C E 1 G Shape of tool used for scraping brass.
Straightforward tool for turning all metals.
Rightand left-hand tools for all metals.
A better form of same.
of Planer Tools.
E, Parting or cutting-off or grooving tool.
F, V tool for grooves.
G, Rightand left-hand tools for V-slots.
H, Ditto for T-slots.
tools. Generally though not invariably the edge of the first is narrow, of the second broad, corresponding with the deep cutting and fine traverse of the first and the shallow cutting and broad.
FIG. 4. - Group of Slotter Tools.
Saws
The saws are a natural connecting link between the chisels and the milling cutters. Saws are used for wood, metal and stone. Slabs of steel several inches in thickness are sawn through as readily as, though more slowly than, timber planks. Circular and band saws are common in the smithy and the boiler and machine shops for cutting off bars, forgings and rolled sections. But the tooth shapes are not those used for timber, nor is the cutting speed the same. In the individual saw-teeth both cutting and scraping actions are illustrated (fig. 14). Saws which cut timber continuously with the grain, as rip, hand, band, circular, have incisive teeth. For though many are destitute of front rake, the method of sharpening at an angle imparts a true shearing cut. But all crosscutting teeth scrape only, the teeth being either of A, Teeth of band and ripping saws. triangular or of M-form, B, Teeth of circular saw for hard wood; variously modified. Teeth shows set. for metal cutting also act C, Ditto for soft wood. strictly by scraping. The D, Teeth of cross-cut saw. pitching of the teeth is E, M-teeth for ditto. related to the nature of the material and the direction of cutting. It is coarser for timber than for metal, coarser for ripping or sawing with the grain than for cross cutting, coarser for soft than for hard woods. The setting of teeth, or the bending over to right and left, by which the clearance is provided for the blade of the saw, is subject to similar variations. It is greatest for soft woods and least for metals, where in fact the clearance is often secured without set, by merely thinning the blade backwards. But it is greater for cross cutting than for ripping timber. Gulleting follows similar rules. The softer the. timber, the greater the gulleting, to permit the dust to escape freely. Milling Cutters. - Between a circular saw for cutting metal and a thin milling cutter there is no essential difference. Increase the thickness as if to produce a very wide saw, and the essential plain edge milling cutter for metal results. In its simplest form the milling cutter is a cylinder with teeth lying across its periphery, or parallel with its axis - the edge mill (fig. 15), or else a disk with teeth radiating on its face, or at right angles with its axis - the end mill (fig. 16). Each is used indifferently for producing flat faces and edges, and for cutting grooves which are rectangular in cross-section. These milling cutters invade the province of the single-edged tools of the planer, shaper and slotter. Of these two typical forms the FIG. 16. - Group of End Mills.
A, End mill with straight teeth. B, Ditto with spiral teeth. C, Showing method of holding shell cutter on arbor, with screw and key. D, T-slot cutter.
A, Narrow edge mill, with straight teeth.
B, Wide edge mill with spiral teeth.
C, Teeth on face and edges.
D, Cutter having teeth like C.
E, Flat teeth held in with screws and wedges.
F, Large inserted tooth mill; with taper pins secure cutters.
F FIG. 15. - Group of Milling Cutters.
FIG. 14. - Typical Saw Teeth.
changes are rung in great variety, ranging from the narrow slitting tools which saw off bars, to the broad cutters of 24 in. or more in width, used on piano-millers.
When more than about an inch in width, surfacing cylindrical cutters are formed with spiral teeth (fig. 15, B), a device which is FIG. 18. - Group of Angular Mills.
A, Cutter with single slope.
B, Ditto, producing teeth in another cutter.
C, Double Slope Mill, with unequal angles.
essential to sweetness of operation, the action being that of shearing. These have their teeth cut on universal machines, using the dividing and spiral head and suitable change wheels, and after hardening they are sharpened on universal grinders. When cutters exceed about 6 in. in length the difficulties of hardening and grinding render the " gang " arrangement more suitable. Thus, two, three or more similar edge mills are set end to end on an arbor, with the spiral teeth running in reverse directions, giving a broad face with balanced endlong cutting forces. From these are built up the numerous gang mills, comprising plane faces at right angles with each other, of which the straddle mills are the best known (fig. 17, A). A common element in these combinations is the key seat type B having teeth on the periphery and on both faces as in fig. 15, C, D. By these combinations half a dozen faces or more can be tooled simultaneously, and all alike, as long as the mills retain their edge. The advantages over the work of the planer in this class of work are seen in tooling the faces and edges of machine tables, beds and slides, in shaping the faces and edges of caps to fit their bearing blocks. In a single cutter of the face type, but having teeth on back and edge also, T-slots are readily milled (fig. 16, D); this if done on the planer would require re-settings of awkwardly cranked tools, and more measurement and testing with templets than is required on a milling machine.
When angles, curves and profile sections are introduced, the capacity of the milling cutter is infinitely increased. The making of the cutters is also more difficult. Angular cutters (fig. 18) are used for producing the teeth of the mills themselves, for shaping the teeth of ratchet wheels, and, in combination with straight cutters in gangs, for angular sections. With curves, or angles and curves in combination, taps, reamers and drills can be fluted or grooved, the teeth of wheels shaped, and in fact any outlines imparted (fig. 19). Here the work of the fitter, as well as that of the planing and allied machines, is invaded, for much of this work if prepared on these machines would have to be finished laboriously by the file.
There are two ways in which milling cutters are used, by which their value is extended; one is to transfer some of their work proper to the lathe and boring machine, the other is by duplication. A "good many light circular sections, as wheel rims, hitherto done in lathes, are regularly prepared in the milling machine, gang mills being used for tooling the periphery and edges at once, and the wheel blank being rotated. Similarly, holes are bored by a rotating mill of the cylindrical type. Internal screw threads are done similarly. Duplication occurs when milling sprocket wheels in line, or side by side, in milling nuts on an arbor, in milling a number of narrow faces arranged side by side, in cutting the teeth of several spur-wheels on one arbor and in milling the teeth of racks several at a time.
One of the greatest advances in the practice of milling was that of making backed-off cutters. The sectional shape behind the tooth face is continued identical in form with the profile of the edge, the outline being carried back as a curve equal in radius to that of the cutting edge (fig. 20). The result is that the cutter may be sharpened on the front faces of the teeth without interfering with the shape which will be milled, because the periphery is always constant in outline. After repeated sharpenings the teeth would assume the form indicated by the shaded portion on two of the teeth. The limit of grinding is reached when the tooth becomes too thin and weak to stand up to its work. But such cutters will endure weeks or months of constant service before becoming useless. The A E F FIG. 21. - Group of Scrapes.
A, Metal-worker's scrape, pushed D, Diamond point used by straightforward. wood-turners.
B, Ditto, operated laterally. E, F, Cabinet-makers' scrapes.
C, Round-nosed tool used by wood-turners.
chief advantage of backing-off or relieving is in its application to cutters of intricate curves, which would be difficult or impossible to sharpen along their edges. Such cutters, moreover, if made with N 0 Q R S T U FIG. 22. - Cross-sectional Shapes of Files.
A, Warding. J, Topping. P, Round.
B, Mill. K, Reaper. Q, Pit-saw or C, Flat. L, Knife. frame-saw.
D, Pillar. M, Three-square. R, Half-round.
E, Square. N, Cant. S, T, Cabinet.
F, G, Swaged reapers. 0, Slitting or U, Tumbler.
H, Mill. feather-edge. I T, Crossing. ordinary teeth would soon be worn down, and be much weaker than the strong form of teeth represented in fig. 20. The relieving is usually done in special lathes, employing a profile tool which cuts the surface FIG. 23. - Longitudinal Shapes of Files.
A, Parallel or blunt. F, Tapered triangular. K, Tapered half B, Taper bellied. G, Parallel round. round.
C, Knife reaper. H, Taper or rat-tail. L, Riffler.
D, Tapered square. J, Parallel half E, Parallel triangular. round.
'/i. ' A B FIG. 17.
A, Straddle Mill, cutting faces and edges.
B, Set of three mills cutting grooves.
A A A B D E F G FI K L ii FIG. 19.
A, Convex Cutter.
B, Concave Cutter.
C, Profile Cutter.
FIG. 20. - Relieved Teeth of Milling Cutter.
of the teeth back at the required radius. Relieved cutters can of course be strung together on a single arbor to form gang mills, by which very complicated profiles may be tooled, beyond the capacity of a single solid mill.
Planing Machines
In the standard planer for general shop purposes (fig. 42) the piece of work to be operated on is attached to a horizontal;y table moving to and fro on a rigid bed, and passing underneath the fixed cutting tool. The tool is gripped in a box having certain necessary adjustments and movements, so that the tool can be carried or fed transversely across the work, or at right angles with the direction of its travel, to take successive cuts, and also downwards or in a vertical direction. The tool-box is carried on a cross-slide which has capacity for several feet of vertical adjustment on upright members to suit work of varying depths. These up- j rights or housings are bolted to the sides of the bed, and the whole framing is so rigidly designed that no perceptible tremor or yielding takes place under the heaviest duty img posed by the stress of cutting.
›?? 'CSw O +, !- - -O b 3 rd o a) ? o 1-, c?d ? ? O -t7 O o ? N s ? a0 r) 5, E a) d bA ?? "0 ? t'?
-6: a Ci - k a, 7j cd [[[Reciprocating Machines]] Moreover, after the required adjustments have been made and the machine started, the travel and the return of the work-table and the feeding of the tool across the surface are performed by self-acting mechanism actuated by the reciprocations of the table itself, the table being driven from the belt pulleys.
To such a design there are objections, which, though their im- portance has often been exaggerated, are yet real. First, the crossrail and housings make a rigid enclosure over the table, which sometimes prevents the admission of a piece that is too large to pass under the cross-rail or between the housings. Out of this a FIG. 43.-20-in. Side Planing Machine.
A, Bed.
B, B, Feet.
C, C, Work tables adjustable vertically on the faces D, D, by means of screws E, E, from handles F, F, through bevel gears.
(G. Richards & Co., Ltd., Manchester.) G, Tool-box on travelling arm H, travelled by fast and loose pulleys J for cutting, and by pulleys K for quick return.
L, Feed-rod with adjustable dogs a, a, for effecting reversals through the belt forks b, b. M, Brickwork pit to receive deep objects.
n?iiiinn FIG. 44.-8-in. Shaping Machine. (Cunliffe & Croom, Ltd., Manchester.) k, A, Base.
B, Work-table, having vertical movement on carriage C, which has horizontal movement along the face of A. D, Screw for effecting vertical movement, by handle E, and bevel gears.
F, Screw for operating longitudinal movement with feed by hand or power.
G, Tool ram.
H, Tool-box.
a, Worm-gear for setting tool-holder at an angle.
b, Crank handle spindle for operating ditto.
c, Handle for actuating down feed of tool.
Driving cone pulley actuating pinion d, disk wheel e, with slotted disk, and adjustable nut moving in the slot of the crank f, which actuates the lever g, connected to the tool ram G, the motion constituting the Whitworth quick return; g is pivoted to a block which is adjustable along a slot in G, and the clamping of this block in the slot regulates the position of the ram G, to suit the position of the work on the table.
Feed disk driven by small gears from cone pulley.
Pawl driven from disk through levers at various rates, and controlling the amount of rotation of the feed screw F. Conical mandrel for circular shaping, driven by worm and wheel 1. ] objection has arisen a new design, the side planer (fig. 43), in which the tool-box is carried by an arm movable along a fixed bed or base, and overhanging the work, which is fastened to the side of the base, or on angle brackets, or in a deep pit alongside. Here the important difference is that the work is not traversed under the tool as in the ordinary planer, but the tool moves over the work. But an evil results, due to the overhang of the tool arm, which being a cantilever supported at one end only is not so rigid when cutting as the cross-rail of the ordinary machine, supported at both ends on housings. The same idea is embodied in machines built in other respects on the reciprocating table model. Sometimes one housing is omitted, and the tool arm is carried on the other, being therefore unsupported at one end. Sometimes a housing is made to be removable at pleasure, to be temporarily taken away only when a piece of work of unusual dimensions has to be fixed on the table.
Another objection to the common planer is this. It seems unmechanical in this machine to reciprocate a heavy table and piece of work which often weighs several tons, and let the tool and its holder of a few hundredweights only remain stationary. The mere reversal of the table absorbs much greater horse-power there is no limitation whatever to the length of the work, since it may extend to any distance beyond the base-plate.
Multiple Spindle Machines
Many of the sensitive machines are fitted with two, three or more spindles operated in unison with a belt common to all. In other machines the multiple spindles are capable of adjustment for centres, as in the machines used by boiler L, Speed cones for driving spindle, through pinion M and wheel N. 0, Frame, carrying the bearings for the cone pulley L, and pivoted to the bed at a, and to the headstock E. This device keeps the gears M and N in engagement in all variations in the height of the spindle D. P, Q, Cones for driving the table R through worm-gears S, T, and spurs U, V, to the table screw.
W, Stop for automatic knock-off to feed.
X, Hand-wheel for turning the same screw through worm-gears Y, Z. a drilling machine for boring holes of moderate size, say up to 8 or io in., by double and treble back-gears. But the real boring machine is of a different type. In the horizontal machines a splined bar actuated by suitable gears carries a boring head which holds the cutters, which head is both rotated with, and traversed or fed along the bar. The work to be bored is fixed on a table which has provision for vertical adjustment to suit work of different dimensions. The boring-bar is supported at both ends. In the case of the largest work the boring-bar is preferably set with its axis vertically, and the framing of the machine is arch-like. The bar is carried in a bearing at the crown of the arch and driven and fed there by suitable gears, while the other end of the bar rotates in the table which forms the base of the machine. Some boring machines for small engine cylinders and pump barrels have no bar proper, but a long boring spindle carrying cutters at the further end is supported along its entire length in a long stiff boss projecting from the headstock of the machine - the snout machine. The work is bolted on a carriage which slides along a bed similar to a lathe bed. Many of these machines have two bars for boring two cylinders simultaneously In milling machines rotary saw-like cutters are employed. To a certain extent these and some gear-cutting machines overlap because they have points in common. Many gear-wheel teeth are produced by rotary cutters on milling machines. In many machines designed for gear cutting only, rotary cutters alone are used. For this reason the two classes of machines are conveniently and naturally grouped together, notwithstanding that a large and increasing group of gearcutting machines operate with reciprocating tools.
The French engineer, Jacques de Vaucanson (1709-1782), is credited with having made the first milling cutter. The first very crude milling machine was made in 1818 at a gun factory in Connecticut. To-day the practice of milling ranks as of equal economic value with that of any other department of the machine shop, and the varieties of milling machines made are as highly differentiated as are those of any other group. An apparent incongruity which is rather striking is the relative disproportion between the mass of these machines and the small dimensions of the cutters. The failures of many of the early machines were largely due to a lack of appreciation of the intensity of the stresses involved in milling. A single-edged cutting tool has generally a very narrow edge in operation. Milling cutters are as a rule very wide by comparison, and several teeth in deep cuts are often in simultaneous operation. The result is that the machine spindle and the arbor or tool mandrel are subjected to severe stress, the cutter tends to spring away from the surface being cut, and if the framings are of light proportions they vibrate, and inaccuracy and chatter result. Even with the very stiff machines now made it is not possible to produce such accurate results on wide surfaces as with the planer using a narrow-edged tool. Because of this great resistance and stress, cutters of over about an inch in width are always made with the teeth arranged spirally, and wide cutters which are intended for roughing down to compete with the planer always have either inserted cutters or staggered teeth. Hence the rotary cutter type of machine has not been able to displace the planing machine in wide work when great accuracy is essential. Its place lies in other spheres, in some of which its position is unassailable. Nearly all pieces of small and medium dimensions are machined as well by milling as by single-edged tools. All pieces which have more than one face to be operated on are done better in the milling machine than elsewhere. All pieces which have profiled outlines involving combinations of curves and plane faces can generally only be produced economically by milling. Nearly all work that involves equal divisions, or pitchings, as in the manufacture of the cutters themselves, or spiral cutting, or the teeth of gear-wheels when produced by rotary cutters, must be done in milling machines. Beyond these a large quantity of work lies on the border-line, where the choice between milling and planing, shaping, slotting, &c., is a matter for individual judgment and experience. It is a matter for some surprise that round the little milling cutter so many designs of machines have been built, varying from each other in the position of the tool spindles, in their number, and in the means adopted for actuating them and the tables which carry the work.
A very early type of milling machine, which remains extremely popular, was the Lincoln. It was designed, as were all the early machines, for the small arms factories in the United States. The necessity for all the similar parts of pistols and rifles being interchangeable, has had the paramount influence in the development of the milling machine. In the Lincoln machine as now made (fig. 47) the work is attached to a table, or to a vice on the table, which has horizontal and cross traverse movements on a bed, but no capacity for vertical adjustment. The cutter is held and rotated on an arbor driven from a headstock pulley, and supported on a tailstock centre at the other end, with capacity for a good range of vertical adjustment. This is necessary both to admit pieces of work of different depths or thicknesses between the table and the cutter, and to regulate the depth of cutting (vertical feed). Around this general design numerous machines small and large, with many variations in detail, are built. But the essential feature is the vertical movement of the spindle and cutter, the support of the arbor (cutter spindle) at both ends, and the rigidity afforded by the bed which supports headand tail-stock and table.
The pillar and knee machines form another group which divides favour about equally with the Lincoln, the design being nearly of an opposite character. The vertical movements for setting and feed are imparted to the work, which in this case is carried on a bracket or knee that slides on the face of the pillar which supports the headstock. Travelling and transverse movements are imparted to the table slides. The cutter arbor may or may not be supported away from the headstock by an arched overhanging arm. None of these machines is of large dimensions. They are made in two leading designs - the plain and the universal. The first embodies rectangular relations only, the second is a marvellous instrument both in its range of movements and fine degree of precision. The first machine of this kind was exhibited at Paris in 1867. The design permits the cutting of spiral grooves, the angle of which is embodied in the adjustment of a swivelling table and of a headstock thereon (universal or spiral head). The latter embodies change-gears like a screw-cutting lathe and worm-gear for turning the head, in combination with an index or dividing plate having several circles of holes, which by the insertion of an index peg permit of the work spindle being locked during a cut. The combinations possible with the division plate and worm-gear number hundreds. The head also has angular adjustments in the vertical direction, so that tapered work can be done as well as parallel. The result is that there is nothing in the range of spiral or parallel milling, or tapered work or spur or bevel-gear cutting, or cutter making, that cannot be done on this type of machine, and the accuracy of the results of equal divisions of pitch and angle of spiral do not depend on the human element, but are embodied in the mechanism.
FIG. 48. - Vertical Spindle Milling Machine. (James Archdale & Co., Ltd.) Main framing.
Knee.
Spindle, having its vertical position capable of adjustment by the sliding of D on A. Driving cone, belt driving over guide pulleys F to spindle pulley G. Enclosed gears for driving spindle by back gear.
Hand-wheel for adjusting spindle vertically.
K, Pulleys over which spindle is counterbalanced.
Feed pulley, driven from counter shaft.
Vertical feed shaft, driven from L through mitre-gears. Change gear box.
Horizontal feed shaft, operating longitudinal and transverse feed of table through spiral and spur-gears.
P, Handles for operating changes in feed speeds, nine in number. Handle for reversing direction of motion of table R. Hand-wheel for longitudinal movement of table.
Hand-wheel for effecting cross adjustments.
Spiral gears indicated for effecting self-acting rotation of circular table W. Hand-wheel for rotation of table.
Hand-wheel for vertical movements of knee B on screw Z. Machines with vertical spindles (fig. 48) form another great group, the general construction of which resembles that either of the common drilling machine or of the slotting machine. In many cases the horizontal position is preferable for tooling, in others the vertical, but often the matter is indifferent. For general purposes, the heavier class of work excepted, the vertical is more convenient. But apart from the fitting of a special brace to the lower end of the spindle which carries the cutter, the spindle is unsupported there and is thus liable to spring. But a brace can only be used with a milling cutter that operates by its edges, while one advantage of the vertical spindle machine is that it permits of the use of end or face cutters. One of the greatest advantages incidental to the vertical position of the spindle is that it permits of profile milling being done. One of the most tedious operations in the machine shop is the production of outlines which are not those of the regular geometric figures, as rectangles and circles, or combinations of the same. There is E, H, V, ] only one way in which irregular forms can be produced cheaply and interchangeably, and that is by controlling the movements of the tool with an object of similar shape termed a " form" or " former," as in the well-known copying lathes, in the cam grinding machine, and in the forming adjuncts fitted to vertical spindle milling machines, so converting those into profiling machines. The principle and its application are alike simple. An object (the form) is made in hardened steel, having the same outlines as the object to be milled, and the slide which carries the cutter spindle has a hardened former pin or roller, which is pulled hard against the edges of the form by a suspended weight, so causing the tool to move and cut in the same path and in the same plane around the edges of the work. Here the milling machine holds a paramount place. No matter how many curves and straight portions may be combined in a piece, the machine reproduces them all faultlessly, and a hundred or a thousand others all precisely alike without any tentative corrections.
Plano-millers, also termed slabbing machines, form a group that grows in value and in mass and capacity. They are a comparatively late development, becoming the chief rivals to the planing machines, for all the early milling was of a very light character. In general outlines the piano-millers closely resemble the planing machines, having bed, table, housings and cross-rail. The latter in the pianomiller carries the bearings for the cutter spindle or spindles under which the work travels and reciprocates. These spindles are vertical, but in some machines horizontal ones are fitted also, as in planers, so that three faces at right or other angles can be operated on simultaneously. The slabbing operations of the piano-millers do not indicate the full or even the principal utilities of these machines. To understand these it must be remembered that the cross-sections of very many parts which have to be tooled do not lie in single planes merely, but in combinations of plane surfaces, horizontal, vertical or angular. In working these on the planing machine separate settings of tools are required, and often successive settings. But milling cutters are built up in " gangs " to deal with such cases, and in this way the entire width of profile is milled at once. Horizontal faces, and vertical and angular edges and grooves, are tooled simultaneously, with much economy in time, and the cutter profile will be accurately reproduced on numbers of separate pieces. Allied to the piano-millers are the rotary planers. They derive their name from the design of the cutters. An iron disk is pierced with holes for the insertion of a large number of separate cutters, which by the rotation of the disk produce plane surfaces. These are milling cutters, though the tools are single-edged ones, hence termed " inserted tooth mills." These are used on other machines besides the rotary planers, but the latter are massive machines built on the planer model, with but one housing or upright to carry the carriage of the cutter spindle. These machines, varied considerably in design, do good service on a class of work in which a very high degree of accuracy is not essential, as column flanges, ends of girders, feet of castings, and such like.
V. - Gear-Cutting Machines The practice of cutting the teeth of gear-wheels has grown but slowly. In the gears used by engineers, those of large dimensions are numerous, and the cost of cutting these is often prohibitive, though it is unnecessary in numbers of mechanisms for which cast wheels are as suitable as the more accurately cut ones. The smallest gears for machines of precision have long been produced by cutting, but of late years the practice has been extending to include those of medium and large dimensions, a movement which has been largely favoured by the growth of electric driving, the high speeds of which make great demands on reduction and transmission gears. Several new types of gear-cutting machines have been designed, and specialization is still growing, until the older machines, which would, afcer a fashion, cut all forms of gears, are being ousted from modern establishments.
The teeth of gear-wheels are produced either by rotary milling cutters or by single-edged tools (fig. 49). The advantage of the first is that the cutter used has the same sectional form as the intertooth space, so that the act of tooth cutting imparts the shapes without assistance from external mechanism. But this holds good only in regard to spur-wheel teeth, that is, those in which the teeth lie parallel with the axis of the wheel. The teeth of bevel-wheels, though often produced by rotary cutters, can never be formed absolutely correctly, simply because a cutter of unalterable section is employed to form the shapes which are constantly changing in dimensions along the length of the teeth (the bevel-wheel being a frustum of a cone). Hence, though fair working teeth are obtained in this way, they result from the practice of varying the relative angles of the cutters and wheel and removing the material in several successive operations or traverses, often followed by a little correction with the file. Although this practice is still commonly followed in bevel-wheels of small dimensions, and was at one time the only method available, the practice has been changing in favour of shaping the teeth by a process of planing with a single-edged reciprocating tool. As, however, such a tool embodies no formative section as do the milling cutters, either it or the wheel blank, or both, have to be coerced and controlled by mechanism outside the tool itself. Around this method a number of very ingenious XXVII. 2 machines have been designed, which may be broadly classed under two great groups - the form and the generating types.
In the form machines a pattern tooth or form-tooth is prepared in hardened steel, usually three times as large as the actual teeth to be cut, and the movement of the mechanism which carries the wheel blank is coerced by this form, so that the tool, reciprocated by its bar, produces the same shape on the reduced dimensions of the wheel teeth. The generating machines use no pattern tooth, but the principles of the tooth formation are embodied in the mechanism itself. These are very interesting designs, because they not only shape the teeth without a pattern tooth, but their movements are automatically controlled. A large number of these have been brought out in recent years, their growth being due to the demand for accurate gears for motor cars, for electric driving, and for general high-class engineers' work. These are so specialized that they can only cut the one class of gear for which they are designed - the bevel-wheels, and these in only a moderate range of dimensions on a single machine of a given size. The principal bevel-gear cutting machines using forms or formers, are the Greenwood & Batley, Le Progres Industriel, the Bouhe.y (cuts helical teeth), the Oerlikon, which includes two types, the single and double cutting tools, the Gleason and the Rice. Generating machines include the Bilgram (the oldest), the Robey-Smith, the Monneret, the Warren, the Beale and the Dubosc.
?v.- ,?? FIG. 49. - Gear Cutting.
D, Action of " Fellows " cutter, planing teeth.
E, Shape of " Fellows " cutter.
F, Hobbing cutter.
G, Tapered hob beginning wormwheel.
H, Ditto finishing.
As the difficult i es of cutting bevel-wheels with rotary cutters, consequent on change of section of the teeth, do not occur in spurgears, there are no examples of form machines for spur-wheel cutting, and only one generating planing type of machine, the Fellows, which produces involute teeth by a hardened steel-cutting pinion, which shapes wheels having any number of teeth of the same pitch, the cutter and blank being partly rotated between each cut as they roll when in engagement.
The worm-gears appropriate a different group of machines, the demands on which have become more exacting since the growth of electric driving has brought these gears into a position of greater importance than they ever occupied before. With this growth the demand for nothing less than perfect gears has developed. A perfect gear is one in which the teeth of the worm-wheel are envelopes of the worm or screw, and this form can only be produced in practice in one way - by using a cutter that is practically a serrated worm (a hob), which cuts its way into the wheel just as an actual worm might be supposed to mould the teeth of a wheel made of a plastic substance. To accomplish this the relative movements of the hob and the wheel blank are arranged to be precisely those of the working worm and wheel. Very few such machines are made. A practical compromise is effected by causing the hob ??% A, Rotary milling cutter producing tooth space.
B, Planer tool operating on tooth flank.
C, Planer form-tool finishing tooth space.
both to drive and cut the blank in an ordinary machine. When worms are not produced by these methods the envelope cannot be obtained, but each tooth space is cut by an involute milling cutter set at the angle of thread in a universal machine, or else in one of the general gear-cutting machines used for spur, bevel and worm gears, and only capable of yielding really accurate results in the case of spur-wheels.
The previous remarks relate only to the sectional forms of the teeth. But their pitch or distance from centre to centre requires dividing mechanism. This includes a main dividing or wormwheel, a worm in conjunction with change gears, and a division plate for setting and locking the mechanism. The plate may have four divisions only to receive the locking lever or it may be drilled with a large number of holes in circles for an index peg. The first is adopted in the regular gear-cutters, the second on the universal milling machines which are used also for gear-cutting. In the largest number of machines this pitching has to be done by an attendant as often as one tooth is completed. But in a good number of recent machines the pitching is effected by the movements of the machine itself without human intervention. With spur-wheels the cutting proceeds until the wheel is complete, when the machine is often made to ring a bell to call attention to the fact. But in bevel-wheels only one side of the teeth all the way round can be done; the attendant must then effect the necessary settings for the other side, after which the pitchings are automatic.
As a general rule only one tooth is being operated on at one time. But economy is studied in spur-gears by setting several similar wheels in line on a mandrel and cutting through a single tooth of the series at one traverse of the tool. In toothed racks the same device is adopted. Again, there are cases in which cutters are made to operate simultaneously on two, three or more adjacent teeth.
Recently a generating machine of novel design has been manufactured, the spur-wheel hobbing machine. In appearance the hob resembles that employed for cutting worm-gears, but it also generates the teeth of spur and spiral gears. The hob is a worm cut to form teeth, backed off and hardened. The section of the worm thread is that of a rack. Though it will cut worm-wheels, spiral-wheels or spur-wheels equally correctly, the method of presentation varies. When cutting worm-wheels it is fed inwards perpendicularly to the blank; when cutting spirals it is set at a suitable angle and fed across the face of the blank. The angle of the worm thread in the hob being about 21°, it has to be set by that amount out of parallel with the plane of the gear to be cut. It is then fed down the face of the wheel blank, which is rotated so as to synchronize with the rotation of the worm. This is effected through change gears, which are altered for wheels having different numbers of teeth. The advantage is that of the hob over single cutters; one hob serves for all wheels of the same pitch, and each wheel is cut absolutely correct. While using a set of single cutters many wheels must have their teeth only approximately correct.
VI.-Grinding Machines The practice of finishing metallic surfaces by grinding, though very old, is nevertheless with regard to its rivalry with the work of the ordinary machine tools a development of the last part of the 19th century. From being a non-precision method, grinding has become the most perfect device for producing accurate results measured precisely within thousandths of an inch. It would be rather difficult to mention any class of machine-shop work which is not now done by the grinding wheel. The most recent developments are grinding out engine cylinders and grinding the lips of twist drills by automatic movements, the drills rotating constantly.
There are five very broad divisions under which grinding machines may be classified, but the individual, well-defined groups or types might number a hundred. The main divisions are: (I) Machines for dealing with plane surfaces; (2) machines for plain cylindrical work, external and internal; (3) the universals, which embody movements rendering them capable of angular setting; (4) the tool grinders; and (5) the specialized machines. Most of these might be again classed under two heads, the non-precision and the precision types. The difference between these two classes is that the first does not embody provision for measuring the amount of material removed, while the second does. This distinction is a most important one.
The underlying resemblances and the differences in the main designs of the groups of machines just now noted will be better understood if the essential conditions of grinding as a corrective process are grasped. The cardinal point is that accurate results are produced by wheels that are themselves being abraded constantly. That is not the case in steel cutting tools, or at least in but an infinitesimal degree. A steel tool will retain its edge for several hours (often for days) without the need for regrinding, but the particles of abrasive in an emery or other grinding wheel are being incessantly torn out and removed. A wheel in traversing along a shaft say of 3 ft. in length is smaller in diameter at the termination than at the beginning of the traverse, and therefore the shaft must be theoretically larger at one end than the other. Shafts, nevertheless, are ground parallel. The explanation is, and it lies at the basis of emery grinding, that the feed or amount removed at a single traverse is extremely minute, say a thousandth or half a thousandth of an inch. The minuteness of the feed receives compensation in the repetition and rapidity of the traverse. The wear of the wheel is reduced to a minimum and true work is produced.
From this fact of the wear of grinding wheels two important results follow. One is that a traverse or lateral movement must always take place between the wheel and the piece of work being ground. This is necessary in order to prevent a mutual grooving action between the wheel and work. The other is that it is essential to provide a large range in quality of wheels, graded according to coarseness and fineness, of hardness and softness of emery to suit all the different metals and alloys. Actually about sixty grades are manufactured, but about a dozen will generally cover average shop practice. With such a choice of wheels the softest brass as well as the hardest tempered steel or case-hardened glass-like surfaces that could not possibly be cut in lathe or planer, can be ground with extreme accuracy.
FIG. 50. - Universal Grinding Machine, 7 in. centres; 3 ft. 6 in. between centres. (H. W. Ward & Co., Ltd., Birmingham.) J, Headstock for carrying and, driving work, used for chuck work or dead centre work; the base is graduated into degrees.
a, Dogs, which regulate automatic reversals. An internal grinding fixture, not shown, is fitted to wheel head.
L, Countershaft pulley driving to wheel pulley.
M, Pulley driving to cones.
N, Pulley driving to work headstock pulley.
0, Belt from line shaft.
P, Water pipe from pump.
Q, Water guards above table.
Plane surfacing machines in many cases resemble in general outlines the well-known planing machine and the vertical boring mill. The wheels traverse across the work, and they are fed vertically to precise fractional dimensions. They fill a large place in finishing plane surfaces, broad and narrow alike, and have become rivals to the planing and milling machines doing a similar class of work. For hardened surfaces they have no rival.
Cylindrical grinders include many subdivisions to embrace external and internal surfaces, either parallel or tapered, small or A, Base or body, with waste water tray round top edge, and interior fitted as cupboards, with shelves and doors.
B, Sliding table.
C, Swivel table.
D, Grinding wheel.
E, Wheel guard.
F, Wheel headstock swivelling in a horizontal plane, and having the base graduated into degrees for angular setting.
G, Slide carrying headstock.
H, Hand-wheel for traversing table.
large. In their highest development they fulfil what are termed " universal " functions (fig. 50), that is, they are capable of grinding both external and internal cylinders, plane faces, tapers, both of low and high angle, and the teeth of various kinds of tools and cutters. These machines occur in two broad types. In one the axis of the revolving wheel is traversed past the work, which revolves but is not traversed. In the other the reverse occurs, the work traversing and the axis of the wheel with its bearings remaining stationary. Equally satisfactory results are obtained by each.
In all external cylindrical grinding, when the work can be rotated, the piece being ground rotates in an opposite direction to the rotation of the wheel (fig. 51, A). In all small pieces ground internally the same procedure is adopted (fig. 51, B). Incidentally, FIG. 51. A, External cylindrical grinding. B, Internal ditto. C, External grinding when the work is fixed. D, Internal ditto.
mention should be made of the fineness of the fitting required and attained in the construction of the spindles which carry the wheels for internal grinding. The perfection of fitting and of the means of adjustment for eliminating the effects of wear in the ordinary spindles for external and internal grinding is remarkable. The spindles for internal work have to revolve at rates ranging from about 6000 to 30,000 times din a minute, yet run so truly that the holes ground do not depart from accuracy by more than say N--oxao to itho of an inch. Yet so long as the work can be revolved no special complication of mechanism is required to ensure good results. The revolution of the wheel and the work is mutually helpful. The real difficulties arise when the work, on account of its mass or awkwardness of shape, cannot be revolved. The principle embodied in machines designed to deal satisfactorily with such cases, though much diversified in detail, is the application of the planet device to the grinding wheels. That is, the wheel spindle rotating at a high speed, 6000 or 7000 revolutions per minute, is simultaneously carried round in a circular path, so that its axis makes about 25 or 30 revolutions per minute (fig. 51, C and D). The diameter of the path is capable of adjustment with minute precision within wide limits to suit bores of different diameters. The periphery of the grinding wheel which lies farthest from its axis of revolution sweeps round in a path the diameter of which equals that of the bore to be ground. These machines are now used largely for grinding out the cylinders of gas and petrol engines, valve seatings, the bushed holes of coupling rods, and similar classes of work. Many of them have their spindles set horizontally, others vertically.
Allied to these are a relatively small but important group of machines used for grinding the slot links of the slide-valve gear of locomotive and other engines. The slot is mounted on a pivoted bar adjusted to the same radius as the slot to be ground, and the slot is moved relatively to the wheel, so producing the required curves.
In another direction much development has taken place in the practice of grinding. The increasing use of the milling cutter has FIG. 52.
A, Grinding front edges of milling cutter. B, Grinding side edges of milling cutter; a, a, Tooth rests. C, Grinding face of formed mill.
been the occasion for the growth and high specialization of the cutter grinding machines. It is essential to the efficiency of such cutters that regrinding shall be done without drawing the temper, and this can only be effected by the use of an abrasive. In the early days of their use the temper had to be drawn to permit of filing and rehardening effected with its inevitable distortion.
Cutter grinding machines must possess universality of movements to deal with the numerous shapes in which milling cutters are made; hence they often resemble in general outlines the universal grinding machines. But as a rule they are built on lighter models, and with a smaller range of movements, because the dimensions of cutters are generally much smaller than those of the ordinary run of engineers' work which has to be ground. Frequently a single pillar or standard suffices to carry the mechanism. In an ordinary universal tool grinder all the teeth of any form of cutter can be ground precisely alike (fig. 52) excepting those having irregular profiled outlines, for which a special machine, or an extra attachment to an ordinary machine, is necessary. But little of this is done, because in such cases, and in many others, the faces of the teeth are ground instead of the edge. This idea, due to the firm of Brown & Sharpe, may seem a trifle, but nevertheless to it the credit is largely due for the economies of cutter grinding. The principle is that in the " formed cutter," as it is termed, the profiles of the teeth are not struck from the axis of revolution, but from another centre (fig. 20); grinding the tooth faces, therefore, has no effect on the shapes of the profiles, but only lessens the tooth thicknesses. Designed originally for the cutters for the teeth of gear-wheels, it has long been applied to profiles which involve combinations of curves. The pitching of the teeth is effected by a strip of metal, or tooth rest a (fig. 52), on which each successive tooth rests and is coerced during the grinding. If teeth are of special form the traverse movement of a spiral tooth along the rest ensures the required movement.
Besides the cutter grinders used for milling cutters, reamers and screwing taps, there are two other groups of tool grinders, one for twist drills only and the other for the single-edged tools used in lathe, planer, shaper and other machines. Both these in their best forms are of recent development. The machines used for grinding twist drills embody numerous designs. Hand grinding is practically abandoned, the reason being that a very minute departure from symmetry on the two cutting lips of the drill results inevitably in the production of inaccurate holes. It is essential that the two lips be alike in regard to length, angle and clearance, and these are embodied in the mechanism of the grinding machines. But formerly in all these the drill holder had to be moved by hand around its pivot, and one lip ground at a time There are now some very beautiful machines of German manufacture in which the necessary movements are all automatic, derived from the continuous rotation of a belt pulley. The drill rotates constantly, and small amounts are ground off each lip in turn until the grinding is finished. The other group for grinding single-edged tools is a very small one. The correct angles for grinding are embodied in the setting of the machine, with the great advantage that any number of similar tools can be ground all alike without skilled attendance.
Lying outside these broad types of machines there is a large and growing number designed for special service. The knife-grinding group for sharpening the planer knives used in wood-working machinery is a large one. Another is that for gulleting or deepening the teeth of circular saws as they wear. Another is designed for grinding the cups and cones for the ball races of cycle wheels, and another for grinding the hardened steel balls employed in ball bearings.
FIG. 53. - Typical Grinding Wheels.
Common disk held on spindle with washers and nuts. Thin disk.
Flanged disk for grinding to shoulders.
Bevelled disk for cutter grinding.
F, Cupped and dished wheels for cutter grinding.
Cup wheel for grinding on face a; diameter remains constant.
Emery grinding is dependent for much of its success on a plentiful supply of water. Dry grinding, which was the original practice, is hardly employed now. The early difficulties of wet grinding were due to the want of a cementing material which would not soften under the action of water. Now wheels will run constantly without damage by water, and they are so porous that water will filter through them. Improvements in the manufacture of wheels, and the increased use of water, have concurred to render possible heavier and more rapid grinding without risk of distortion due to heating effects. In the best modern machines the provisions for water supply are a study in themselves, including a centrifugal pump, a tank, jointed piping, spraying tube, guards to protect the bearings and slides from damage, and trays to receive the waste water and conduct it back to the tank.
There are two points of view from which the modern practice of grinding is now regarded - one as a corrective, the other as a B G, formative process. The first is the older and is still by far the most important. The second is a later ideal towards which design and practice have been extending. As yet grinding cannot compete with the work of the single-edged tools and milling cutters when large quantities of material have to be removed. Just as some leading firms have been designing stiffer machines having fuller lubrication with a view to increase the duty of grinding wheels, the advent of the high-speed steels has given a new lease of life to the single-edged cutting tools. The rivalry now lies not with the tools of carbon temper steel, but with highspeed varieties. But as a corrective process grinding never occupied so important a position as it does to-day, and its utility continues to extend.
The commoner forms in which grinding wheels are made are shown in fig. 53. These are varied largely in dimensions, from tiny cylindrical rollers a fraction of an inch in diameter for hole grinding, to big wheels of 3 ft. or more in diameter. Safety mountings, two examples of which are shown in fig. 54, embody means of retaining the broken pieces of a wheel in case it bursts.
Sand-blast
The well-known erosive action of sand when driven against rocks and stones by the wind is utilized industrially in the sand-blast apparatus, the invention of B. C. Tilghman. The sand is propelled by a current of steam or air, and being delivered through a nozzle is directed against the surface of B, Cup wheel with encircling of e the k en utti n g t numbbr of e a rains ring, moved backwards striking the face, each removing a very as the wheel face wears. minute quantity of material. The action is very gentle, and may be modified by varying the class of sand and its velocity. Other materials, such as emery, chilled iron globules, &c., are employed for certain classes of work. In some instances the powder is used dry, in others it is mixed with water, being then in the condition of fluid mud. The plant includes an air-compressing engine, an air reservoir and the blast nozzle through which the air passes and propels the sand in the form of a jet. The pressures range from 8 lb up to about 60 lb per sq. in., depending on the class of work which is done.
The peculiar advantage of the sandblast lies in its adaptability to the working of irregular surfaces, which could not be touched by any other class of grinding. The blast penetrates hollows and recesses, and acts over an entire surface. There are many classes of operation done with the sand-blast, including cleaning, frosting, ornamentation, engraving and sharpening. In engineers' works a large amount of cleaning is effected upon castings, forgings, sheets and other products, either preparatory to machining or to painting, enamelling, tinning, galvanizing or plating. Cycle frames are cleaned with the sand-blast after brazing. The teeth of files are sharpened by directing a stream of sand and water against their backs, with the result that the burr thrown up by the chisel when cutting is obliterated, and a strong form of tooth is produced. Worn files may also be sharpened up to equal new ones by sand-blasting them. Frosting glass is another useful application of the sand-blast, and by attaching suitable patterns or designs to the surface the sand may be caused to work ornamental figurings. It is a peculiar circumstance that the sand has little effect upon soft and yielding substances in comparison with the abrasion it produces on hard surfaces, so that the pattern will remain undamaged, while the glass or other object beneath is frosted where the sand reaches it, through the openings. Not only can designs be worked on glass, or cut in stone, but perforations may be made in glass, &c., by the continued action of the sand, without any risk of fracture occurring. Much sandblasting is performed inside closed chambers, having panes through which the workman watches the progress of the operation. But when the blast must be used in the open, protection is necessary and is afforded to the operator by a special helmet, which keeps out the flying dust and gives a supply of pure air through a tube in a similar fashion to the diver's helmet.
VII. - Sawing Machines Metal-sawing machines are employed extensively in engineering works for cutting off bars, shafts, rails, girders and risers on steel castings, and for getting out curved pieces which would be difficult and expensive to slot. There are three classes of these saws, circular, band and reciprocating. The first named are used for straightforward work, operating at right or other angles, the second for straight cuts and also for curves which cannot be treated with circular saws, and the third for small pieces. The circular saws embody a stiff spindle, carrying the saw disk and driven by gearing. This spindle may be mounted in a sliding bearing to carry it past the work held on a fixed table, or the spindle may be stationary and the work be moved along past the saw. The method of feeding should be sensitive, so that it will " give " and prevent damage FIG. 54. - Safety Devices.
A, Grinding wheel, with coned washer to retain broken pieces in case of fracture.
to the teeth, should undue stress come upon the saw. This is usually effected by the use of weights or springs, which allow a certain freedom or latitude to the driving gears. The work is held by screw clamps, V-blocks being required in the case of circular objects. A number of pieces, such as shafts, rails or girders, can be fastened down close together in a pile and cut through in one operation.
There is a very useful class of circular saw, the flush-side (fig. 55), that is valuable for cutting close up to a surface. The disk is bolted to a flange on the end of the spindle with countersunk bolts, so that the face is quite flat. Another class of saw used for dealing with girders and bars is carried in bearings upon a pivoted arm, which is pulled downwards by a weight to give the feed. The work is bolted to a table below the saw. Ample lubrication, by oil or soapy water, is essential in cutting wrought iron and steel; it is pumped on the blade, keeping it cool and washing away the cuttings.
Band-saw machines resemble in outline the familiar types employed for sawing wood, but they are necessarily stronger and stiffer, and the saws run at a much lower speed. The tables, moreover, differ in possessing compound slides for moving the work and in the provision of a series of slots on the top table, whereby the object to be sawn is secured with bolts and clamps. The tables are moved automatically or by hand. The rate of cutting must be varied according to the thickness of metal. Lubrication is effected by running the lower saw pulley in a bath of oil or soapy water, which is carried up, so keeping the blade cool and " easing " the cut.
The reciprocating class of saw has until recently been confined to small types for workshop use, termed hack saws, v i thich have a small blade ranging from 12 to 18 in. long. This is strained between a couple of bearings in a frame which is reciprocated above the work clamped in a vice. An arrangement of weights feeds the saw downwards. The larger hack saws cut off bars and girders up to 12 in. across, and in some there is a provision introduced for giving intermittent rotation to the bar, thus presenting fresh faces to the saw. The hack saw is of great utility for comparatively light work, and, as the smallest blades are cheap enough to be thrown away when worn out, there is no trouble and expense connected with their sharpening, as in the circular and band saws. An adaptation of the reciprocating saw is that of the jig type, which has a small blade set vertically and passing up through a table on which the work is laid. It is handy for cutting out dies and various curved outlines, in the same manner that fret-sawing in wood is done.
Viii.-Shearing And Punching Machines These have much in common as regards their mode of operation. They are actuated either by belt and spur gearing, by steam-engine, by electric motor, or hydraulically. The first named is only suitable where arrangements can be made for driving from a line shaft. In view of the great convenience of the other methods of driving, they are coming into greater use, especially for ship-yards and other works where shafting is undesirable or inconvenient.
For boiler makers' and platers' use the function of punching, and shearing are usually combined in one machine, the rams being placed at opposite ends and actuated from the same source of power. The last shaft in the train of gearing is set to bring its ends within the boxes containing the rams, and eccentrics on the shaft are moved within die blocks fitted to the rams, so that as the shaft revolves it causes the rams to move up and down and operate the shear blade and { FIG. 57. - Steam Hammer, small Overhanging Type. (B. & S. Massey, Manchester).
Standard. B, Base-plate.
Anvil block (independent of standards).
Tup or hammer head.
E, Pallets, or forging blocks, attached to anvil and tup. Steam cylinder.
Piston, solid with piston rod H. Piston valve, regulating period of admission of steam, operated by hand by lever K or lever N. Stop or throttle valve for controlling admission of steam to valve chest, operated by hand lever M. Lever in contact with roller on tup D, which moves the valve J automatically as the tup rises and falls.
Lever for pre-adjusting the range of movement of N and J, according to its setting in the notches of the quadrant from a to b. Steam supply pipe from boiler. Q, Exhaust steam pipe.
A, J, L, FIG. 56. - Hydraulic Punching and Shearing Machine. (Musgrave Brothers, Leeds.) A, Frame. E, Punch. J, K, Main and return rams for B Shear blades, set angularly. F & G, Main and return rams ditto.
C, Ram for operating blade. for punch. L, M, N, Attendant's control D, Small ram for returning ditto. H, Angle shear. ling handles.
the punch attached to the bottom end. Another class of machines is worked by means of massive levers, pivoted in the framing, and actuated by cams on the driving shaft which cause the levers to rock and move the punches or shears up and down by the opposite ends. The punch slides are constructed to " dwell " for a short period at the top of the stroke at each revolution, thus giving the attendant time to place and a djust the plate accurately beneath the punch. The same effect is obtained in the eccentric types of machines mentioned above, by a disengaging motion,which is thrown in by touching a lever, thus stopping the punch until the operator is ready for its descent. The more complete machines have an angle shear situated centrally, with V-blades for severing angle iron. The largest forms of shears, for massive plates, usually have the blade reciprocated by crank or eccentrics on the driving shaft, coupled by connectingrods to the slide.
Hydraulic punching and shearing machines are used largely on account of their convenience, since they dispense with all belts, engines or motors in the vicinity, and give a very powerful stroke. The hydraulic cylinder is generally direct-connected to the slides, and the operator turns on the pressure water by a lever. The machine shown in fig. 56 is a very complete example of the hydraulic type, combining punching and shearing with angle-cutting.
Circular shears are used for the thinner plates and for sheet-metal work; they embody two circular blades placed with their axes parallel, and the sharp bevelled edges nearly in contact. The blades being rotated sever the plate as it is fed between them. Either straight or circular cuts may be made; true circles or disks are produced by mounting the plate on a fixed stud and rotating it through a complete revolution past the cutters.
IX.-Hammers And Presses The growth in the use of hammers actuated by steam and compressed air, and of presses worked by water power, has been remarkable. The precursors of the power hammers were the helve and the Oliver; the first named was operated by gravity, being lifted by a circle of cams, while the second was lifted by a spring pole overhead and pulled down by the foot of the workman, acting on a lever - the hammer shaft. The first was used by the ironworkers and the second by the smiths, until displaced by the Nasmyth hammer and its extensive progeny. Even now the old helve and Oliver survive in some unprogressive shops.
Pneumatic Hammers
A successful type of hammer for the ordinary operations of the smithy is that which is actuated by compressed air. Though designs vary the principle is the same, namely, air compressed in a controlling cylinder (fig. 58), and brought into an operating or hammer cylinder above the piston. Cushioning,or release of the air below the piston, is under control, as is the pressure of the air above it. Drop Hammers. - The requirements of forged work have, besides the power hammers operated by a positive down stroke, been the cause of the develop- (W. & J. Player, Birmingham.). ment of an equally large group A, Standards. which are gravity hammers only B, Base-plate. - the drop hammers. They are C, Anvil block. put into operation by a belt or D, Tup. belts, but the function of the E, E, Pallets. belt is simply to lift the hammer G, Hammer cylinder, the piston to the height desired, at which rod of which is attached point it is released and falls.
to D. The place of the drop hammer H, Air compressing cylinder. is in the lighter class of smith's N, Belt pulleys which reciprocate work, as that of the steam by means of the crank 0, hammer lies in the heavier, but the piston in H. there is much overlapping, since R, Handle controlling the valve small steam hammers are rivals between H and G. to the others in light forging.
But, speaking generally, the largest volume of repetitive die forging or stamping of light articles is done under drop hammers. The small arms factories and the regular stamping shops scarcely use any other type. They may be roughly divided into three great groups; the belt, the board and the latest form - the Brett lifter. In each the hammer head or tup is lifted to any height within the range of lift, the height being controlled by the attendant at each blow. In most machines setting can be done at any constant height and the blows delivered automatically. Control is effected by hand or foot or both. Drop hammers generally have the advantage of working with greater rapidity than steam hammers.
The original drop hammers, which are believed to have originated with the locksmiths of Birmingham and district, consisted of a hammer head attached to a rope, one end of which ran up over a loose pulley suspended in the roof, and the other was pulled by a man or two men, so lifting the hammer, which was then allowed to drop. The principle is embodied in many belt hammers to-day, but the pulley is driven constantly by shafting, and when the attendant pulls at the free end of the belt the friction of the pulley draws the belt over and lifts the hammer until the attendant lets it go. The weight lifted is greater than in the old type, but the labour is nevertheless very severe, and the blows are not rapid enough for quick forging. A far better machine is the board hammer. In this (fig. 59) the place of the belt is taken by an ordinary strip of board which passes between two rollers at the top of the hammer, which rollers are belt driven. The rollers are fitted on eccentric FIG. 59. - Drop Hammer - board type. Manchester.) A, A, Standards.
B, Anvil, or baseblock.
C, Tup.
D, Board, fitting in slot in tup.
E, F, Rollers gripping and lifting board.
G, H, Pulleys actuating rollers through eccentrics J, K. L, Rod by which the amount of lift is regulated.
a, Dog and lever adjustable on L, which strikes the edge b of the tup, releasing eccentrics and roller and allowing tup to fall.
c, Catch on which tup rests previous to release, fitted into either one of the row of holes beneath, to suit various heights of drop.
M, Mechanism struck by the edge d of the tup, which either keeps the roller F clear of the board D, allowing the tup to fall, or brings the rollers E and F into contact, and lifts the board and tup.
N, Hand-lever for operating hammer.
0, Foot-lever for ditto, connected by chain e. f, Spring for lifting levers.
P, Rod with nuts g, to compensate for wear on the rollers by the adjustment of roller E. B. & S. Massey, pins, so that the movement of levers causes them to grip the board for the lift, or release it for the fall, these levers being under the control of the attendant. They can also be set to operate automically for any height of lift.
These types are all subject to much concussion and vibration, because the machines are self-contained; anvil, standards and heads being rigidly bolted together, the concussion of every blow is transmitted through the entire mechanism. The Brett hammers (fig. 60) are designed to lessen this, in some cases by making the anvil distinct from the superstructure, and in all by connecting the lifting ropes to the ends of long levers which act something like elastic springs, absorbing vibration. The driving mechanism is also original, comprising a cylinder with a wing piston, which is rotated by steam pressure through an arc of a circle only, sufficiently to operate the lifting levers. Another advantage is that the lifter cylinder need not be immediately over the hammer, but may be situated elsewhere. The hammer can be operated by hand directly for each stroke, or be set to work automatically.
60.-5 cwt. Belt Drop Hammer with Brett's Lifter. (Brett's Patent Lifter Co., Ltd., Coventry.) h, Buffer blocks which arrest motion of lever c. d, Lever for automatic regulation of valve.
Lever for regulating amount of opening of valve by hand. by K, Foot lever for holding tup in either of the stops L. e, Spring for foot lever.
Spring Hammers are a rather smaller group than the others. In these a belt-driven pulley actuates the tup through the medium of elastic leaf springs. The length of stroke is adjustable across the face of a slotted disk on the driving shaft.
Forging Presses
These are rivals to the hammers, especially for heavy forgings, from which hammers are being rapidly displaced (fig. 61). It is now well understood that a hammer will not effect the consolidation of a massive forging right to the centre as a press will. The force of the hammer blow is not transmitted to the centre as is that of a press, nor is the hammer so useful in work of large dimensions but of no great weight. In railway and wagon shops the presses are used far more frequently than the hammers. A great advantage of the press is that two and three rams can be brought into operation so that a forging may be pressed from above, from below and to one side, which is of great value in complicated forms and in welding, but is not practicable in the hammers. Hence the forging presses have become developed for work of average dimensions as well as for the most massive. Many are of horizontal type, termed bull-dozers.
Power presses for working sheetmetal articles include those for cutting out the blanks, termed cuttingout or blanking presses, and those for cupping or drawing the flat blank into shape if desired (fig. 62). The lower dies are held upon a bed, and the upper in a sliding ram, moved FIG. 61. - Hydraulic Forgup and down by a cam or cranking Press. (Fielding & Platt, shaft. A clutch mechanism is fitted, Ltd., Gloucester.) by means of which this shaft is connected with or disconnected from the heavy driving-wheel at will to give a single stroke or a series of strokes to the ram. In the normal; state the ram remains stationary at) the top position. The lightest presses are driven direct by belt on the crank-shaft pulley, but in the heavier classes spur-gearing must be interposed between the pulley shaft and the final shaft. The operation of drawing requires an encircling die which presses on the blank as it lies on its die, the cupping of the blank being effected by the downward motion of the plunger..
Sectional Elevation. Front Elevation. FIG. 62. - Power Press.
A, Main frame.
B, Bed for attaching dies.
C, Central slide.
D, Outer slide.
E, Belt pulleys on shaft, geared to wheel F thrown in by clutch to drive its shaft, which has two crank pins to reciprocate D and a cam disk actuating C.
G Extractor rocked downwards as slide rises to raise lever H and work an ejector rod, forcing finished article out of die.
This is why the machine shown in fig. 62 has an outer slide D, which is made to " dwell " with an even pressure, while the middle ram is moving down and drawing out the article. Blanking and cupping may be done as one continuous operation if the work is shallow.
Inclinable presses are employed for certain classes of work, the object being to let the stamped articles slide down the slope of the bed as rapidly as they are produced, instead of having to be removed by the operator. Much work can be placed on the dies by hand, but for producing large quantities of small articles automatic feeds FIG.
A, Uprights.
Anvil. Tup. Belt.
Lifter cylinder.
Valve casing.
Rod operating valve lever H. Rock shaft.
a, A, Table.
B, Vertical ram.
C, Drawback ram for returning B. D, Horizontal ram.
E, Controlling valves.
are employed whenever possible. A good deal of work is produced from flat sheet, supplied in the form of a roll and fed through rollers by intermittent movements to the dies. Circular turn-tables are also used, operated by ratchet devices, which turn the tables round to bring a ring of pockets, carrying the pieces, successively under the dies; the attendant keeps the pockets supplied, but his hands do not come near the dies.
X. - Portable Tools The growth of portable machine tools is one of the remarkable movements of the present day. To some extent they have always been used, notably in the drilling and tapping operations of locomotive fire-boxes, but not until recently to any important extent in the ordinary fitting and erecting shops. The main reason lay in the difficulties due to transmission of power by ropes or shafts. The employment of compressed air, water, electricity and flexible shafts, by which long distances can be covered, has given new life to the portable system, which is destined to occupy a place of even greater importance than it does at present. The reason for the growing desirability of these tools is to be seen in the massive character of much engine and machine construction of the present time. Although firms that undertake the largest work can generally arrange to tool the individual parts on machines of massive sizes, that only meets a part of the difficulty. Very big work cannot be treated like that of small or even medium dimensions, done repetitively; that is, it is not practicable to drill and bore and ream and provide for the fitting of every piece by the aid of templets and jigs, while the work lies on the machine, but a great deal of adjustment and mutual fitting has to be accomplished in the course of erection. Therein lies the opportunity for the portable machine. If this is not used the alternatives are partial dismantling of the work and the transference of certain portions to machines or hand work. Another cause has been the substitution of machining for much hand work formerly done on massive constructions.
The principal operations for which portable tools are designed are the following: Drilling, screwing, cutting the seatings for keys, planing short portions of work, facings for the attachment of other pieces, as brackets and bearings, hammering operations, as in making welded joints, caulking the edges of boiler plates, chipping with hammer and chisel, riveting, ramming sand in foundry moulds, planing ships' decks, and some operations of lesser magnitude.
Portable tools are used in various ways. The first and most obvious is to attach them directly to the casting, forging or machine which is being built up. Thus a drilling machine will be clamped just where it is required to operate. Or if it has to be used on a large plane surface as a ship's deck, an electrical machine is suitable, in which magnetic attraction is set up between the foot of the machine and the deck sufficient to hold it down. A key-seating machine will be clamped on the shaft in which a keygroove has to be cut. A drilling machine may be fastened to a pipe with a chain embracing the pipe. Very many of the drills, and all the caulking and chipping hammers, are grasped in the hands and so thrust to their work. The tapping of screw holes is mostly done in this way, a common example being the holes for the stay bolts in the fire-boxes of steam boilers.
Another later method which has been introduced and practised in a few shops consists in installing a cast-iron floor-plate of large area, planed truly and provided with bolt holes and slots. On this a massive casting, forging or piece of work undergoing erection will be bolted. Then the portable tools - planers, drills, &c., as required - will be bolted to the table and brought into operation on the various sections of the work, several sometimes operating simultaneously. This method is to a certain extent coming into rivalry with the abnormal growth of machine tools, the development of which has been greatly accelerated by the massive dimensions of productions which only became possible by the substitution of steel made by the Bessemer and Siemens processes for iron.
The reciprocating motion necessary to effect hammering, chipping or caulking operations is produced by the action of a solid piston, sliding in a cylinder (fig. 63) and driven sharply against the end of the tool by the inrush of compressed air, being then returned for another stroke. The strokes range in number up to as many as 2000 per minute in some cases. For heavy riveting a " longstroke " hammer is employed, having a longer barrel than the chipping hammer shown in fig. 63, in order to obtain a greater force of blow. The operator grasps the hammer by the handle, with his fingers or thumb on the controlling lever, and as long as this is held down the blows continue. The air-supply pipe is flexible, so that it does not impede the movements of the workman. The tools at the end of the cylinder are simply held in asocket, so that they can be changed rapidly.
Rotative motion can be produced either by electric or pneumatic motors, and both systems are in wide use. Pneumatic motors are very suitable when an air-compressing plant is already laid down for other tools, while if electricity is used in the works portable tools operated by this agent may be employed instead of the pneumatic ones. In the electric drills (fig. 64) a small motor is fitted within the body and connected by spur-gears to the spindle to effect suitable speed reduction. A switch provides for stopping and starting the motor; the current is brought through a flexible cable which, like pneumatic hose, is armoured with wire to protect it from damage. The smallest drills are simply gripped in the operator's hand and FIG. 63. - Tierney Pneumatic Chipping Hammer. (The Globe Pneumatic Engineering Co., Ltd.) A, Cylinder.
B, Tool socket, carrying chisel C.
D, Piston, which strikes the back of C.
E, Handle, screwed and clamped to A. F, Trigger or lever clasped by operator's hand and opening valve G, admitting compressed air through connexion H, up passage J, through valve-box K, past valve L, and so against end of D, moving it towards C. As soon as the groove in the piston D registers with the hole M, air is admitted from a small hole (not shown), passes round the groove through hole M and passage N to the rear of the valve. This acting on the back of the valve throws it forward, thus shutting off the supply to the rear of the piston and permitting a small quantity of air to flow to the forward end of the piston for driving it in a backward direction. As soon as the air pressure is relieved on the back of the valve by the uncovering of exhaust holes (not seen) by the piston D, the valve is returned to the original position, owing to the air constantly pressing on the small area of the valve.
pushed up to the work; larger ones are supported by a pillar and arm, against which the thrust is taken, and the feed given by turning a screw at intervals.
FIG. 64. - Electrically-driven Hand Drill. (Kramos Ltd., Bath.) A, Body, cast in aluminium, with handles a, a. B, Motor, with revolving armature C, connected by spur-gears D, to the drill spindle E, fitted with ball thrust bearings.
F, Switch, operated by attendant pushing in a plug; the current is brought by flexible wires through the right-hand handle a. Pneumatic drills are usually worked by little motors having oscillating cylinders, by which the air and exhaust ports are covered and uncovered. They run at a high speed and are geared down to the spindle. In some cases two cylinders are used, but often four are fitted to give a powerful and equable turning moment. Grinding machines are also built with air motors directly coupled to the wheel spindle, the machines being moved about over the work by handles.
Another class of portable tools is driven, not by self-contained motors, but from an outside source of power, which is conveyed to the tools through flexible shafts built up of a series of spiral springs, or through flexible joints which form a connexion that permits the shaft to bend round corners and accommodate itself to any position in which the tool may be placed. The advantage of this is that the tool itself is much lightened, since there is no motor, and it can therefore be easily handled. Thus a drill simply contains the spindle, running in a frame which carries bevel-gears for transmitting the motion of the flexible shaft. Portable grinders also have nothing but the spindle, wheel and frame.
XI. - Appliances Appliances are vastly more numerous in a modern shop than in the older works, largely on account of the more repetitive character ?..?. i?? ? v.s y ///// //.? " ?y !??
ll?
7 ? %? ? idi.;...;,; ] of the operations done and of the desire to eliminate human labour, with its greater cost and chances of inaccuracy in the finished product. On all machines there are numerous aids by which the fixing of the work is facilitated. Many of these consist of simple packing blocks, by which heights are adjusted. These reach their higher developments in wedge-shaped packings, some of which are operated by a screw, while others act directly by screws. In some cases the exact height can be ascertained by observing graduations on the packings. Circular work is held in V-blocks, which occur in numerous modified forms. Various kinds of straps, clamps and bolts are used for gripping work with sufficient security to enable it to withstand the stress of the heaviest cutting. The highest development of all is attained in the templets and jigs, which are now indispensable in all modern shops, and which increase in number and complexity as the product of the shop becomes more specialized. A templet is a piece of metal cut to a definite shape, which being laid upon the work becomes a guide for striking the same shape on the surface of the work with a pointed scriber, and by which the tooling of any number of similar pieces is done without the labour of lining out each separate piece. Obviously, in such a case the degree of accuracy of the tooling still depends on the machine hand, who may work exactly, or only approximately, to these lines. Hence a great advance is made in the jig, which may be defined generally as a templet that is clamped rigidly to the work, or a box in which the work to be tooled is held. No marking off is done, but the jig becomes the actual guide for the operation of the cutting tools. The operation most frequently performed in jigs is drilling. Then the holes in the jig receive and coerce the drills, so that the holes made cannot vary in the least degree from those already in the jig. As it will often happen that hundreds or thousands of similar pieces will have to be tooled in this manner, holes in jigs are generally bushed with hardened steel, which is capable of enduring very lengthy service, and which can be renewed when worn. This is a simple illustration, but many jigs are of an extremely elaborate character, for it is obvious that the cost of a jig, though it may run into many pounds, becomes a mere trifle when spread over some thousands of pieces of work.
XII. - Wood-Working Machinery There is a large range of various classes of tools for performing the operations on timber, from the rough log to the finished product. Division is effected by saws, planing and finishing to outlines by knives or cutters, boring by augers and smoothing by sandpaper.
The first operation is that of tree-felling, which is often effected by machine, consisting of a reciprocating blade, working horizontally in a frame and moved by a steam cylinder. The boiler is separate, so that the machine may be transported about and set to work over a considerable area, steam being conveyed to it by a flexible pipe. When the trees are brought into the saw-mills in the form of logs, i.e. with the branches lopped off, they are often cross-cut to reduce them to suitable lengths. This operation is effected either by a reciprocating saw, operated by a pulley and crank, or by an electric motor, or else with a circular saw, travelling on a carriage which moves the saw through the log laid in front of it. The next operation, that of division or breaking-down into smaller portions, is done by saws of various types, according to the class of work. The oldest form of machine is the frame-saw, which is still used very largely. It comprises a framing within which a saw-gate or sawframe is reciprocated up and down by a crank; the frame holds a number of saws or webs of flat form, strained up tightly with wedges or cotters between the top and bottom of the frame, the distance between the saws being capable of variation to suit boards of all thicknesses. The log is fed longitudinally to the gang of saws upon carriages, which are of two types. In the roller-feed, which is suitable for comparatively even and straight logs, ribbed rollers in front and behind the saws obtain a bite on the top and bottom of the timber and feed it forward by their rotation. In the rack-feed the log is mounted bodily upon a long carriage that runs by rollers upon a set of rails, and the carriage is travelled along by pinions and racks, which give a positive feed regardless of the shape of the log. The carriage in the roller-feed machines is only represented by a couple of plain trolleys supporting the timber at back and front. The feed is obtained through a friction wheel of V-shape, with a smooth pawl, called the silent feed; the wheel is given a partial rotation at each down stroke of the saw-gate to turn the rollers or the pinions for carrying forward the log. The division of the timber may be either into deals or flitches, or planks or boards. In the last-named case as many as fifty saw-blades are sometimes held in a frame.
For the more valuable hardwoods a single blade reciprocating saw, operated horizontally, is used very largely, the machine being termed a board-cutter. The log is clamped to a travelling table, passing underneath the saw, which is strained in a frame sliding on a cross-rail that can be adjusted up or down on a couple of uprights like a planing machine. The saw is worked from a crank and connecting-rod. As only one board is sawn at a time the attendant is able to see the figuring of the timber and to avoid waste when bad places are encountered.
A machine much more rapid in operation is the horizontal band XXVII. 2 a saw, modelled on the lines of the above machine, but with a bandsaw blade running over two pulleys, at a high speed, of about 7000 ft. per minute. The saws are very thin, so that a minimum of wood is wasted in the cut or " kerf,' a very important consideration in dealing with costly woods. Vertical band-saws, having one pulley above the other so that the blade runs vertically, are very popular in America; they occupy less floor space than the horizontal types. It is necessary to present the log from the side, and it is therefore clamped by dogs upon a carriage running on rails, with provision for feeding the log laterally to the saw by sliding ways on the carriage. The use of circular saws for breaking-down is confined chiefly to squaring up heavy balks, which need only a cut on each side, or for cutting thick slabs. The thickness of the saw entails considerable waste of wood, and a large amount of power is required for driving. The machines are termed rack-benches, and comprise a long divided table built up of thin plates and travelling past the fixed saw upon rollers, the movement being effected by a rack and pinion.
Re-sawing machines are those designed for further cutting-up deals, flitches, planks, &c., already broken out from the log, into boards and other scantlings. The deal and flitch frames are built on the model of the frame-saws first described, but with the differences that roller feed is always used, because the stuff is smooth and easily fed, and that the back of the timber is run against fences to keep it moving in a straight line. In the double equilibrium frames, which are much favoured, there are two sets of saws in separate frames connected by rods to opposite crank-shafts, so that as one frame is rising the other is going down; the forces are thus balanced and vibration is diminished, so that the machines can be speeded rather higher. Re-sawing is also done on circular and band saws of various types, fitted with fences for guiding the timber and controlling the thicknesses.
The cross-cut saws constitute another large group. They are employed for cutting-off various classes of stuff, after breaking-down or re-sawing, and are of circular saw type. The pendulum saw is a suspended form, comprising a circular saw at the bottom of a hanging arm, which can be pulled over by the attendant to draw the saw through a piece of wood laid on a bench beneath. Circular saws are also mounted in tables or benches and made to part off stuff moved laterally upon a sliding-table. When there is sufficient repetition work machines with two or more saws are used to cut one or more pieces to accurate length without the necessity for measurement.
The lighter classes of circular and band-saws, employed for sawing up comparatively small pieces of timber, embody numerous provisions for quickening output. The plain saw benches, with circular saws, are the simplest class, consisting merely of a framed table or bench carrying bearings for the saw spindle and a fence on the top to guide the wood. A mechanical feed is incorporated in the heavier machines to push the timber along. The rope-feed mechanism includes a drum driven at varying rates and giving motion to a rope, which is connected with a hook to the timber, to drag it along past the saw, roller supports on rails taking the weight at each end of the bench. Roller-feed saws propel the stuff by the contact of vertical fluted rollers placed opposite the fence. Other classes of saws for joinery work, &c., are constructed with rising and falling spindles, so that the saw may be made to project more or less from the table, this provision being necessary in grooving and tonguing with special types of saws. The same effect is obtained by making the table instead of the spindle rise and fall.
As it is necessary to use different saws for ripping (with the grain) and cross-cutting, some machines embody two saws so that work can be cut to shape on the same machine. These " dimension saws " have two spindles at the opposite ends of a pivoted arm that can be turned on a central pin to bring one or the other saw above as required. In cases where much angular and intricate sawing is done universal benches are employed, having in addition to the double saws a tilting motion to the table, which in conjunction with various special fittings enables the sawyer to produce a large range of pieces for any class of construction.
Band-saws, which have a thin narrow blade, are adapted especially for curved sawing and cutting-out work which the circular saw cannot manage. The usual design of machine (fig. 65) comprises a stiff standard supporting a lower pulley in fixed bearings, and an upper one in a sliding bearing, which by means of a weight or spring is caused to rise and maintain an even tension on the saw blade as it is driven by the lower pulley, and runs the upper one. India-rubber tires are placed around the pulley rims to prevent damage to the saw teeth. The table, placed between the pulleys, may be angled for cutting bevel work. It is necessary, in order to do true work, to guide the saw blade above and below the cut, and it is therefore run in guides consisting of flat strips, in combination with antifriction rollers which take the backward thrust of the saw. Fret or jig saws are a small class with a vertical reciprocating blade, employed chiefly for cutting out interior portions which necessitate threading the saw first through a hole.
Planing machines, used for truing up the surfaces of wood after sawing, depend for their action upon rapidly revolving knives fastened to flat-sided cutter blocks. The simplest machines, the hand-planers, have a cutter cylinder revolving between two flat [[[Wood-Working Machinery]] table slides adjustable for height to support the wood while it is pushed along over the knives by the hand. A fence guides it in a straight line. Exact thicknessing is done on another type of machine, the panel planer or thicknesser, in which the cutter cylinder revolves above the table and the stuff is fed through by rollers above FIG. 65. - Band-sawing Machine with 30 in. pulleys. (Thomas White & Sons, Paisley.) A, Cast-iron cored frame.
B, Fast and loose pulleys driving pulley C.
D, Belt shipper operated by handle E. F, Upper saw pulley, with its shaft carried in swivel bearing.
G, Screw for raising or lowering F to suit saw.
H, Spring to maintain even tension on saw, by raising E. J, Counterbalanced guide bar, having a Jackson guide K at bottom; K has wooden strips embracing the saw and a ball-bearing roller against which the back runs, while J is adjusted up or down to bring K as near to the work as convenient.
L, Table, with slit for saw; it may be canted for bevel sawing, by means of hand worm-gear M. N, Protective casing to saw.
0, Guard to prevent saw flying over in case of breakage.
and below. By altering the height of the table the thickness of wood can be varied. Double machines include a cutter cylinder above and below the timber, so that the upper and under sides are planed simultaneously. A combination of the hand-planer and the thicknesser is useful in cases where space or expenditure must be limited.
When large quantities of planed stuff are wanted, such as for flooring-boards, &c., other types of machines are employed. The four-cutter planers are the most rapid in output, and the timber is passed through them at a high rate, ranging up to 150 ft. per minute. There is first a revolving cutter cylinder, which roughs off the underside of the stuff, whence it passes (being propelled by rollers) to a fixed knife which imparts a very smooth face. A little farther on in the machine two vertical cutter blocks are encountered which carry cutters to plane or tongue or mould the edges, after which another cylinder above finishes the top face. Similar types of machines are made to produce mouldings, using four cutters shaped to suit the pattern required.
Moulding is also done on the vertical spindle shapers, which carry a cutter or cutters at the top of a spindle projecting through a flat table. The work is slid over the table and controlled by touching a collar below the cutter. Any form may be given to the cutters to produce different profiles. Some special moulding machines use a cutter at the end of a spindle projecting downwards from an arm overhanging a table, an arrangement which enables recessing and carving to be performed.
Boring machines comprise rotating spindles and feeding mechanism to actuate augers. The single spindle machines are satisfactory enough for ordinary work, but when a number of differently sized holes have to be bored in a single piece of work, or in rapid succession, it is the practice to employ a machine with a number of spindles, so that a succession of augers of graduated diameters may be ready to use at will.
Mortising or cutting slots is done in vertical machines with a reciprocating spindle, operated either by hand or by crank disk and pulleys. The tool that cuts the mortise resembles a woodworker's chisel, but is of stouter form and has a suitable shank to fit in the spindle. The latter can be reversed to turn round and let the chisel face in the opposite direction for cutting at each end of a FIG. 66. - Mortising and Boring Machine with graduated stroke. (John McDowall & Sons, Johnstone.) A, Frame.
B, Auger head, driven by belt C. D, Mortising chisel reciprocated up and down by crank-disk E. F, G, Levers connecting crank-pin to spindle of D. H, Treadle connected to F; a gradually increasing stroke is imparted to the chisel by depressing H, which brings F, G into play and continually lengthens the stroke of D, cutting the mortise without shock.
J, Fast and loose pulleys driving E. K, Cord actuated from shaft of J, which reverses the chisel when the handle L is moved and makes it cut in the reverse position.
M, Knee raised or lowered by hand-wheel and screw.
N, Cross-slide, adjusted by hand-wheel and screw.
0, Longitudinal slide, moved by rack and pinion and handwheel.
P, Timber vice.
mortise. A boring spindle is often incorporated with the machine to make holes for the mortising chisel to start in (fig. 66). Another class of mortiser employs a square hollow chisel, inside of which an auger rotates and first bores a hole, leaving to the chisel the duty of finishing out the corners. The chain mortiser is another type; it has an endless chain of flat links, sharpened to make cutting teeth, and is run around a bar and a roller at a high speed, so that when fed into the wood a recess or mortise is cut out.
Tenoning machines, designed to cut the reduced ends or tenons to fit in mortises, perform their work by the aid of cutter blocks, revolved on horizontal sp; ndles above and below the timber, which is fed laterally upon a sliding carriage.
Dovetailing is effected by revolving cutters in machines having mechanism for pitching out the cuts, or if the work warrants it an entire row of dovetails is made at one traverse, by fitting a row of cutters and feeding simultaneously. Corner-locking, or cutting parallel tongues and grooves in the edges of boxes, &c., is a rather more rapid operation than dovetailing, and is done with suitable cutter blocks or disks of appropriate thickness and pitching apart.
The general joiner, as its name implies, will do a large variety of operations, and is used in shops and on estates where a complete plant of machines would be out of the question. It usually has a circular saw and sometimes a band-saw also, together with planing and moulding apparatus, a moulding spindle, boring spindle and tenoning apparatus.
The lathes used in woodworking comprise the plain hand types with a simple T-rest on which the turner rests the tools to deal with the work revolving between centres, and the copying or Blanchard lathes, in which a master form or copy is rotated and caused by the contact and coercion of a roller to move the cutter rest in a corresponding fashion, so that the work is cut away until it exactly matches the shape of the copy.
Sand-papering machines, which finish the surface of wood to a high degree, deal with both flat and curved faces. Flat boards, panels, &c., can be done by contact against revolving drums or disks covered with glass-paper, being fed along over them by hand or by rotating rollers. In one class of machine a revolving disk is placed at the end of a series of jointed arms, by which the disk can be moved about over the work resting on a table underneath.
XI II. - Measurement An advance of the greatest importance made in mechanical engineering is that of measurement. Since the beginning of the t9th century steady movement has been going on in this direction until it seems impossible that much greater refinement can now be looked for. Probably the chief advances to be expected will lie in the general extension in workshop practice of the knowledge already acquired, rather than in the acquisition of higher degrees of refinement.
Methods of measurement adopted in woodworking have but little application in high-class engineers' work. They are adopted, however, to a considerable extent in the metal trades which are allied to engineering, as sheet metal working, girder work, &c. When a carpenter or joiner sets about constructing a door, window sash, roof or box he takes a two-foot rule, a flat lead pencil, and marks off the dimensions and lines by which he intends to work. If he has to work very carefully, then instead of using a pencil he cuts a line with the edge of a keen scriber or chisel-like tool, by which to saw, plane or chisel. If outlines are curved, the compasses are brought into requisition, and these cut a fine line or lines on the surface of the wood. But in any case the eye alone judges of the coincidence of the cutting with the lines marked. Whether the tool used be saw, chisel, gouge or plane, the woodworker estimates by sight alone whether or not the lines marked are worked by.
The broad difference between his method and that of the engineer's machinist lies in this, that while the first tests his work by the eye, the second judges of its accuracy or otherwise by the sense of touch. It may seem that there cannot be very much difference in these two methods, but there is. To the first, the sixty-fourth part of an inch is a fine dimension, to the second one-thousandth of an inch is rather coarse. Now the thickness of tissue paper is about one-thousandth of an inch, and no one could possibly work so closely as that by the eye alone. Engineers' steel rules usually have one inch which is divided into one hundred parts. Tolerably keen sight is required to distinguish those divisions, and few could work by them by ocular measurement alone, that is, by placing them in direct juxtaposition with the work. A '. thousandth part of an inch seems by comparison a fine dimension. But it is very coarse when considered in relation to modern methods of measurement. In what are called " limit gauges " the plugs and rings are made of slightly different dimensions. If a plug is made a thousandth of an inch less than its ring it will slip through it easily with very perceptible slop. The common rule is therefore scarcely seen in modern machine shop, while the common calipers fill but a secondary place, their function having been invaded by the gauges. A minute dimension cannot be tested by lines of division on a rule, neither can a dimension which should be fixed be tested with high precision with a movable caliper of ordinary type. Yet it must not be supposed that the adoption of the system of gauging instead of the older methods of rule measurement relieves men of responsibility. The instruments of precision require delicate handling. Rough forcing of gauges will not yield correct results. A clumsy workman is as much out of place in a modern machine shop as he would be in a watch factory. Without correctness of measurement mechanical constructions would be impossible, and the older device of mutual fitting of parts is of lessening value in face of the growth of the interchangeable system, of international standards, and of automatic machine tools which are run with no intervention save that of feeding stock.
The two broad divisions of measurement by sight and by contact are represented in a vast number of instruments. To the firstnamed belong the numerous rules in wood and metal and with English and metric divisions, and the scales which are used for setting out dimensions on drawings smaller than those of the real objects, but strictlyproportional thereto. The second include all the gauges. These are either fixed or movable, an important subdivision. The first embrace two groups - one for daily workshop service, the other for testing and correcting the wear of these, hence termed " reference gauges." They are either made to exact standard sizes, or they embody " limits of tolerance," that is, allowances for certain classes of fits, and for the minute' degrees of inaccuracy which are permissible in an interchangeable system of manufacture. The movable group includes a movable portion, either corresponding with one leg of a caliper or having an adjustable rod, with provision for precise measurement in the form of a vernier or of a screw thread divided micrometrically. These may be of general character for testing internal or external diameters, or for special functions as screw threads. Subtitles indicate some particular aspect or design of the gauges, as " plug and ring," " caliper," " horseshoe," " depth," " rod," " end measure," &c. So severe are the requirements demanded of instruments of measurement that the manufacture of the finer kinds remains a speciality in the hands of a very few firms. The cost and experience necessary are so great that prices rule high for the best instruments. As these, however, are not required for ordinary workshop use, two or three grades are manufactured, the limits of inaccuracy being usually stated and a guarantee given that these are not exceeded.
Vernier Calipers
The vernier fitting, so named after its inventor, Pierre Vernier, in 1631, is fitted to numerous calipers and caliper rules. It is applied to calipers for engineers' use to read to i o 0 0 of an inch without requiring a magnifier. The beam of the caliper is divided into inches and tenths of the inch, and each tenth into fourths and the vernier into twenty-five parts, or the beam is divided into fiftieths of an inch (fig. 70) and the vernier has 20 divisions to 19 on the rule. The caliper jaws are adapted to take both external and internal dimensions. These " beam calipers " are also made for metric divisions. Minor variations in design by different manufacturers are numerous.
H FIG. 69. - Calipers.
A, Ordinary external type, adjusted by tapping the legs.
B, Type adjusted by screw in auxiliary leg.
C, Screw calipers, opened by contraction of curved spring and closed by nut.
D, Self-registering caliper, with pointer moving over quadrant.
E, Common internal type.
F, Screw type with spring.
G, Combined internal and external for measuring chambered holes.
H, Compass caliper for finding centres.
J, Keyhole caliper for measuring from hole to outside of boss.
FIG. 70. - Vernier Caliper.
A, Beam; B, vernier; C, fixed jaw; D, movable jaw; E, clamping head; F, abutment head, with adjusting screw a, for fine adjustment of D. FIG. 7r. - Measuring Machine. (The Newall Engineering Co.) A, Hollow base or bed, mounted on three points.
B, Measuring or fast headstock.
C, Movable head, or tailstock.
D, Spirit-level to indicate alterations in length of piece being measured due to changes in temperature, termed the indicator or comparator.
E, Measuring screw.
F, Nut for rapid adjustment of ditto.
G, Knob of speed screw for slow movement of ditto.
H, Dividing and measuring wheel.
J, Vernier or reading bar.
a, a, Points between which contact is made.
Micrometer Calipers are the direct offspring of the Whitworth measuring machine. In the original form of this machine a screw of 20 threads to the inch, turned by a worm-wheel of 200 teeth and single-threaded worm, had a wheel on the axis of the worm with 250 divisions on its circumference, so that an adjustment of ID o oo bb of an inch was possible. The costly measuring machines made to-day have a dividing wheel on the screw, but they combine modifications to ensure freedom from error, the fruits of prolonged experience. Good machines are made by the Whitworth, the Pratt & Whitney, the Newall (fig. 71), and the Brown & Sharpe firms. These are used for testing purposes. But there are immense numbers of small instruments, the micrometer calipers (fig. 72), made for general shop use, measuring directly to io160 of an inch, and in the (Brown & Sharpe Mfg. Co.) Adjusting nuts for taking up wear.
Clamping nut.
Ratchet stop,which slips under undue pressure to ensure uniform measurement.
hands of careful men easily to half and quarter thousandths; these cost from £I to £I, Ios. only. In these the subdivision of the turns of the screw is effected by circular graduations. Usually the screw d FIG. 73. - Beam Micrometer Calipers.
A, Beam. C, Abutment block with screw B, Head, adjustable by equal c for fine adjustment. inch divisions, by lines a, a, d, Clamping screws.
or holes b, b, and plug b' D, Micrometer.
holes bushed. e, Anvil.
pitch is 40 to the inch, and the circular divisions number 25, so that a movement of one division indicates that the screw has been advanced of o or i o D of an inch. Provision for correcting or taking up the effects of wear is included in these designs (e.g. at a in fig. 72), and varies with different manufacturers. A vernier is sometimes fitted in addition, in very high class instruments, to the circular divisions, so that readings of ten thousandths of an inch can be taken. Beam micrometer calipers (fig. 73) take several inches in length, the micrometer being reserved for fractional parts of the inch only.
or 