 | .07 | ---- " 4th " | .05 | .17 | ---- " 5th " | .05 | .17 | ---- ------------------+------------+----------------+----------------
"It may be remarked, that if the bars be heated to white heat a slight contraction does occur, as shown by Experiment No. 4, where a bar of the same dimensions as No. 3 contracted .17 per cent. after the fifth cooling. As, however, the further remarks on this subject have only reference to bars heated to redness and then cooled, the writer would summarize the results of Experiments Nos. 1, 2, and 3, by stating that wrought-iron bars heated to redness permanently contract in their length along the fibre when cooled in water of ordinary temperature; but when cooled in air, they remain unchanged in length.
"To show that this is true as applied to circular hoops, Experiment No. 5 was made upon a wrought-iron bar of 1-1/8 inches square in section, welded into a circular hoop, 57.7 inches outside circumference.
"Experiment No. 5.--Wrought-iron hoop, 1-1/8 inches square by 57.7 inches outside circumference, heated to a dull red, then cooled suddenly in water.
------------------+------------+--------------+----------------------- | |Percentage of | |Contraction.| original | Remarks. | |circumference.| ------------------+------------+--------------+----------------------- | Inches. | | After 1st cooling | .06 | .10 | Red heat. " 2nd " | .06 | .10 | This was nearly white, " 3rd " | .16 | .28 | but before cooling " 4th " | .26 | .45 | red hot. " 5th " | .35 | .61 | " 6th " | .46 | .80 | " 7th " | .54 | .93 | " 8th " | .60 | 1.04 | " 9th " | .68 | 1.18 | " 10th " | .76 | 1.32 | " 11th " | .80 | 1.38 | " 12th " | .87 | 1.51 | " 13th " | .94 | 1.63 | " 14th " | 1.00 | 1.73 | " 15th " | 1.08 | 1.90 | " 20th " | 1.30 | 2.25 | On opposite edge 1.66; " 25th " | 1.76 | 3.05 | hoop splitting. ------------------+------------+--------------+-----------------------
"This hoop was heated to redness and cooled in water twenty-five times, the circumference of the hoop being accurately measured after each cooling.[23]
[23] The lengths of circumference were taken, in this and other hoops, after each cooling, by encircling the periphery with a very fine piece of "crinoline" steel, the ends of which were made just to meet round the original hoop. By again encircling the hoop with the same piece of steel the expansion was shown by a gap between the ends, and a contraction by an overlap, either of which was measured with great accuracy by means of a finely divided scale.
"Two wrought-iron bars, 1-1/8 inches square and 30.05 inches long, were selected.[24] No. 1 was of common "Crown" quality; No. 2 of a superior quality known as "Tudhoe Crown." These bars were heated to redness in a furnace and then plunged into water of ordinary temperature, the length being accurately measured after each cooling. After fifteen heatings and coolings the permanent contraction on No. 1 bar was 2.26 per cent. of the original length, and that on No. 2 bar 1.86 per cent., or an average on the two bars of about .13 per cent. after each cooling, the increment of contraction being nearly equal after each successive operation. It is noticeable that after the first two coolings the better quality of iron did not contract quite so much as the common quality, and that in the latter the contraction was going on as vigorously at the fifteenth as at the first cooling.
[24] In some of these experiments the original sizes of the iron were only measured with an ordinary foot-rule, in which case the dimensions are given in the ordinary fraction used in expressing the mercantile sizes of iron. When accurate measurement was taken decimals are invariably used both in this paper and the Tables of Experiment.
"Similar bars of wrought iron, heated to redness and then allowed to cool in air at ordinary temperature, do not appear to suffer any permanent change in their length.
"Experiment No. 3 was made to verify this.
"Experiment No. 3.--Wrought-iron bar, 1-1/8 inches square by 30 inches long heated to a dull red and cooled gradually in air.
------------------+------------+----------------+----------- |Contraction.| Percentage on | | |original length.| Remarks. ------------------+------------+----------------+----------- After 1st cooling | No change. | ---- | ---- " 2nd " | " | ---- | ---- " 3rd " | " | ---- | ---- " 4th " | " | ---- | ---- " 5th " | " | ---- | ---- ------------------+------------+----------------+-----------
The plate was subjected to fifty heatings to redness and subsequent coolings in water of ordinary temperature. At every tenth cooling accurate measurements were taken of the contraction in superficial dimensions, and Fig. 1430 shows the final form after fifty coolings. The intermediate measurements at every tenth cooling showed a uniform and gradual decrease in the superficial dimensions, but the thicknesses were only measured after the fifty coolings had been completed. The thickness appears to have varied considerably; in some places, notably towards the centre and outside edges, being much reduced. Between the centre and outside edges the thickness appears to have increased, and in some few places the plate has been split open. The average dimensions in inches before and after the experiment were as follows (dimensions of cracks being allowed for):--
----------------------+---------+----------+----------+----------- | | | | Cubic | Average | Average | Average | inches | length. | breadth. |thickness.|capacity. +---------+----------+----------+---------- | Inches. | Inches. | Inches. | Original | 11.995 | 5.98 | .74 | 53.08 After 50 coolings | 11.25 | 5.59 | .774 | 48.72 Per cent. variation { |Decrease |Decrease | Increase | Decrease from original { | of | of | of | of { |6.2 p. c.|6.52 p. c.| 4.6 p. c.| 8.2 p. c. ----------------------+---------+----------+----------+----------
"Three triangular pieces of iron were then cut out of the plate from positions indicated on the diagram; No. 1A from the part most reduced in thickness, No. 3A from the part most increased in thickness, and No. 2A from a part where the thickness was a mean between the thickest and thinnest part. The specific gravities were accurately determined as follows:--
No. 1A 7.552 thinnest part. No. 2A 7.574 average thickness. No. 3A 7.560 thickest part.
"The average of these specific gravities is 7.562.
"The average before experiment was 7.64. Hence the average loss in specific gravity has been 1.02 per cent.
"The small triangular piece No. 1A, specific gravity 7.552 (already subjected to fifty heatings when forming part of the solid plate), was next heated and cooled fifty times more. The specific gravity at the end of the one hundred total coolings was 7.52, being .43 per cent. lower than after fifty heatings in plate, and 1.57 per cent. lower than 7.64, the original mean specific gravity of the plate.
"The same piece, 1A, was then heated twenty-five times more, making 125 in all. On taking the specific gravity it was found to be 7.526, or practically the same as after 100 total heatings and coolings.
"It thus appears that there is an undoubted decrease in specific gravity on repeated heating and cooling as described up to one hundred coolings, the specific gravity decreasing as much as 1.57 per cent.; that this percentage appears to be less when the pieces of iron operated upon are very small; that while there is a decrease of specific gravity there is also a decrease of total volume.
"From the above it was evident that the volume was affected by several causes:--
"1. By the permanent contraction of the outer skin, either the volume would be lessened, or relief by bulging out the sides must occur.
"2. By the decrease of specific gravity an increase of volume must occur, which could also find relief in bulging.
"3. A diminution of the whole mass must occur through scaling of the surface.
"Having determined the change in specific gravity by Experiment 6, we only now want to determine the loss of volume due to surface scaling, and we can then infer the actual contraction of the outer skin.
"Experiment No. 7.--To ascertain the amount of scaling which took place in heating and cooling under same conditions as Experiment No. 6, a wrought-iron plate was cut from the same piece as No. 6, thickness .74 in., planed on both surfaces and all edges to a form nearly rectangular, and to the dimensions given in Fig. 1431.
"The only difference (except the very small difference in the dimensions) between this and 1430, was that the principal grain of the iron was in 1431 in the direction of the arrow, whereas in the other it was lengthwise of the plate.
"This piece was subjected to fifty heatings to redness and sudden coolings in water of ordinary temperature, as in the case of No. 6. The change in form was exactly the same in general character, but the contraction was not quite so great either in length or breadth; the increase in thickness, however, was proportionately greater, the volume (measured by displacement of water) after fifty heatings being 48.6 cubic inches, which is nearly the same as in No. 6 after the same number of heatings. The weight of the piece:--
Avoirdupois. lbs. oz. dr. Before heating 14 10 15 After fifty heatings 13 5 10 ------------ Difference 1 1 5
"This represents a loss of 9.07 per cent. of the original weight by scaling, and upon the whole original surface (sides and edges) represents a thickness of .0284 of an inch for the fifty immersions, or .00057 of an inch for the thickness of the film lost at each immersion over the whole surface.
"Calculating the weight of No. 6 before and after experiment from the volumes and specific gravities, we find the following:--
Mean Weight of specific cubic inch Volume. gravity. water. Pounds. Weight before heating should be 53.08 × 7.64 × .036 = 14.599 " after " " 48.72 × 7.562 × .036 = 13.262 ------ Difference in weight 1.337
the ascertained difference in the case of No. 7 being 1.332, thus sufficiently accounting for the discrepancy between specific gravity and change of volume by the scaling.
"By Experiment 7 it has been shown that the loss of thickness due to scaling after fifty immersions was .0284 inch over the whole surface (sides and edges.) Therefore, assuming this scaling as uniform over the surface, the girth, whether measured lengthwise or breadthwise, should be eight times .0284, or .23 inch less after immersion than before. Now the gross loss of girth is:--
--------------------------------------+-----------+------------ |Lengthwise.|Breadthwise. --------------------------------------+-----------+------------ | Inches. | Inches. In No. 6 | 1.38 | .86 In No. 7 | 1.2 | .52 +-----------+------------ Or for both experiments a mean of | 1.29 | .69 Deducting from them the loss of | | girth due to scaling | .23 | .23 +-----------+------------ Net contraction after fifty immersions| 1.06 | .46 Or in percentage of original girths, | | which were | 25.46 | 13.43 | per cent. | per cent. We have a percentage of | 4.16 | 3.42 Or for each immersion an average of | .083 | .07 --------------------------------------+-----------+------------
"Comparing these results with those of Experiments Nos. 1, 2, and 5, we find that the contraction of the skin of the plate is less for each immersion than that of a bar or hoop, in the proportion of .125 to .083. This is what might be expected, as the contraction of the plate is resisted by the volume of heated matter inside, which is eventually displaced by bulging, while the bar finds relief endwise without having to displace the interior.
"We have now before us the following facts, substantiated by the experiments described:--
"1. That in heating to redness, and then cooling suddenly in water at ordinary temperatures, bars and plates of wrought iron, a reduction of specific gravity takes place, the amount being about 1 per cent. after fifty immersions, and 1.57 per cent. after one hundred immersions, further heatings and coolings not appearing to produce further change.
"2. That a reduction of the surface takes place after each heating and cooling, this being due to two causes:--
"a. The scaling of the surface, which is shown to amount to a film over the (sides and edges) entire area of .00057 inch in thickness for each immersion, or 0.284 inch for fifty immersions (Experiment 7).
"b. A persistent contraction, which takes place after each immersion. This varies according to the form of the iron, being in plates from .07 per cent. to 0.83 per cent. (Experiment 6), while in long bars it varies from .122 to .15 per cent. (Experiments 1, 2, and 5). This contraction continues vigorously up to fifty immersions, and probably much farther.
"3. That in the case of plates a bulging takes place on the largest surfaces, increasing the thickness towards the centres, although the edges diminish in thickness.
"4. That wrought-iron bars heated to redness, and allowed to cool slowly in air, do not show any change in dimensions (Experiment 3).
"The reduction of specific gravity, and the bulging out of the sides, have been explained as follows by the learned Secretary of the Royal Society, Professor Stokes, who has taken considerable interest in these experiments, and who has kindly allowed the author to publish the explanation:
"'When the heated iron is plunged into water, the skin tends everywhere to contract. It cannot, however, do so to any significant extent by a contraction which would leave it similar to itself, because that would imply a squeezing in of the interior metal, which is still expanded by heat, and is almost incompressible. The endeavor, then, of the skin to contract is best satisfied, consistently with the retention of volume of the interior, by a contraction of the skin in the two longish lateral directions, combined with a bulging out in the short direction. The still plastic state of the interior permits of this change.
"'Conceive an india-rubber skin of the form of the plate in its first state, the skin being free from tension, and having its interior filled with water, treacle, or pitch. I make abstraction of gravity. It would retain its shape. But suppose, now, the india-rubber to be endowed with a tension the same everywhere similar to that of india-rubber that has been pulled out, what would take place? Why, the flat faces of considerable area, being comparatively weak to resist the interior pressure, would be bulged out, and the vessel would contract considerably in the long directions, increasing in thickness. This is just what takes place with the iron in the first instance. But when the cooling has made further progress, and the solidified skin has become comparatively thick and strong, the further cooling of the interior tends to make it contract. But this it cannot well do, being encased in a strong hide, and accordingly the interior tends to be left in a porous condition.'
"The reduction by scaling does not require any explanation. The only fact which appears unaccounted for is this persistent contraction of the cooled iron skin, which does not appear to be explicable on any mechanical grounds; and we are, therefore, obliged to look upon it as the result of a change in the distance of the molecules of the iron, caused by the sudden change of temperature in the successive coolings.
"Our next subject is the curious effect of cooling bars or rings by partial immersion in water. Bearing in mind the results at which we have arrived, viz., that wrought iron contracts when immersed in water after heating, and that when allowed to cool in air it remains of the same dimensions, let us ask what would be the behavior of a bar or circular hoop of iron cooled half in water and half in air, the surface of the water being parallel to the fibre and at right angles to the axis of the hoop?
"Arguing from the results of Experiments 1, 2, and 5, it might be expected that the lower portion cooled in water would suffer permanent contraction; and, arguing from Experiment 3, that the upper or air-cooled edge would not alter. This apparently legitimate conclusion is completely disproved by experiments. This will be seen by a reference to Experiments 8, 9, and 10.
"In No. 8 a circular hoop of wrought iron was forged out of a 3-1/2-inch by 1/2-inch bar, the external diameter being about 18 inches, the breadth, 1/2 inch, being parallel to the axis of the hoop. This hoop, Fig. 1432, was heated to redness, then plunged into cold water half its depth, the upper half cooling in air. The changes in the external circumference of the hoop were accurately measured after each of twenty successive coolings, at the end of which the external circumference of the water-cooled edge had increased 1.24 inches, or 2.14 per cent. of its original length, and the air-cooled edge had contracted 7.9 inches, or 13.65 per cent.
"Experiment No. 8.--Wrought-iron hoop, 3-1/2 inches by 1/2 inch by about 18 inches in diameter, or exactly 57.85 inches in circumference at top, and 57.95 inches at bottom edge.
-------------+--------------------+--------------------+-------------- | Top Edge. | Bottom Edge. | +--------+-----------+--------+-----------+ |Contrac-|Percentage | Expan- |Percentage | | tion. |of original| sion. |of original| | | circum- | | circum- | Remarks. | | ference. | | ference. | -------------+--------+-----------+--------+-----------+-------------- | Ins. | | Ins. | | After 1st dip| .50 | .86 | .08 | .14 | " 2nd " | .99 | 1.71 | .08 | .14 | " 3rd " | 1.47 | 2.54 | .26 | .45 | " 4th " | 1.92 | 3.32 | .30 | .52 | " 5th " | 2.30 | 3.97 | .34 | .59 | " 6th " | 2.60 | 4.49 | .40 | .70 |Slight crack | | | | |in expanded | | | | |edge. " 7th " | 2.94 | 5.25 | .44 | .76 | " 8th " | 3.40 | 5.98 | .50 | .86 | " 9th " | 3.70 | 6.39 | .56 | .96 | " 10th " | 4.40 | 7.60 | .62 | 1.07 | " 11th " | 4.42 | 7.64 | .66 | 1.14 | " 12th " | 4.85 | 8.40 | .70 | 1.22 | " 13th " | 5.24 | 9.02 | .78 | 1.34 | " 14th " | 5.74 | 9.92 | .80 | 1.39 | " 15th " | 6.00 | 10.37 | .86 | 1.49 | " 20th " | 7.90 | 13.65 | 1.24 | 2.14 |After de- | | | | |ducting for a | | | | |crack .06 inch | | | | |wide which | | | | |appeared at | | | | |sixth dip. -------------+--------+-----------+--------+-----------+--------------
"It will be observed that we have here two remarkable phenomena: 1. The reversal of the expansion and contraction as described. 2. The very large amount of contraction on the upper edge compared with what was exhibited in Experiment 5 of entire submersion.
"The table showing Experiment 5 gives a contraction of 2.25 per cent. after the twentieth cooling, whereas the contraction on the air-cooled edge of Experiment 8 is 13.65 per cent., or six times the contraction of an entirely submerged hoop.
"To ascertain whether these unexpected phenomena had any connection with the circular form of the hoop, Experiment 9 was made with a straight bar of iron 3-1/2 inches deep by 1/2 inch thick by 28.4 inches long.
"Experiment No. 9.--Wrought-iron bar, 3-1/2 inches by 1/2 inch by 28.4 inches long, heated to a dull red, then quenched half its depth in water.
------------------+--------------------+-------------------- | Bottom Edge. | Top Edge. +--------+-----------+--------+----------- | Expan- |Percentage |Contrac-|Percentage | sion. |on original| tion. |on original | | length. | | length. ------------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling | .05 | .18 | .26 | .91 " 2nd " | .10 | .35 | .43 | 1.51 " 3rd " | .10 | .35 | .54 | 1.90 " 4th " | .14 | .49 | .75 | 2.64 " 5th " | .20 | .70 | .92 | 3.24 " 6th " | .30 | 1.05 | 1.25 | 4.40 " 7th " | .34 | 1.20 | 1.50 | 5.28 " 8th " | .38 | 1.34 | 1.56 | 5.53 " 9th " | .39 | 1.37 | 1.66 | 5.84 " 10th " | .40 | 1.40 | 1.76 | 6.19 " 11th " | .41 | 1.43 | 1.84 | 6.48 " 12th " | .44 | 1.55 | 1.96 | 6.90 ------------------+--------+-----------+--------+-----------
"This was cooled half in air and half in water, and the length of the two edges measured accurately after each of twelve coolings. At the end of this experiment the air-cooled edge had contracted 6.9 per cent., while the water-cooled edge had expanded 1.55 per cent. of the original length. The effect on the bar was to make it gradually curve, the water-cooled or extended edge becoming convex, the air-cooled or contracted edge concave.
"Experiment No. 10 was made in order to show the effect of reversing this cooling process. After five coolings, a bar of iron, 28 inches long, 3-1/2 inches deep, and 1/2 inch thick, was curved so that the versed sine of its air-cooled edge was 1-1/2 inches. The coolings were then reversed, what was the air-cooled edge being then immersed in water. After five more coolings the bar was restored to within 1/8 inch of being straight, and the eleventh cooling threw the concavity on the other side of the bar.
"Experiment No. 10.--Wrought-iron flat bar, 28 inches long by 3-1/2 inches by 1/2 inch, heated to dull red, then quenched half its depth in water, up to five heats, then the opposite edge dipped.
-----------+-----------+------------+------------------ | | | Reversed Cooling. | | +------------------ |Versed sine| | Versed sine |of concave,| | of concave, | i.e. | | i.e. now |air-cooled | | water-cooled | edge. | | edge. -----------+-----------+------------+------------------ | Inches. | | Inches. 1st cooling| 5/16 | 6th cooling| 1-3/16 2nd " | 9/16 | 7th " | 7/8 3rd " | 13/16 | 8th " | 3/4 scant. 4th " | 1-3/8 | 9th " | 3/8 full. 5th " | 1-1/2 |10th " | 1/8 | |11th | Brought concavity | | | 1/8 in. on other | | | side. -----------+-----------+------------+------------------
"When the author had proceeded thus far, these curious results were shown to several leading scientific men, who expressed interest in the subject, which encouraged the author to extend his experiments under varied conditions with a view of ascertaining the cause for these anomalous effects. These experiments (Nos. 11 to 17) are fully recorded, and the results shown on the diagrams; the actual rings are also on the table before you.
"Experiment No. 11.--Wrought-iron hoop, turned and bored, 37.1 inches, outside circumference, by 2.95 inches deep by .44 inch thick, the grain of the iron running the short way of the bar from which the hoop was made, heated to redness, then cooled half its depth in water (see Fig. 1437 at A for final form of hoop after ten heatings and coolings).
-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge. +--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |on original| sion. |on original | | length. | | length. -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling| .3 | .83 | .05 | .13 " 2nd " | .64 | 1.72 | .12 | .32 " 3rd " | 1.02 | 2.75 | .22 | .60 " 4th " | 1.38 | 3.72 | .30 | .80 " 5th " | 1.62 | 4.37 | .37 | 1.00 " 10th " | 3.14 | 8.46 | .76 | 2.05 -----------------+--------+-----------+--------+-----------
"Experiment No. 12.--Wrought-iron hoop, turned and bored, 6 inches diameter (18.85 inches circumference) outside, by 2 inches deep by .375 inch thick, heated to redness, then cooled, with lower edge barely touching the water (see Fig. 1437 at B for final form of hoop after twenty heatings and coolings).
-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge. +--------+-----------+--------+----------- |Contrac-|Percentage |Contrac-|Percentage | tion. |of original| tion. |of original |Outside | circum- |Outside | circum- |circum- | ference. |circum- | ference. |ference.| |ference.| -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 5th cooling| .10 | .53 | .16 | .85 " 10th " | .22 | 1.17 | .34 | 1.80 " 15th " | .32 | 1.70 | .48 | 2.54 " 20th " | .48 | 2.54 | .62 | 3.30 -----------------+--------+-----------+--------+-----------
"Experiment No. 13.--Wrought-iron hoop, turned and bored, 6 inches diameter (18.85 inches circumference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled one-fourth its depth in water (see Fig. 1437 at C for final form of hoop after twenty heatings and coolings).
-----------------+--------------------+-------------------------------- | Top Edge. | Bottom Edge. +--------+-----------+-------------------+----------- |Contrac-|Percentage | |Percentage | tion. |of original| |of original | | circum- | Extension. | circum- | | ference. | | ference. -----------------+--------+-----------+-------------------+----------- | Inches.| | Inches. | After 1st cooling| .06 | .32 | .02 | .10 " 5th " | .28 | 1.50 {|A hair's breadth | | | {|contraction. | " 10th " | .56 | 3.00 { |Returned to origi- | | | { |nal circumference. | " 15th " | .78 | 4.14 | .02 contraction. | .10 " 20th " | 1.12 | 6.00 | .02 contraction. | .10 -----------------+--------+-----------+-------------------+-----------
"Experiment No. 14.--Wrought-iron hoop, turned and bored. 6 inches diameter (18.85 inches circumference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled one-half its depth in water (see Fig. 1437 at D for final form of hoop after twenty heatings and coolings).
-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge. +--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |of original| sion. |of original |Outside | circum- |Outside | circum- |circum- | ference. |circum- | ference. |ference.| |ference.| -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 5th cooling| .46 | 2.44 | .06 | .32 " 10th " | .96 | 5.00 | .09 | .48 " 15th " | 1.34 | 7.10 | .18 | .96 " 20th " | 1.80 | 9.10 | .26 | 1.38 -----------------+--------+-----------+--------+-----------
"Experiment No. 15.--Wrought-iron hoop turned and bored, 6 inches in diameter (18.85 inches circumference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled three-fourths its depth in water (see Fig. 1437 at E for final form of hoop after twenty heatings and coolings).
-----------------+--------------------+------------------------------- | Top Edge. | Bottom Edge. +--------+-----------+-------------------+----------- |Contrac-|Percentage | |Percentage | tion. |of original| |of original | | circum- | Expansion. | circum- | | ference. | | ference. -----------------+--------+-----------+-------------------+----------- | Inches.| | Inches. | After 1st cooling| .05 | .26 | .015 | .08 " 5th " | .30 | 1.60 | .02 | .10 " 10th " | .56 | 3.00 {| A hair's breadth | | | {| contraction. | " 15th " | .74 | 3.92 { | .02 |} .10 | | { | contraction. |} " 20th " | 1.02 | 5.40 {| .03 | } .10 | | {| contraction. | } -----------------+--------+-----------+-------------------+-----------
"Experiment No. 16.--Cast-copper ring, turned and bored to same dimensions as Nos. 12, 13, 14, and 15, heated to redness, then cooled half its depth in water (see Fig. 1437 at F for final form of hoop after twenty heatings and coolings).
-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge. +--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |of original| sion. |of original | | circum- | | circum- | | ference. | | ference. -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling| .01 | .05 | .05 | .26 " 2nd " | .01 | .05 | .08 | .42 " 3rd " | .02 | .10 | .14 | .75 " 4th " | .02 | .10 | .17 | .90 " 5th " |} No change from | .22 | 1.17 " 10th " |} original size | .40 | 2.13 " 15th " |} from 5th to | .56 | 3.00 " 20th " |} 20th cooling. | .70 | 3.70 -----------------+--------------------+--------+-----------
"It will be unnecessary to occupy much time in analyzing the experiments, as any one who takes a practical interest in the subject will have full information in the diagrams and tables. Professor Stokes drew attention to the fact that, in 1863, similar phenomena had been noticed by Colonel Clark, of the Royal Engineers. His experiments, made at the Royal Arsenal, Woolwich, were published in the 'Proceedings of the Royal Society,' and Professor Stokes had himself attached an explanatory note, the outline of which was as follows:--
"Imagine a cylinder divided into two parts by a horizontal plane at the water-line, and in this state immersed after heating. The under part, being in contact with water, would rapidly cool and contract, while the upper part would cool but slowly. Consequently by the time the under part had pretty well cooled, the upper part would be left jutting out; but when both parts had cooled their diameters would again agree. Now in the actual experiments the independent motion of the two parts is impossible on account of the continuity of the metal; the under part tends to pull in the upper, and the upper to pull out the under. In this contest the cooler metal, being the stronger, prevails, and so the upper part gets pulled in a little above the water-line while still hot. But it has still to contract in cooling, and this it will do to the full extent due to its temperature, except in so far as it may be prevented by its connection with the rest. Hence, on the whole, the effect of this cause is to leave a permanent contraction a little above the water-line, and it is easy to see that the contraction must be so much nearer to the water-line as the thickness of the metal is less, the other dimensions of the hollow cylinder and the nature of the metal being given. When the hollow cylinder is very short, so as to be reduced to a mere hoop, the same cause operates, but there is not room for more than a general inclination of the surface, leaving the hoop bevelled.
"The expansion of the bottom edge was not noticed in Colonel Clark's paper, perhaps owing to the much smaller hoops which he used in experimenting. Accepting Professor Stokes' explanation of the top contraction, it appears that expansion of the bottom may be accounted for by the reacting strain put on the cooled edge when forcing in the top edge, acting in such a way as to prevent the cooled edge coming quite to its natural contraction, and this, when sufficiently great, expresses itself in the form of a slight expansion.
"Experiment No. 14.--Forged steel hoop, turned and bored, 18.53 inches in circumference outside by 2.375 inches deep by .27 inch thick, heated to redness, then cooled one-half its depth in water (see Fig. 1437 at G for final form of hoop after three heatings and coolings).
-----------------+--------------------+-------------------+------------- | Top Edge. | Bottom Edge. | +--------+-----------+-------+-----------+ |Contrac-|Percentage | Expan-|Percentage | | tion. |of original| sion. |of original| | | length. | | length. | -----------------+--------+-----------+-------+-----------+------------- | Inches.| |Inches.| | | | | | {|Cracked at | | | | {|water- After 1st cooling| .06 | .32 | -- | -- {|cooled | | | | {|edge one- | | | | {|third depth | | | | {|of ring. | | | | | " 2nd " | .12 | .64 | -- | -- | | | | | | | | | | {|After allow- | | | | {|ing for " 3rd " | .20 | 1.08 | .05 | .27 {|three small | | | | {|cracks in | | | | {|bottom edge." -----------------+--------+-----------+-------+-----------+-------------
The shrinkage of iron and steel by cooling rapidly is sometimes taken advantage of by workmen to refit work, the principles involved in the process being as follows:--
Suppose in Fig. 1438 a a represents a piece of wrought-iron tube that has been heated to a bright red and immersed in cold water c c from the end B to D, until that end is cold. The part submerged and cold will be contracted to its normal diameter and have regained its normal strength, while the part above the water, remaining red-hot, will be expanded and weak. There will be, then, a narrow section of the tube, joining the heated and expanded part to the cooled and contracted part, and its form will be conical, as shown at D D. Now, suppose the tube to be slowly lowered in the water, the cold metal below will compress the heated metal immediately above the water-line, the cone section D being carried up into the metal before it has had time to cool; and the tube removed from the water when cold will be as shown in Fig. 1438, from c to D, representing the part first immersed and cooled. To complete the operation the tube must be heated again from the end c to a short distance past D, and then immersed from E nearly to D, and held still until the submerged part is cold, when the tube must be slowly lowered to compress the end c D, making the tube parallel, but smaller in diameter and in bore, while leaving it of its original length, but thickening its wall.
This process may, in many cases, be artificially assisted. Suppose, for example, a washer is too large in its bore; it should have its hole and part of its radial faces filled with fire-clay, as shown in Fig. 1439, in which A is the washer and B B the clay, c c being pieces of wire to hold the fire-clay and prevent its falling off. The washer should be heated to a clear red and plunged in the water D D, which will cool and shrink the exterior and exposed metal in advance of the interior, which will compress to accommodate the contraction of the outer metal, hence the hole will be reduced. This operation may be repeated until the hole be entirely closed.
Another method of closing such a piece as an eye of large diameter compared to its section, is shown in Fig. 1440; first dipping the heated eye at A and holding it there till cold and then slowly lowering it into the water, which would close the diameter across C, and, after reheating, dipping at D till cold, and then slowly immersing, which would close the eye across E. To shrink a square ring, the whole ring would require to be heated and a side of the square dipped, as shown in Fig. 1441, until quite cold, and then immersed slowly for about an inch, the operation being performed with a separate heating for each side. Connecting rod straps, wheel-tires, and a large variety of work may be refitted by this process, but in each case the outside diameter will be reduced.
XV. MEASURING TOOLS
For what may be termed the length measurements of lathe work it is obvious that caliper gauges, such as shown in Fig. 1402, may be employed. Since, however, these length measurements rarely require to be so accurate as the diametrical measurements, the ordinary lineal rule is very commonly employed in work not done under the standard gauge system. It is obvious, however, that when a number of pieces are to be turned to corresponding lengths, a strip of sheet iron, or of iron rod made to the required length, may be employed; a piece of sheet iron filed to have the necessary steps being used where there are several steps in the work; but if the lineal measuring rule is used, and more than one measurement of length is to be taken, some one point, as one end of the work, should be taken wherefrom to measure all the other distances. Suppose, for example, that Fig. 1442 represents a crank pin requiring to have its end collar 1/4 inch thick, the part A 2 inches long, part B 3 inches long, collar C 1/2 inch thick, and the part D 7 inches long. If the length of each piece were taken separately and independently of the others, any errors of measurement would multiply; whereas, if some one point be taken as a point wherefrom to measure all the other distances, error is less liable to occur, while at the same time an error in one measurement would not affect the correctness of the others. In the case of the crank pin shown, the collar C would be the best point wherefrom to take all the other measurements. First, it would require to be made to its proper thickness, and the lengths of B, A, and the end collar should be measured from its nearest radial face. The length of D should then be measured from the same radial face, the thickness of the collar being added to the required length of D, or D may be measured from the nearest radial face of C, providing C be of its exact proper thickness. In measuring the length of the taper part D, a correct measurement will not be obtained by laying the rule along its surface, because that surface does not lie parallel to its axis, hence it is necessary to apply the measuring rule, as shown in Fig. 1443, in which S is a straight-edge held firmly against the radial face of the crank pin (the radial face being of course turned true), and R is the measuring rule placed true with the axial line of the crank pin. Whenever the diameters of the lengths to be measured vary, this mode of measuring must be employed. On small work, or on short distances requiring to be very exact, a gauge such as shown in Fig. 1444 at A may be employed, which will not only give more correct results, but because it is more convenient, as it can be conveniently held or tried to the work with one hand while the other hand is applied to the feed screw handle to withdraw the cutting tool at the proper moment, and to the feed nut to unlock it and stop the feed.
On long work a wooden strip is the best, especially if the work has varying diameters and a number of pieces of work require to be made exactly alike. In Fig. 1445 S represents the wooden strip, and W the work. The strip is marked across by lines representing the distances apart the shoulders of the work require to be; thus the lines A, B, C, D, E, F, G, represent the distances apart of the radial faces a, b, c, d, e, f, g, on the work, and these lines will be in the same plane as the shoulders if the latter are turned to correct lengths. To compare the radial faces with the lines, a straight-edge must be held to each successive shoulder (as already described) that is of smaller diameter than the largest radial face on the work.
If the wooden strip be made the full length of the work the dog or clamp driving the work will require to be removed every time the wooden gauge is applied, and since the work must be turned end for end in the lathe to be finished, it would be as well to let the length of the wood gauge terminate before reaching the work driver, as, say, midway between E and F.
When a lineal distance is marked by lines, and this distance is to be transferred to another piece of work and marked thereon by lines, the operation may be performed, for short distances or radii, by the common compasses employed to mark circles, but for greater distances where compasses would be cumbersome, the trammels are employed.
Fig. 1446 represents a pair of trammels made entirely of metal, and therefore suitable for machinists' use, in which the points require to be pressed to the work to mark the lines. A A represents a bar of square steel; or for very long trammels wood may be used. B represents a head fastened tightly to one end, and through B passes the leg or pointer C, which is thus adjustable as to its projecting distance, as C can be fastened in any position by the thumb-screw D. The head E is made to a good sliding fit upon the bottom and two side faces of A A; but at the top there is sufficient space to admit a spring, which passes through E. F is the leg screwed into E, which is locked in position by the thumb-screw G. The head E is thus adjustable along the whole length of the bar or rod A A. The object of the spring is as follows:--If the head E were made to fit the bar A A closely on all four sides, the burrs raised upon the top side of the rod A A by the end of the thumb-screw G would be likely to impede its easy motion. Then again, when the sliding head E has worn a trifle loose upon the bar A A, and is loosened for adjustment, it would be liable to hang on one side, and only to right itself when the screw G brought it to a proper bearing upon the under side of the bar A A, and thus tightening the head E would alter the adjustment of the point. The spring, however, always keeps the lower face of the square hole through E bearing evenly against the corresponding face of the bar, so that tightening the screw G does not affect the adjustment, and, furthermore, the end of the set-screw, bearing against the spring instead of against the top of the rod, prevents the latter from getting burred.
The flat place at I I is to prevent the burrs raised by the thumb-screw end from preventing the easy sliding of leg C through B.
In some cases a gib is employed, as shown at A in Fig. 1447, instead of a spring, the advantage being that it is less liable to come out of place when moving the head along the bar.
The trammels should always be tried to the work in the same relative position as that in which they were set, otherwise the deflection of the bar may vitiate the correctness of the measurement; thus, if the rod or bar stood vertical when the points were adjusted for distance to set them to the required distance, it should also stand vertical upon the work when applied to transfer that distance, otherwise the deflection of the bar from its own weight will affect the correctness of the operation. Again, when applied to the work the latter should be suspended as nearly as convenient in the same position as the work will occupy when erected to its place.
Thus, suppose the trammels be set to the crank pin centres of a locomotive, then the bar will stand horizontally. Now the side rod, or coupling rod, as it may be more properly termed, should be stood on edge and should rest on its ends, because its bearings wherever it will rest when on the engine are at the ends; thus the deflection of the trammel rod will be in the same direction when applied to the work as it was when applied to the engine, and the deflection of the coupling rod will be in the same direction when tried by the trammel as when on the engine. The importance of this may be understood when it is mentioned that if the coupling rod be a long one, resting it on its side and supporting it in the middle instead of at its ends will cause a difference of 1/50th inch in its length.
Another lineal measuring gauge employed in the machine shop is shown in Fig. 1448. It is employed to measure the distance between two faces, and therefore in place of inside calipers, in cases where from the extreme distance to be measured it would require the use of inside calipers too large to be conveniently handled. Its application is more general upon planing machine work than any other, although it is frequently used by the lathe hand or turner, and by the vice hand and erector. It consists of two legs A and B, held together by the screws C D, which screw into nuts. These nuts should have a shoulder fitting into the slots in both legs, so as to form a guide to the legs. The screws are set up so as to just bind both legs together but leaving them free enough to move under a slight friction. The gauge is then set to length by lightly striking the ends E, and when adjusted the screws C D are screwed firmly home. The ends E are rounded somewhat, as is shown, to prevent them from swelling or burring by reason of the blows given to adjust them.
For striking circles we have the compasses or dividers, which are made in various forms.
Thus, Fig. 1449 represents a pair of spring dividers, the bow spring at the head acting to keep the points apart, and the screw and nut being employed to close and to adjust them.
Another form is shown in Fig. 1450, the legs being operated by a right and left-hand screw, which may be locked in position by the set-screw shown.
For very small circles the fork scriber shown in Fig. 1451 is an excellent tool, since it may be used with great pressure so as to cut a deep line in the surface of the work. This tool is much used by boiler makers, but is a very useful one for the machinist for a variety of marking purposes, which will be described with reference to vice work.
For larger work we have the compasses, a common form of which is shown in Fig. 1452, in which the leg A is slotted to receive the arc piece C, which has a threaded stem passing through E, and is provided with a nut at B; at D is a spring which holds the face of the nut B firmly against the leg E; at A is a thumb-screw for securing the leg to the arm C. The thumb-screw A being loosened, the compass legs may be rudely adjusted for distance apart, and A is then tightened. The adjustment is finally made by operating the nut B, which, on account of its fine thread, enables a very fine adjustment to be easily made.
It is often very convenient to be able to set one leg of a pair of dividers to be longer than the other, for which purpose a socket B, Fig. 1453, is provided, being pierced to receive a movable piece A, and split so that by means of a set-screw C the movable piece A may be gripped or released at pleasure.
For finding the centres of bodies or for testing the truth of a centre already marked, the compass calipers shown in Fig. 1454, are employed. It is composed of one leg similar to the leg of a pair of compasses, while the other is formed the same as the leg of an inside caliper. The uses of the compass calipers are manifold, the principal being illustrated as follows:--
Let it be required to find the centre of a rectangular block, and they are applied as in Fig. 1455, the curved leg being rested against the edge and a mark being made with the compass leg. This being done from all four sides of the work gives the centre of the piece.
In the case of a hole its bore must be plugged and the compass calipers applied as in Fig. 1456.
For marking a line true with the axial line of a cylindrical body, we have the instrument W in Fig. 1457, which is shown applied to a shaft S. The two angles of the instrument are at a right angle one to another, so that when placed on a cylindrical body the contact will cause the edge of W to be parallel with the axis of the shaft. The edge is bevelled, as shown, so that the lines of division of inches and parts may come close to the work surface, and a scriber may be used to mark a line of the required length. A scriber is a piece of steel wire having a hardened sharp point wherewith to draw lines.
On account of the instrument W finding its principal application in marking key seats upon shafts, it is termed the "key-seat rule."
For marking upon one surface a line parallel to another surface, the scribing block or surface gauge shown in Fig. 1458 is employed. It consists of a foot piece or stand D, carrying a stem. In the form shown this stem contains a slot running centrally up it. Through this slot passes a bolt whose diameter close to the head is larger than the width of the slot, so that it is necessary to file flat places on the side of the slot to permit the bolt to pass through it.
On the stem of the bolt close to the head, and between the bolt head and the stem of the stand, passes the piece shown at F. This consists of a piece of brass having a full hole through which the bolt passes clear up to the bolt head. On the edge view there is shown a slot, and on each side of the slot a section of a hole to receive a needle. A view of the bolt is given at E, the flat place to fit the slot in the stem being shown in dotted lines, and the space between the flat place and the bolt head is where the piece of brass, shown in figure, passes. This piece of brass being placed on the bolt, and the bolt being passed through the slot in the stem, the needle is passed through the split in the brass, and the thumb-nut is screwed on so that tightening up the thumb-nut causes the needle to be gripped in the brass split in any position in the length of the stem slot in which the bolt may be placed. The advantage of this form over all others is that the needle may be made of a simple piece of wire, and therefore very readily. Again, the piece of brass carrying the needle may be rotated upon the pin any number of consecutive rotations backwards and forwards, and there is no danger of slacking the thumb-nut, because the needle is on the opposite side of the stem to what the thumb-nut is, and the flat place prevents the bolt from rotating. Furthermore, the needle can be rotated on the bolt for adjustment for height without becoming loosened, whereas when the thumb-nut is screwed up firmly the needle is held very fast indeed, and finally all adjustments are made with a single thumb-nut.
The figure represents a view of this gauge from the bolt head and needle side of the stem, the thumb-nut being on the opposite side.
This tool finds its field of application upon lathe work, planer work, and, indeed, for one purpose or another upon all machine tools, and in vice work and erecting, examples of its employment being given in connection with all these operations.
Fig. 1459 represents a scribing block for marking the curves to which to cut the ends of a cylindrical body that joins another, as in the case of a [T]-pipe. It is much used by pattern-makers. In the figure A is a stem on a stand E. A loose sleeve B slides on A carrying an arm C, holding a pencil at D. A piece of truly surfaced wood or iron W, has marked on it the line J. Two [V]s, G, G, receive the work P. Now, if the centres of G, G and of the stand E all coincide with the line J then E will stand central to P, and D may be moved by the hand round P, being allowed to lift and fall so as to conform to the cylindrical surface of P, and a line will be marked showing where to cut away the wood on that side, and all that remains to do is to turn the work over and mark a similar line diametrically opposite, the second line being dotted in at K.
The try square, Fig. 1460, is composed of a rectangular back F, holding a blade, the edges of the two being at a right angle one to the other and as straight as it is possible to make them. The form shown in the figure is an [L]-square.
Fig. 1461 represents the [T]-square, whose blade is some distance from the end of the back and is sometimes placed in the middle. When the square edges are at a true right angle the square is said to be true or square, the latter being a technical term meaning at practically a true right angle.
The machinists' square is in fact a gauge whereby to test if one face stands at a right angle to another. It is applied by holding one edge firmly and fairly bedded against the work, while the other edge is brought to touch at some part against the face to be tested.
If in applying a square it be pressed firmly into the corner of the work, any error in the latter is apt to escape observation, because the square will tilt and the error be divided between the two surfaces tested. To avoid this the back should be pressed firmly against one surface of the work and the square edge then brought down or up to just touch the work, which it will do at one end only if the work surface is out of square or not at a right angle to the face to which the square back is applied.
An application of the [T]-square is shown in Fig. 1462, in which W is a piece of work requiring to have the face A of the jaw C at a right angle to the face B C. Sometimes the [L]-square is employed in conjunction with a straight-edge in place of the [T]-square. This is usually done in cases where the faces against which the square rests are so far apart as to require a larger [T]-square than is at hand. It is obvious that if the face A of the work is the one to be tested, the edge B is the part pressed to the work; or per contra, if B C is the face to be tested, the edge of the blade is pressed to the work.
The plane of the edges of a square should, both on the blade and on the back, stand at a right angle to the side faces of the body or stock, and the side of the blade should be parallel to the sides of the back and not at an angle to either side, nor should it be curved or bent, because if under these conditions the plane of the square edge is not applied parallel with the surface of the work the square will not test the work properly. This is shown in Fig. 1463, in which W is a piece of work, and S a square having its blade bent or curved and applied slightly out of the vertical, so that presuming the plane of the blade edge to be a right angle to the stock or back of the square the plane of the blade edge will not be parallel with the plane of the work, hence it touches the work at the ends A B only, whereas if placed vertically the blade edge would coincide with the work surface all the way along. It is obvious then that by making the edge of the blade at a right angle, crossways as well as in its length, to the stock, the latter will serve as a guide to the eye in adjusting the surface of the blade edge parallel to that of the work by placing the stock at a right angle to the same.
There are three methods of testing the angle of a square blade to the square back. The first is shown in Fig. 1464, in which A is a surface plate having its edge a true plane. The square S is placed in the position shown by full lines pressed firmly to the edge of the surface plate and a fine line is drawn with a needle point on the face of the surface plate, using the edge of the square blade as denoted by the arrow C as a guide. The square is then turned over as denoted by the dotted lines and the edge is again brought up to the line and the parallelism of the edge with the line denotes the truth, for whatever amount the blade may be out of true will be doubled in the want of coincidence of the blade edge with the line.
A better plan is shown in Fig. 1465, in which A is the surface plate, B a cylindrical piece of iron turned true and parallel in the lathe and having its end face true and cupped as denoted by the dotted lines so as to insure that it shall stand steadily and true. The surface of A and the vertical outline of B forming a true right angle we have nothing to do but make the square S true to them when placed in the position shown.
If we have two squares that are trued and have their edges parallel, we may test them for being at a right angle by trying them together as in Figs. 1466 and 1467, in which A, B, are the two squares which, having their back edges pressed firmly together (when quite clean), must coincide along the blade edges; this being so we may place them on a truly surfaced plate as shown in Fig. 1468, in which S is one square and S´ the other, P being the surface plate. Any want of truth in the right angle will be shown doubled in amount by a want of coincidence of the blade edges.
For some purposes, as for marking out work on a surface plate, it is better that the square be formed of a single piece having the back and blade of equal thickness, as shown in Fig. 1469, which represents a side and edge view of an [L]- and [T]-square respectively.
For angles other than a right angle we have the bevel or bevel square (as it is sometimes called), shown in Fig. 1470, A representing the stock or back, and B the blade, the latter being provided with a slot so that it may be extended to any required distance (within its scope) on either side of the stock. C is the rivet, which is made sufficiently tight to permit of the movement by hand of the blade, and yet it must hold firmly enough to be used without moving in the stock. Instead of the rivet C, however, a thumb-screw and nut may be employed, in which case, after the blade is set to the required angle, it may be locked in the stock by the thumb-screw.
Fig. 1471 represents a Brown and Sharpe bevel protractor, with a pivot and thumb-nut in the middle of the back with a half-circle struck from the centre of the pivot and marked to angular degrees. The pointer for denoting the degrees of angle has also a thumb-screw and nut so that the blade may, by loosening the pivot and pointer, be moved to project to the required distance on either side of the back.
Swasey's improved protractor, however, is capable of direct and easy application to the work, forming a draughtsman's protractor, and at the same time a machinist's bevel or bevel square, while possessing the advantage that there is no protruding back or set-screw to prevent the close application of the blade to the work. This instrument is shown in Fig. 1472. The blade A is attached to the circular piece D, the latter being recessed into the square B B, and marked with the necessary degrees of angle, as shown, while the mark F upon the square B serves as an index point. The faces of A, B B, and D are all quite level, so that the edges will meet the lines upon the work and obviate any liability to error. The piece D is of the shape shown in section at G, which secures it in B B, the fit being sufficient to permit of its ready adjustment and retain it by friction in any required position. The dotted lines indicate the blade as it would appear when set to an angle, the point E being the centre of D, and hence that from which the blade A operates.
On account, however, of the numerous applications in machine work of the hexagon (as, for instance, on the sides of both heads and nuts), a special gauge for that angle is requisite, the usual form being shown in Fig. 1473. The edges A, B, form a hexagon gauge, and edges C, D, form a square, while the edge E serves as a straight-edge.
All these tools should be made of cast steel, the blades being made of straight saw blade, so that they will not be apt to permanently set from an ordinary accidental blow; while, on the other hand, if it becomes, as it does at times, necessary to bend the blade over to the work, it will resume its straightness and not remain bent.
For testing the straightness, in one direction only, of a surface the straight-edge is employed. It consists in the small sizes of a piece of steel whose edges are made straight and parallel one to the other. When used to test the straightness of a surface without reference to its alignment with another one, it is simply laid upon the work and sighted by the eye, or it may have its edge coated with red marking, and be moved upon the work so that its marking will be transferred to the high spots upon the work. The marking will look of the darkest colour in the places where the straight-edge bears the hardest. The most refined use of the straight-edge is that of testing the alignment of one surface to the other, and as this class of work often requires straight-edges of great length, as six or ten feet, which if made of metal would bend of its own weight, therefore they are made of wood.
Fig. 1474 represents an example of the use of straight-edge for alignment purposes. It represents a fork and connecting rod, and it is required to find if the side faces of the end B are in line with the fork jaws. A straight-edge is held firmly against the side faces of B in the two positions S and S´, and it is obvious that if they are in line the other end will be equidistant from the jaw faces, at the two measurements.
Figs. 1474, 1475, 1476, 1477, and 1478 represent the process of testing the alignment of a link with a straight-edge. First to test if the single eye E is in line with the double eye F at the other end, the straight-edge is pressed against the face of E, as in Fig. 1475, and the distance I is measured. The straight-edge is then applied on the other side of E, as in Fig. 1476, and the distance H is measured, and it is clear that if distances H and I are equal, then E is in line with the double eye. To test if the double eye F is in line with the single eye E, the straight-edge is pressed against the face of the double eye in the positions shown in Figs. 1477 and 1478, and when distances J and K measure equal the jaws of the double eye F are in line with those of the single eye E.
It is obvious, however, that we have here tested the alignment in one direction only. But to test in the other direction we may use a pair of straight-edges termed winding strips, applying them as in Fig. 1479, to test the stem, and as in Fig. 1480 to test the eye E, and finally placing the winding strip C on the eye of F while strip D remains upon E, as in Fig. 1480. The two strips are sighted together by the eye, as is shown in Fig. 1481, in which S and S´´ are the strips laid upon a connecting rod, their upper edges being level with the eye, hence if they are not in line the eye will readily detect the error. Fig. 1482 represents an application to a fork ended connecting rod. Pattern-makers let into their winding strips pieces of light-coloured wood as at C, C, C, C, in Fig. 1483, so that the eye may be assisted in sighting them.
It is obvious that in using winding strips they should be parallel one to the other; thus, for example, the ends A, B, in Fig. 1481, should be the same distance apart as ends C, D.
If less than three straight-edges or parallel strips are to be trued they must be trued to a surface plate or its equivalent, but if a pair are to be made they should have the side faces made true, and be riveted together so that their edges may be trued together, and equal width may be more easily obtained. For this purpose copper rivets should be used, because they are more readily removable, as well as less likely to strain the work in the riveting.
By riveting the straight-edges together the surface becomes broader and the file operates steadier, while the edges of the straight-edge are left more square. Furthermore parallelism is more easily obtained as one measurement at each end of the batch will test the parallelism instead of having to measure each one separately at each end. If three straight-edges are to be made they may be riveted together and filed as true as may be with the testing conveniences at hand, but they should be finally trued as described for the surface plate.
In using straight-edges to set work, the latter is often heated to facilitate the setting, and in this case the straight-edge or parallel strips should be occasionally turned upside down upon the work, for if the heated work heats one side of the straightedge more than the other the increased expansion of the side most heated will bend the straight-edge or strips, and throw them out of true.
In applying a straight-edge to test work it must never be pressed to the work surface, because in that case it will show contact with the work immediately beneath the parts where such pressure is applied. Suppose, for example, a true straight-edge be given a faint marking, and be applied to a true surface, the straight-edge itself being true; then if the hands are placed at each end of the straight-edge, and press it to the work while the straight-edge is given motion, it will leave the heaviest marks at and near the ends as though the work surface was slightly hollow in its length; while were the hand pressure applied to the middle of the length of the straight-edge the marks on the work would show the heaviest in the middle as though the work surface were rounding. This arises from the deflection due to the weakness of the straight-edge.
For testing the truth of flat or plane surfaces the machinist employs the surface plate or planometer. The surface plate is a plate or casting having a true flat surface to be used as a test plate for other surfaces. It is usually made of cast iron, and sometimes of chilled cast iron or hardened cast steel, the surface in either of these two latter cases being ground true because their hardness precludes the possibility of cutting them with steel tools. A chilled or hardened surface plate cannot, however, be so truly surfaced as one that is finished with either the scraper or the file.
The shape of the surface plate is an element of the first importance, because as even the strongest bars of metal deflect from their own weight, it is necessary to shape the plate with a view to make this deflection as small as possible in any given size and weight of plate. In connection, also, with the shape we must consider the effect of varying temperatures upon the metal, for if one part of the plate is thinner than another it will, under an increasing temperature, heat more rapidly, and the expansion due to the heating will cause that part to warp the plate out of its normal form, and hence out of true. The amount that a plate will deflect of its own weight can only be appreciated by those who have had experience in getting up true surfaces, but an idea may be had when it is stated that it can be shown that it is easily detected, in a piece of steel three inches square and a foot long.
Now this deflection will vary in direction according to the points upon which the plate rests. For instance, take two plates, clean them properly, and rest one upon two pieces of wood, one piece under each end, and then place another plate upon the lower one and its face will show hollow, and, if the upper plate is moved backwards and forwards laterally it will be found to move from the ends as centres of motion. Then rest the lower plate upon a piece of wood placed under the middle of its length, and we shall find that (if the plates are reasonably true) the top one will move laterally with the middle of its length as a centre of motion. Now although this method of testing will prove deflection to exist, it will not show its amount, because the top plate deflects to a certain extent, conforming itself to the deflection of the lower one, and if the test is accurately made it will be found that the two plates will contact at whatever points the lower one is supported.
If plates, tested in this manner, show each other to have contact all along however the lower one is supported, it is because they are so light that the upper one will readily bend to suit the deflection of the lower one, and true work is, with such a plate, out of the question.
To obviate these difficulties the body of the plate is heavily ribbed, and these ribs are so arranged as to be of equal lengths, and are made equal in thickness to the plate, so that under variations of temperature the ribs will not expand or contract more quickly or slowly than the body of the plate, and the twisting that would accompany unequal expansion is avoided.
In Fig. 1484 is shown the form of surface plate designed by Sir Joseph Whitworth for plates to be rested upon their feet. The resting points of the plate are small projections shown at A, B, and C. The object of this arrangement of feet is to enable the plate to rest with as nearly as possible an equal degree of weight upon each foot, the three feet accommodating themselves to an uneven surface. It is obvious, however, that more of the weight will fall upon C than upon A or B, because C supports the whole weight at one end, while at the other end A and B divide the weight.
Fig. 1485 shows the form of plate designed by Professor Sweet.
In Fig. 1486 is shown a pair of angle surface plates resting upon a flat one. The angle plates may be used for a variety of purposes where it is necessary to true a surface standing at a true right angle to another.
The best methods of making surface plates are as follows:--
The edges of the plates should be planed first, care being taken to make them square and flat. The surfaces should then be planed, the plates being secured to the planer by the edges, which will prevent as far as possible the pressure necessary to hold them against the planing tool cut from springing, warping, or bending the plates. Before the finishing cut is taken, the plates or screws holding the surface plate should be slackened back a little so as to hold them as lightly as may be, the finishing cut being a very light one, and under these circumstances the plates may be planed sufficiently true that one will lift the other from the partial vacuum between them.
After the plates are planed, and before any hand work is done on them, they should be heated to a temperature of at least 200° Fahr., so that any local tension in the casting may be as far as possible removed.
Surface plates for long and narrow surfaces are themselves formed long and narrow, as shown in Fig. 1487, which represents the straight-edge surface plate made at Cornell University.
The Whitworth surfacing straight-edge, or long narrow surface plate, is ribbed as in Fig. 1488, so as to give it increased strength in proportion to its weight, and diminish its deflection from its own weight. The lugs D are simply feet to rest it on.
Straight-edges are sometimes made of cast steel and trued on both edges. These will answer well enough for small work, but if made of a length to exceed about four feet their deflection from their own weight seriously affects their reliability. The author made an experiment upon this point with a very rigid surface plate six feet long, and three cast steel straight-edges 6 feet long, 4-1/2 inches wide, and 1/2 inch thick. Both edges of the straight-edges were trued to the surface plate until the light was excluded from between them, while the bearing surface appeared perfect; thin tissue paper was placed between the straight-edges and the plate, and on being pulled showed an equal degree of tension. The straight-edges were tried one with the other in the same way and interchanged without any apparent error, but on measuring them it was found that each was about 1/50 inch wider in the middle of its length than at the ends, the cause being the deflection. They were finished by filing them parallel to calipers, using the bearing marks produced by rubbing them together and also upon the plate; but, save by the caliper test, the improvement was not discernible.
In rubbing them together no pressure was used, but they were caused to slide under their own weight only.
A separate and distinct class of gauge is used in practice to copy the form of one piece and transfer it to another, so that the one may conform to or fit the other. To accomplish this end, what are termed male and female templates or gauges are employed. These are usually termed templates, but their application to the work is termed gauging it.
Suppose, for example, that a piece is to be fitted to the rounded corner of a piece F, Fig. 1489, and the maker takes a piece of sheet metal A, and cuts it out to the line B C D, leaving a female gauge E, which will fit to the work F. We then make a male gauge G, and apply this to the work, thus gauging the round corner.
Fig. 1490 represents small templates applied to a journal bearing, and it is seen that we may make the template as at T, gauging one corner only, or we may make it as at T´, thus gauging the length of the journal as well as the corners.
Fig. 1491 represents a female gauge applied to the corner of a bearing or brass for the above journal, it being obvious that the male and female templates when put together will fit as in Fig. 1492.
For measuring the diameters of metal wire and the thickness of rolled sheet metal, measuring instruments termed wire gauges and sheet metal measuring machines are employed. A simple wire gauge is usually formed of a piece of steel containing numerous notches, whose widths are equal to the intended thickness to be measured in each respective notch. These notches are marked with figures denoting the gauge-number which is represented by the notch.
For wire, however, a gauge having holes instead of notches is sometimes employed, the wire being measured by insertion in the hole, an operation manifestly impracticable in the case of sheet metal.
In Fig. 1493 is shown one of Brown and Sharpe's notch wire-gauges, the notches being arranged round the edge as shown:
The thickness of a given number of wire-gauge varies according to the system governing the numbering of the gauge, which also varies with the class of metal or wire for which the gauge has been adopted by manufacturers. Thus, in the following table are given the gauge-numbers and their respective sizes in decimal parts of an inch, as determined by Holtzapffel in 1843, and to which sizes the Birmingham wire-gauge is made. The following table gives the numbers and sizes of the Birmingham wire-gauge.
BIRMINGHAM WIRE GAUGE.
-----+------++------+------++------+------++------+------ Mark.| Size.|| Mark.| Size.|| Mark.| Size.|| Mark.| Size. -----+------++------+------++------+------++------+------ 36 | .004 || 26 | .018 || 16 | .065 || 6 | .203 35 | .005 || 25 | .020 || 15 | .072 || 5 | .220 34 | .007 || 24 | .022 || 14 | .083 || 4 | .238 33 | .008 || 23 | .025 || 13 | .095 || 3 | .259 32 | .009 || 22 | .028 || 12 | .109 || 2 | .284 31 | .010 || 21 | .032 || 11 | .120 || 1 | .300 30 | .012 || 20 | .035 || 10 | .134 || 0 | .340 29 | .013 || 19 | .042 || 9 | .148 || 00 | .380 28 | .014 || 18 | .049 || 8 | .165 || 000 | .425 27 | .016 || 17 | .058 || 7 | .180 || 0000 | .454 -----+------++------+------++------+------++------+------
In this gauge it will be observed that the progressive wire gauge numbers do not progress by a regular increment.
This gauge is sometimes termed the Stubs wire-gauge, Mr. Stubs being a manufacturer of instruments whose notches are spaced according to the Birmingham wire-gauge. Since, however, Mr. Stubs has also a wire-gauge of his own, whose numbers and gauge-sizes do not correspond to those of the Birmingham gauge, the two Stubs gauges are sometimes confounded. The second Stubs gauge is employed for a special drawn steel wire, made by that gentleman to very accurate gauge measurement for purposes in which accuracy is of primary importance.
From the wear of the drawing dies in which wire is drawn, it is impracticable, however, to attain absolute correctness of gauge measurement. The dies are made to correct gauge when new, and when they have become worn larger, to a certain extent, they are renewed. As a result the average wire is slightly larger than the designated gauge-number. To determine the amount of this error the Morse Twist-Drill and Machine Company measured the wire used by them during an extended period of time, the result being given in table No. 2, in which the first column gives the gauge-number, the second column gives the thickness of the gauge-number in decimal parts of an inch, and the third column the actual size of the wire in decimal parts of an inch as measured by the above Company.
DIAMETER OF STUBS'S DRAWN STEEL WIRE IN FRACTIONAL PARTS OF AN INCH.
-------+-------+--------++-------+-------+--------++-------+-------+-------- No. by |Stubs's|Measure-||No. by |Stubs's|Measure-||No. by |Stubs's|Measure- Stubs's|Dimen- |ment by ||Stubs's|Dimen- |ment by ||Stubs's|Dimen- |ment by wire- |sions. | Morse || wire- |sions. | Morse || wire- |sions. | Morse gauge. | | Twist- ||gauge. | | Twist- ||gauge. | | Twist- | | Drill || | | Drill || | | Drill | | and || | | and || | | and | |Machine || | |Machine || | |Machine | | Co. || | | Co. || | | Co. -------+-------+--------++-------+-------+--------++-------+-------+-------- 1 | .227 | .228 || 23 | .153 | .154 || 45 | .081 | .082 2 | .219 | .221 || 24 | .151 | .152 || 46 | .079 | .080 3 | .212 | .213 || 25 | .148 | .150 || 47 | .077 | .079 4 | .207 | .209 || 26 | .146 | .148 || 48 | .075 | .076 5 | .204 | .206 || 27 | .143 | .145 || 49 | .072 | .073 6 | .201 | .204 || 28 | .139 | .141 || 50 | .069 | .070 7 | .199 | .201 || 29 | .134 | .136 || 51 | .066 | .067 8 | .197 | .199 || 30 | .127 | .129 || 52 | .063 | .064 9 | .194 | .196 || 31 | .120 | .120 || 53 | .058 | .060 10 | .191 | .194 || 32 | .115 | .116 || 54 | .055 | .054 11 | .188 | .191 || 33 | .112 | .113 || 55 | .050 | .052 12 | .185 | .188 || 34 | .110 | .111 || 56 | .045 | .047 13 | .182 | .185 || 35 | .108 | .110 || 57 | .042 | .044 14 | .180 | .182 || 36 | .106 | .106 || 58 | .041 | .042 15 | .178 | .180 || 37 | .103 | .104 || 59 | .040 | .041 16 | .175 | .177 || 38 | .101 | .101 || 60 | .039 | .040 17 | .172 | .173 || 39 | .099 | .100 || 61 | .038 | .039 18 | .168 | .170 || 40 | .097 | .098 || 62 | .037 | .038 19 | .164 | .166 || 41 | .095 | .096 || 63 | .036 | .037 20 | .161 | .161 || 42 | .092 | .094 || 64 | .035 | .036 21 | .157 | .159 || 43 | .088 | .089 || 65 | .033 | .035 22 | .155 | .156 || 44 | .085 | .086 || | | -------+-------+--------++-------+-------+--------++-------+-------+--------
The following table represents the letter sizes of the same wire:--
LETTER SIZES OF WIRE.
A. 0.234 | J. 0.277 | S. 0.348 B. 0.238 | K. 0.281 | T. 0.358 C. 0.242 | L. 0.290 | U. 0.368 D. 0.246 | M. 0.295 | V. 0.377 E. 0.250 | N. 0.302 | W. 0.386 F. 0.257 | O. 0.316 | X. 0.397 G. 0.261 | P. 0.323 | Y. 0.404 H. 0.266 | Q. 0.332 | Z. 0.413 I. 0.272 | R. 0.339 |
By an Order in Council dated August 23rd, 1883, and which took effect on March 1st, 1884, the standard department of the British Board of Trade substituted for the old Birmingham wire-gauge the following:--
+-------------+--------------++---------------------------+ | Descriptive | Equivalents || Descriptive | Equivalents | | number | in parts || number | in parts | | B. W. G. | of an inch. || B. W. G. | of an inch. | +-------------+--------------++-------------+-------------+ | No. | Inch. || No. | Inch. | | 7/0 | 0.500 || 23 | 0.024 | | 6/0 | .464 || 24 | .022 | | 5/0 | .432 || 25 | .020 | | 4/0 | .400 || 26 | .018 | | 3/0 | .372 || 27 | .0164 | | 2/0 | .348 || 28 | .0148 | | 0 | .324 || 29 | .0136 | | 1 | .300 || 30 | .0124 | | 2 | .276 || 31 | .0116 | | 3 | .252 || 32 | .0108 | | 4 | .232 || 33 | .0100 | | 5 | .212 || 34 | .0092 | | 6 | .192 || 35 | .0084 | | 7 | .176 || 36 | .0076 | | 8 | .160 || 37 | .0068 | | 9 | .144 || 38 | .0060 | | 10 | .128 || 39 | .0052 | | 11 | .116 || 40 | .0048 | | 12 | .104 || 41 | .0044 | | 13 | .092 || 42 | .0040 | | 14 | .080 || 43 | .0036 | | 15 | .072 || 44 | .0032 | | 16 | .064 || 45 | .0028 | | 17 | .056 || 46 | .0024 | | 18 | .048 || 47 | .0020 | | 19 | .040 || 48 | .0016 | | 20 | .036 || 49 | .0012 | | 21 | .032 || 50 | .0010 | | 22 | .028 || | | +-------------+--------------++-------------+-------------+
The gauge known as the American Standard Wire-Gauge was designed by Messrs. Brown and Sharpe to correct the discrepancies of the old Birmingham wire-gauge by establishing a regular proportion of the thirty-nine successive steps between the 0000 and 36 gauge-number of that gauge. In the American Standard (which is also called the Brown and Sharpe gauge) the value of 0.46 or 46/100 has been taken as that for 0000 or the largest dimension of the gauge. Then by successive and uniform decrements, each number following being obtained from multiplying its predecessor by 0.890522 (which is the same thing as deducting 10.9478 per cent.), the final value for number 36 is reached at 0.005, which corresponds with number 35 of the Birmingham wire-gauge. The principle of the gauge is shown in Fig. 1495, which represents a gauge for jewelers, having an angular aperture with the gauge-numbers marked on the edge, the lines and numbers being equidistant.
The advantage of this system is that the instrument is easy to produce, the difference between any two gauge-numbers being easily found by calculation; and the gauge is easy to originate, since the opening, being of the proper width at the open end, the sides terminating at the proper distance and being made straight, the intermediate gauge-sizes may be accurately marked by the necessary number of equidistant lines.
Wire, to be measured by such a gauge, is simply inserted into and passed up the aperture until it meets the sides of the same, which gives the advantage that the size of the wire may be obtained, even though its diameter vary from a gauge-number. This could not be done with a gauge in which each gauge-number and size is given in a separate aperture or notch. A comparison between the Brown and Sharpe and the Birmingham wire-gauge is shown in Fig. 1494, in which a piece of wire is inserted, showing that No. 15 by the Birmingham gauge is No. 13 by the Brown and Sharpe gauge.
The gauge-numbers and sizes of the same in decimal parts of an inch, of the American standard or Brown and Sharpe gauge, are given in the table following:--
------+--------------------------++------+-------------------------- |American or New Standard. || | American or New Standard. +--------------------------++ +------------+------------- No. of|Size of each| Difference ||No. of|Size of each| Difference Wire- | number in | between ||Wire- | number in | between Gauge.| decimal | consecutive ||Gauge.| decimal | consecutive | parts of | numbers in || | parts of | numbers in | an inch. |decimal parts|| | an inch. |decimal parts | | of an inch. || | | of an inch. ------+------------+-------------++------+------------+------------- 0000 | .460 | ---- || 19 | .03589 | .00441 000 | .40964 | .05036 || 20 | .03196 | .00393 00 | .36480 | .04484 || 21 | .02846 | .00350 0 | .32495 | .03994 || 22 | .02535 | .00311 1 | .28930 | .03556 || 23 | .02257 | .00278 2 | .25763 | .03167 || 24 | .0201 | .00247 3 | .22942 | .02821 || 25 | .0179 | .00220 4 | .20431 | .02511 || 26 | .01594 | .00196 5 | .18194 | .02237 || 27 | .01419 | .00174 6 | .16202 | .01992 || 28 | .01264 | .00155 7 | .14428 | .01774 || 29 | .01126 | .00138 8 | .12849 | .01579 || 30 | .01002 | .00123 9 | .11443 | .01406 || 31 | .00893 | .00110 10 | .10189 | .01254 || 32 | .00795 | .00098 11 | .09074 | .01105 || 33 | .00708 | .00087 12 | .08081 | .00993 || 34 | .0063 | .00078 13 | .07196 | .00885 || 35 | .00561 | .00069 14 | .06408 | .00788 || 36 | .005 | .00061 15 | .05707 | .00702 || 37 | .00445 | .00055 16 | .05082 | .00625 || 38 | .00396 | .00049 17 | .04525 | .00556 || 39 | .00353 | .00043 18 | .0403 | .00495 || 40 | .00314 | .00039 ------+------------+-------------++------+------------+-------------
This gauge is now the standard by which rolled sheet brass and seamless brass tubing is made in the United States. It is also sometimes used as a gauge for the copper wire used for electrical purposes, being termed the American Standard; but unless the words "American Standard" are employed, the above wire is supplied by the Birmingham wire-gauge numbers. The brass wire manufacturers have not yet adopted the Brown and Sharpe gauge; hence, for brass wire the Birmingham gauge is the standard.
Gauges having simple notches are not suitable for measuring accurately the thickness of metal, because the edges of the sheets or plates frequently vary from the thickness of the body of the plate. This may occur from the wear of the rolls employed to roll out the sheet, or because the sheets have been sheared to cut them to the required width, or to remove cracks at the edges, which shearing is apt to form a burr or projection on one side of the edge, and a slight depression on the other.
Again, a gauge formed by a notch requires to slide over the metal of the plate, and friction and a wear causing an enlargement of the notch ensues, which destroys the accuracy of the gauge. To avoid this source of error the form of gauge that was shown in Fig. 1370 may be used, it having the further advantage that it will measure thicknesses intermediate between the sizes of two contiguous notches, thus measuring the actual thickness of the sheet when it is not to any accurate sheet metal gauge thickness.
It is to be observed that in the process of rolling, the sheet is reduced from a greater to a lesser thickness, hence the gauge will not pass upon the plate until the latter is reduced to its proper thickness.
In applying the gauge, therefore, there is great inducement for the workman to force the gauge on to the sheet, in order to ascertain how nearly the sheet is to the required size, and this forcing process causes rapid wear to the gauge.
It follows, therefore, that a gauge should in no case be forced on, but should be applied lightly and easily to the sheet to prevent wear. Here may be mentioned another advantage of the Brown and Sharpe gauge, in that its gauge-number measurements being uniform, it may be more readily known to what extent a given plate varies from its required gauge thickness.
Suppose, for example, a sheet requiring to be of Number 1 Birmingham gauge is above the required thickness, but will pass easily through the 0 notch of the gauge, the excessive variation of those two gauge numbers (over the variations between other consecutive numbers of the gauge) leaves a wider margin in estimating how much the thickness is excessive than would be the case in using the Brown and Sharpe gauge. Indeed, if the edge of the plate be of uniform thickness with the body of the plate, the variation from the required thickness may be readily ascertained by a Brown and Sharpe gauge, by the distance the plate will pass up the aperture beyond the line denoting the 0 gauge number, or by the distance it stands from the 1 on the gauge when passed up the aperture until it meets both sides of the same.
In addition to these standard gauges, some firms in the United States employ a standard of their own; the principal of these are given in comparison with others in the table following.
DIMENSIONS OF SIZES, IN DECIMAL PARTS OF AN INCH.
------+---------+--------+----------+---------+---------+------------ Number| American|Birming-| Washburn | Trenton | G. W. |Old English, of | or Brown| ham, | & Moen |Iron Co.,|Prentiss,| from Brass Wire | & | or | Mfg. Co.,| Trenton,| Holyoke,| Manu- Gauge.| Sharpe. |Stubs's.|Worcester,| N. J. | Mass. | facturers' | | | Ms. | | | List. ------+---------+--------+----------+---------+---------+------------ 000000| ---- | ---- | .46 | ---- | ---- | ---- 00000| ---- | ---- | .43 | .45 | ---- | ---- 0000| .46 | .454 | .393 | .4 | ---- | ---- 000| .40964 | .425 | .362 | .36 | .3586 | ---- 00| .3648 | .38 | .331 | .33 | .3282 | ---- 0| .32495 | .34 | .307 | .305 | .2994 | ---- 1| .2893 | .3 | .283 | .285 | .2777 | ---- 2| .25763 | .284 | .263 | .265 | .2591 | ---- 3| .22942 | .259 | .244 | .245 | .2401 | ---- 4| .20431 | .238 | .225 | .225 | .223 | ---- 5| .18194 | .22 | .207 | .205 | .2047 | ---- 6| .16202 | .203 | .192 | .19 | .1885 | ---- 7| .14428 | .18 | .177 | .175 | .1758 | ---- 8| .12849 | .165 | .162 | .16 | .1605 | ---- 9| .11443 | .148 | .148 | .145 | .1471 | ---- 10| .10189 | .134 | .135 | .13 | .1351 | ---- 11| .090742 | .12 | .12 | .1175 | .1205 | ---- 12| .080808 | .109 | .105 | .105 | .1065 | ---- 13| .071961 | .095 | .092 | .0925 | .0928 | ---- 14| .064084 | .083 | .08 | .08 | .0816 | .083 15| .057068 | .072 | .072 | .07 | .0726 | .072 16| .05082 | .065 | .063 | .061 | .0627 | .065 17| .045257 | .058 | .054 | .0525 | .0546 | .058 18| .040303 | .049 | .047 | .045 | .0478 | .049 19| .03539 | .042 | .041 | .039 | .0411 | .04 20| .031961 | .035 | .035 | .034 | .0351 | .035 21| .028462 | .032 | .032 | .03 | .0321 | .0315 22| .025347 | .028 | .028 | .027 | .029 | .0295 23| .022571 | .025 | .025 | .024 | .0261 | .027 24| .0201 | .022 | .023 | .0215 | .0231 | .025 2S| .0179 | .02 | .02 | .019 | .0212 | .023 26| .01594 | .018 | .018 | .018 | .0194 | .0205 27| .014195 | .016 | .017 | .017 | .0182 | .01875 28| .012641 | .014 | .016 | .016 | .017 | .0165 29| .011257 | .013 | .015 | .015 | .0163 | .0155 30| .010025 | .012 | .014 | .014 | .0156 | .01375 31| .008928 | .01 | .0135 | .013 | .0146 | .01225 32| .00795 | .009 | .013 | .012 | .0136 | .01125 33| .00708 | .008 | .011 | .011 | .013 | .01025 34| .006304 | .007 | .01 | .01 | .0118 | .0095 35| .005614 | .005 | .0095 | .009 | .0109 | .009 36| .005 | .004 | .009 | .008 | .01 | .0075 37| .004453 | ---- | .0085 | .00725 | .0095 | .0065 38| .003965 | ---- | .008 | .0065 | .009 | .00575 ------+---------+--------+----------+---------+---------+------------
In the Whitworth wire-gauge, the mark or number on the gauge simply denotes the number of 1/1000ths of an inch the wire is in diameter; thus Number 1 on the gauge is 1/1000 inch, Number 2 is 2/1000ths inch in diameter, and so on.
Below is given the Washburn and Moen Manufacturing Company's music wire-gauge.
SIZES OF THE NUMBERS OF STEEL MUSIC WIRE-GAUGE.
+--------+------------------++--------+------------------+ | No. of | Size of each No. || No. of | Size of each No. | | Gauge. | in decimal parts || Gauge. | in decimal parts | | | of an inch. || | of an inch. | +--------+------------------++--------+------------------+ | 12 | .0295 || 21 | .0461 | | 13 | .0311 || 22 | .0481 | | 14 | .0325 || 23 | .0506 | | 15 | .0343 || 24 | .0547 | | 16 | .0359 || 25 | .0585 | | 17 | .0378 || 26 | .0626 | | 18 | .0395 || 27 | .0663 | | 19 | .0414 || 28 | .0719 | | 20 | .043 || ---- | ---- | +--------+------------------++--------+------------------+
These sizes are those used by the Washburn and Moen Manufacturing Company, of Worcester, Mass., manufacturers of steel music wire.
In the following table is the French Limoges wire-gauge.
-------+-----------+-------++--------+-----------+------ Number | Diameter, | Inch. || Number | Diameter, | Inch. on | milli- | || on | milli- | gauge. | mètre. | || gauge. | mètre. | -------+-----------+-------++--------+-----------+------ 0 | .39 | .0154 || 13 | 1.91 | .0725 1 | .45 | .0177 || 14 | 2.02 | .0795 2 | .56 | .0221 || 15 | 2.14 | .0843 3 | .67 | .0264 || 16 | 2.25 | .0886 4 | .79 | .0311 || 17 | 2.84 | .112 5 | .90 | .0354 || 18 | 3.40 | .134 6 | 1.01 | .0398 || 19 | 3.95 | .156 7 | 1.12 | .0441 || 20 | 4.50 | .177 8 | 1.24 | .0488 || 21 | 5.10 | .201 9 | 1.35 | .0532 || 22 | 5.65 | .222 10 | 1.46 | .0575 || 23 | 6.20 | .244 11 | 1.68 | .0661 || 24 | 6.80 | .268 12 | 1.80 | .0706 || | | -------+-----------+-------++--------+-----------+------
The following table gives the Birmingham wire-gauge for rolled sheet silver and gold.
+---------+------------++---------+------------+ | Gauge | Thickness. || Gauge | Thickness. | | number. | || number. | | +---------+------------++---------+------------+ | | Inch. || | Inch. | | 1 | .004 || 19 | .064 | | 2 | .005 || 20 | .067 | | 3 | .008 || 21 | .072 | | 4 | .010 || 22 | .074 | | 5 | .013 || 23 | .077 | | 6 | .013 || 24 | .082 | | 7 | .015 || 25 | .095 | | 8 | .016 || 26 | .103 | | 9 | .019 || 27 | .113 | | 10 | .024 || 28 | .120 | | 11 | .029 || 29 | .124 | | 12 | .034 || 30 | .126 | | 13 | .036 || 31 | .133 | | 14 | .041 || 32 | .143 | | 15 | .047 || 33 | .145 | | 16 | .051 || 34 | .148 | | 17 | .057 || 35 | .158 | | 18 | .061 || 36 | .167 | +---------+------------++---------+------------+
The following table gives the gauge thickness of Russia sheet iron,[25] the corresponding numbers by Birmingham wire gauge, and the thicknesses in decimal parts of an inch.
[25] This iron comes in sheets 28 × 56 inches = 10.88 square feet of area.
+----------+------------+-------------------+ | Russia | Birmingham | Thickness in | | gauge | wire-gauge | decimal | | number. | number. | parts of an inch. | +----------+------------+-------------------+ | 7 | 29 | .013 | | 8 | 28 | .014 | | 9 | 27 | .016 | | 10 | 26 | .018 | | 11 | 25 | .020 | | 12 | 24-1/2 | .021 | | 13 | 24 | .022 | | 14 | 23-1/4 | ---- | | 15 | 22-3/8 | ---- | | 16 | 21-1/2 | ---- | +----------+------------+-------------------+
The following table gives the gauge numbers to which galvanized iron is made.[26]
[26] Galvanized iron is made to the Birmingham wire-gauge, the thickness includes the galvanizing, the sheets being rolled thinner to allow for it.
+---------+------------++---------+------------+ | Gauge | Thickness. || Gauge | Thickness. | | number. | || number. | | +---------+------------++---------+------------+ | | Inch. || | Inch. | | 14 | .083 || 23 | .025 | | 16 | .065 || 24 | .022 | | 17 | .058 || 25 | .02 | | 18 | .049 || 26 | .018 | | 19 | .042 || 27 | .016 | | 20 | .035 || 28 | .014 | | 21 | .032 || 29 | .013 | | 22 | .028 || | | +---------+------------++---------+------------+
In the following table is given the American gauge sizes and their respective thicknesses for sheet zinc.
--------------------------------++-------------------------------- Gauge and Thickness. || Gauge and Thickness. -------+-----------+------------++-------+-----------+------------ Number.|Approximate|Thickness in||Number.|Approximate|Thickness in |Birmingham |fractions of|| |Birmingham |fractions of |wire-gauge.| an inch. || |wire-gauge.| an inch. -------+-----------+------------++-------+-----------+------------ 1 | ---- | 0.0039 || 16 | ---- | 0.0447 5 | ---- | 0.0113 || 17 | ---- | 0.0521 6 | ---- | 0.0132 || 18 | ---- | 0.0596 7 | ---- | 0.0150 || 19 | ---- | 0.0670 8 | 28 | 0.0169 || 20 | ---- | 0.0744 9 | 27 | 0.0187 || 21 | ---- | 0.0818 10 | 26 | 0.0224 || 22 | ---- | 0.0892 11 | 25 | 0.0261 || 23 | ---- | 0.0966 12 | 24 | 0.0298 || 24 | ---- | 0.1040 13 | ---- | 0.0336 || 25 | ---- | 0.1114 14 | ---- | 0.0373 || 26 | ---- | 0.1189 15 | ---- | 0.0410 || | | -------+-----------+------------++-------+-----------+------------
The Belgian sheet zinc gauge is as follows:
+---------+-------------++---------+-------------+ | Gauge | Thickness in|| Gauge | Thickness in| | number. |decimal parts|| number. |decimal parts| | | of an inch. || | of an inch. | +---------+-------------++---------+-------------+ | 1 | .004 || 14 | .037 | | 2 | .006 || 15 | .041 | | 3 | .008 || 16 | .045 | | 4 | .009 || 17 | .052 | | 5 | .011 || 18 | .059 | | 6 | .013 || 19 | .067 | | 7 | .015 || 20 | .074 | | 8 | .017 || 21 | .082 | | 9 | .019 || 22 | .089 | | 10 | .022 || 23 | .097 | | 11 | .026 || 24 | .104 | | 12 | .030 || 25 | .111 | | 13 | .034 || 26 | .120 | +---------+-------------++---------+-------------+
The gauge sizes of the bores of rifles are given in the following table,[27] in which the first column gives the proper gauge diameter of bore, and the second the actual diameter containing the errors found to exist from errors of workmanship. The standard diameters are supposed to be based upon the number of spherical bullets to the pound weight, if of the same diameter as the respective gauge sizes.
[27] From The English Mechanic.
No. of Diameter of Bore. Gauge. 4 varies from 1.052 to 1.000 6 " .919 " .900 8 " .835 " .820 10 " .775 " .760 12 " .729 " .750 14 " .693 " .680 16 " .662 " .650 20 " .615 " .610 24 " .579 " .577 28 " .550 " .548
The following table gives the result of some recent experiments made by Mr. David Kirkaldy, of London, to ascertain the tensile strength and resistance to torsion of wire made of various materials:
+-----------------------+--------------------------+ | |Pulling stress per sq. in.| | Kind of wire tested. +-------------+------------+ | | Unannealed. | Annealed. | +-----------------------+-------------+------------+ | | Pounds. | Pounds. | |Copper | 63,122 | 37,002 | |Brass | 81,156 | 51,550 | |Charcoal iron | 65,834 | 46,160 | |Coke iron | 64,321 | 61,294 | |Steel | 120,976 | 74,637 | |Phosphor bronze, No. 1 | 159,515 | 58,853 | | " No. 2 | 151,119 | 64,569 | | " No. 3 | 139,141 | 54,111 | | " No. 4 | 120,900 | 53,381 | +-----------------------+-------------+------------+
+-----------------------+------------+----------------------+ | | Ultimate | No. of twists in | | Kind of wire tested. |extension in| 5 inches. | | | per cent. +-----------+----------+ | | Annealed. |Unannealed.| Annealed.| +-----------------------+------------+-----------+----------+ |Copper | 34.1 | 86.8 | 96 | |Brass | 36.5 | 14.7 | 57 | |Charcoal iron | 28 | 48 | 87 | |Coke iron | 17 | 26 | 44 | |Steel | 10.9 | [28] | 79 | |Phosphor bronze, No. 1 | 46.6 | 13.3 | 66 | | " No. 2 | 42.8 | 15.8 | 60 | | " No. 3 | 44.9 | 17.3 | 53 | | " No. 4 | 42.4 | 13 | 124 | +-----------------------+------------+-----------+----------+
[28] Of the eight pieces of steel tested, three stood from forty to forty-five twists, and five stood one and a half to four twists.
The following, on some experiments upon the elasticity of wires, is from the report of a committee read before the British Association at Sheffield, England.
"The most important of these experiments form a series that have been made on the elastic properties of very soft iron wire. The wire used was drawn for the purpose, and is extremely soft and very uniform. It is about No. 20 B.W.G., and its breaking weight, tested in the ordinary way, is about 45 lbs. This wire has been hung up in lengths of about 20 ft., and broken by weights applied, the breaking being performed more or less slowly.
"In the first place some experiments have been tried as to the smallest weight which, applied very cautiously and with precautions against letting the weight run down with sensible velocity, will break the wire. These experiments have not yet been very satisfactorily carried out, but it is intended to complete them.
"The other experiments have been carried out in the following way: It was found that a weight of 28 lbs. does not give permanent elongation to the wire taken as it was supplied by the wire drawer. Each length of the wire, therefore, as soon as it was hung up for experiment, was weighted with 28 lbs., and this weight was left hanging on the wire for 24 hours. Weights were then added till the wire broke, measurements as to elongation being taken at the same time. A large number of wires were broken with equal additions of weight, a pound at a time, at intervals of from three to five minutes--care being taken in all cases, however, not to add fresh weight if the wire could be seen to be running down under the effect of the weight last added. Some were broken with weights added at the rate of 1 lb. per day, some with 3/4 lb. per day, and some with 1/2 lb. per day. One experiment was commenced in which it was intended to break the wire at a very much slower rate than any of these. It was carried on for some months, but the wire unfortunately rusted, and broke at a place which was seen to be very much eaten away by rust, and with a very low breaking weight. A fresh wire has been suspended, and is now being tested. It has been painted with oil, and has now been under experiment for several months.
"The following tables will show the general results of these experiments. It will be seen, in the first place, that the prolonged application of stress has a very remarkable effect in increasing the strength of soft iron wire. Comparing the breaking weights for the wire quickly broken with those for the same wire slowly broken, it will be seen that in the latter case the strength of the wire is from two to ten per cent. higher than in the former, and is on the average about five or six per cent. higher. The result as to elongation is even more remarkable, and was certainly more unexpected. It will be seen from the tables that, in the case of the wire quickly drawn out, the elongation is on the average more than three times as great as in the case of the wire drawn out slowly. There are two wires for which the breaking weights and elongations are given in the tables, both of them 'bright' wires, which showed this difference very remarkably. They broke without showing any special peculiarity as to breaking weight, and without known difference as to treatment, except in the time during which the application of the breaking weight was made. One of them broke with 44-1/4 lbs., the experiment lasting one hour and a half; the other with 47 lbs., the time occupied in applying the weight being 39 days. The former was drawn out by 28.5 per cent. on its original length, the latter by only 4.79 per cent.
"It is found during the breaking of these wires that the wire becomes alternately more yielding and less yielding to stress applied. Thus from weights applied gradually between 28 lbs. and 31 lbs. or 32 lbs., there is very little yielding, and very little elongation of the wire. For equal additions of weight between 33 lbs. and about 37 lbs. the elongation is very great. After 37 lbs. have been put on, the wire seems to get stiff again, till a weight of about 40 lbs. has been applied. Then there is a rapid running down till 45 lbs. has been reached. The wire then becomes stiff again, and often remains so till it breaks. It is evident that this subject requires careful investigation."
TABLES SHOWING THE BREAKING OF SOFT IRON WIRES AT DIFFERENT SPEEDS.
I.--WIRE QUICKLY BROKEN.
+------------------------+-----------+---------------+ | | Breaking | Per cent. of | | Rate of adding weight. | weight in | elongation on | | | pounds. | original | | | | length. | +------------------------+-----------+---------------+ | Dark Wire.[29] | | | | 0-1/4 lb. per minute | 45 | 25.4 | | 1 " 5 minutes | 45-1/4 | 25.9 | | " 5 " | 45-1/4 | 24.9 | | " 4 " | 44-1/4 | 24.58 | | " 3 " | 44-1/4 | 24.88 | | " 3 " | 45-1/4 | 29.58 | | " 5 " | 44-1/4 | 27.78 | | Bright Wire.[29] | | | | 1 lb. per 5 minutes | 44-1/4 | 28.5 | | " 5 " | 44-1/4 | 27.0 | | " 4 " | 44-1/4 | 27.1 | +------------------------+-----------+---------------+
[29] The wire used was all of the same quality and gauge, but the "dark" and "bright" wire had gone through slightly different processes for the purpose of annealing.
II.--WIRE SLOWLY BROKEN.
+--------------------+------------+--------------------+ | Weight added and | Breaking | Per cent. of | | number of | weight in | elongation on | | experiment. | pounds. | original length. | +--------------------+------------+--------------------+ | 1. 1 lb. per day | 48 | 7.58 | | 2. " " | 46 | 8.13 | | 3. " " | 47 | 7.05 | | 4. " " | 47 | 6.51 | | 5. " " | 47 | 8.62 | | 6. " " | 47 | 5.17 | | 7. " " | 46 | 5.50 | | 8. " " | 47 | 6.92 bright wire | | 1. 3/4 lb. per day | 49 | 8.50 | | 2. " " | 48-1/4 | 8.81 | | 3. " " | Broken by accident. | | 4. " " | 46 | 7.55 | | 5. " " | 46 | 6.41 | | 6. " " | 45-1/2 | 6.62 | | 1. 1/2 lb. per day | 48 | 8.26 | | 2. " " | 50 | 8.42 | | 3. " " | 49 | 7.18 | | 4. " " | 47 | 4.79} | | 5. " " | 46-1/2 | 6.00} bright wires | +--------------------+------------+--------------------+
The American Standard diameters of solid drawn or seamless brass and copper tube are as in the following table.
+----------+-----------------+---------------+---------------+ | Outside |Thickness Stubs's| Weight per | Weight per | |diameter. | wire-gauge. | running foot. | running foot. | | | | Brass tubes. | Copper tubes. | +----------+-----------------+---------------+---------------+ | 5/8 | 18 | 3/8 | 3/8 | | 3/4 | 17 | 1/2 | 1/2 | | 13/16 | 17 | 9/16 | 9/16 | | 7/8 | 17 | 5/8 | 5/8 | | 15/16 | 16 | 11/16 | 11/16 | | 1 | 16 | 3/4 | 3/4 | | 1-1/8 | 16 | 7/8 | 7/8 | | 1-1/4 | 12 and 14 | 1-1/4 | 1-1/4 | | 1-3/8 | 12 " 14 | 1-3/8 | 1-3/8 | | 1-1/2 | 12 " 14 | 1-1/2 | 1-6/10 | | 1-5/8 | 12 " 14 | 1-5/8 | 1-7/10 | | 1-3/4 | 12 " 14 | 1-3/4 | 1-8/10 | | 1-13/16 | 12 " 14 | 1-13/16 | 1-9/10 | | 1-7/8 | 12 " 14 | 1-7/8 | 1-15/16 | | 1-15/16 | 12 " 14 | 2 | 2-1/10 | | 2 | 12 " 14 | 2-1/8 | 2-1/4 | | 2-1/8 | 12 " 14 | 2-1/4 | 2-3/8 | | 2-1/4 | 12 " 14 | 2-3/8 | 2-1/3 | | 2-3/8 | 12 " 14 | 2-1/2 | 2-2/3 | | 2-1/2 | 11 " 13 | 2-3/4 | 3 | | 2-5/8 | 11 " 13 | 3 | 3-1/8 | | 2-3/4 | 11 " 13 | 3-1/8 | 3-1/4 | | 2-7/8 | 11 " 13 | 3-1/4 | 3-3/8 | | 3 | 11 " 13 | 3-3/8 | 3-1/2 | | 3-1/8 | 11 " 13 | 3-1/2 | 3-3/4 | | 3-1/4 | 11 " 13 | 3-7/8 | 4-1/8 | | 3-3/8 | 11 " 13 | 4-1/8 | 4-1/4 | | 3-1/2 | 11 " 13 | 4-1/4 | 4-3/8 | | 4 | 11 " 13 | 5 | 5-1/4 | | 4-1/4 | 11 " 13 | 6 | 6-1/2 | | 5 | 10 " 12 | 7 | 8 | | 6 | 10 " 12 | 9 | 10 | +----------+-----------------+---------------+---------------+
XVI. SHAPING AND PLANING MACHINES
The office of the shaping machine is to dress or cut to shape such surfaces as can be most conveniently cut by a tool moving across the work in a straight line.
The positions occupied among machine tools at the present time by shaping and planing machines are not as important as was the case a few years ago, because of the advent of the milling machine, which requires less skill to operate, and produces superior work.
All the cutting tools used upon shaping and planing machines have already been described with reference to outside tools for lathe work, and it may be remarked that a great deal of the chucking done on the shaping and planing machine corresponds to face plate chucking in the lathe. Both shaping machines and small planing machines, however, are provided with special chucks and work-holding appliances that are not used in lathe work, and these will be treated of presently. On large planing machines chucks are rarely used, on account of the work being too large to be held in a chuck. Shaping machines are also known as shapers and planing machines as planers.
The simplest form of shaping machine, or shaper as it is usually termed in the United States, is that in which a tool-carrying slide is reciprocated across the work, the latter moving at the end of each back stroke so that on the next stroke the tool may be fed to its cut on the work. Fig. 1496 represents a shaper of this kind constructed by Messrs. Hewes and Phillips, of Newark, New Jersey, in which P is a cone pulley receiving motion from a countershaft, and driving a pinion which revolves the gear-wheel Q, whose shaft has journal bearing in the frame of the machine. This shaft drives a bevel pinion gearing with a bevel-wheel in one piece with the eccentric spur-wheel S, which is upon a shaft having at its lower end the bevel-wheel B to operate the work-feeding mechanism. S drives an eccentric gear wheel R, fast upon the upper face of which is a projection E, in which is a [T]-shaped groove to receive and secure a wrist or crank pin which drives a connecting rod secured to the slide A by means of a bolt passing through A, and secured to the same by a nut D.
When the gear-wheel R revolves, the connecting rod causes slide A to traverse to and fro endways in a guideway, provided on the top of the frame at X. On the end of this slide is a head carrying a cutting tool T, which, therefore, moves across the work, the latter being held in the vise V, which is fast upon a table W upon a carriage saddle or slider p, which is upon a horizontal slide that in turn fits to a slide vertical upon the front of the machine, and may be raised or lowered thereon by means of an elevating screw driven by a pair of mitre-wheels at F. The slider and table W (and therefore the vise and the work) are moved along the horizontal slide to feed the work to the tool cut as follows. A short horizontal shaft (driven by the bevel pinions at B), drives at its outer end a piece C, having a slot to receive a crank pin driving the feed rod N, which operates a pawl K engaging a ratchet wheel which is fast upon the horizontal screw that operates slider p.
The diameters of the eccentric gear-wheels E and S are equal; hence, C makes a revolution and the cross feed is actuated once for every cutting stroke. The swivel head H is bolted to the end of the slide or ram, as it is sometimes called, A, and is provided with a slide I upon which is a slider J, carrying an apron containing the tool post holding the cutting tool, the construction of this part of the mechanism being more fully shown in Fig. 1497. The eccentric gear-wheels R S are so geared that the motion of the slide A during the cutting stroke (which is in the direction of the arrow) is slower than the return stroke, which on account of being accelerated is termed a quick return. Various mechanisms for obtaining a quick return motion are employed, the object being to increase the number of cutting strokes in a given time, without accelerating the cutting speed of the tool, and some of these mechanisms will be given hereafter.
Referring again to the mechanism for carrying the cutting tool and actuating it to regulate the depth of cut in Fig. 1497, G is the end of the slide a to which the swivel head H is bolted by the bolts a b. The heads of these bolts pass into [T]-shaped annular grooves in G, so that H may be set to have its slides at any required angle. I is a slider actuated on the slide by means of the vertical feed screw which has journal bearing in the top of H, and passes through a nut provided in I. To I is fastened the apron swivel J, being held by a central bolt not seen in the cut, and also by the bolt at c. In J is a slot, which when c is loosened permits J to be swung at an angle. The apron K is pivoted by a taper pin L, which fits into both J and K. During the cutting stroke the apron K beds down upon J, but during the back stroke the tool may lift the apron K swinging upon the pivot L. This prevents the cutting edge of the tool from rubbing against the work during the return stroke.
Thus in Fig. 1498 is a piece of work, and it is supposed that a cut is being carried down the vertical face or shoulder at A; by setting the apron swivel at an angle and lifting the tool during the return stroke, its end will move away from the face of the shoulder. The slider I obviously moves in a vertical line upon slides M.
To take up the wear of the sliding bar A, various forms of guideways and guides are employed, a common form being shown in Fig. 1499. There are two gibs, one on each side of the bar, and these gibs are set up by screws to adjust the fit. In some cases only one gib is used, and in that event the wear causes the slide to move to one side, but as the wear proceeds exceedingly slowly in consequence of the long bearing surface of the bar in its guides, this is of but little practical moment. On the other hand, when two gibs are used great care must be taken to so adjust the screws that the slide bar is maintained in a line at a right angle to the jaws of the work-holding vice, so that the tool will cut the vertical surfaces or side faces of the work at a right angle to the work surface that is gripped by the vice.
To enable the length of stroke of slide A, Fig. 1496, to be varied to suit the length of the work, and thus not lose time by uselessly traversing that slide, E is provided with a [T]-slot as before stated, and the distance of the wrist pin (in this slot) from the centre of wheel E determines the amount of motion imparted to the connecting rod, and therefore to slide A. The wrist pin is set so as to give to A a rather longer stroke than the work requires, so that this tool may pass clear of the work on the forward stroke, and an inch or so past the work on the return stroke, the latter giving time to feed the tool down before it meets the work.
The length of the stroke being set, the crank piece E (for its slot and wrist pin correspond to a crank) is, by pulling round the pulley P, brought to the end of a stroke, the connecting rod being in line with slide A. The nut D is then loosened and slide A may then be moved by hand in its slideway until the tool clears the work at the end corresponding to the connecting rod position when nut D is tightened and the stroke is set.
Now suppose it is required to shape or surface the faces f and f´, the round curve S and the hollow curve C of the piece of work shown held in a vice chuck in Fig. 1500, and during the cutting stroke the slide a will travel in the direction of n in the figure, while during its return stroke it will traverse back in the direction of i. The sliding table W in Fig. 1496 would continuously but gradually be fed or moved (so much per tool traverse, and by the feeding mechanism described with reference to Fig. 1501) carrying with it the vice chuck, and therefore the work. When this feeding brought the surface of curve S, Fig. 1500, into contact with the tool, the feed screw handle in figure would be operated by hand so much per feed traverse, thus raising the slider, and therefore the tool, in the direction of l, and motion of the work to the right and the left of the tool (by means of the feed handle) would (if the amount of tool lift per tool stroke is properly proportioned to the amount of work feed to the right) cause the tool to cut the work to the required curvature. When the work had traversed until the tool had arrived at the top of curve S, the direction of motion of the feed-screw handle Z in Fig. 1496 must be reversed, the tool being fed down so much per tool traverse (in the direction of m) so as to cut out the curves from the top of S to the bottom of c, the face f´ being shaped by the automatic feed motion only.
The feed obviously occurs once for each cutting stroke of the tool and for the vertical motion of the tool, or when the tool is operated by the hand feed-screw handle in Fig. 1496, the handle motion, and therefore the feed should occur at the end of the back stroke and before the tool again meets the work, so as to prevent the cutting edge of the tool from scraping against the work during its back traverse.
In this connection it may be remarked that by setting the apron swivel over, as in Fig. 1498, the tool is relieved from rubbing on the back stroke for two reasons, the first having been already explained, and the second being that to whatever amount the tool may spring, bend, or deflect during the cutting stroke (from the pressure of the cut), it will dip into the work surface and cut deeper; hence on the back stroke it will naturally clear the surface, providing that the next cut is not put on until the tool has passed back and is clear of the work.
Referring now to the automatic feed of the sliding table W, in Fig. 1496, the principle of its construction may be explained with reference to Fig. 1501, which may be taken to represent a class of such feeding mechanisms. A is a wheel corresponding to the wheel marked M in Fig. 1496, or, it may be an independent wheel in gear with the feed wheel. On the same shaft as A is pivoted an arm B having a slot S at one end to receive a pin to which the feed rod E may connect. F is a disk rotated from the driving mechanism of the shaping machine, and having a [T]-shaped slot G G, in which is secured a pin to actuate the rod E. As F rotates E is vibrated to and fro and the catch C on one stroke falls into the notches or teeth in A and causes it to partly rotate, while on the return stroke of E it lifts over the teeth, leaving A stationary.
The amount of motion of B, and therefore the quantity of the feed, may be regulated at either end of E; as, for example, the farther the pin from the centre of G the longer the stroke of E, or the nearer the pin in S is to the centre of B the longer the stroke, but usually this provision is made at one end only of E.
To stop the feed motion from actuating, the catch C may be lifted to stand vertically, as shown in dotted lines in position 2, and to actuate the feed traverse in an opposite direction, C may be swung over so as to occupy the position marked 3, and to prevent it moving out of either position in which it may be set a small spring is usually employed.
Now suppose that the tool-carrying slide A, Fig. 1496, is traversing forward and the tool will be moving across the work on the cutting stroke, as denoted by the arrow k in Fig. 1502, the line of tool motion for that stroke being as denoted by the line c a. At a is the point where the tool will begin its return stroke, and if the work is moved by the feeding mechanism in the direction of arrow e, then the line of motion during the return stroke will be in the direction of the dotted line a b, and as a result the tool will rub against the side of the cut.
It is to obviate the friction this would cause to the tool edge, and the dulling thereto that would ensue, that the pivot pin L for the apron is employed as shown in Fig. 1497, this pin permitting the apron to lift and causing the tool to bear against the cut with only such force as the weight of the apron and of the tool may cause. Now suppose that in Fig. 1503 we have a piece of work whose edge A A stands parallel to the line of forward tool motion, there being no feed either to the tool or the work, and if the tool be set to the corner f its line of motion during a stroke will be represented by the line f g. Suppose that on the next stroke the feed motion is put into action and that feeding takes place during the forward stroke, and the amount of the feed per stroke being the distance from g to h, then the dotted line from f to h represents the line of cut. On the return stroke the line of tool motion will be from h along the dotted line h k, and the tool will rest against the cut as before. Suppose again that the feed is put on during the return stroke, and that c c´ represents the line of tool motion during a cutting stroke, and the return stroke will then be along the line from c´ to b, from c to b representing the amount of feed per stroke; hence, it is made apparent that the tool will rub against the cut whether the feed is put on during the cutting or during the return stroke. Obviously then it would be preferable to feed the work between the period that occurs after the tool has left the work surface on the return stroke and before it meets it again on the next cutting stroke. It is to be observed, however, that by placing the pin actuating the rod E, Fig. 1501, on the other side of the centre of the slot G in F, the motion of E will be reversed with relation to the motion J of the slide; hence, with the work feeding in either direction, the feed may be made to occur during either the cutting or return stroke at will by locating the driving pin on the requisite side of the centre of G.
An arrangement by Professor Sweet, whereby the feed may be actuated during the cutting or return stroke (as may be determined in designing the machine), no matter in which direction the work table is being fed, is shown in Fig. 1504. Here there are two gears A and D, and the pawl or catch C may be moved on its pivoted end so as to engage either with A or D to feed in the required direction.
Suppose the slide to be on its return stroke in the direction of L, and F be rotated as denoted by the arrow, then the pawl C will be actuating wheel A as denoted by its arrow, but if C be moved over so as to engage D as denoted by the dotted outline, then with the slide moving in the same direction, C will pull D in the direction of arrow K´, and wheel A will be actuated in the opposite direction, thus reversing the direction of the feed while still causing it to actuate on the return stroke.
Since the feed wheel A must be in a fixed position with relation to the work table feed screw, and since the height of this table varies to meet the work, it is obvious that as the work table is raised the distance between the centres of A and F in the figure is lessened, or conversely as that table is lowered the distance between those centres is increased; hence, where the work table has much capacity of adjustment for height, means must be provided to adjust the length of rod E to suit the conditions. This may be accomplished by so arranging the construction that the rod may pass through its connection with wheel F, in the figure, or to pass through its connection with B.
Fig. 1505 represents a shaper that may be driven either by hand or by belt power. The cone pulley shaft has a pinion that drives the gear-wheel shown, and at the other end of this gear-wheel shaft is a slotted crank carrying a pin that drives a connecting rod that actuates the sliding bar, or ram, as it is sometimes termed. The fly-wheel also affords ready means of moving the ram to any required position when setting the tool or the work.
Fig. 1506 represents a shaping machine by the Hewes and Phillips Iron Works, of Newark, N.J. The slide or ram is operated by the Whitworth quick return motion, whose construction will be shown hereafter. The vice sets upon a knee or angle plate fitting to vertical slideways on the cross slide, and may be raised or lowered thereon to suit the height of the work by means of the crank handle shown in front. The vice may be removed and replaced by the supplemental table shown at the foot of the machine. Both the vice and the supplemental table are capable of being swivelled when in position on the machine. The machine is provided with a device for planing circular work, such as sectors, cranks, &c., the cone mandrel shown at the foot of the machine bolting up in place of the angle plate.
HOLDING WORK IN THE SHAPER OR PLANER VICE.--The simplest method of holding work in a shaper is by means of a shaper vice, which may be employed to hold almost any shape of work whose size is within the capacity of the chuck. Before describing, however, the various forms of shaper vices, it may be well to discuss points to be considered in its use.
The bottom surface a a, Fig. 1507, of a planer vice is parallel with the surfaces d, d´ and as surface a is secured to the upper face of the slider table shown in figure, and this face is parallel to the line of motion of the slide A, and also parallel with the cross slide in that figure, it follows that the face d is also parallel both with the line of motion of slide A and with the surface of the slider table. Parallel work to be held in the vice may therefore be set down upon the surface d (between the jaws), which surface will then form a guide to set the work by. The work-gripping surfaces b and e, Fig. 1507, of the jaws are at a right angle to surface a, and therefore also to d, therefore the upper surface of work that beds fair upon d, or beds fair against b, will be held parallel to the line of motion X of the tool and the line Z of the feed traverse. Similarly the upper surfaces A, B of the gripping jaws are parallel to a a, hence they may be used to set the work true with the line of feed traverse. The sliding jaw, however, must be a sufficiently easy fit to the slideways that guide it to enable it to be moved by the screw that operates it, and as a result it has a tendency to lift upon its guideways so that its face e will not stand parallel to b or at a right angle to d. In Fig. 1508, for example, is a side view of a vice holding a piece of work W, the face f of the work being at an angle. As a consequence there is a tendency to lift in the direction of C. If the jaw does lift or spring in this direction it will move the work, so that instead of its lower face bedding down upon face d, Fig. 1507, it will lie in the direction of H, Fig. 1508, while its face parallel to f, instead of bedding fair against the face of jaw J, will lie as denoted by the line g, and as a result the work will not be held fair with either of those faces and the value of faces b, d and e in Fig. 1507 is impaired.
This lifting of the movable or sliding jaw is prevented in some forms of chuck, to be hereafter described, by bolts passing through which hold it down, but the tendency is nevertheless present, and it is necessary to recognise it in treating of chucking or holding work in such vices.
The work gripping face b, Fig. 1507, of the fixed jaw, however, is not subject to spring, hence it and the surface d are those by which the work may be set. The work, however, is held by the force of the screw operating the sliding jaw, hence the strain is in the direction of the arrow P in Fig. 1508, which forces it against the face of the fixed jaw. All the pressure that can be exerted to hold work down upon the surface d, Fig. 1507, is that due to the weight of the work added to whatever effort in that direction there may be induced by driving the work down by blows upon surface d after the jaws are tightened upon the work. This, however, is not to be relied upon whenever there is any tendency for the work not to bed down fair. It follows, then, that surface b of the work-gripping jaw is that to be most depended upon in setting the work, and that the surface that is to act as a guide at each chucking should be placed against this surface unless there are other considerations that require to be taken into account.
For example, suppose we have a thin piece of work, as in Fig. 1509, and the amount of surface bearing against the fixed jaw is so small in comparison to its width between the jaws that e would form no practical guide in setting the work. If then the edges of such a piece of work were shaped first the face or faces may or may not be made at a right angle to them, or square as it is termed. But if the faces were shaped first, then when the work was held by them to have the edges shaped there would be so broad an area of work surface bedding against the jaw surface, that the edges would naturally be shaped square with the faces.
In cases, therefore, where the area of bedding surface of the work against the faces of the jaws is too small to form an accurate guide and the work is not thick enough to rest upon the surface d, Fig. 1507, it is set true to that surface by a parallel piece.
If the work is wide or long enough to require it, two parallel pieces must be used, both being of the same thickness, so that they will keep the work true with the surface d.
Pieces such as P, Fig. 1510, are also used to set work not requiring to be parallel. Thus in figure are a number of keys placed side by side and set to have their edges shaped, and piece P is inserted not only to lift the narrow ends of the keys up, but also to maintain their lower edges fair one with the other, and thus insure that the keys shall all be made of equal width.
They are also serviceable to interpose between the work and the vice jaws when the work has a projection that would receive damage from the jaw pressure.
Thus in Fig. 1511 the work W has such a projection and a parallel piece P is inserted to take the jaw pressure. By placing the broadest work surface g against the fixed jaw the work will be held true whether the movable jaw springs or not, because there will be surface g and surface H guiding it.
But if the work were reversed, as in Fig. 1512, with the broadest surface against K, then if K sprung in the direction of C, the work would not be shaped true.
When the work is very narrow, however, the use of a parallel piece to regulate its height is dispensed with, and the top surface B of the jaw, in Fig. 1513, is used to set the work by. A line is marked on the work surface to set it by and a surface gauge is set upon the face B, its needle point being set to the line in a manner similar to that already explained with reference to chucking work in the lathe.
All work should be so set that the tool will traverse across the longest length of the work, as denoted by the tool in Fig. 1502, and the arrow marking its direction of traverse.
The general principles governing the use of the shaper vice having been explained, we may now select some examples in its use.
Fig. 1514 represents a simple rectangular piece, and in order to have the tool marks run lengthwise of each surface (which is, as already stated the most expeditious) they must be in the direction of the respective arrows. In a piece of such relative proportions there would be little choice as to the order in which the surfaces should be shaped, but whatever surface be operated on first, that at a right angle to it should be shaped second; thus, if a be first, either b or d should be second, for the following reasons.
All the surfaces have sufficient area to enable them to serve as guides in setting the work, hence the object is to utilize them as much as possible for that purpose. Now, suppose that surface a has been trued first, and if c be the next one, then the bedding of surface a upon the vice surface or the parallel pieces must be depended upon to set a true while truing c. Now the surfaces b and d may both, or at least one of them, may be untrue enough to cause the work to tilt or cant over, so that a will not bed fair, and c will then not be made parallel to a. It will be preferable then to shape a first and at the second chucking to set a against the stationary jaw of the vice, so that it may be held true.
The sliding jaw will in this case be against face c, and if that face is out of true enough to cant the work so that a will not bed fair, then a narrow parallel piece may be inserted between the sliding jaw and the work, which will cause a to bed fair. The third face should be face c, in which case face a will rest on one surface and face b will be against the fixed jaw, and there will be two surfaces to guide the work true while c is being trued. In this case also, however, it is better to use a parallel piece P, Fig. 1515, between the work and the sliding jaw, so as to insure that the work shall bed fair against the fixed jaw; and if necessary to bring up the top surface above the jaws, a second parallel piece P´ should be used.
Suppose now that we have a connecting rod key to shape, and it is to be considered whether the faces or the edges shall be shaped first. Now if the side faces are out of parallel it will take more filing to correct them than it will to correct the same degree of error in the edges; hence it is obviously desirable to proceed with a view to make all surfaces true, but more especially the side faces. As the set of the key while shaping these faces is most influenced by the manner in which the fixed jaw surface meets the work, and as an edge will be the surface to meet the fixed jaw faces when the side faces are shaped, it will be best to dress one edge first, setting the key or keys, as the case may be, as was shown in Fig. 1510, so as to cut them with the tool operating lengthways of the key; one edge being finished, then one face of each key must be shaped, the key being set for this purpose with the surfaced edge against the fixed jaw. As the width of the key is taper, either a chuck with a taper attachment that will permit the sliding jaw to conform itself to the taper of the key must be used (vices having this construction being specially made for taper work as will be shown hereafter), or else the key must be held as in Fig. 1516, in which K represents the key with its trued edge against the fixed jaw, at P is a piece put in to compensate for the taper of the key, and to cause the other edge to bed firmly and fairly against the fixed jaw.
The first side face being trued, it should be placed against the fixed jaw while the other edge is shaped. For the remaining side face we shall then be able to set the key with a trued edge against the fixed jaw, and a true face resting upon a parallel piece, while the other edge will be true for the piece P, Fig. 1516, to press against, and all the elements will be in favor of setting the key so that the sides will be parallel one to the other, and the edges square with the faces.
In putting in the piece P, Fig. 1516, the key should be gripped so lightly that it will about bear its own weight; piece P may then be pushed firmly in with the fingers, and the vice tightened up.
If there are two keys the edges and one face may be trued up as just described, and both keys K, Fig. 1517, chucked at once by inverting their tapers as shown in figure. But in this case unless the edges are quite true they may cause the keys not to bed fair on the underneath face, and the faces therefore to be out of parallel on either or both of the keys. If there are a number of keys to be cut to the same thickness it may be done as follows:--
Plane or shape first one edge of all the keys; then plane up one face, chucking them with one planed edge against each vice jaw, and put little blocks (A, B, C, D, Fig. 1518) between the rough edges; then turn them over, chuck them the same way and plane the other face, resting them on parallel pieces; then plane the other edges last.
In place of the small blocks A, B, C, D, a strip of lead, pasteboard, or wood, or for very thin work a piece of lead wire, may be used.
Cylindrical work may be held in a vice chuck, providing that the top of the vice jaws is equal in height to the centre of the work, as in Fig. 1519, a parallel piece being used to set the work true. When, however, the work is to be shaped at one end only, it is preferable to hold it as in Fig. 1520, letting its end project out from the side of the chuck. In some vices the jaws are wider than the body of the chuck, so that cylindrical work may be held vertical, as in Fig. 1521, when the end is to be operated upon.
Fig. 1522 represents a simple form of shaper or planer chuck, such chucks being used upon small planing machines as well as upon shaping machines.
The base A is bolted to the work table, and is in one piece with the fixed jaw B. The movable jaw C is set up to meet the work by hand, and being free to move upon A may be used for either taper or parallel work. To fasten C upon the work, three screws threaded through F abut against the end of C; F being secured to the upper surface of A by a key or slip, which fits into a groove in F, and projects down into such of the grooves in the upper surface of A as may best suit the width of work to be held in the vice; C is held down by the bolts and nuts at G.
The operation of securing work in such a chuck is as follows:--The screws both at F and at G being loosened, and jaw C moved up to meet the work and hold it against the fixed jaw B, then nuts G should be set up lightly so that the sliding jaw will be set up under a slight pressure, screws F may then be set up and finally nuts G tightened.
This is necessary for the following reasons:--The work must, in most cases, project above the level of the jaws so that the tool may travel clear across it; hence, the strain due to holding the work is above the level of the three screws, and the tendency, therefore, is to turn the jaw C upwards, and this tendency the screws G resist. A similar chuck mounted upon a circular base so that it may be swivelled without moving the base on the work table is shown in Fig. 1523. The capacity to swivel the upper part of the chuck without requiring the base of the chuck to be moved upon the table is a great convenience in many cases.
Fig. 1524 represents an English chuck in which the fixed jaw is composed of two parts, A which is solid with the base G, and D which is pivoted to A at F. The movable jaw also consists of two parts, B which carries the nut for the screw that operates B, and C which is pivoted to B at E. The two pivots E, F being above the surface of the gripping jaws C, D, causes them to force down upon the surface of G as the screw is tightened, the work, if thin, being rested, as in the case of the chuck shown in Fig. 1523, upon parallel pieces.
Fig. 1525 represents a chuck made by W. A. Harris, of Providence. The jaws in this case carry two pivoted wings A, B, between the ends of which the work C is held, and the pivots being above the level of the work the tendency is here again to force the work down into the chuck, the strain being in the direction denoted by the arrows.
Here the work rests on four pins which are threaded in the collars H, so that by rotating the pins they will stand at different heights to suit different thicknesses of work, or they may be set to plane tapers by adjusting their height to suit the amount of taper required. The spiral springs simply support the pins, but as the jaws close the pins lower until the washer nuts H meet the surface of recess I.
Figs. 1526 and 1527 represent Thomas's patent vice, which possesses some excellent conveniences and features.
In Fig. 1526 it is shown without, and in Fig. 1527 with a swivel motion. The arrangement of the jaws upon the base in Fig. 1526 is similar to that of the chuck shown in Fig. 1522, but instead of there being a key to secure the piece F to the base, there is provided on each side of the base a row of ratchet teeth, and there is within F a circular piece G (in Fig. 1528) which is serrated to engage the ratchet teeth. This piece may be lifted clear of the ratchet teeth by means of the pin at H, and then the piece F may be moved freely by hand backwards or forwards upon the base and swung at any required angle, as in Fig. 1528, or set parallel as in Fig. 1527; F becoming locked, so far as its backward motion is concerned, so soon as H is released and G engages with the ratchet teeth on the base. But F may be pushed forward toward the fixed jaw without lifting H, hence the adjustment of the sliding jaw to the work may be made instantaneously without requiring any moving or setting of locking keys or other devices.
It is obvious that it is the capability of G to rotate in their sockets that enables F to be set at an angle and still have the teeth of G engage properly with those on the base plate.
The mechanism for swivelling the upper part or body upon the base and for locking it in its adjusted position is shown in Figs. 1529 and 1530. The body D is provided with an annular ring fitting into the bore of the base, which is coned at Q. The half-circular disks R fit this cone and are held to the body of the chuck by four bolts N, which are adjusted to admit disks R to move without undue friction. K is a key having on it the nut V, which receives a screw whose squared end is shown at S. By operating S in one direction key K expands disks R, causing them to firmly grip the base at the bevel Q, hence the base and the body are locked together. By operating S to unscrew in the nut V, K is moved in the opposite direction and R, R release their grip at Q and the body D may be swung round in any position, carrying with it all the mechanism except base P.
To enable the body to be readily moved a quarter revolution, or in other words, moved to a right angle, there is provided a taper pin, the base having holes so situated that the body will have been moved a quarter revolution when the pin having been removed from one hole in the base is seated firmly home in the other.
Referring again to Fig. 1526, there are shown one pair of parallel pieces marked respectively A, having bevelled edges, and another pair marked respectively B. Both pairs are provided with a small rib fitting into a groove in the jaws of the chuck, as shown in the figure.
These ribs and grooves are so arranged that the upper pair (A, A) may be used in the place of the lower ones, and the uses of these pieces are as follows:--
Suppose a very thin piece of work is to be planed, and in order to plane it parallel, which is ordinarily a difficult matter, it must bed fair down upon the face of the vice, which it is caused to do when chucked as in Fig. 1531, in which the work is shown laid flat upon the face of the vice, and gripped at its edges by the pieces A, A.
These pieces, it may be noted, do not bed fair against the gripping faces of the jaws, but are a trifle open at the bottom as at e, e, hence when they are pressed against the work they cant over slightly and press the work down upon the chuck face causing it to bed fair. Furthermore, the work is supported beneath its whole surface, and has, therefore, less tendency to spring or bend from the holding pressure; and as a result of these two elements much thinner work can be planed true and parallel than is possible when the work is lifted up and supported upon separate parallel pieces, because in the latter case the work, being unsupported between the parallel pieces, has more liberty to bend from the pressure due to the tool cut, as well as from the holding pressure.
Fig. 1532 shows the chuck holding a bracket, having a projection or eye. The work rests on pieces B, B, and is gripped by pieces A, A. It will be observed that A, A being beveled enables the cut to be carried clear across the work.
Fig. 1533 represents the chuck in use for holding a piece of shafting S to cut a keyway or spline in it. In this case a bevelled piece J is employed, its bevelled face holding the work down upon the chuck face.
Fig. 1534 represents a chuck termed shaper centres, because the work is held between centres as in the case of lathe work. The live spindle is carried in and is capable of motion in a sleeve, the latter having upon it a worm-wheel, operated by a worm, so that it can be moved through any given part of a circle, and has index holes upon its face to determine when the wheel has been moved to the required amount.
For work that is too large to be operated upon in the class of shaping machine shown in Fig. 1506, and yet can be more conveniently shaped than planed, a class of machine is employed in which the tool-carrying slide is fed to the work, which is chucked to a fixed table or to two tables.
Fig. 1535 represents a machine of this class. The tool-carrying slide A, in this case, operates in guideways provided in B, the latter being fitted to a slideway running the full length of the top of the frame M. The base slider B is fed along the bed by means of a screw operating in a nut on the under side of B, this screw being operated once during each stroke of the tool-carrying slide A, by means of a pawl feeding arrangement at F, which corresponds to the feeding device shown in Fig. 1501.
Two vertical frame pieces D, D are bolted against the front face of the machine, being adjustable along any part of the bed or frame length, because their holding bolts have heads capable of being moved (with the frame pieces D) along the two [T]-shaped grooves shown, their [T]-shape being visible at the end of the frame or bed. To frames D are bolted the work-holding tables E, E, the bolts securing them passing into vertical [T]-grooves in D, so that E may be adjusted at such height upon D as may be found necessary to bring the work within proper range of the cutting tool. The work tables E, E are raised or lowered upon D by means of a vertical screw, which is operated by the handle H, this part of the mechanism accomplishing the same end as the elevating mechanism shown in Fig. 1496. The swivel head J is here provided at its top with a segment of a worm-wheel which may be actuated to swivel that head by the worm G.
The swivel head may thus be operated upon its pivot, causing the tool point to describe an arc of a circle of which the pivot is the centre. To steady the swivel head when thus actuated, there is behind the worm segment a [V]-slide that is an arc, whose centre is also the centre of the pivot.
The tool-carrying slide A is operated as follows: The driving pulley P rotates a shaft lying horizontal at the back of the machine. Along this shaft there is cut a featherway or spline driving a pinion which operates a link mechanism such as described with reference to Fig. 1550.
The means of adjusting the distance the head of A shall stand out from B, are similar to that described for Fig. 1496, a bolt passing through A, and in both cases attaching to a connecting rod or bar.
At K is a cone mandrel such as has been described with reference to lathe work upon which is chucked a cross-head C. By means of suitable mechanism, this mandrel is rotated to feed the circular circumference of the cross-head jaws to the cut, the slider B remaining in a fixed position upon the bed M.
To support the outer end of the cone mandrel a beam L is bolted to the two tables E, E. On L is a slideway for the piece P. At S is a lug upon E through which threads a screw R, which adjusts the height of the piece P, while Q is a bolt for securing P in its adjusted position. This cone mandrel and support is merely an attachment to be put on the machine as occasion may require.
Fig. 1536 represents a shaping machine by the Pratt and Whitney Company. In this machine a single sliding head is used and the work remains stationary as in the case of the machine shown in Fig. 1535. The vice is here mounted on a slide which enables the work to be finely adjusted beneath the sliding bar independently of that bar, which is provided with a Whitworth quick-return motion.
As the tool-carrying slide of a shaping machine leaves its guideways during each stroke, the tool is less rigidly guided as the length of slide stroke is increased, and on this account its use is limited to work that does not require a greater tool stroke than about 18 inches, and in small machines not to exceed 12 inches. The capacity of the machine, however, is obviously greatest when the length of the work is parallel to the line of motion of the feed traverse. Work whose dimension is within the limit of capacity of the shaper can, however, be more expeditiously shaped than planed because the speed of the cutting tool can be varied to suit the nature of the work, by reason of the machine having a cone pulley, whereas in a planing machine the cutting speed of the tool is the same for all sizes of work, and all kinds of metal. In shaping machines such as shown in Fig. 1537, or in similar machines in which the work table is capable of being traversed instead of the head, the efficiency of the work-holding table and of the chucking devices may be greatly increased by constructing the table so that it will swivel, as in Fig. 1538, which may be done by means of the employment of Thomas's swivelling device in Fig. 1530. By this means the ends of the work may be operated upon without removing it from the chuck. Or the work may be shaped taper at one part and parallel at another without unchucking it.
Fig. 1539 shows a circular table swivelled by the same device, sitting upon a work table also swivelled.
Fig. 1540 represents a general view of a shaping machine having the motion corresponding in effect to a planing machine, the object being to give a uniform rate of speed to the tool throughout, both on its cutting and return stroke. The feed always takes place at the end of the return stroke, so as to preserve the edge of the tool, and the length of the stroke may be varied, without stopping the machine, by simply adjusting the tappets or dogs, the range of stroke being variable from 1/4 inch to 20 inches, while the return stroke is 40 per cent. quicker than the cutting one. There are two different rates of cutting speed, one for steel and the other for the softer metals.
The ram or bar is provided with a rack (Z, Fig. 1545) which engages with a pinion S, Fig. 1541, H being the driving shaft driven by the belt cones A and B. These two cones are driven by separate belts, but from the same counter-shaft, one being an open and the other a crossed belt. The open belt drives either the largest step of pulley B, giving a cutting speed suitable for steel, or the smaller step, giving a cutting speed for softer metals, as cast iron, &c. The crossed belt drives, in either case, the pulley A for the quick-return stroke, and this pulley revolve upon a sleeve or hub C, which revolves upon the shaft H. The sleeve or hub C is in one piece with a pulley C, whose diameter is such as to leave an annular opening between its face and the bore of the largest step of cone pulley B, and pulley A is fast to the hub or sleeve C. It will be seen that as the driving belts from the counter-shaft are one open and one crossed, therefore pulley A runs constantly in one direction, while pulley B runs constantly in the other, so that the direction of motion of the driving shaft H depends upon whether it is locked to pulley A or to pulley B.
In the annular space left between the face of pulley C and the cone B is a steel band G, Fig. 1542, forming within a fraction a complete circle, and lined inside and out with leather, and this band is brought, by alternately expanding and contracting it, into contact with either the bore of the largest cone step of B or with the outside face of pulley C. The ends of this band are pivoted upon two pins F, which are fast in two arms E and D, in Fig. 1542. Arm E is fastened to the driving shaft H, and its hub has two roller studs K, Fig. 1541, these being diametrically opposite on the said hub. The hub of arm D is a working fit upon the hub of E, and has two slots to admit the above rollers. Hub D is also provided with two studs and rollers placed midway between the studs K. These latter rollers project into the spiral slots K´ of the ring in Fig. 1543, this ring enveloping the hub of D and being enveloped by the sleeve M, which contains two spiral grooves diametrically opposite, and lying in an opposite direction to grooves K´, Fig. 1543. Sleeve M is prevented from revolving by rollers on the studs O, which are screwed into the bearing bush R, and carry rollers projecting into the slots in M.
It is evident that if the ring L, Fig. 1543, is moved endways with M, then the arms E, D, together with the band G, will be expanded or contracted according to the direction of motion of the ring, because the motion of M, by means of its spiral grooves, gives a certain amount of rotary motion to the ring L, and the spiral grooves in the ring give a certain amount of rotary motion to the arms D and E, Fig. 1542. When this rotary motion is in one direction the band is expanded; while when it is reversed it is contracted, and the direction of motion of shaft H is reversed.
The outer sleeve M carries the rod T, Figs. 1544 and 1545, which is connected to the lever U, the upper arm of which is operated by the tappets or dogs X on the ram or sliding bar, and it is obvious that when U is vibrated sleeve M is operated in a corresponding direction, and the ring L also is moved endwise in a corresponding direction, actuating the band as before described, the direction of motion being governed, therefore, by the direction in which U is moved by the tappets or dogs. A certain degree of friction is opposed to the motion of lever U in order to keep it steady, the construction being shown in Fig. 1546, where it is seen that there is on each side of its nut a leather washer, giving a certain amount of elasticity to the pressure of the nut holding it in place on the shaft U.
The mechanism for actuating the feed at the end of the return stroke only, is shown in Fig. 1547. The shaft V (which is also seen in a dotted circle in Fig. 1545) carries a flange c, on each side of which is a leather disk, so that the pressure of the bolts which secure b to the sleeve a causes c to revolve under friction, unless sleeve a, slotted bar b, and flange c all revolve together, or, in other words, c revolves under friction when it revolves within a b.
Fig. 1548 is an end view of Fig. 1547.
Fig. 1549 gives a cross-sectional view of the shaft sleeve, &c. The sleeve a is provided with two pins i, i, and a pin k is fast in the frame of the machine, and it is seen that a and V may revolve together in either direction until such time as one of the pins i meets the stationary pin k, whereupon the further revolving of a will be arrested and V will revolve within a, and as flange c, Fig. 1547, revolves with V, it will do so under the friction of the leather washers. The pins i and the pin k are so located that a can have motion only when the ram or sliding-bar is at the end of the return stroke, and the feed-rod f, being connected to b, is therefore actuated at the same time.
Among the various mechanisms employed to give a quick return to the tool-carrying slide of shaping machines, those most frequently employed are a simple crank, a vibrating link, and the Whitworth quick-return motion, the latter being the most general one.
The principle of action when a vibrating link is employed may be understood from Fig. 1550, in which P is a pinion driven by the cone pulley and imparting motion to D. At L is a link pivoted at C. At A is a link block or die capable of sliding in the slot or opening in the link and a working fit upon a pin which is fast in the wheel D. As D rotates the link block slides in the slot and the link is caused to travel as denoted by the dotted lines. R is a rod connecting the tool-carrying slide S to the upper end of link L, and therefore causing it to reciprocate with L. But S being guided by its slide in the guideway traverses in a straight line.
Since the rotation of P and D is uniform, the vibrations of the link L will vary in velocity, because while the link block is working in the lower half of the link slot it will be nearer to the centre of motion C of the link, and the upper end of C will move proportionately faster. The arrangement is such that during this time the tool-carrying slide is moved on its return stroke, the cutting stroke being made while the link block is traversing the upper half of the slot, or in other words, during the period in which the crank pin in A is above the horizontal centre of wheel D.
Now suppose the arrangement of the parts is such that the front of the machine or the cutting tool end of the slide is at the end K of S, then S will be pushed to its cut by the rod R at an angle which will tend to lift S in the slideways. But suppose the direction of rotation of wheel D instead of being as denoted by the arrow at D be as denoted by the arrow at E, then S will be on its back stroke, the front of the machine being at J. In this case rod R will pull S to the cut, and S will, from the angularity of R, be pulled down upon the bed of the slideway guiding it, and will therefore be more rigidly held and less subject to spring, because the tendency to lift is resisted on one side by the adjustable gib only, and on the other by the projecting V, whereas the tendency to be pulled downwards is resisted by the strength of the frame of the machine.
Furthermore, as the pressure on the cutting tool is below the level of the tool-carrying slide it tends to force that slide down upon the slideway, and it will therefore be more rigidly and steadily guided when the force moving the slide and the tool pressure both act in the same direction.
To vary the length of stroke of S pin A is so attached to wheel D that it may be adjusted in its distance from the centre of D.
The Whitworth quick-return motion is represented in Fig. 1551. At P is the pinion receiving motion from the cone pulley or driving pulley of the machine and imparting motion to the gear-wheel G, whose bearing is denoted by the dotted circle B. Through B passes a shaft C, which is eccentric to B and carries at its end a piece A in which is a slot to receive the pin X, which drives rod R whose end Z is attached to the ram of the machine. At D is a pin fast in gear-wheel G and passing into a slot in A.
Taking the position the parts occupy in the figures, and it is seen that the axis of B is the centre of motion of G and is the fulcrum from which the pin D is driven, the power being delivered at X. The path of motion of the driving pin D is denoted by the dotted circle H´, and it is apparent that as it moves from the position shown in the figure it recedes from the axis of C, and as the motion of G is uniform in velocity therefore D will move A faster while moving below the line M than it will while moving above it, thus giving a quick return, because the cutting stroke of the ram occurs while D is above the line M and the return stroke occurs while D is below M.
In some constructions the pin X and pin D work in opposite ends of the piece A, as shown in Fig. 1552. This, however, is an undesirable construction because the shaft C becomes the fulcrum, and as the power and resistance are on opposite ends of the lever A, the wheel G is therefore forced against its bearing, and this induces unnecessary friction and wear.
We may now consider the tool motion given by other kinds of slide operating mechanism.
In Fig. 1553 is a diagram of the tool motion given when the slide is operated by a simple crank C, the thickened line R representing the rod actuating the slide and line on the line of motion of the cutting tool. The circle H denotes the path of revolution of the crank pin, and the black dots 1, 2, 3, 4, &c., equidistant positions of the crank pin.
Line m represents the path of motion of the cutting tool.
If a pair of compasses be set to the full length of the thick line R, that is from the centre of the crank pin to end B of line R, and these compasses be then applied to the centre of crank pin position 1, and to the line m, they will meet m at a point denoted by line a, which will, therefore, represent the position of the tool point when the crank pin was in position 1. To find how far the tool point is moved while the crank pin moves from position 1 to position 2, we place the compass point on the centre of crank pin position 2 and mark line b. For crank position 3 we have by the same process line c, and so on, the twelve lines from a to l representing crank positions from 1 to 12.
Now let it be noted that since the path of the crank pin is a circle, the tool point will on the backward stroke occupy the same position when the crank pin is at corresponding positions on the forward and backward strokes. For example, when the crank pin is in position 7 the tool point will be at point g on the forward stroke, and when the crank pin is in position 17 the tool will be at point g on the backward stroke, as will be found by trial with the compasses; and it follows that the lines a, b, c, &c., for the forward stroke will also serve for the backward one, which enables us to keep the engraving clear, by marking the first seven positions on one side of line m, and the remaining five on the other side of m, as has been done in the figure.
Obviously the distances apart of the lines a, b, c, d, &c., represent the amount of tool motion during equal periods of time, because the motion of the crank pin being uniform it will move from position 1 to position 2 in the same time as it moves from position 2 to position 3, and it follows that the cutting speed of the tool varies at every instant in its path across the work, and also that since the crank pin operates during a full one-half of its revolution to push the tool forward, and during a full one-half to pull it backward, therefore the speed of the two strokes are equal.
We may now plot out the motion of the link quick return that was shown in Fig. 1550, the dotted circle H´, in Fig. 1554, representing the path of the pin A, and the arc H representing the line of motion of the upper end of link L, and lines N, O, its centre line at the extreme ends of its vibrating motion. In Fig. 1554 the letters of reference refer to the same parts as those in Fig. 1550. We divide the circle H´ of pin motion into twenty-four equidistant parts marked by dots, and through these we draw lines radiating from centre C and cutting arc H, obtaining on the arc H the various positions for end Z of rod R, these positions being marked respectively 1, 2, 3, 4, &c., up to 24. With a pair of compasses set to the length of rod R from 1 on H, as a centre, we mark on the line of motion of the slide line a, which shows where the other end of the rod R will be (or, in other words, it shows the position of bolt B in Fig. 1550), when the centre of A, Fig. 1550, is in position 1, Fig. 1554.
From 2 on arc H, we mark with the compasses line b on line M, showing that while the pin moved from 1 to 2, the rod R would move slide S, Fig. 1550, from a to b, in Fig. 1554. From 3 we mark c, and so on, all these marks being above the horizontal line M, representing the line of motion, and being for the forward stroke. For the backward stroke we draw the dotted line from position 17 up to arc H, and with the compasses at 17 mark a line beneath the line M of motion, pursuing the same course for all the other pin positions, as 18, 19, &c., until the pin arrives again at position 24, and the link at O, and has made a full revolution, and we shall have the motion of the forward stroke above and that of the backward one below the line of motion of the slide.
On comparing this with the crank and with the Whitworth motion hereafter described, we find that the cutting speed is much more uniform than either of them, the irregularity of motion occurring mainly at the two ends of the stroke.
In Fig. 1555 we have the motion of the Whitworth quick return described in Fig. 1551, H´ representing the path of motion of the driving-pin D about the centre of B, and H´ the path of motion of X about the centre C, these two centres corresponding to the centres of B and C respectively in Fig. 1551. Let the line M correspond to the line of motion M in Fig. 1551. Now, since pin D, Fig. 1551, drives, and since its speed of revolution is uniform, we divide its circle of motion H´ into twenty-four equal divisions, and by drawing lines radiating from centre B, and passing through the lines of division on H´, we get on circle H twenty-four positions for the pin X in Fig. 1551. Then setting the compasses to the length of the rod (R, Fig. 1551), we mark from position 1 on circle H as a centre, line a; from position 2 on H we mark line b, and so on for the whole twenty-four positions on circle H, obtaining from a to n for the forward, and from n to y for the motion during the backward stroke. Suppose, now, that the mechanism remaining precisely the same as before, the line M of motion be in a line with the centres C, B, instead of at a right angle to it, as it is in Fig. 1551, and the motion under this new condition will be as in Fig. 1556, the process for finding the amount of motion along M from the motion around H being precisely as before.
The iron planing machine, or iron planer as it is termed in the United States, is employed to plane such surfaces as may be operated upon by traversing a work table back and forth in a straight line beneath the cutting tool. It consists essentially of a frame or bed A, Fig. 1557, provided on its upper surface with guideways, on which a work carrying table T may be moved by suitable mechanism back and forth in a straight line.
This frame or bed carries two upright frames or stanchions B, which support a cross-bar or slide C, to which is fitted a head which carries the cutting tool.
To enable the setting of the tool at such a height from the table as the height of the work may require, the cross slide C may be raised higher upon the uprights B by means of the bevel gears F, G, H, and T, the latter being on a shaft at the top of the machine, and operating the former, which are on vertical screws N, which pass down through nuts that are fast upon the cross slide C.
To secure C at its adjusted height, the uprights are provided with [T]-shaped slots H H, and bolts pass through C, their heads being in the [T]-grooves, and their nuts exposed so that a wrench may be applied to them.
The faces of the cross slide C are parallel one to the other, and stand at a right angle to the [V]-guideways on which the work table (or platen as it is sometimes termed) slides; hence the cross slide will, if the table is planed true or parallel with this cross slide, be parallel with the table at whatever height above the table it is set, providing that the elevating screws, when operated, lift each end of C equally.
The construction of the head D corresponds to that of the head shown in Figs. 1497 and 1498 for a shaper, except that in this case the swivel head is secured to a saddle that slides along C, being provided with a nut operated by a feed screw J, which moves D along C.
The mechanism for operating the work table or platen T is as follows:--P P´ are two loose pulleys and P´´ is a driving pulley fast on the same shaft. This shaft drives, within the casing at Q, a worm operating a worm-wheel, which actuates inside the frame A and beneath the work table a train of gears, the last of which gears with a rack, provided on the underneath side of the table.
The revolutions of this last wheel obviously cause the work table to slide back and forth while resting on the [V]-guideways provided on top of the frame A, the direction of table motion being governed by the direction in which the wheel revolves.
This direction is periodically reversed as follows:--The pulley P is driven by a crossed belt, while pulley P´ is driven by an open or uncrossed one, hence the direction of revolution of the driving pulley P´´ will be in one direction if the belt is moved from P to P´´, and in the other if the belt is moved from P´ to P´´. Mechanism is provided whereby first one and then the other of these belts is moved so as to pass over upon P´´ and drive it, the construction being as follows:--
To the edge of the work table there is fixed a stop R, which as the table traverses to the right meets and moves a lever arm S, which through the medium of a second lever operates the rod X, which operates a lever u, which has a slot through which one of the driving belts passes. The lever u operates a second lever w on the other side of the pulleys, and this lever also has a slot through which the other driving belt passes.
When the stop R moves the lever arm S levers u and w therefore move their respective belts, one moving from the tight pulley P´´ to a loose one as P, and the other moving its belt from the loose pulley as P´ to the tight one P´´, and as the directions of belt motions are opposite the direction of revolution of P´´ is reversed by the change of belt operating it. There are two of the stops R, one on each side of the lever S, hence one of these stops moves the lever S from left to right and the other from right to left.
Suppose, then, that the table is moving from right to left, which is its cutting stroke, and the driving belt will be on the pulley P´´ while the other belt will be on pulley P. Then as the stop R moves S and operates X the arm u will move its belt from P´´ to P´, and arm w will move its belt from P to P´´, reversing the direction of motion of P´´, and therefore causing the table T to move from left to right, which it will continue to do until the other stop corresponding to R meets S and moves it from right to left, when the belts will be shifted back again. The stroke of the table, therefore, is determined by the distance apart of the stops R, and these may be adjusted as follows:--
They are carried by bolts whose heads fit in a dovetail groove Z provided along the edge of the table, and by loosening a set screw may therefore be moved to any required location along the bed.
To give the table a quick return so that less time may be occupied for the non-cutting stroke, all that is necessary is to make the countershaft pulley that operates during the back traverse of larger diameter than that which drives during the cutting traverse of the table.
In order that one belt may have passed completely off the driving pulley P´´ before the other moves on it the lever motions of u and w are so arranged that when the belt is moving from P´´ to P lever u moves in advance of lever w, while when the other belt is being moved from P´´ to P´ lever w moves in advance of lever u.
To enable the work table to remain at rest, one driving belt must be upon P and the other upon P´, which is the case when the lever arm S is in mid position, and to enable it to be moved to this position it is provided with a handle K forming part of lever S.
To cause the tool to be fed to its cut before it meets the cut and thus prevent it from rubbing against the side of the cut, as was described with reference to Fig. 1503, the feed takes place when the table motion is reversed from the back or return stroke to the cutting or forward stroke by the following mechanism:--
At a is a rack that is operated simultaneously with S and by the same stop R. This rack operates a pinion b, which rotates the slotted piece c, in which is a block that operates the vertical rod d, which is attached to a segmental rack e, which in turn operates a pinion which may be placed either upon the cross-feed screw J, or upon the rod above it; the latter operates the vertical feed of the tool through mechanism within the head D and not therefore shown in the engraving. Thus the self-acting tool feed may take place vertically or across the work table at will by simply placing the pinion upon the cross-feed screw or upon the feed rod, as the case may be.
Fig. 1558 represents a planer by David W. Pond, of Worcester, Massachusetts, in which the rod x is connected direct from S to a pivoted piece y in which is a cam-shaped slot through which pass pins from the belt-moving arms u and W. The shape of the slot in y is such as to move the belt-moving arms one in advance of the other, as described with reference to Fig. 1566.
The feed motions are here operated by a disk C, which is actuated one-half a revolution when the work table is reversed. This disk is provided on its face with a slide-way in which is a sliding block that may be moved to or from the centre of C by the screw shown, thus varying at will the amount of stroke imparted to the rod which moves the rack by means of which the feed is actuated through the medium of the gear-wheels at f. The handle g is for operating the feed screw when the self-acting feed is thrown out of operation, which is done by means of a catch corresponding in its action to the catch shown in Fig. 1501. S and S´ are in one piece, S´ being to move the two driving belts on to the loose pulleys so as to stop the work table from traversing.
The size of a planer is designated from the size of work it will plane, and this is determined by the greatest height the tool can be raised above the planer table, the width between the stanchions, and the length of table motion that can be utilized while the tool is cutting; which length is less than the full length of table stroke, because in the first place it is undesirable that the rack should pass so far over the driving wheel or pinion that any of the teeth disengage, and, furthermore, a certain amount of table motion is necessary to reverse after the work has passed the tool at the end of each stroke.
Fig. 1559 represents a method employed in some English planing machines to drive the work table and to give it a quick return motion. In this design but one belt is used, being shifted from pulley A, which operates the table for the cutting stroke, to pulley J, which actuates the table for the return stroke. The middle pulley K is loose upon shaft B, as is also pulley J, which is in one piece with pinion J´. Motion from A is conveyed through shaft B and through gear C, D, E to F, and is reduced by reason of the difference in diameter between D and E and between F and G. Motion for the quick return passes from J direct to F without being reduced by gears D, E, hence the difference between the cutting speed and the speed of the return stroke is proportionate to the relative diameters or numbers of teeth in D and E, and as E contains 12 and D 20 teeth, it follows that the return is 8/12 quicker than the cutting stroke.
In this design the belt is for each reversal of table motion moved across the loose pulley K from one driving pulley to the other, and therefore across two pulleys instead of across the width of one pulley only as in American machines.
In American practice the rack R, Fig. 1559, is driven by a large gear instead of by a pinion, so that the strain on the last driving shaft S, in Fig. 1560, shall be less, and also the wheel less liable to vibration than a pinion would be, because in the one case, as in Fig. 1559, the power is transmitted through the shaft, while in the other, as in Fig. 1560, it is transmitted through the wheel from the pinion P to the rack R.
Fig. 1561 represents a planer, designed for use in situations where a solid foundation cannot be obtained, hence the bed is made of unusual depth to give sufficient strength and make it firm and solid on unstable foundations, such as the floors in the upper stories of buildings. In all other respects the machine answers to the general features of improved planing machines.
As the sizes of planing machines increase, they are given increased tool-carrying heads; thus, Fig. 1562 represents a class in which two sliding heads are used, so that two cutting tools may operate simultaneously. Each head, however, is capable of independent operation; hence, one tool may be actuated automatically along the cross slide to plane the surfaces of the work, while the other may be used to carry a cut down the sides of the work, or one tool may take the roughing and the other follow with the finishing cut, thus doubling the capacity of the machine.
In other large planers the uprights are provided with separate heads as shown in the planer in Fig. 1563, in which each upright is provided with a head shown below the cross slide. Either or both these heads may be employed to operate upon the vertical side faces of work, while the upper surface of the work is being planed.
The automatic feed motion for these side heads is obtained in the Sellers machine from a rod actuated from the disk or plate in figure, this rod passing through the bed and operating each feed by a pawl and feed wheel, the latter being clearly seen in the figure.
To enable the amount of feed to be varied the feed rod is driven by a stud capable of adjustment in a slot in the disk.
Fig. 1563 represents a planing machine designed by Francis Berry & Sons, of Lowerby Bridge, England. The bed of the machine is, it will be seen, [L]-shaped, the extension being to provide a slide to carry the right-hand standard, and permit of its adjustment at distances varying from the left-hand standard to suit the width of the work. This obviously increases the capacity of the machine, and is a desirable feature in the large planers used upon the large parts of marine engines.
ROTARY PLANING MACHINE.--Fig. 1564 is a rotary planing machine. The tools are here carried on a revolving disk or cutter head, whose spindle bearing is in an upper slide with 2 inches of motion to move the bearing endways, and thereby adjust the depth of cut by means of a screw. The carriage on which the spindle bearing is mounted is traversed back and forth (by a worm and worm-wheel at the back of the machine) along a horizontal slide, which, having a circular base, may be set either parallel to the fixed work table or at any required angle thereto.
By traversing the cutter head instead of the work, less floor space is occupied, because the head requires to travel the length of the work only, whereas when the work moves to the cut it is all on one side of the cutter at the beginning of the cut, and all on the other at the end, hence the amount of floor space required is equal to twice the length of the work.
The disk or cutter head is in one piece with the spindle, and carries twenty-four cutters arranged in a circle of 36 inches in diameter. These cutters are made from the square bar, and each cutting point should have the same form and position as referred to one face, side, or square of the bar, so that each cutter may take its proper share of the cutting duty; and it is obvious that all the cutting edges must project an equal distance from the face of the disk, in which case smooth work will be produced with a feed suitable for the whole twenty-four cutters, whereas if a tool cuts deeper than the others it will leave a groove at each passage across the work, unless the feed were sufficiently fine for that one tool, in which case the advantage of the number of tools is lost.
The cutters may be ground while in their places in the head by a suitable emery-wheel attachment, or if ground separately they must be very carefully set by a gauge applied to the face of the disk.