The modern machinist ...

Front matter

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A PRACTICAL TREATISE ON MODERN MACHINE SHOP METHODS

Especially adapted to the use of Machinists, Apprentices, Designers, Engineers and Constructors

Preface

It has become almost a custom in writing a treatise pertaining to " machine-shop practice " to devote a considerable portion of the contents to a description of the machine tools — and the cutting tools employed therewith.

On general principles it may be said that the improvements in the construction of machine tools for general machine-shop work have not been so "marked" as the improved methods of and appliances for handling the work thereon. Hence it is thought that the omission of the usual description of the ordinary machine tools and the cutting tools employed therewith will not be in any way detrimental, but that a more useful purpose will be served by endeavoring to omit as far as practicable anything that has heretofore appeared in print on this subject,describing and illustrating in the place thereof the means actually employed for performing the operations on various classes of work in many of the most prominent machine shops in this country and in England.

IV PREFACE.

Modern machine-shop practice, according to the author's conception of the term, consists of the methods and means of doing work which are or can be employed in the majority of machine shops where the facilities consist not in " special " but in " ordinary " machine tools and appliances; therefore while we do not in the least underestimate the value, advantages and capabilities of " special machine tools," we have confined ourselves exclusively to the methods and appliances which are usually available or can be readily made in any ordinary machine shop, and which can be used on or in connection with the ordinary forms of machine tools.

Essentially in showing and describing the means employed for doing work of any kind, reference must at all times be made directly to the work under consideration. But it does not necessarily follow that the means and devices shown can only be employed for doing that particular piece of work. It is a matter of some difficulty to select in every instance such parts of work as will show the general utility of the methods and appliances employed for doing the work thereon to the best advantage; but great care has been exercised in choosing the work and parts thereof, to let it be such as is most familiar to the machinist in general practice, and such as will readily show the applicability of the methods and devices to a wider range of machine-shop work.

In making so many of the descriptive drawings in perspective instead of by the ordinary rules of projection, an innovation has been introduced which we believe has never been carried out on so large a scale before in a work

PREFACE. V

of this kind. This has naturally increased the cost and labor of compilation considerably, and it is hoped that the value of the book is proportionately enhanced thereby, inasmuch as a more intelligent and comprehensive idea of the subject is gained.

We wish to acknowledge with thanks the kind assistance rendered by many prominent firms and mechanics, in furnishing sketches of and permission to insert the devices employed by them in their own practice.

The Author.

New York, 1895.

Preface To The Fifth Edition

The gratifying success of the previous editions of this work has rendered necessary the printing of this, the Fifth Edition.

The publishers hope this edition may prove a valuable assistance to its readers and hereby wish to acknowledge thanks to the mechanical journals and others who have endorsed this work so highly.

The Publishers.

New York, 1904.

CHAPTER I. Measuring Instruments

PAGE.

Measuring Instruments used in former times 23

Recent improvements in graduated "beam calipers " ... 23 The evolution of "micrometer measuring" machines and calipers, and their relation towards the duplication and

perfection in size of parts in machine construction . . 23

Inside " micrometer calipers" 24

The necessity of compensating for the wear of the tools employed in machine-shop practicei 26

The non-adjustability of " snap gauges" 27

Adjustable "snap gauges " for outside measurements ... 27

Adjustable "snap gauges " for inside measurements ... 30 Changes in measuring instruments, to be made and tested by

the tool-maker 31

Lapping " snap gauges " to size . 31

Supposed wear of " snap gauges " — caused by expansion . . 31 Hardening the arms of the gauges to avoid the above expansion 32

CHAPTER II. Vise Work

Vise work simplified by the improvements in the various

methods and tools for doing the work » 33

The ability of the vise hand to simplify his own methods and to improve the methods, processes, and work in every other branch of the profession 33

Templates ; templates for various purposes 34

Vlll CONTENTS.

JIGS.

PAGE.

The uses and possibilities of jigs on vise work 35

Skilled labor dispensed with by the use of jigs 35

Classification of jigs for vise work, jigs for the alignment

and location of parts, with examples of their application . 35

Filing jigs ; their uses and application 37

CHAPTER III. Vise Work. — Continued

Drifts ; their uses, classification, and forms 41

Drift and drift plug for cutting key ways ( . . 41

Drift jigs, with example of their application 42

The methods and principles of fitting keys 45

CHAPTER IV. Vise Work.— Continued

INSERTING PIECES IN SEAMS.

The reasons for and methods of inserting pieces in seams . 48 Inserting pieces of larger dimensions in metal work, where

imperfections exist 49

PEENING AND STRAIGHTENING METAI,.

Peening metal work to straighten it or change- its shape . 50

Peening not considered good practice when it can be avoided 50

Straightening cast-iron work by heating (with examples) . 50

Advantages of the latter over the former method . . . . 52

CHAPTER V. Chasing

The art of chasing 53

Tools employed in chasing • . 54

Examples of the application of the tools employed in chasing 54 Methods of holding the work while it is being " chased " .56

CONTENTS. IX

CHAPTER VI Erecting

PAGE.

General erecting, and the importance of a thorough knowledge of the principles and methods involved in the erection of machinery and other work 59

The necessity of having tools adapted to the work, and the influence the possession of such tools is likely to exert on the standing of the machinist 59

SETTING OR FINING SHAFTING.

Lining shafting with a transit level 60

The inadvisability of depending on an ordinary spirit level

to secure the accurate alignment of shafting 60

Lining shafting with a mounted straight-edge and level . . 61

Lining shafting with a hanging straight-edge and level . . 62 Lining shafting by means of a water level and distance

pieces fixed on the floor of the shop 63

Testing the alignment of shafting after the pulleys and belts

are all in position 64

To align shafting that has to be extended from one room or

building to another 65

Setting machinery in position, with regard to the work to be

performed thereon 66

Moving heavy machinery 67

Setting machinery permanently on its foundation .... 69

CHAPTER VII. Erecting. — Continued

General principles of erecting, as exemplified in the erection

of traction engine work 70

The similarity in the methods pursued in erecting traction and

locomotive engines 70

Methods of obtaining the center lines on the boilers, by and

from which the various parts are to be fitted and located . 70

Fitting and aligning the cylinder brackets 74

Marking and cutting the holes in which the bolts are inserted, which hold the various parts to the boiler, and the tools employed therefor 76

X CONTENTS.

PAGB.

Fitting on the cylinders 78

Fitting the crank-shaft bracket 78

Babbitting the crank-shaft bearings and the various methods and appliances employed for securing the correct alignment of the crank-shaft 79

Reaming the crank-shaft bearings . 85

The various methods and appliances employed for locating and

aligning the parts of the " propelling " mechanism ... 86

CHAPTER VIII. ErKCTing. — Continued

Erecting, as exemplified in the erection of stationary engine

work 94

Further development of the methods and principles already shown, as applied in the construction of a higher grade

of work 94

The necessity of laying out castings that have to be machined to ascertain if there is a sufficiency of metal on all the parts and surfaces to admit of their being cleaned or trued up 94 Laying off the bed of a stationary engine, in the rough. . . 95

Solid and adjustable trams 97

Locating and aligning the crank-shaft by means of jigs from the guides, guide- ways and other parts of the engine bed, with examples of the most approved methods for securing

the same ends 98

Aligning the valve rods and valve rod slides by means of jigs . 102 Boring and facing engine beds by means of a "boring rig" . . 102 Expanding the babbitt in the crank-shaft bearings .... 105 Aligning the parts of vertical engines by jigging 106

CHAPTER IX. Erecting .—Con tin ued

Device for driving cross-heads and piston-rods apart .... 109 Balancing pulleys and rotary parts of machinery no

CONTENTS. XI

PAGE.

Counter-balancing pulleys on the line shaft in

Balancing armatures, beater-drums for threshing machines,

etc 112

The adaptation of jigs in the erection of machinery in general 113

CHAPTER X. Planing, Shaping, Slotting

Principles and methods of chucking work 115

The springing of work by improper methods of chucking . .116 Method of chucking thin work 117

CHAPTER XI. Planing, Shaping, Slotting. — Cmtinued

CHUCKING TAPER WORK.

Simple method of chucking taper work ina" parallel-jawed "

Improved form of" monitor-chuck " for general chucking purposes ... 120

Examples of chucking work on the above chuck ..... 121

CHAPTER XII. Planing, Shaping, Slotting. — Continued

SUPPLEMENTARY CHUCKING-PLATES.

The employment of supplementary chucking-plates, to avoid the necessity of having to release and re-chuck the work when one surface has been operated on 123

Classification and forms of supplementary chucking-plates . 123

Reasons for compounding, and the avoidance of the same by

pivoting 124

Planing key seats in crank-shafts, and methods of securing the

accurate location of the same 126

Xll CONTENTS.

CHAPTER XIII. Planing, Shaping, Slotting. — Continued

CHUCKING ENGINE BEDS, CYLINDERS, ETC., FOR PLANING.

PAGE.

Chucking the frames of vertical engines 129

Chucking the beds of horizontal engines, for planing the

under side or base 130

Cutting key ways on the planer and slotter 131

Planing work between centers 133

Adjustable parallel to be used in connection with planer centers 133

Angle-plate, to be used in the same connection 134

CONCAVE AND CONVEX PLANING.

Methods and appliances used in planing " concaved " or "convexed " surfaces '. . 134

Principles on which the above appliances are based .... 136

CHAPTER XIV. Planing, Shaping, Slotting. — Continued

Gauge for planing V's and V-ways 137

Facilitating the adjustment of planer tools by means of a graduated planer head 139

Stud bolts and nuts — an improvement over the ordinary solid-headed bolts for planing and other machines 139

CHAPTER XV. Milling

modern milling practice.

The important position occupied by the milling machine . . 142

Selecting a machine with a view to its adaptability for the

work to be done thereon 142

Improvements made in " milling practice " by individual

operators and superintendents 143

How the " ordinary practice " of one individual or concern would be considered " advanced practice " by other individuals or concerns 144

CONTENTS. Xlll

PAGE.

"Double gang" milling, as exemplified in milling a lathe

bed by means of two rows or gangs of mills 145

11 Facet " and " surface " milling 147

Inclining the vertical spindle (arbor) to prevent the cutters from dragging on the work after their circuit of cutting contact has been completed 148

CHAPTER XVI. Miujng. — Continued

"END" OR " FACK " MIUJNG.

Inefficient methods of chucking 149

Monitor-chucks the best for end milling 150

Double " end " or face milling 151

Ordinary methods of double " end " and " face " milling . .151

Improved methods of external double face milling .... 152

Ordinary methods of internal double face milling 153

Improved methods of internal double face milling .... 155 Internal double face milling, by means of cutters arranged and operated in advance of the main spindle of the

machine 158

The prevailing practice of the modern milling machine

operator 161

Capacity and capabilities of the milling machine 161

Improvements and progress in milling machine practice . . 162

CHAPTER XVII. Lathe Work

The ordinary and special forms of the lathe 163

The lathe the most important of all metal-cutting machine

tools 163

What constitutes the most ' ' advanced ' ' practice of the

present day 163

What constitutes the most " approved " practice 163

XIV CONTENTS.

Capacity and possibilities of the lathe, and the improvements

for expediating the processes and operations thereon . . 164

The inexpensive nature of such improvements, and the advantages to be derived therefrom 164

Cutting speeds for metals, and the conditions upon which the

speeds are dependent 165

CHAPTER XVIII. Lathe) Work. — Continued

BORING TOOLS.

Improved form of cutter-bore for boring „ . . 168

Boring and drilling attachments for lathes ....... 170

Cutter-heads for boring-bars, and the objections existing in the

ordinary forms 171

Improved form of cutter-head, wherein all the above objections are obviated 174

Boring spherical holes, and the tools and methods employed therefor 174

CHAPTER XIX. LaThk Work. — Continued

Lining up lathe-spindles 178

Boring and turning work on the monitor-chuck . . . . .179 Ordinary methods of chucking work on the face-plate of the lathe that has two or more surfaces to be operated on, which stand at different angles, but with their axes on

the same horizontal plane 179

Simple method of chucking the work so that the different surfaces can be operated on at one setting on the supplementary chucking-plate, but a different setting on the angle-plate 180

Improving on the above method and securing greater precision by chucking the work on a monitor-chuck .... 180 Examples of chucking connecting-rod brasses, cross-heads, elbows, globe, gate and check- valve boxes on the monitor-chuck for, boring and turning 181

CONTENTS. XV

CHAPTER XX. Lathe Work.— Continued

PAGE.

Simultaneous boring and turning, as exemplified by boring and turning a casting from which packing rings are cut at one operation 186

Double-tongued " parting or cutting-off " tool 187

Method of compressing and chucking packing rings for boring

and turning 189

Improved method of expanding the linings of babbitted bearings and copper-lined cylinders, and the tools employed therefor 192

CHAPTER XXI. I^athe; Work. — Continued

Support for live-spindles when turning and boring heavy

work chucked on the face-plate 194

Extending the capacity of a face-plate to take in work of a

greater diameter than itself 196

SLIDING I.ATHE CHUCKS.

Sliding lathe chuck employed as an adjustable chucking arbor, for turning pulleys, eccentrics and work of a similar nature 196

Improved form of sliding lathe chuck employed (in addition to holding the above classes of work) for holding templates, jigs, die plates and other work requiring to be accurately spaced and bored 198

Turning work on the above chuck 199

Spacing and drilling holes on the above chuck, and methods

of holding and locating the work 199

Methods to be pursued for accurately spacing the holes in

hardened die-plates 199

XVI CONTENTS.

CHAPTER XXII. Lathe Work. — Continued

PAGE.

Turning curved surfaces 203

Determining the nature of the former turning appliances, by the space in which the turning tools are to operate, the manner in which they can be attached to the lathe, and

the form of the surface to be turned 203

Former appliance for turning car axles 204

Former appliance for turning pulleys, etc 204

Spherical turning principles on which the tools operate . . 208 Examples of spherical turning 209

CHAPTER XXIII. Lathe Work. — Continued

Lathe work, as exemplified in the turning and boring of pulleys 211

The practice of turning work on a driven arbor objectionable . 212 Turning work on an arbor which is made a sliding fit in the

bore (preferable) . 212

Face-plate arbor screwed onto the nose of the live-spindle, to

secure greater rigidity and avoid the jarring in turning the

work ; operated on the same principle 213

The same form of arbor as arranged to be held between the

lathe centers 214

Method of chucking the work on the above arbors . . . .215 Simultaneous boring and turning, as applied in boring and

turning pulleys 215

Examples of the appliances and methods employed therefor . 215

CONTENTS. x V i i

CHAPTER XXIV. Lathe Work.— Continued

PAGE.

Advanced practice of turning and boring as exemplified in the

turning and construction of cranks 221

Difficulties experienced in turning solid-cranks, and how they

can be minimized or obviated . .221

The important operations involved in the construction of

built-up cranks ' 224

Making " driving fits" 224

Methods of" roughing out "the "crank-pin holes" in "crank

discs" 224

Principles governing the accurate "shrinking" together of

machine parts 225

Rules and allowances for making ' ' shrinkage fits " . . . . 227 Method of boring (finishing) the holes in cranks for the crank-pin after the crank has been fitted and keyed on the shaft 228

Shrinking the cranks together 229

Shrinking the crank-pins in, in single cranks 231

Re-turning crank-pins that are worn or bent out of truth without removal from the crank 232

CHAPTER XXV. Lathe Work. — Continued

Methods of chucking the cylinders for ' 'steam engines, ' ' pumps, ammonia and "air-compressors," and other machinery, for boring and turning - . . 234

Boring and turning the cylinders and guides of vertical engines

(frames and cylinders combined) 239

XV111 CONTENTS.

CHAPTER XXVI. Lathe Work. — Continued

PAGE.

Ordinary methods of turning and boring taper work, and rules

for setting the lathe to turn tapers 244

Simplified methods of setting the lathe to turn and bore tapers 246

Simple taper- turning attachment 249

Device for adjusting the tool to the cut, in the tool-post . . 250

CHAPTER XXVII. Lathe Work. — Continued

Turning " formed" work 252

Turning and boring "elliptic" forms 253

Turning a cam-shaft 255

" Cam " turning 257

CHAPTER XXVIII. Lathej Work — Continued

Boring and turning bushings 259

Hollow spindle-lathes 262

Arranging lathes in " series " or " gangs " on one lathe bed 263

Making provision for turning " extra long " work .... 263

CONTENTS. Xix

CHAPTER XXIX Lathe Work. — Continued. PAGE

Circular turning tools 266

Examples of turning by means of circulancutters or turning

tools 266

Circular chaser or threading tools 268

Box-tools — fitted on the tail-spindle of the lathe 270

Box-tools — fitted on the slide-rest . . 270

Box-tools — with circular cutters .... 271

CHAPTER XXX. Lathe Work. — Continued

Measuring Instruments — for use on the lathe 275

Making provision in plug gauges for the escape of air . . . 277 Improved form of "ring" or "collar" gauge, "disc" gauges . 279 Handy collar-tram gauge 281

CHAPTER XXXI. Items of Interest

Odd-legged calipers, and their uses 282

Measuring the bore of a semicircular bearing by means of the

" odd-legged calipers " 282

Measuring other forms of vise and machine work — by the

same means 284

Accurate spacing and measurement of holes — by the same and

other means 284

Test-bar — for measuring purposes 286

XX CONTENTS.

CHAPTER XXX T I Items oe Interest.— Continued.

PAGE.

A convenient form of parallel or distance piece for face-plates 287

Device for making helical springs . . . ' 288

Fluting taps and reamers in the lathe 289

Grinding 291

Grinding on the lathe 291

Regulation style of grinder head for the lathe ..'.... 293

Universal grinding attachment for lathes 293

How to change the shape of and make grinding wheels of

small diameter 294

How to fasten a grinding wheel on the arbor 295

CHAPTER XXXIII. Items oe INTEREST. — Continued

Grinding plane surfaces 297

Advantages of grinding over other methods of shaping and

finishing work 297

Surfacing device . . . 298

Objections to high velocity grinding . 298

How these objections can be avoided 300

Horizontal surfacing machine 300

Grinding parallel work 301

Grinding the edges of thin work 303

"Lead-Laps" • 304

CHAPTER XXXIV. Items of Interest.— Continued

POLISHING— BY GRINDING.

Different means employed for polishing 306

Charging (coating) the wheels and belts with emery, etc. . . 307 Buffing wheels 308

CONTENTS. XXI

CHAPTER XXXV. Drilling

PAGE.

A knowledge of tools necessary to the intelligent running of a

machine 309

Hand versu s machine ground drills 310

Requirements for jigging work to be drilled 311

Locating holes without jigs 311

Singlejigs 312

Double or compound jigs 313

Index 315

CHAPTER I. Measuring Instruments

In former times the only measuring instruments employed were the measuring bars, graduated rules (or scales), and graduated beam calipers. The latter being in all probability among the oldest measuring instruments with which we are acquainted; and the subsequent improvement of the same by the addition of the " Vernier" adjustment and its adaptation to inside measurements render this tool one of the most accurate and reliable tools which can be used for this purpose.

The evolution of the micrometer calipers and measuring machines was the greatest advance ever made towards the duplication and perfection in size of parts in machine construction.

It was some time after the micrometer calipers for outside measurements had been in general use before micrometer calipers for inside measurements were introduced, and it took a still longer time to place them successfully upon the market, as micrometer calipers for inside measuring purposes were not as favorably received as were those for outside measuring purposes.

As most, if not all, of the micrometer calipers for both outside and inside measurements have been profusely illustrated in the trade journals and in books and catalogues, and as they are in constant use in most workshops, we shall mention such only as have not been shown and described elsewhere,

INSIDE MICROMETER CALIPERS.

The inside micrometer caliper shown at Figures 1 and 2 was designed by the author for his own use several years ago, and subsequently patented but never placed on the market.

Fig. 1.

Figure 1 is a side elevation half longitudinal section of the instrument, and Figure 2 is a similar elevation of the same with longer (plain) tail-piece.

The instrument as shown in Figure 1 consists of a cylindrical body A, which is bored and threaded at B to receive the tail-piece E and the chuck screw C. The body A is also threaded on the inner end, on the outside at G, to receive the adjusting nut J (which is cylindrical and of the same diameter as the body A, thereby serving to steady the sleeve K), and on the inside at G' to receive the measuring screw F. The body has on the inner end two radial cuts or slits H, to admit of adjustment for wear on the measuring screw F in an obvious manner by means of the adjusting screw J. The sleeve K is screwed onto the

MEASURING INSTRUMENTS.

measuring screw F, and held in a fixed relation with the measuring screw and terminals by means of the nut M, which arrangement permits of adjustment for wear on the measuring terminals. The chuck nut C has a radial cut or slit on one side, which serves to permit of the bore of the chuck to collapse somewhat when the screw is forced into the threaded bore B, thus forming, when used in connection with a plain

A F tail-piece E (Figure 2), a chuck. The bore of the chuck screw C is likewise extended through the shoulder of the body A, as shown near G (Figure 1), and nearly throughout the entire length of the measuring screw F, as shown at N. This permits of a plain tail-piece E (Figure 2) being used instead of a tail-piece E with the location collar on it, as shown at Q (Figure 1), when the instrument is to be used for other than standard measurements. The graduations on the body A and the sleeve K are of the usual form.

In using the above instrument for standard measurements, the tail-pieces with collars on are used, the capacity of the instrument being increased or decreased by means of the measuring screw, and by the insertion of longer or shorter tail-pieces, as required. But when making shrinkage, tight or loose fits, where a stated allowance for the same is merely required, then the straight tail-piece may be used, the tail-piece being made to slide in or out to the size required and held by compression by merely tightening up the chuck screw C, the adjustment to correct size being made by the measuring screw.

ADJUSTABLE SNAP GAUGES FOR STANDARD MEASURE- MENTS.

The absolute necessity of some arrangement for compensating for the wear of the various tools employed in machine-shop practice has engaged the attention of the machinists in all branches of the profession. In the case of taps and reamers, the necessity of some means of adjustment was seen many years ago, and was promptly met by the introduction of expanding taps and reamers, which filled the requirements of the case in every particular in a very satisfactory manner. We have adjustable mandrels (arbors), calipers, and other tools too numerous to mention ; in fact, nearly every tool we use is adjustable in some way or other.

The standard snap gauges now so extensively used may very justly be said to be as far ahead of any and all other forms of measuring instruments for general use in the workshop for ensuring absolute uniformity and accuracy of machine parts as the micrometer caliper is ahead of the ordinary two-legged caliper.

MEASURING INSTRUMENTS.

But snap gauges appear to be an exception to the rule of supplying a means of adjustment for wear, no provision whatever being made for this purpose in general practice, or in any instrument now on the market, and consequently when such adjustment is necessary the gauge must in most cases be annealed

Fig. 3.

and closed or expanded and then rehardened and ground or lapped to size. Some years ago, Mr. A. D. Pentz introduced in his own practice (and subsequently described and illustrated in the " Iron Age ") an adjustable snap gauge, which for simplicity and accuracy probably could not be improved upon.

Fig. 4.

Fig. 5,

The construction of this gauge is shown in Figures 3, 4 and 5. Figure 3 is a side elevation of the gauge (single ended). Figure 4 is a side elevation of the gauge (double ended in this case, in the form of a limit gauge). Figure 5 is an end elevation of either or both of the above.

As shown in the figures, the gauge consists of a body A and two or four (for single or double gauge) pieces or measuring terminals B B r and C C, which are bolted to the parallel surfaces a a' and bb' of the body A by means of the counter sunk screws (plainly shown by the dotted lines).

The beauty of this form of gauge is that the surfaces a a' and bb' are made parallel with each other and of the same distance apart as the gauge is to be, thereby making it possible to always maintain or restore the standard of the gauge, for when the measuring surfaces have become worn beyond the allowable limit it is only necessary to remove the pieces B B' or CC from the body A and grind or lap the surfaces ab or a' b' of these pieces until they are true again, and then replace them on the body A and the gauge is adjusted to standard.

Fig. 6.

Figure 6 shows side elevation of an adjustable snap gauge which is easy to maintain at or restore to the given standard.

The arms of the body A (the body may be of any pattern desired) terminate in the form of hubs ; these hubs B W are bored out parallel with each other and faced off on both ends of the hubs. The jaws CC

MEASURING ENSTRUMENTS.

which form the measuring terminals are turned and hardened and inserted in the hubs B B'. The flanges a a' are made either round or square as preferred. As the jaws may be sprung somew T hat in hardening, a slight allowance is made for grinding or lapping the gauge to size after they are inserted in the hubs. The collar nut bb'^'is made preferably round, with holes drilled therein for a pin or spanner wrench, to prevent any possibility of the gauge being tampered with. When it is necessary to adjust the gauge for wear, very thin metallic or paper washers are inserted between the flange C a and the hub B, and if necessary the gauge is relapped or ground to size. This instrument can be used for different sizes by inserting jaw r s of such thickness as to reduce the gauge to the size required.

Fig. 7.

Another form of adjustable snap gauge is shown in Figure 7. The body A (which is of an ordinary pattern) is slotted at B to receive the distance piece or liner C, and drilled and tapped at D for the binding screw E. When the slot B has been cut the jaws are sprung apart somewhat to create a continual tendency to close together, and the liner C is fitted closely in the slot B, while the jaws are in this position, after w T hich the liner is hardened and inserted in the slot and the binding screw tightened up. The jaws are then ground and lapped to size.

THE MODERN MACHINIST.

To adjust the gauge for wear the liner is taken out of the slot and reduced in thickness as much as required ; it is then replaced, and, if necessary, the jaws are relapped to size.

Fig. 8.

Fig. 9.

Figures 8 and 9 represent an adjustable snap gauge for internal measurements, Figure 8 showing a side and Figure 9 an end elevation of the instrument. The blade B is inserted in the body A in a dovetailed slot, the bottom of which is an inclined plane. When the instrument is worn below size it is only necessary to drive the blade B further into the slot, and by that means enlarge the diameter of the gauge as much as required.

Figure 10 represents another form of adjustable snap gauge for internal use. A slot B is cut in the body A, two adjusting screws C C r are inserted in the body on one side of the slot and a binding screw D on the opposite side. To adjust the gauge the screw D is loosened and the screws C C are tightened up until the gauge is expanded as much as required. After expanding either of the above gauges they should, if necessary, be reground to size.