Let P, Fig. 192, be a division plate that has a 30 circle, but not one of 29 or 31 divisions. Divide the circumference of a disc d, seen on edge, into a large number of parts in the engine, 360 for example, and fix it to the end of the index, at the same time attaching a finger, i, to the support s. Now advance the screw of the index through a distance corresponding to the angle l P k included between the two successive points of the 30-division circle. To measure this distance a pointer should be previously fixed to the frame to correspond with the middle point of a hole in the circle under consideration, and the motion should be arrested when it coincides with the next succeeding hole. Assume that this amount of displacement has required three complete turns of the screw; 1,080 divisions on the disc have thus passed under the finger i. Dividing this number by 31, we obtain 34.83.
After observing the division on d that coincides with the pointer i, cut the first space of the wheel; then cause 34.83 divisions to pass under i, in such a direction that the plate is drawn with the arrow, and transfer the index to the next hole of the circle, rotating this time opposite to the arrow; the second space can now be cut, and so on.
With a view to diminish errors arising from the omission of fractions, since 31 does not divide evenly into 360, a number of multiples of the number 34.83 should be determined. Thus 4 times 34.83 is 139.32, so that, when the fourth space is cut, the pointer i must be at this number of divisions from its initial position.
The index should be so situated that, when half the arc l k has been traversed, as explained above, s a is at right angles to the radius P r of the division-plate. If it is desired to move d in a reverse direction, it must be moved backwards to a considerable distance and then forward up to the required point so as to avoid error due to backlash. The screw of the index should fit the support s firmly and without any shake.
400. To Cut a Wheel with any Given Number of Teeth. When the given number does not occur on the division plate, proceed as follows: Take a strip of metal, for example a pliant piece of soft steel, and cut in it a series of equal and equidistant notches as shown at B, Fig. 193. Cut the band to such a length that it has the same number of pairs of teeth and spaces as the wheel is required to have teeth. Now turn a lead disc of a diameter that the strip of metal will exactly enclose; fix this strip round the circumference with pins, screws, or in any convenient manner, as is shown at C. We thus obtain a temporary division plate which can replace the permanent one or be attached to its upper or under surface, and, when an index has been adapted to it, the wheel can be divided into the requisite number of parts.
When employing an engine the division plate of which is worked by a tangent screw, the above affords an easy means of making the divided head for the screw with any desired number of divisions.
401. With a view to insure accuracy, it is advisable to employ a disc of large diameter as the errors of division are thereby rendered less important and the metallic blade can be made to lie closer to the rim.
The blade is subdivided by a saw to which a guide is attached as indicated at H, Fig. 193, or the saw can with advantage be replaced by a file that only cuts on its edge and not on either face, or by a pair of mills or revolving cutters united together as shown at S. The following plan, however, appears to be more expeditious and to involve less trouble to ensure accuracy.
A hole a, Fig. 194 is drilled in a metallic band by means of a semi-cylindrical drill fixed in the chuck of a lathe or in a wheel-cutting engine, etc. It will be convenient if the drill can be set vertical. Beneath it is a brass bed-plate in which are fixed two pins equal in diameter to the hole a; this hole having been placed over one pin b, the band is held firmly against the other, while the second hole is drilled. This is then transferred to the pin, and so on.
In the absence of a suitable tool, a well made measure can be employed for marking a series of points with the aid of an eyeglass; the holes are then drilled with the bow or in any other manner.
402. To Cut a Wheel, Ratchet or Pinion on an Ordinary Lathe. When only a moderate degree of accuracy is required, the ordinary lathe can be adapted for cutting the teeth of minute wheels, ratchets, pinions, etc., by making the following appliance:
The piece B, Fig. 195, provided with a stud at p, slides on two horizontal and parallel cylindrical rods fixed to the slide C, or it may move in a dovetail. The cannon d, carrying a ferrule k and a file-cutter f, rotates on the foot at p without shake; and the cord of a wheel or bow passes round k.
R, the wheel to be cut, is supported between the runners, the divided plate V, which may even be an old wheel with the required number of teeth, being fixed to the axis of R. V is held stationary during the operation of cutting, by the index l. The mode of action hardly requires explanation: while f is rotating, advance B until it is arrested by the stop t; then draw B back, advance l to the next division on the plate, and so on.
403. We have said enough on this subject to enable any watchmaker to make such a tool, modifying it or completing it according to his requirements. We would only remark that: (1) If a cannon of the form d is used, the stud should be diminished in diameter at its middle part for about three-quarters of its length, so that friction occurs only at extremities; and (2) if a wheel is used to rotate k, there should be an idle pulley at m supported on a fixed arm independent of B, either attached to the lathe-bed or bench, or fixed in the vise, so that the ferrule k can move backwards or forwards without altering the tension of the cord, in the manner indicated at Y.
404. Wheel-cutting Arbor-chucks. These appliances are specially useful in making wheels that are required to be rigorously true, such, for example, as escape wheels. The form is represented in Fig. 196.
It is simply the arbor of an ordinary lathe, formed in two pieces, b a and b c, the body b d being very accurately fitted into the conical hole in the plate of the wheel-cutting engine. If now a wheel is fixed with wax on the extremity z and turned in the lathe to the required form, it is only necessary to unscrew b c and introduce b d into the socket of the wheel-cutting engine; then having cut the teeth, the piece b c is replaced, and the whole is set in the lathe, if required to test its truth, without the wheel having been displaced from the chuck.
It will, of course, be evident that the two parts must be accurately fitted together; the tapped hole and the screw must be true with the axis. M. Millot, with whom we have seen this form of arbor in use, has not been able to detect any eccentricity, although he often employs them.
405. They might be formed in one piece, as a d b, with a point at p. A boxwood ferrule is then fitted onto the portion b d, where it is clamped by two screws, and these can be released when it is desired to insert the chuck into the wheel-cutting engine. The points of these screws should be received in recesses in order to avoid the production of any roughness on the surface of b d.
Wheel-cutting engines have been made to receive these arbor-chucks without removing the pulley. The point c is placed in a hole and the upper end is enclosed in a collar, which is tightened by means of a screw.
The arbor used by M. Millot had a lantern chuck, and this is very convenient in making objects that require to be measured during the progress of the work.
406. Modification of the Ordinary Arrangement for Holding the Wheel While Cutting. In the wheel-cutting engine as usually met with, the wheel (when not mounted on an axis) is held against the chuck by a hollow steel cone, on which presses an arm that slides on a vertical pillar and can be clamped in any position. The hole at the end of this arm does not always, therefore, correspond with the point of the cone, and, as a consequence, the wheel often gets displaced during cutting. This inconvenience can be avoided by adopting the following device, which we have seen in use with several watchmakers.
The pillar with its sliding arm is replaced by an iron or steel piece of the form G, Fig. 197. The point a is received by the central hole at the lower end of the division-plate axis, while the screw b presses on the point of the cone, clamping it firmly. Further explanation seems unnecessary; we would only add that the piece G must be made strong and perfectly rigid.
407. For making the teeth of the wheels of a train, a special form of cutter, set to revolve on an axis, is employed, and it may be constructed on either of three distinct systems.
(1) A single cutter mounted on an arbor, as at A, B, Figs. 198 and 199; this may be termed a single cutter.
(2) A circular cutter, formed of a series of such single cutters, which will be termed a multiple blade or composite cutter. Two specimens are shown at F, J, Fig. 200.
(3) The pinion, or steel wheel cutter or mill, formed of a single piece of metal, as seen in Figs. 201, 202 and 203. These may be described as mill or file cutters.
408. To Make a Single Cutter. The form shown at A, Fig. 198, is roughed out to as nearly as possible the required form in good steel. Some makers, possessed of exceptional skill, make them entirely by hand, and they make very beautiful teeth by this means; but as a rule watchmakers cannot look for such success, so that it is better to complete the formation of the cutter in a specially arranged tool.
The two sides may be made in the wheel-cutting engine, with the same mill cutter, which is inclined when used to undercut the acting edge; but this operation is not as easy as it appears at first sight, and the watchmaker will find it to his advantage to make the following device:
A spindle, b d, Fig. 204, supported between the runners, t, v, serves as an axis for the arm f g h, which is bent at g so as to afford a support to a conical cutter a, driven on the ferrule c. The descent of this arm is limited by an adjustable stop, fixed to the bed of the turns.
Having removed the T-rest, replace it by the rod N, to which the cutter is clamped by a screw k, after being roughed out so as to reduce the work required of the cutter.
Place N so that the conical cutter occupies the position indicated at z, and, if a slight pressure be applied at h while a is caused to revolve, both the straight and curved portion of the side will be formed, and the side will, at the same time, be bevelled to an angle corresponding with that of the cone. The curved portion of the side will be more or less undercut, according as the arm h is depressed below the horizontal plane passing through the axis of the lathe. The opposite side is formed by inverting the piece f g h.
In smoothing or polishing it is only requisite to replace the cutter by a smooth conical roller, and to work as before.
409. The cutter is sometimes fixed in the arbor as shown in Fig. 198. The arbor itself is thick and perforated with a round hole in which the tail of the cutter accurately fits, a slight pressure applied by the screw m being sufficient to make it steady.
For cutting the escape-wheels of clocks the arbor should have a velocity of about 200 turns a second.
M. Peupin, a skilful watchmaker who adopts the practice here given, having observed that with a sharp cutting edge he did not obtain a sufficiently smooth surface, succeeded in obviating the difficulty by drawing a polisher with rouge along the cutting edge, maintaining it at right angles to the plane of the cutter. This operation, if carefully executed, will serve to remove the feather-edge, to make the edge even and yet not dull, and to secure a highly polished cut surface. The sides of the teeth will present a proportionately better surface, according as the portion c a (M, Fig. 198,) approximates towards the dotted line c d.
His escape-wheel teeth are cut in successive stages. The last stroke of the cutter is given by advancing it against the side of the wheel, so that the cutter axis remains in the plane of the wheel.
410. Triangular Cutters. When a cylindrical or conical mill is not available for finishing and sloping the sides of a cutter, it may be replaced by a triangular cutter (T or C, Fig. 205,) and when the application of much force is required there may be a pointed bearing; but this is seldom necessary.
If carefully hardened and set, such a cutter gives a clean cut; of course it will not act for as long a period as the conical form above described, but this is of comparatively little importance, since the blank cutters are always roughed out previously to nearly the requisite shape.
411. To Make Several Cutters at Once. By adopting the following method, it is possible to make several such cutters in one operation.
Turn a steel disc of the form of an ordinary mill cutter, as shown at l p, Fig. 200. To finish it, giving the same curvature to the two sides, take a piece of steel, C, and shape the corner r to exactly correspond with the side of the point or ogive of a tooth, bevelling it so as to give a cutting edge at the upper surface; then harden and smooth it with care. Having fixed it in position in the tool that carries the arbor a and the roughed out disc (whether this be the lathe, wheel or pinion-cutting engine, or a special device) in the required position, one side of the disc may be finished. The arbor a is then reversed and the other side finished in the same manner, so that both sides have the same curvature in opposite directions.
Of course the tool C may be advanced against l p, either sideways from r towards l, or radially in the direction l p, as is most convenient. Or the tool might remain fixed and the disc advance against it radially or laterally.
The traverse slide in a lathe is usually provided with a stop; it would then be very easy to form one side of the disc in such a tool, afterwards reversing the arbor and forming the other side.
If a very good cutting edge is desired, the sides should be smoothed and, when the disc is completed, it may be divided into pieces similar to B, Fig. 199, each of which will serve as a cutter. It will be noticed that the acting edge is not undercut behind; it is thus necessary to slope the cutter a little as shown at B, as otherwise the rim will choke in the spaces of the wheel, straining it without cutting.
412. Composite Cutter Formed of a Succession Of Single Cutters. By mounting a series of identical single cutters round the circumference of a disc, a circular cutter can be formed in the manner indicated in Fig. 206. The upper portion represents the arrangement of the pieces while they are being turned, and the lower portion shows their positions when the cutter is ready to be used. M. A. Croutte, to whom we are indebted for several of the details here given, was much surprised that this form of cutter is not better known, since it possesses certain special advantages; we will summarize his remarks on the subject.
The separate cutters b, g, etc., Fig. 206, are not undercut from the acting edge backward; they are merely reversed, so that this acting edge is towards the front, in other words it lies along the radius. These separate pieces possess a special advantage in that they can be used until the steel is quite worn out by the setting; in this respect differing from the undercut cutters, for they are not altered either in form or thickness by setting.
As a set-off against this important advantage, they are characterized by the inconvenience of requiring that the two sides of the blade be exactly in a plane at right angles to the axis, and that the slide carrying the cutter-arbor shall move in a direction parallel to this plane. And even when this double condition is satisfied, there will be friction of the two sides above the dotted line i j, Fig. 199, against the sides of the teeth; and if the above named conditions are not satisfied, the cutter, being presented edgeways, will be choked with brass, and the results will be unsatisfactory.
413. In order to ascertain whether such a fault exists, it is only necessary to notice whether the cutter becomes brass-colored on one side towards the point, and on the other more inwards, and the sides of the teeth exhibit striæ or scores in opposite directions, as indicated at E, Fig. 207. The white strip, 1, 1, corresponds to the bottom of a space between two teeth; 2, 2, and 3, 3, the two sides of this space, spread out like an open book.
By examining the marks with care, and noticing the direction in which they are inclined, it will be possible to ascertain both whether the separate cutters are out of place, and in which direction the arbor should be moved in order to correct any error.
We must, then, repeat that all the cutters must satisfy this condition, because if only one is wrong it will produce the scores here referred to.
The necessity of these precautions in the use of such a composite cutter, and the fact that the friction of the portion above the line i j, Fig. 199, renders it difficult to obtain a polished cut (which is essential for such delicate depths as those of watches), have doubtless prevented its use becoming general. For work that is somewhat larger or rough, it will be found to give satisfactory results and will last longer than a single cutter. A lubricant, such as glycerine or oil, should be applied to it.
414. Composite Cutters with the Cutting Edges Undercut. An old Paris clockmaker, Brisson, used a cutter of the form F, Fig. 200, for the teeth of his wheels. He undercut the two sides of the blades by means of a small special tool. Strictly speaking, the operation can be performed by hand.
In order to ensure that the curves that form the ogives of teeth are alike on the two sides of a cutter, he made a series of templates or standards of the form C, Fig. 206, in which were two holes, C and c, of equal diameter. The upper one, which might be funnel-shaped so as to give a cutting edge, was half cut away, and, after being hardened and set, could be used to give a final stroke to the circumference of two discs of equal diameter. These two discs, or one cut through a diameter would suffice, having been brought by a file to the form H, and joined as shown at r s, can be mounted eccentrically so as to present a cutting edge to the roughed out cutter A; the two sides can thus be made even. The disc may then be finished by cutting away the metal so as to give the form shown at F, Fig. 200.
By the aid of the standards he could easily reproduce the same forms of teeth when required.
Fig. 200 comprises, at J, a cutter for the teeth of watch wheels of the form employed successfully by M. A. Phillippe. The figure will explain itself.
We have known a Geneva wheel cutter who employed these composite cutters with advantage in making duplex wheels. The principal difficulty he experienced arose from the distortion of the metal in hardening, because the acting portion naturally lengthened a little. This form of composite cutter certainly demands careful workmanship, but, if the construction, hardening and polishing are good, it will produce fine work and will last a long time.
415. General Observations on Cutting the Teeth of Brass Wheels with a Single or Compound Cutter. High-class English watches, the movements for which are made at Prescot, in Lancashire, have the wheel teeth made by a composite cutter after the wheels are riveted to their pinions. We have remarked that these watches make less noise when running down than those in which the teeth have been formed with a mill or continuous action cutter.
Success in forming teeth with cutters depends mainly on the securing of a good form as regards the cutting edge, and on its being maintained in good condition; on the steadiness of the entire machine, so as to avoid vibration; on the weight of the wheel, and on the velocity of the cutter being sufficient. A cutter ought never to assume a brassy color except when it requires setting; if it does so, and this is not the case, it proves that the metal is being strained or scraped with friction. The velocity must be very considerable; greater with a single cutter than with one that is composite. The velocity is limited by that point at which the heat generated would cause the oil to evaporate, soften the cutter, distort, and sometimes even displace, the wheel operated on. The engagement of the cutter with the metal must be very slight, and should never be increased suddenly.
Attempts have been made to enclose the arbor bearings in horn, but it is liable to be distorted by the heat.
Before dividing the disc into cutters it is essential that the two edges be carefully smoothed, and this without their being distorted. This can easily be done in an old depthing tool, using an arrangement like that shown in Fig. 208. The lap must be of hard wood, and its right-hand corner rounded off so as to resemble the side of a tooth; it is set to engage with one side of the cutter. We say the right-hand corner, because a lateral pressure can then be applied. It is important that the surface as left by the graver be clean cut, because if the smoothing is too much prolonged, it will deform the cutter.
416. In some factories it is usual to use discs about 2½ inches in diameter, for cutting the teeth of brass wheels in timepieces. The single cutters are arranged round the circumference as follows: One forms a space between two teeth; the one immediately preceding forms the right-hand side of the ogive, and that which follows forms the left-hand side. By adopting such an arrangement of separate cutters, if their side that lies against the disc is slightly inclined backwards it is no longer necessary to bevel off the cutting edge.
417. Pinions, Keyless Wheels, Etc. The cutters that last for the longest period when used for cutting steel are those formed like a file; but a watchmaker is not always in a position to make them himself; we will, therefore, here only speak of those he can make, the description of the first few being taken from a work by M. A. Phillippe, of Geneva, Les montres sans clefs (keyless watches).
418. Cutter for Forming the Inclined Teeth of Winding Pinions. Fig. 201 shows at S a section along the axis of such a cutter, and at P a side view. When it is believed to be of the required form, rest a piece of lead on the T-rest of the lathe and press it against the rotating disc. The impression made in the lead will afford a means of ascertaining both whether the form is correct, and whether the surfaces are smooth enough. This last point is important.
The cutting edges are formed by merely making a number of notches around the circumference with a tool for cutting ratchet teeth. Then advance this ratchet cutter so that it may engage with the convex edge of the cutter operated upon, and against the back of the teeth of this cutter; the ratchet cutter is then in a position to form a second face, o i, by which the teeth of the cutter are undercut at the back, but in such a manner that a small flat surface o a is left in order to retain the form. When a cutter made in this way will no longer bite, it may be set by passing a hard slip of whetstone over the faces of the teeth.
The ratchet cutter employed for making this cutter should never be pressed against it heavily.
419. Cutter for Ordinary Wheel Teeth. We will now pass to the consideration of cutters for forming teeth of the usual shape, of intermediate steel wheels, set-hands wheels, pinions, etc. They may be made as follows:
The rim is indented with small fine ratchet teeth, b d, Fig. 202. Any burr produced on the sides is then carefully removed, and the cutter is placed in the wheel-cutting engine, and notches, c, c′, c′′, c′′′, etc., are formed on either side with a flat square-edged cutter of such a thickness that the circumference is about equally divided into hollows and prominences. It is important to note that the right side of the teeth must be but slightly roughed, not more than is required in order to raise a slight burr, all that is necessary to form the cutting edge of this portion of the disc. In roughing these sides, at least one out of every two of the small ratchet teeth on the circumference should be left untouched, so as to ensure the required thickness being maintained.
The cutter shown in section and elevation at S and P, Fig. 201, might be cut on the side n in the manner here explained, and the convex portion k might be indented with a fine ratchet-toothed cutter, carried in the hinged cutter-frame of the wheel-cutting engine. The degree of penetration may be determined by fixing an ivory disc against the cutter and concentric with it, the two differing in diameter by the depth the cuts are to be made. The teeth will be rather too square towards the circumference, but their form can be carefully corrected by hand. It is obvious that the very greatest caution is necessary in hardening cutters.
420. Rose-Cutters or Forming Pinion Cutters. As the edges of pinion cutters are rounded, they can be made in the manner suggested by Thevenin. Supporting the roughed out cutter in the cutter-frame of a wheel-cutting engine, he fitted in the axis of the division-plate a kind of rose-cutter, N, Fig. 205. Its extremity, n, instead of being flat, is hollowed out as indicated by the dotted line, and, by presenting the cutting edge thus obtained endwise to the grooved edge of the cutter, the correct form can be given to it. With a mushroom-headed piece of steel and oilstone dust, the cutting edge of the rose-cutter can be made more or less acute by modifying the angle of this steel lap.
421. Other Forms of Pinion Cutter. When a cutter is merely required for a special piece of work, and not for continuous use, it will often be sufficient to make it as shown at A, Fig. 203; this is made by grooving the disc (c), or forming its edges as at d, after which a series of teeth are cut on the periphery with a revolving cutter, taking care to leave no more burr on one side than on the other. Then pass a smooth worn file (or a worn flat cutter) over the faces of the teeth, applying oil at the same time, so as to produce a slight burr on the edges; if the file is not allowed to bite too much and is well managed, these minute ridges will be uniform. After hardening, the cutter is ready for use.
If the faces were smoothed without subsequently applying the file, the cutter would not bite; for its action depends on the slight projection of metal that corresponds to the file-cuts. The cutter is nothing more than a circular file, with two cuts per tooth. If the corners are turned over evenly by means of a very hard burnisher the same effect will be produced; but this operation is delicate, as the amount of metal turned over must be the same in every case.
When a cutter does not bite, it must be softened and restored to its initial condition.
422. Or the following method may be adopted when it is required to make a cutter for a special purpose.
Proceed at first in the manner just described, but the periphery is divided into a greater number of teeth with a flat cutter, and to a rather greater depth, as at E, Fig. 203. Bend backward each tooth to a distance equal to about half a space by any convenient method; for example, by a lever resting at the bottom of each space and pressing against the corner of the tooth, etc. Before bending the first tooth introduce a piece of brass into the space behind it, of a thickness equal to about half this space, so as to avoid bending too far; for succeeding teeth the thickness must be about equal to a space; thus E will become E′. An inspection of Fig. 203 will suffice to make the operation evident; it amounts to bending back a series of separate cutters. The disc is then hardened, and the faces of the teeth are smoothed when they do not cut well; or merely smooth those that are the first to become dull.
It is important to employ soft steel that has previously been well annealed.
423. Cutter for Making Square Spaces. The teeth of such a cutter can be easily formed with a file, as shown at L, Fig. 209, the edge of the cutter, f, being passed backwards and forwards in the direction of the arrows, applying considerable pressure and at the same time slowly rolling f around. Or the cutter may be set up on a short arbor between the centers of the lathe; then pass the file backwards and forwards across the edge until the cuts are formed, slowly advancing the file in the meanwhile, so as to form the cuts around the circumference without once raising the file. The cutter must then, of course, be hardened.
424. Forming Cutters with a Milling Tool. The roughing of a round-edged, or even of a square cutter, can also be effected with the aid of a milling or “nurling” tool, proceeding in the same manner as when milling the heads of screws, etc. The tool must be in good condition, well provided with oil, and applied with considerable pressure against very soft steel.
If necessary, the workman can make the mill for himself; it is shown at M, Fig. 210. F shows the method of applying it to the cutter, and by partly turning the mill (of course carried in a strong holder) around its point of contact with the cutter, as indicated by the dotted lines, the rim of F will be evenly roughed all around.
With good steel fairly satisfactory results are obtained in this manner, but it is needless to observe that such cutters never bite as well as those made in the usual manner.
425. General Observations. When cutters are used with steel they must be driven at a less velocity than when cutting brass, and, as M. A. Phillippe has observed, it is best to make the cutters for steel of small diameter (about half an inch). They are more easily made and are less distorted in the hardening. The velocity should diminish as the diameter increases; for too great a velocity, especially when the diameter is great, will dull the cutter and soften it, owing to the heat produced.
Cutters must be turned very true: it is advisable to give them a last stroke with the graver after they are fitted to the cutter-arbor that will subsequently carry them.
When operating on steel it is best that the cutter frame of the wheel-cutting engine be advanced by a screw so as to give it a slow and easy motion; the results obtained are more satisfactory than when it is advanced by hand or with a lever.
The following practice is not uncommon in factories when it is desired to reproduce the exact form of a cutter. A notch is made with the cutter in the edge of a piece of steel, X, Fig. 211, or a series of notches o o′, etc., can be made by several cutters in the circumference of a disc Z (same figure). After being hardened and sharpened at the cutting edge, this disc is fixed at the center of the division-plate of a wheel-cutting engine, and can then be used to complete the grooving of any cutter that is set in position on the cutter-arbor before hardening. The positions opposite to which the notches were cut should be marked on the chuck, so that they may always be set-square to the cutter.
426. Besides the forms of cutter above described for operating on steel, we may mention that circular cutters may be used in which all the notches around the circumference have been polished, thus removing the burr, and preventing them from acting in the manner of a file. But while, with the former kind, a somewhat rapid rotation is necessary (although not so rapid as when cutting brass), with this latter class the movement must be comparatively slow, and produced by means of a hand-wheel; otherwise they will not cut, since the action depends rather on the application of pressure, and resembles that of a slide-rest cutter. The distance apart and width of the teeth of the cutter, as well as their inclination, are of importance; if too far apart they occasion a waste of time; if too large the machine will act in a jerky manner, and when too narrow, an excessive pressure will be needed in order to make the cutter bite the steel, which, it is to be observed, must always be thoroughly annealed. The edge must be well supplied with oil or soapy water when in action.
It is generally found best to advance the cutter against the edge of the steel rather than across it.
427. The instruments usually employed for making cutters for the teeth of wheels and pinions are complicated and expensive, but the author has designed one for his own use that is comparatively simple, and can be made by any watchmaker. When the reader has grasped the principle on which it acts he will be able, without difficulty, to modify it so as to suit his requirements.
The frame B B b, Figs. 212 and 213, consists of the body of the tool, B B, and a bar b b, which is attached to it by screws. Between the two the division-plate P rotates on an axis E R. The end E of this axis is formed as a chuck to receive the cutter f, which is clamped by a screw t.
The support S s J is held with friction in the lower part of this frame, to carry the cutter-holder A L M. This cutter-holder is hinged at n, so that it can receive a double motion, revolving about a horizontal axis J, and about an inclined axis n.
The portion A L of the cutter-holder carries a perforated arbor a c, with a ferrule c that receives the tail of the small rose-cutter, which will presently be described.
The end M rests against a guide G, held by a vane o z, which is pivoted on a pillar z, and can be clamped in either of the directions z y, z x, or by one of the screws o, o.
428. We will now consider the mode of action of the machine. Having set the little arbor c a in rotation, rest the end M of the arm against the guide, and gradually advance the rose-cutter towards f; the edge of d will form the first notch in the grooved rim of the cutter, and then will be raised from contact with it, owing to the influence of the guide G. After moving the tool-holder back to its initial position, advance the wheel P by a tooth, repeat the operation, and so on.
429. If the cutter f has to be notched on both sides, it must be reversed on the chuck; turn the guide so as to point in the direction z x, corresponding exactly to z y; then having set the cutter-holder in the line z h, recommence operations. The two grooves of the cutter will then necessarily be of similar form.
Teeth can be cut on the rim of f by using a cutter of the form F, Fig. 214, and holding M against a straight vertical guide.
With a given divided wheel, P,
the teeth can be brought nearer together by reducing the diameter
of the cutter, and vice versa. It is well to have some change wheels, but a better plan
is to advance
the division plate by the aid of a tangent screw.