The art of pattern-making

Front matter

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Chap. ZX^.^Xl^-O

Preface

The author's extensive experience in connection with pattern-making in nearly all of its variations impressed him with the belief that great benefit would be derived by many members of the craft by acquiring a more general knowledge of the business. No individual can have had the experience of many. The acquisition, then, of the knowledge of others must be gained through lectures or literature. The literature pertaining to pattern-making is by no means as extensive as the importance of the business warrants. There are many pattern-makers competent to treat the subject in a satisfactory manner, but have been deterred by the amount of time and labor necessary to do the subject justice.

The subjects chosen for illustration herein are chiefly those with which the author has had personal experience and were originally written for publication in "Machinery." He also records the experience of others in pattern -making ; these examples have been selected chiefly from the correspondence of the ''American Machinist." He has

iii

IV PREFACE.

embodied whatever in his opinion would be of interest to the pattern-making fraternity.

Providing for the interior of castings, or core-box work, is correctly regarded as the most intricate and important part of pattern-making. Amongst the subjects several excellent examples of core-box work will be found.

Screw propellers are a special feature, and the examples given are thoroughly elucidated.

The author has always entertained a deep interest in pattern -making owing to its intricacy, the skill and intelligence required for its execution. In presenting this volume to its readers he hopes and believes it will be found a useful and desirable acquisition to the literature of pattern-making.

Contents

PAGE

I. Introduction ^

II. Equipment of a Modern Pattern-shop 13

Introduction

The art of pattern-making comprises the modeling of objects that are intended to be cast of metals. Its origin is contemporaneous with that of the casting of bronze, and, like that of the latter, the period of its inception is lost in the oblivion of remote ages.

The first patterns were probably made of clay or of similar material, and were models of those rude bronze castings that have been found in ancient ruins. At a later period wax was employed for patterns which represented the more artistic bronze articles. In both these methods the models were usually destroyed in the process of moulding, and their consequent disappearance, in conjunction with the then existent limited knowledge of bronze founding, made the castings rare and valuable.

In the ancient wax process the modeling was done directly in the wax. When the object was large a core representing the interior form of the object was made of the same materials that formed the mould. Over this the wax was modeled and the mould was built around the model or pattern thus formed. In building the mould, inlets or gates through which the metal entered, and vents through which the gases escaped from the mould, were provided; these were also represented in wax. When the mould was heated in the process of baking, the wax melted and escaped through outlets provided for the purpose during the construction of the mould.

Wax is still used for patterns, although chiefly for ornamental work. In the modem process the modeling is done in clay, and a plaster mould made of the object thus modeled. The wax model is then produced by filling the plaster mould with molten wax. Plaster patterns are also used to a large extent in ornamental work. The process of producing them is similar to that of making wax patterns.

For many kinds of patterns plaster is a convenient material. It will readily take impressions with fidelity, its durability is such that it will withstand repeated use, and it is sufficiently cohesive to allow of a pattern being made in sections for convenience in moulding.

As the various arts requiring castings advanced and demanded larger and more complicated castings, the art of founding progressed with it. To meet this created demand it became necessary to produce larger and more complicated as well as more durable patterns.

INTRODUCTION. 3

Wood, then, of all materials, has been found to possess the qualities which are requisite in the construction of large and intricate patterns at moderate expense. Of the various kinds of wood suitable for pattern work, clear, dry white pine stands preeminent. Its abundance and cheapness, the ease with which it can be worked, combined with its constancy in retaining its form, has induced its employment for pattern work to a greater extent than all other materials combined. The kind of pine that grows in the neighborhood of the Great Lakes is the best. It is better without knots or sap, although a small knot or a little sap occasionally is not objectionable, especially for large patterns, provided the wood is thoroughly seasoned and dry, for this latter quality is of the first importance.

The shrinkage of white pine across the grain is well understood. It has been asserted that it will also shrink with the grain lengthwise, and under certain conditions this is possible to a small extent when the wood is of curly or cross-grained nature. A case of apparent shrinkage in length of white pine was related to the writer by a reliable person. In making a pattern he joined together two pieces of white pine and then planed off their ends, thus insuring their being of the same length. Subsequently, after the pattern had been used for moulding and had been stored in the pattern loft for some time, it was noticed that the two pieces were of imequal lengths. From the nature of the construction of the pattern and the position of the two pieces in it, the opinion was formed that the shorter piece had shrunk in length. The resistance that soft, white pine offers to compression is not very great. If a piece of this wood, of cross-section small in comparison to its length, is left standing on end a sufficient space of time, it is possible for it to decrease in length owing to its small power of withstanding compression, and thus create the belief that shrinkage was the cause of the change. For all practical purposes it may be said that soft, straightgrained white pine will not change its length by shrinkage.

When patterns are to be subjected to rough usage, or are to be used for many castings, harder woods, such as baywood, cherry, ash, maple, etc., are selected. The first-named of these possesses some of the qualities of white pine, in that it is easily worked and will hold its shape well; but it is the most expensive of the woods used. Of late years redwood has been largely employed in making patterns, but, although somewhat cheaper, it does not work as freely as white pine. Except for large and plain patterns, where the cost of material amounts to a large proportion of the entire expense of construction, the use of redwood for pattern work is of doubtful economy.

Metal patterns are also largely employed, but of course the original must have been made of wood or other material, and the metal pattern produced by process of founding.

Green-sand moulding is practiced to a greater

INTRODUCTION. 5

extent than other methods, because it is the cheapest for producing castings, especially for small work that is to be much duplicated. In .this the moulding is done in a suitable sand, moistened sufficiently to make it adhere together. Patterns for green-sand moulding are models of the object to be cast, and are made in such a manner that they may be readily withdrawn from the sand without mutilating the mould. To enable this to be accomplished the pattern is made in two or more sections, as the case necessitates, and so joined together as to allow the different parts to be withdrawn separately and in a manner depending on the form and position of the part. Core-prints are provided where necessary to locate and support the cores. Cores are bodies of prepared sand, baked. Their exterior form corresponds to an interior part of a casting, or to undercuts on its exterior that will prevent a model of it being withdrawn from the sand. In such a case the pattern is provided with core-prints which abolish the imdercuts and leave impressions into which cores are inserted to supply the part or parts of the mould made vacant by the core-prints.

Dry-sand moulding is next in importance. In this method the moulding is done in sand mixed with raaterials that will cause it, after being baked in an oven, to adhere firmly together and withstand greater pressure without distortion than with green sand. Another advantage the dry-sand method possesses is that the mould may be "cheeked," as foundrymen say; that is, it may be divided into

6 THE yiRT OF PATTERN-MAKING.

a number of parts and those parts lifted away to relieve undercuts and similar places in the patterns. Statuary is moulded in this manner.

Patterns for dry-sand moulding are constructed and finished in a similar manner to those for green sand, except that they can often be made with fewer pieces when the mould is to be " cheeked ' ' and drawbacks employed.

Loam moulding is used for the larger and heavier castings. In this method the moulding is not done in a flask, as in the case of the two previously described methods, but is built up of brickwork, strengthened by rods and plates where necessary. The moulding material is a mixture of sand and other materials of about the consistency of mortar. It is worked into the mould between the pattern and brickwork. By this method the mould can be made into any number of necessary sections, which can be disjointed, thus relieving the pattern and allowing its withdrawal. When the sections are assembled in a pit and clamped together with sand firmly rammed around the mould the latter is prepared for the metal.

In constructing a pattern to be moulded in loam it is advisable to use wood sparingly, and where it is used provision should be made for its swelling, which it will do by absorbing moisture from the loam. A strike or sweep used in loam moulding is a flat piece of board with the edge so shaped as to conform to the profile of a part of the desired casting by revolving it on a spindle or moving it

INTRODUCTION. 7

along guides, as the case requires. The required part of the mould can be formed without necessitating the pattern being worked out for it. A pattern to be moulded in loam is often but a skeleton of woodwork, some parts of it representing corresponding parts of the intended casting and other parts forming guides for sweeps. For instance, the mould for a plain cylinder may be formed altogether with sweeps by securing them to a spindle and revolving them while building up the mould.

Wooden patterns are usually finished with a coating of shellac dissolved in alcohol. This method is quick, furnishing a smooth surface, and provides protection against dampness when the pattern does not remain in the mould very long, as generally is the case with green-sand moulding. But when the pattern reraains in the mould for a length of time, especially in a loam mould, which is very wet, shellac does not afford a very good protection against the absorption of moisture by the pattern, and swelling is then the result. Painting the pattern is the alternative in this case, but it is seldom practiced in this country, in consequence of its inconvenience. Thoroughly oiling the pattern previously to its being placed in a loam mould is the usual practice.

All metals in passing from the liquid to the solid state suffer expansion when in the plastic condition. It is this feature in the transition that enables metals to take and retain the impressions of moulds with such fidelity. In cooling from the plastic condition to the solid state metals contract; the amount of this contraction to normal temperature will vary for the various kinds of metals. Patterns have therefore to be made larger than the intended casting by this amount, and here occurs the necessity on the part of the pattern-maker for the use of discreet judgment based upon extended experience in order to obtain the best possible results, because different kinds of varying mixtures of iron as well as that of alloys will contract with varying amounts. Moreover, the varying proportions of castings when made of the same material will vary in their amount of contraction. Thus an extended and plain casting will contract differently from one of more compact form, though both may be of equal weight and cast at the same time and of the same material. It is necessary also to make an allowance for the parts of a casting that are to be finished, taking into consideration the liability of imperfection in the form of the casting.

All woods contain moisture to some extent. Wood kept for several years in a dry place will contain 15 or 20 per cent, of water. Wood that has been thoroughly kiln-dried will, when exposed to the air under ordinary circumstances, absorb 5 per cent, of moisture in the first three days, and will continue to absorb until it approximates 15 per cent, of water. Wood, however dry, is subject to change; it will swell or shrink according to the humidity of the atmosphere or the hygrometric conditions under which it is placed. These circumstances

INTRODUCTION. 9

must be taken into consideration when a pattern is about to be constructed, and the material so manipulated that its swelling and shrinking will counteract each other in order that the pattern may retain its form and dimensions as nearly as possible.

There is another peculiarity of wood — its tendency to warp in one direction, the cause of which needs to be considered when a structure is to be built up with pieces of wood of various shapes and dimensions.

When a tree is sawn across it is observed apparently to be made up of a number of annular rings. One ring is reckoned for each year in the age of the tree. These rings are composed of numerous minute tubes known as capillary tubes. The sap which gives life and growth to the tree is absorbed by its roots from the soil through which they run. This sap is conveyed through the capillary tubes or veins of the tree by a mysterious force known as capillary attraction. When the capillary tubes are deprived of moisture they contract in diameter and consequently the system which they compose becomes smaller.

Fig. I illustrates a section of a tree with the capillary tubes somewhat exaggerated. If such a piece is cut at a season of the year when the tubes contain sap, it will split in the course of drying, as shown by Fig. 2, because the outside tubes dry out first and in shrinking the tenacity of the wood is not sufficient to overcome the resistance to compression offered by the wood within, which has not shrunk lo

THE ART OF PATTERN-MAKINC.

SO much, and consequently as the shrinkage occurs with great force the outer wood is pulled apart. To prevent this tendency to split, a hole is often bored through the center with the grain; this enables the

Fig. 1.

Fig.

wood to dry and shrink from the inside as well as from the periphery. Fig. 3 shows the section cut with the grain into three parts, and Fig. 4 shows it cut into six parts ; they also show the direction in

Fig.

Fig. 4.

which the shrinkage and warping occur. A knowledge of this tendency of wood to shrink and warp in

INTRODUCTION. ii

drying is important to possess, and a proper regard for it in joining woodwork will avoid many difficulties.

Pattern-making is of infinite variety, and the pattern-maker is never done learning. New forms and devices are continually appearing ; these necessitate constant study and scheming on the part of the pattem-rriaker to meet the new conditions. An extended range of thought, skill, and experience is necessary for efficient pattern-making. A model of an object is not necessarily a pattern, because it may be made in such a manner that it will be impracticable to mould it.

To become an expert pattern-maker necessitates talents superior to those required for any of the branches of the machine business except designing. The pattern-maker should possess the qualifications of a moulder and also a draftsman, and must be able to read any mechanical drawing readily and conceive the form and intention of the object illustrated by the draftsman, and comprehend its details in the minutest degree. He must be able to determine how and in what manner the object is to be moulded before he can intelligently begin the construction of the pattern, and avoid the errors likely to occur by his inability to do so. Expert pattern-makers are classed with the best general mechanics.

It is a mistaken opinion of some persons that any mechanic working in the trades where the chief material used is wood can work at pattern-making. The pattern-maker is trained to the greatest refinement in the art of working wood. There are few employments which require greater speciaHzed knowledge of rather a wide range than that of pattern-making.

Good carpenters and cabinet-makers can become pattern-makers after the necessary training, their degree of success as pattern-makers depending in a great measure on how great an impression the habits acquired in their respective trades have made upon them.

II. Equipment Of A Modern Pattern-shop

The most advantageous arrangement that can be given a modem pattern-shop depends upon the floorplan.

Assuming that the room is rectangular, of ample dimensions, and is sufficiently lighted on the sides, the most convenient disposition is to place the work-benches along one side and the machines along the other. By this arrangement the dust and shavings can be kept under better control and the transmission of the power to the machines facilitated. Where the dimensions of the floor are about equal lengthwise and across, and there is sufficient room for the benches along both sides, it is advisable to place the machines in the middle or at one end of the workshop. A room in which to keep the various articles used about the shop by the workmen and belonging to the works, such as hand-screws, clamps, and other tools, should be partitioned off. It should be the duty of the sweeper to see that these articles, when not in use, are kept in a place provided for them.

Stands or shelves should be erected at each lathe, and the various attachments, such as chucks, centers, etc., kept upon them when not in use. Similar fixtures should also be provided, where necessary, for the other machines.

The line shaft should run from 250 to 300 revolutions per minute. All wood-working machines require high speeds. With a moderately high speed to begin with, the necessary speed of the machines can be transmitted from the line shaft to better advantage than when a lowerer speed of the shaft prevails.

Wood-turning lathes are indispensable in a pattern-shop, and there should be several of them, their number depending on the number of workmen employed. In a shop having a force of forty pattern-makers at least four lathes are necessary. One of these should be a face-lathe for large diameters, ten feet or thereabouts. Another should be a combined face and tailstock lathe, having an ovei*- hanging face-plate capable of swinging pieces of about six feet in diameter, and a capacity of two feet in diameter between the centers. The others should be ordinary wood-turning lathes of smaller capacity, one of which should be suitable for the smallest work. Wooden cones are preferable for wood-turning lathes, and they should be carefully balanced. The speed for wood-turning may vary from 1200 to 2500 feet per minute, according to the nature of the work.

In a shop of the foregoing capacity two circularsaw machines are necessary, both of which should be provided with an iron table and an arrangement by which the vertical height of the saw may be adjusted. One of these should be capable of receiving a saw 28 inches in diameter, and the other a saw 14 inches in diaraeter. The smaller machines should combine both cross-cut and rip saws, and be so arranged that they can be made to ''wabble" for rabbeting.

The usefulness of the machines depends largely on the condition in which they are kept. An excellent system is to have the teeth of circular saws shaped as in Fig. 5, and do all the filing on their front or cutting sides, the backs of the teeth being spiral curves. By this method, when the teeth are all filed equally on their fronts, the saw will be reduced uniformly in diameter, the amount of reduction depending on the spirality of the backs of the teeth and the extent of the filing.

To gum such a saw, a rotary or milling tool should be used. There are various neat little machines of this kind on the market, using mills of various sizes which can be clamped on the saw and the mill revolved by means of a crank, while it is fed to the tooth automatically. The mills make a rounded throat, which should extend slightly under the face of the teeth, so that in filing it will be unnecessary to extend the filing to the throat. This method requires but little filing to keep the saw sharp. If the saw is of sufficient size to admit of the employment of a swage for the setting of the teeth, this method should be adopted, as with it better results can be obtained from the saw than by bending the points of adjacent teeth in opposite directions. An i6

THE ART OF PATTERN-MAKING.

excellent swaging-tool is on the market with which the swaging is done by a cam operated with a lever. The style of tooth here commended is shown at Fig. 5.

Fig. 5.

The bearings for the arbor of circular saws should be of ample length and babbitted. They require careful attention, and should be taken apart and cleaned periodically, as it is practically impossible to prevent dust working into them.

Circular saws give good results when running at speeds of from 8000 to 10,000 feet per minute.

Circular saws are usually belted so that the revolutions of the arbor cannot be varied. In course of time saws become worn until their diameters are reduced considerably from their original dimensions; consequently there may be several saws of different diameters used on the same arbor, and of course their speeds will vary in proportion to their diameters. These conditions are met and the best results obtained from the machine by driving the arbor to the hmit of speed for the largest diameter of saw to be used; that is, at about 10,000 feet per minute for the periphery of the teeth.

A handy device for use when dressing saws is shown in Fig. 5. It consists of a T frame with the horizontal bar secured to a bench. The upright has a slot for the vertical adjustment of the saw. To the right is a swage, whose pivot can be adjusted on the horizontal bar; to the left is a small vise, 7, to receive one tooth of a saw. This vise is adjustable on the horizontal bar, to which it can be clamped by a thumb-screw. By gluing a piece of paper around the end of the file and keeping it bearing on the shelf while filing, all the teeth can be filed alike without difficulty.

The next most important tool for a pattern-shop is the band-saw machine. In a shop of the beforementioned capacity there should be at least two of these, one to carry saws up to ij inches wide, and the other to carry saws up to one inch. One great disadvantage in the use of these machines is the want of stiffness in the frames. There are but few made which are not deficient in this respect.

Band-saws give good results when run at a speed of 3500 to 4000 feet per minute. These machines are usually provided with breaks for the stoppage of the saw, and should always be so arranged that a pressure on a pulley beyond a certain fixed limit cannot be produced by them. If they are not so provided and the saw is stopped very suddenly, it is likely to break in consequence of the strain thus created. A great drawback to the use of these machines is the cost of the saws, which consequently break. That a band-saw will give way in the course of time is inevitable. Every time that a saw passes over the wheels while running, it bends and straightens again. This fatigues the material, and with continued running it is distressed beyond ultimate endurance, just as any similar piece of metal would be broken by being bent back and forth a sufficient number of times.

The breakage of saws may be reduced by careful attention to their condition and that of the machine. In joining them they should be scarfed and lapped two teeth and brazed with silver solder. Immediately the tongs are removed from the joint, a few drops of oil should be dropped on the saw by the side of the lap. If not so treated, the saw is likely to become too soft on either side of the joint and will break there earlier than at any other part.

Band-saws should always be kept sharp and have a proper set to the teeth, and the wooden jaws on the guide-bar of the machine should be kept set up close to the saw. The mouth-block in the table also requires frequent attention, as the deflection of the saws, especially the smaller ones, cuts them away.

An excellent little machine for sharpening and setting band-saws is to be found on the market. It can be secured to a post and occupies little room.

Being driven by power, a saw can be put in, the machine set going and allowed to run without further attention until the saw is finished.

Another important machine in the pattern-shop is a hand-planer. There should be two of these machines, one with 16-inch knives, to be kept for rough work, the other with 24-inch knives, to be reserved exclusively for the cleaner and finer class of work, because, if allowed to be used indiscriminately, the latter will seldom be in the condition essential for the kind of work required of it and for which the machine is specially adapted. The back table of a hand-planer should be provided with a locking arrangement, in order that its position cannot be changed after having been adjusted to the knives.

The speed recommended for hand-planers is 4000 feet per minute, but they will work satisfactorily between that speed and 3500.

A surface or cylinder planer is also a useful machine in a pattern-shop. An improved machine of this kind does not require a great amount of attention; it suffices to have the knives kept in proper condition and the bearings inspected occasionally, to see that the oil is properly performing its functions.

The speed is the same as for the hand-planer. When it is difficult to obtain 4000 feet per minute, a speed between that and 3500 feet will give satisfaction.

A Daniels planer is very useful in a pattern-shop. It is simple, effective and durable, requiring but little instruction regarding its care and use. With this planer the lumber can be planed out of wind, which cannot be done with a cylinder planer, although the work is not so rapidly done as with the latter.

The cutters of a Daniels planer should run at a high rate of speed, say from 10,000 to 1 1,000 feet per minute. The style of cutters recommended for a Daniels planer are shaped like the letter J, the cutting edge being on the side.

A jig-saw is required in a pattern-shop for inside sawing. The band-saw, which has supplanted it for outside sawing, is not adapted for positions bounded entirely by the material.

An advisable speed for this machine is from 500 to 1000 strokes per minute, according to the character of the machine.

A vertical boring-machine is also useful in a pattern-shop. One having a capacity for boring holes up to 2 inches in diameter is preferable, and should be arranged with two speeds, one to produce 850 or 900 revolutions of spindle, for bits more than i\ inches in diameter, the other 1200 or 1300 revolutions, for smaller bits.

A core-box machine is another very useful machine in a pattern-shop. A machine of this kind is on the market, on which core-boxes of any length and from f to 20 inches in diameter can be worked. Staves and similar pieces can also be worked accurately and rapidly on their hollow sides by this machine.

Among the minor power machines that a pattern-shop should have are a grinder for planer-knives, a wet emery -grinder for bench-tools, and two grindstones, one of the latter being corrugated for the convenience of grinding inside bevel gouges.

Trimmers are indispensable in a modem pattern-shop. It is advisable to have at least two of the largest size for the general use of the shop, and several of smaller size, one being located convenient to each two benches.

There are several other necessary adjuncts to the complete equipment of a pattern-shop, but these are so well known that description of them is here unnecessary.

The bearings of wood-working machinery require very careful attention, in consequence of the high speed at which it revolves and their liability to the deteriorating effects of dust. Bearings should always be provided with tallow-boxes, which should be kept filled with tallow or, better, with Albany grease. A small hole should be made through the grease near each end of the bearing, into which a little oil should be dropped before starting the machine ; then, should the oil work off with continuous running, the grease will continue to keep the bearing lubricated.