A steel rod n, Fig. 149, is fixed in a handle T; it terminates in a cone a and is drilled with a fine hole as indicated by the dotted lines. A thin wing b, pointed at its extremity, is also attached to the handle.
Holding the balance between the fingers of the left hand and the tool in the right, the blade b is introduced into the slit in the collet while a rests on the balance staff shoulder, the pivot being within the hole n. Now rotate to the right or left until the stud is opposite to the mark on the balance rim, and this may be done without danger, providing the tool is held firmly and vertical.
326. Watch-hand Holder. A very convenient form of tool, in which to clamp a hand while enlarging the center hole is represented in Fig. 150. Two brass plates, f and g, are hinged at m like a sector. A collar, a b, surrounding the two is pivoted at a and has a clamping-screw b by which the two plates can be forced together. Several circular sinks of different sizes and equally divided between the two plates, are cut of a depth varying from one-half to two-thirds that of the plates, and they must be made to increase in diameter as they get deeper, thus resembling the internal groove that receives a barrel cover. The plate a is cut away along the portion c d and grooves are formed to leave passages open between this surface and the bottom of the sinks in g and f.
When it is required to enlarge the hole of a watch-hand, place it, inverted, in the hole of suitable size, as shown at c of the figure, and tighten the screw b. Held round the whole or greater part of its circumference, the hand is thus firm and its center hole can be enlarged without risk, either with a drill or broach; the hand will not show marks due to the pressure with which it has been held.
327. Common Hand fitting Pliers. The sliding tongs with large flat head, perforated with a number of holes in which the head of a hand is clamped when the opening requires to be enlarged, are often useful, but we feel them to be less so than the holder just described. It is desirable that the inner faces of their jaws, which are usually left rough, be at least smoothed.
328. Another form of Watch-hand Holder. M. Fiquemont has devised the simple little tool shown in Fig. 151. It consists of a short brass rod R, perforated lengthwise and having a thread cut externally on the surface a b. It should be reduced in thickness below this tapped portion. The rod, shown also in longitudinal section at P, is cut into four quarters by two slits from a to b, which are at right angles and leave the points as indicated apart at d. The elasticity of these four quarters should make them take the form of a reversed cone when holding a hand, so that the ascent of the screw c shall tighten them.
Within the head a of the tool is formed a circular recess, so that, if the reversed head of a watch-hand be placed within it and the screw made to ascend, it will be held very firmly by the circumference, as seen in the figure. The hand will thus be perfectly free to adjust in any way that is needed for fitting it while held at the end of the tool, and without being removed before the work is complete. Three or four sizes will suffice for all ordinary watch-hands.
A tool may be made in a similar manner, except that the screw is not divided by the longitudinal slits, and the hand is held against the point by a lantern (similar to those of a screw-point tool), which must be cut away in the manner indicated in Fig. 150, explained above (326). An assortment of three or four lanterns will render the tool serviceable for all sizes of hands.
329. Clip for Holding Escapewheels while Cleaning. A mere inspection of M, Fig. 152, will make the arrangement of this little tool evident. The fork is made of a piece of brass rod and its two arms are elastic, a handle being screwed into the lower extremity.
Two small steel jaws are fixed to the upper ends inclined towards each other, and, in using the tool, it is only necessary to press with two fingers on the heads of the screws, when the jaws will open. Having placed the escape wheel pinion between them, the wheel will be firmly held so that its teeth can be easily cleaned, etc.
330. The appliance shown in Fig. 153 can be used for a similar purpose, and is further especially serviceable for holding an escape-wheel that is not riveted to its pinion. It consists of two parts, a handle T, shown separate at t, which is drilled throughout its length and tapped externally at the portion t, and a collar or nut D, the end of which is traversed by two cuts at right angles that resemble the letter T in section. If the tool is intended for holding escape-wheels that have three instead of four arms, this cross must be replaced by three radiating grooves of similar section. The position occupied by the wheel is indicated by the dotted lines r r, and it will be evident that, when the flat end of T is screwed up against this wheel, after dropping it into the cross and slightly turning round the axis as in a bayonet joint, it may be firmly held. The safest mode of introducing the wheel is by holding it on a broach, which is subsequently removed.
331. Tool for Testing the Truth of a Cylinder Escapewheel. The small tool shown at D, Fig. 154, can be advantageously used in place of the plain arbor commonly employed for testing the equality of the spaces in such a wheel. The plate D, which may be mounted on three feet, is traversed at its center by the smooth conical portion f of the screw f v, tapped somewhat tightly into a cock fixed to the other side of the plate. There is a radial slot, a c, cut in the plate large enough to allow an escape-wheel pinion to move freely. An inspection of the figure will make evident the manner in which the tool is to be used: a wheel being placed as shown, or with reverse side upwards, is made to slide towards the center, gradually raising the screw until the largest space is found to admit f with contact at both sides. All the smaller spaces are then carefully opened until they admit the cone in the same manner as the largest.
332. Novel tool for the same purpose. When the spaces are adjusted in the manner explained above, or if the length of the teeth is measured in a narrow gauge plate, there will nearly always remain a certain degree of irregularity in the teeth. A more efficient means would be for the gauge to embrace both a tooth and space, and this condition is satisfied by the following appliance.
The slide k k, Fig. 155, is dovetailed into a plate, level with its surface, so that k k can be moved in a vertical direction by a screw; it is perforated with a series of holes of gradually decreasing diameter. To the same plate are also fixed: (1) a smooth tongue, b, with a foot and screw; and (2) a second tongue, j, terminating in an index x n, which is movable about a pivot, x, and held against a pin in the plate by a light straight or spiral spring. The extremity, n, traverses a graduated arc.
Having introduced the pinion of the wheel, or the arbor on which it is held, into a hole of the slide that it fits without shake, and brought this hole to the position indicated in the figure, apply a slight pressure to the wheel in the direction of its rotation. With one tooth resting against b the tongue j will be held by the spring against the next and the reading of the index is to be noted accurately. Withdraw the wheel slightly, and, placing the succeeding tooth against b, take a second reading, and so on around the entire circumference.
Of course, the delicacy of the instrument will be increased by lengthening x n in comparison with x j.
333. Tool for Removing Studs. Fig. 156 represents a small tool which may be employed for this purpose. It consists of a thick strip of metal, C, spreading out like the letter T at the end which is not shown, so as to form two feet, the screw, j, being a third, so arranged that the T rests horizontally. The disc, d (shown also in plan), rotates on the screw, j, and is partially enclosed in a horizontal slot. Around the circumference of d are four rectangular notches of different sizes. The holes indicated by black dots on the plan receive the point of the screw, v, which clamps the disc when the notch corresponding in size with the stud to be removed has been brought under the small cone projecting from the spring, b; the other end of b is fixed to the T-shaped piece, C. The mode of using this little instrument will at once be evident. Resting the right arm on the bench, and, with the left-hand, bringing the wing of the cock above the notch in d, the other hand presses upon the milled button of b, forcing the conical pin against the stud and thus removing it from the cock. The screw, a, can be adjusted so as to prevent too great force being applied.
334. Tweezers for Removing Studs. One form is shown in Fig. 157. The upper arm, H, is bent downwards as indicated at g. The lower arm is shorter and carries a separate piece, n m, which slides under two screws, s, and is pressed forward by a spring, r. The action will be easily understood; the extremity, m, rests against the stud, and m n is forced backwards until the point, g, is exactly over the stud pin. A simple pressure of the finger will then suffice to remove the stud.
A still more simple pair of tweezers for this purpose may be made by filling a square notch in the end of one prong of an ordinary pair with broad noses, and setting a pin opposite to its center in the end of the other prong.
335. Staking Tool. The modern staking tool will perform the same work as the last two tools described and many other operations. It consists of a shifting table, around which holes of various sizes are arranged in a circle, so that any desired hole may be brought under a suitable punch moving in a vertical holder. Usually twenty-four tempered steel punches and four stumps are provided, which will be found sufficient to cover all the operations in the ordinary run of watch repairs, and the ingenious workman can from time to time add to these by making punches in his spare moments, if he finds from experience that he is in need of punches of a different shape. Fig. 158 illustrates the Johanson combination staking tool, on the front end of which a hairspring stud indicator is arranged.
336. The staking tool can be used as a cannon pinion tightener by making a punch for it having a blunt chisel edge. When a cannon pinion is placed on a stump which is slightly dished in that portion of its face opposite to the punch, and the punch gently struck with a hammer, it will be sufficiently contracted to insure the requisite adherence to the set-hands arbor. If fears are entertained lest the pinion should be cracked with the blow, it may be placed loosely on an arbor and held in position.
337. It may also be used to advantage for tightening the set-hands arbor in the center or cannon pinion, but care must be exercised or the arbor may be bent so that the minute hand which it carries passes nearer the dial at one place than another.
An arbor that is too loose is introduced into a suitable stump and at the top and bottom of the slack portion two punch marks are made opposite one another. The punch having a conical or three-sided point, will occasion an expansion of the metal round each mark; if a smooth file be passed over the surface so as to remove the burr, which would not offer any permanent resistance, sufficient projecting metal will be left to secure a sound and lasting friction when a little oil is applied.
If the arbor is well supported immediately beneath the punch, it will not be distorted by any moderate impact. It is advisable before operating on the metal to ascertain its degree of hardness.
338. It may also be used as a pinion riveting tool. The pinion, with its wheel in position, is placed on the hardened steel stump, the end to be riveted being upwards. The riveting is then struck with the polished end of a hollow punch. If it be required to spread the riveting, a punch must first be used that is rounded from within outwards, to be followed with a perfectly flat punch. A little practice will at once enable a workman to select the best form of punch.
The stump should be very hard and polished, funnel-shaped downwards and carefully fitted to the bed, so as to be firm and central with the punch. If these precautions are not taken the pinion will spring and the riveting will be imperfect.
339. The staking tool may also be used for closing up barrel holes, screw-holes, etc. In repairing watches it is often found that the screws hold badly or not at all, and the holes at times cannot be satisfactorily bushed. In such cases it becomes necessary to close them, an operation which any intelligent workman can perform very well in the following manner: Make a stump rounded at the top and provided with a pump-center. This can be merely a pointed steel rod that passes through the stump from below with slight friction, and is forced upwards by a light spring fixed by a screw, so that, on undoing the screw, the rod can be removed. The one pump-center can be used for various stumps as the openings are funnel-shaped downwards. Center the hole to be closed by means of the pump-center, then bring down the hollow punch and strike it as in riveting a pinion. A small circular groove will be formed around the hole, which, if the punch is in good order, will be perfectly even. The form of the punch is very important; the watchmaker must decide for himself by trial as to the most convenient shape. The thickness of the ring of metal may be modified; it is rounded off in a semicircle by some, and curved inwards or outwards by others.
Instead of a pump-center below we have used punches that were themselves provided with a pump center and helical spring. Either form gives satisfactory results.
The holes of barrels can be closed with a punch that is only depressed at its center enough to avoid the point of the pump-center. When the face is more or less rounded the hole will be closed by forming a cup as with a chamfering tool. The tool may then be enlarged if requisite with a round broach or an arbor covered with white wax. It will thus be hardened, and the cup-shaped recess will serve to retain the oil, while the somewhat thinner hole will probably be in a condition to resist friction as long as formerly.
When the hole is of moderate thickness, and it does not require much reduction in diameter, this method will be found satisfactory; barrels that have been thus treated have been found to stand ten years without appreciable wear. When the metal is thicker, however, the spreading inwards is very slight, and there is some danger, in using a round broach to do it, of straining the metal or detaching the central ring of the barrel or its cover.
It should be observed that the methods explained above are absolutely useless for closing pivot-holes, and should only be resorted to for barrels, on an emergency.
340. Drifting Tool. This appliance, shown in Fig. 159, is very useful for making holes of round, oval or square, or, indeed, any required form. It takes the place of a punching machine for light work.
The punch, or “drift,” is screwed into the stock C C′. A pin, p, fixed in C C′ prevents its rotation while allowing an end motion along the slot m n. The end C′ is hollowed out to receive the point of a screw, B, and a pin, shown near C′, is received in a groove turned in B, thus enabling it to draw the stock in the direction C C′. The part H is gripped in the jaws of a vise, and a strong handle, E, is used to advance the screw B B′. With a tool about three times the size of the figure there is no difficulty in punching the eyes of mainsprings, square holes in stop fingers, etc., and it can be made by an apprentice. Of course its strength depends on the pitch of the screw and the radius of the handle E.
341. For heavier work it will be necessary to resort to the punching machine. There are several constructions in use, but the most usual is essentially the same as that of the tool just described. The screw works vertically in a strong bridge that is fixed to the bed in which the counterpart of the punch is held. Great use is made of this machine in factories at the present day, almost every part of a watch being in the first instance roughly shaped by its means. Indeed, thin metal is often left as it comes from the punch, and very perfect crossings of wheels, etc., are thus produced.
Steel does not cut well in the press unless it is soft and homogeneous, and the final dimensions of the object can be more nearly approached according as these conditions are satisfied. Attempts have been made to cut levers, etc., of the exact dimensions required, but it is better to leave a slight excess of metal to be afterwards removed by a mill cutter or other means. The crossings of steel lever and cylinder escape-wheels are punched out, but the metal used is of special excellence. Before introducing a piece of steel into the press it is advisable to remove any scale, etc., by pickling, or with a file.
342. Draw-Plate. Every watchmaker should possess a plate for drawing round wire so as to be able to obtain it of any required diameter. They are to be had at all material houses. In bushing holes in a brass plate, it not unfrequently happens that the brass used for the bushing is not of the same color as the plate. To avoid such a difference cut off a piece from a plate of the same color and round it by hand, making one end to taper. Fixing the draw-plate in the vise, pass this end through one of its holes, and, gripping it in the hand-vise, pull the brass through the plate. Continue this operation through successive holes until the requisite thickness is attained.
No special precautions are necessary, further than keeping the holes well greased and annealing the brass from time to time so as to counteract the hardening caused by the operation.
Such a plate can also be used for steel wire, and plates with holes of special form, for example those for drawing click and pinion wire, are well known in the trade.
343. The Grammaire, or Dividing Plate. This tool is shown in Fig. 160. To mark out the crossings of a wheel, etc., fix it by the conical-headed screw t to the middle of the plate, on which are traced a series of concentric circles (not shown) divided into 6, 8, 10 and 12 equal parts. By laying the little ruler r r over the wheel blank and using these division marks as a guide, 3, 4, 5 or 6 radii can be drawn to serve as guides for cutting out the arms.
If it is desired to indicate the width of the arms instead of a mere central line, a series of holes must be drilled at the division marks and screws with tapered points tapped into them from below. Resting the ruler against these cones, the arms can be drawn of any required width, according to the distance to which the screws project. No further explanation is necessary, for the figure shows: (1) a grammaire adapted to mark out a four-armed wheel, these arms being indicated by the dotted lines; and (2) the small ruler r r cut away at the middle so as to avoid coming into contact with the conical-headed screw.
344. Jewel-resetting Tools. Hopkins’ patent jeweling and staking tool, shown in Fig. 161, is an ingenious device, and one that will be found very useful to the watch repairer. As the spindle, or handle, to which the cutters and burnishers P P P are attached, is sustained in upright position when in use, by the long bearings through which it passes in the upright F, independently of the lower center, the hole to be cut may be centered either from above or below as preferred; and the depth to which it is desired the cutter shall work is regulated by adjustment of the sliding collar E, and this being a correct uprighting, as well as jeweling tool, with it a pivot hole, or a jewel setting, the correct center (upright) of which has been lost, may readily be corrected, or its true center again found, and, what in some cases would be a very desirable consideration, by careful manipulation with the cutter, which is under perfect control of the operator, the position of jewel settings may be changed so as to alter the depth of locking of the wheels to any desired extent. To regulate the depth to which it is desired a cutter shall work below the surface of a plate, lower the spindle D until, when moved out sufficiently far, the end of the cutter will rest down on the top of the plate to be operated upon, and fasten it there by lightly tightening the screw K; this done adjust and fasten the collar E on the spindle D, to the same height above the top of the upright F as it is desired the cutter shall work below the surface of the plate on which it now rests. This, when the spindle D has been again set free by loosening the screw K, will of course allow the cutter to sink into the hole to be operated upon to the exact distance the collar E had been set above top of F. In adjusting the collar, E, the graduated wedge No. 4, or the jewel to be set, as preferred, may be used as a gauge. The burnishers, No. 9, are used both for opening and closing settings; the same burnisher, having chosen one of proper size, is used for both purposes; the side being used for opening the setting, and the beveled and rounded end for burnishing it down again over the jewel. The pieces 13 and 14 are made to fit in the lower end of the spindle D (the cutter P having been removed), same as an ordinary drill-stock, and are used for burnishing the edges of a jewel setting down flat over the jewel, countersinking screw heads, giving end-shake to wheels, etc.; and being easily made, any one owning the tool can make these for himself, of forms and sizes to suit the particular work in hand. For uprighting purposes, withdraw the spindle D and substitute No. 5, the rings, No. 3, being intended for laying the work on, on the tool bed. For upright drilling through watch plates, mark the place to be drilled (prick punch it slightly) with the cone point of No. 5; which done turn the spindle No. 5 upside down and rest the upper end of the drill in the countersink in its end, the drill being operated with a fiddle bow acting on a collet placed on its shank for the purpose. For cutting off bushings level with a watch plate, either a cutter of the No. 13 or 14 class, or one of the P cutters can be used. For staking or riveting wheels upright on their pinions, lay the stake No. 7 level on the tool bed (the center M having been fastened down out of the way), and with No. 5 center accurately the hole to be used in the stake, and fasten it there by means of the clamps N; then remove the cone end of No. 5, and place a punch with a hole in its end of the required size, on the part m, and proceed as in an ordinary upright staking tool.
345. Tool for Flat Polishing. A thick brass plate is provided with three strong screws arranged in triangular form (G, Fig. 162), and far enough apart to ensure that, if the plate is reversed and rests on their heads, it will remain flat when moved by hand over a polishing surface.
The screws should fit tightly or be provided with lock-nuts.
We believe that every watchmaker must be acquainted with this little tool. The object to be smoothed or polished is fixed with shellac or sealing-wax to the middle of the triangle formed by the screws; the level is then adjusted so that, when resting on a flat surface, the object to be polished coincides exactly with it. The polisher (for example, a sheet of ground glass) is charged with oilstone dust or polishing rouge, and the object is passed over it until perfectly flat and smooth.
346. For smoothing, it is best to use a large sheet of iron or steel. For polishing, copper or bronze is preferred. Ground glass may be employed for both operations; it must be hard and perfectly flat.
A disc rotating in the lathe or mandril, etc., is often used.
The tool may be inverted and rest firmly on a cork, the polisher being then moved backwards and forwards by hand, and always in contact with the three screws.
It is best to use pith for cleaning the polished surface; in its absence use soap, then wash and dry with a soft linen rag. The object is detached by heating the tool, and is cleaned by boiling in alcohol; afterwards pass through pure alcohol at the ordinary temperature and dry.
347. This tool can be employed for polishing small surfaces, such as the end of a rod, of a barrel-arbor or a screw-head, as well as for those of greater extent. But it appears needless to enter into further detail.
Instead of three screws some workmen only use two, at some distance apart. The object to be polished, being placed at the third corner of the triangle, takes the place of the remaining screw.
Lastly, if a band be fitted to one side of the brass plate, as shown at b, Fig. 162, and held by two screws, it will often be of service as a clamp for fixing the object, as at s.
348. Flat pieces can be polished on a revolving lap worked by the foot, being simply held in the hand or in a piece of soft leather; but a certain amount of practice is needed in order to do this successfully.
ACCESSORIES
AND MISCELLANEOUS OPERATIONS TO BE PERFORMED IN THE
UNIVERSAL HEAD.
349. With a view to simplify the work, we will here give, in a collected form, a number of operations that may be performed in the mandril, or universal head, among which the practical watchmaker will easily be able to distinguish those that can be done in the ordinary lathe; we will also describe numerous accessories that the workman should make for himself, if he is desirous of making his mandril or universal head still more generally useful.
350. Prepare a number of chucks of the form shown in Fig. 163. Some of these carry a small bar with screws, by which an object may be clamped firmly to the chuck, an arrangement which is also shown at A, Fig. 163; others have a hole drilled through their axis; others again have a projecting arbor, etc. They may also be made with a flat face on which to cement objects in the ordinary manner.
As it is often necessary to have a considerable surface to cement, for example, a watch-plate, one or more may be made of the form shown at T, Fig. 164. The lower plate being clamped in the dogs, the disc e will be free. If this disc be made of bronze or steel it may be used as a lap; if of brass, it may be turned true and used as a wax chuck, etc.
The chucks should, as far as possible, be well made, so that they can be truly centered by means of the pump-center.
TO CENTER AN OBJECT.
351. When there is a hole at the center on the side towards the face-plate, in the universal head, as is usually the case, it is only necessary to place this hole over the point of the pump, pressing it inwards, and then to clamp the object in the dogs; the pump is then drawn within the body of the arbor. Very often, however, there is no central hole, or there is only a mark on the face that is towards the cutter; in such a case it becomes necessary to center from the front or by the circumference.
352. To Center from the Front. If the object is held by wax on a plate, it may be centered as in the ordinary lathe while the plate is hot, by resting a piece of pegwood on the T-rest with a point placed in the central hole, and observing whether its free end remains stationary.
After the plate has cooled, the accuracy of the centering should be tested by means of a long piece of pegwood which rests on the T-rest brought close up to the object. The pegwood is held parallel to the lathe-bed, and, if the centering is satisfactory, its outer end will not move. The detection of any slight movement is greatly facilitated by placing some fixed object close to the free end of the pegwood. If a motion is still observed the centering is imperfect, and must be corrected in the manner explained below (354).
353. Perrelet’s method of Centering. In principle, this is identical with the one just described; but the pegwood index is replaced by the small apparatus shown in Fig. 165.
A hollow cylinder, of which a c c a′ is a section, is firmly held by friction by its portion a b b′ a′ in the tailstock. In the front of this cylinder is fixed a steel ring that is thick at the circumference and tapers inward, so that the central hole has a cutting edge. The two black triangles represent a section of this ring. The rod r n passes without play through this hole, and carries a projecting ring at s to determine the distance to which it enters the collar c c; there is also a small key that corresponds with a nick in c c, and thus prevents rotation.
An inspection of the figure will show that, when s rests against c c, if the finger be placed on r and communicate motion to it, the rod n r will be able to oscillate in any direction, and to an extent limited by the diameter of the hole in the cylinder.
The error in the centering at r will be multiplied at n in the proportion of n s to s r; thus if n s is ten times s r, the motion at n will be ten times as great as the actual error at r.
354. The instrument is used as follows: The object to be centered being placed between the jaws, having the centering spindle in position in tailstock. Slide tailstock towards the face-plate until the point r of the rod enters the hole, or central mark of the object, and, setting the T-rest close to the point n, rotate the face-plate. If the centering is exact, the point n will remain stationary. If n moves to and fro, give a gentle blow against the edge of the object, which should not be held firmly in the dogs; the blow must be on the side opposite to that at which n shows the greatest deviation from the point of reference. Repeat the process until the centering is perfect or sufficiently accurate; then clamp the dogs firmly, taking care not to disturb anything.
In centering from a jewel hole, an aluminium rod n s may be employed on account of its lightness, and it may be terminated in an ivory cone at r.
355. There is one precaution to be observed, as it facilitates the use of this appliance; it is advisable that the portion a b b′ a′ of the cylinder be somewhat long and well made, in order that, while being in the first instance inserted in tailstock up to the shoulder, the cylinder may be partially withdrawn and still held firmly. The reason for this is as follows: When the tailstock is pushed along, a considerable amount of friction resists its motion, and, as the hand cannot always control this motion, it may happen that r comes up against the object with some force. To avoid this, bring the point near the hole and then rotate the collar in the tailstock so as to gently withdraw it to the requisite amount. The cylinder may, if desired, be fixed by a small screw after the point r has been set in position.
356. Another Centering Device. The centering indicator shown in Fig. 166 will also be found useful for testing for exact center. The body of the indicator is made of sheet brass, and should be about five inches long by two inches in width at the larger end. The shank C is made to fit in rest holder, and is either riveted or soldered to the body; R is steel or copper wire sharpened to a fine point, and balances on a pivot at 1; B is a clock hand pivoted to the body at 1; 2 and 2 are pivot joints only, and do not go through the body; C will perhaps give a better idea of the end R. To center with this tool, unscrew your rest and remove it, then place the shaft C in rest holder and adjust it till the needle point R touches the top of hole, as shown at A. The index hand will then note the variations as the head revolves. If too low, the hand will point above center, and if high, vice versa.
357. To Center from the Circumference. Two cases may occur: Either the entire rim of the object is exposed, as when the teeth are to be cut in a wheel blank; or the rim can only be used as a means of determining the center, as when a barrel has been bushed with an undrilled bushing.
358. The tool shown in Fig. 166 may also be used for the test if the short end of arm R rests against the under side of the object that it is desired to center.
359. When it is required to drill or merely to center the hole in a wheel, barrel, etc., that does not run true, clamp a piece of sheet brass in the dogs and turn out a sink that will exactly receive the wheel, etc., but allowing it to project slightly. Now unscrew one dog and advance it a little, so as to grip the edge of the object as well as the plate; move the other dogs inwards in succession, and it will only remain to drill or true the hole with a suitable drill.
UPRIGHTING AND DRILLING.
360. When the Lathe is Provided with a Tailstock. Let it be required to mark and drill a pivot-hole in the cock when the plate-hole is accurately centered by means of the pump-center. Place the tailstock in position on the lathe-bed, and mark the position of the hole with a center, as in an ordinary uprighting tool; then, if the hole is to be very fine, make it with an ordinary pivot-drill.
If the hole to be drilled is somewhat large, it may be drilled with the twist drill, the bed of the lathe being, as usual, horizontal.
361. When the Lathe is not Provided with a Tailstock. In such a case it is possible to upright and drill by using fine drills, and making points so formed as to take the place of the cutter. Or a stock may be made to receive drills, points, etc., and it may be well here to remark that stocks of the same form are convenient for receiving chamfering or sinking tools.
This stock is shown in Fig. 167. An inspection of E c will suffice to show its form, and it may be used for holding either a drill or a marking point, or a small hollow center in which to support a pivot drill.
The following method should be adopted for securing accuracy in the adjustment of these stocks:
There must be no shake of the stock in the tool-holder; it is especially important to avoid any displacement during the act of clamping. If there is any reason for doubt on this point, drill a hole at the foot of the cutter in which an index, y, can be temporarily inserted; any displacement can be detected by its deviation from a fixed mark. As a rule, however, there will be no occasion for doubt if the plate that is screwed down upon the stock is parallel to the bed of the tool-holder.
The cutter is then replaced by a stock of the form shown at E′, in which a hole has been previously drilled to receive the drill or other bit, but somewhat smaller than it is required finally to be. The pump-center must now be replaced by an accurately fitting piece B that terminates in a short semi-cylindrical drill.
It will be evident that if the mandrel be revolved, and, at the same time, the tool-holder advanced towards this drill, the hole in the stock E′ will be enlarged and smoothed, and its axis will accurately coincide with that of B. Any drill, chamfering tool, etc., that has been turned true, will, therefore, on being inserted in the stock, prove to be strictly in the axis of the lathe.
362. To Drill a Series of Holes. Mount on a stock similar to that just described, a small frame carrying a drill-stock, as shown in Fig. 168. If this be fixed in the slide-rest in place of the cutter, it can be used for drilling a hole or a series of holes previously marked out, or, if the pitch of the transverse screw of the slide-rest is known, for a series of equidistant holes in a horizontal line. When it is required to drill a series of holes in a circle, as, for example, in the escape-wheel of the pin-escapement, bring the point of the drill onto the circumference and then proceed as when using the ordinary wheel-cutting engine provided with a vertical drill-holder, taking care to fix the face-plate by means of an index.
This index should have a means of slightly modifying its length, so that the point of the drill may always be brought into exact coincidence with the points that have been previously marked on the object.
It will be observed that, if the drill were replaced by a round milling tool, the U’s of a cylinder escape-wheel might be polished, or, indeed, cut, the concave ends of the teeth of the star-wheel in a Geneva stopwork could be corrected, etc. But it is unnecessary further to insist upon the many uses to which this form of tool can be applied.
363. To Cut the Teeth of a Ratchet, Minute-Wheel, Etc. When the face-plate is divided on the circumference, it is easy to cut the teeth of an ordinary wheel of a timepiece, escape-wheel, barrel ratchet, to cut or true a star-wheel for the stopwork, etc. After mounting the wheel on a chuck and carefully centering it, replace the cutter by a small revolving cutter-frame after the model of that shown in Fig. 168.
The stock d, shown in both plan and elevation, carries a piece c at right angles, which has a slot cut throughout its length. In this slot a U-shaped support can be clamped by a nut in any position. The U portion forms a bearing for a cutter, such as is shown at f in the figure, and the axis projects so as to receive a ferrule for rotating the cutter.
It will be evident that, with such an arrangement, the height of the cutter can be adjusted in accordance with the teeth to be cut.
364. To Cut a Circular or Elliptic Groove. For this purpose no special accessory is needed; an ordinary cutter will suffice.