Pinions.
Well made as to truth of centring, of division, of form of leaves, and polish, are, as the trade well knows, of vital importance to the value of the time-piece.
The making and finishing is one of the most troublesome, as well as most expensive of all the processes in watch work. The nature of the material renders it difficult as it approaches so nearly in hardness to the tools used in cutting. In the ordinary Yankee clock, thelantern pinionhas entirely superseded the solid leaf, which substitution was the greatest element of success in their cheap construction. The lantern pinion is really a nearer approximation to the required anti-frictional form than a majority of cut pinions in ordinary clocks. In the process of manufacture of the cut variety, the first consideration is the quality of the steel to be used. For this purpose it should be carefully selected by trial, thus ascertaining its fineness, uniformity, softness when annealed, together with its capacity for taking a good temper, with the least amount of springing during the hardening process. Very few pinions are cut from the solid piece—the drawn pinion wire being quite good enough, when milled and finished, for the ordinary run of watch work.
The steel wire having been selected, the first process is to cut it up in lengths a trifle larger than the required pinion. The separated pieces are then centred with care, and having been placed in a lathe, the staff and pivot are turned up to nearly the required gauge, leaving a portion of the whole piece the full size for the leaves. They are now taken to the milling tool to have the proper form given to the leaves. As this form is of the highest importance, it may be as well to give here the reasons. Supposing a wheel of 60 teeth, depthing into a pinion of 8 leaves, it can readily be seen that the arc of the motion of the wheel tooth is of greater radius than that of the leaf of the pinion, and it follows that if the teeth and the leaves are made in taper form with straight sections, there must occur a sliding motion on the surfaces of both—the power thus absorbed being totally wasted; but if we curve the surfaces we may approach a form so nearly perfect that the wheel teeth, being motors, really roll on the leaves, avoiding almost entirely the friction caused by sliding; the necessity for this curvature becoming greater the more the wheel exceeds the pinion in diameter. This curve, which has been demonstrated by very profound mathematical researches, is the “epicycloidal;” theoretically it should give no more sliding motion than the surfaces of two plain wheels revolving on each other. To obtain this perfect form, very great pains have been taken and expenses incurred, especially by the makers of the best time-keepers.
In the American factories the cutters are very elaborately made, the section being an object of great solicitude—it being an exact counterpart of the space between any two leaves, and also of one-half the top of theleaf from the curvature to the point, so that in milling, the space made by the cutter is its shape, leaving the leaf of the proper form. Generally the pinion passes under two cutters; the first to strike down the rough stock, the other to dress it to size and shape, with a light cut. The care and skill required to make these is certainly very great, and it is a proof of the wonderful ingenuity of man that they are made so perfect as to shape and cutting power.
A very ingenious device is used for dividing the leaves under the cutter, which revolves at a moderate speed over a slide, carrying a pair of centres, between which the turned up piece of pinion wire is placed. The slide is now pushed up to and under the cutter, and in its passage as much of a cut is taken as is desirable; in drawing back the slide the fresh cut space passes under a flat piece of thin steel, screwed on the frame, and set at a slight angle to the axis of the centres. On moving the slide towards the cutter for a fresh cut, the steel plate takes the last cut, and in passing by it the pinion is turned just as much as the angularity of the plate, which must be just one leaf. By this very clever device the division is effected without an index plate. This process, however, is not good enough for work intended to be very accurate—the pinion wire not being always, or indeed rarely correctly divided, the original error will be perpetuated in all the subsequent processes. These are all milled, with oil or soda water for a lubricator, and it follows that the speed of the cutter is regulated to get the greatest cut without dulling the tool. When dull, however, the mill is sharpened on thefaceof the cutting tooth by means of small grinders of iron, using Arkansas oil-stone dust for the first grinding, and giving the necessary delicacy of the edge by means of crocus, or sharp, followed, when fine work is needed, by rouge.
It is necessary that this care should be taken, for if the edge is left coarse it will become speedily dulled, and leave a very unequal and rough surface on the cut of the pinion, which in the subsequent grinding gives rise to error in shape and size. The pinions, thus cut to gauge, are dried in sawdust, hardened, and tempered; the staff and pivots are now turned up to size, and then pass to the polishers. In the factory they are finished by means of what are calledWig-Wags, which it may be interesting to the reader to have a general description of.
Two Vs are arranged as centres, the pinion is placed between them, the circular parts resting in each V, but free to turn on its own axis. Immediately above the Vs is a frame on which a slide, carrying the polisher, may traverse—generally about two inches. This slide is movable vertically so as to accommodate itself to the pinion; attached to the slide is a connection which leads to a vertical lever, which is put in motion from a crank on the counter shaft. The grinding is effected by bringing the grinder, charged with oil-stone dust in oil, in one of the spaces of the pinion, which, of course, is so arranged as to bring it parallel and central with the grinder. The power being applied, the slide takes a very rapid reciprocatory motion, and the face of the grinder, so charged, rapidly reduces the uneven surface left by the cutter to what is called thegray.
The form of this grinder must be as perfect as the cutters, and the care taken to get the requisite parallelism is in equal proportion, and in all the best polishers is planed up while in its position. The grinder is composed of tin and lead, with sometimes a slight admixture of antimony, rolled to an even thickness, cut off in suitable lengths, and then mounted in the carrier of the Wig-Wag to be planed up to shape. There are too many minute adjustments in the machine to render a full description in this article admissible. It is large compared with the work it has to perform, but it is very admirably made, as indeed all the tools are, in the American factories.
The polishing of the leaves is the next step, and this is effected by means precisely the same as grinding. In each stage the pinions are thoroughly cleansed before entering on another. The polisher is made precisely like the grinder; but instead of oil-stone dust, crocus mixed with oil is substituted. Owing to the less cutting quality of the material used, the polisher loses its form sooner than the grinder, and has to be more frequently reshaped. In very fine work the crocus is succeeded by fine well-levigated rouge to bringup that jet black polish, which is considered a mark of quality by chronometer and watch makers.
With the exception of turning up the staff and pivots, all the work hitherto described has been expended on the leaves—a very tedious process, yet done, when the tools and materials are in proper order, with marvellous rapidity; but tedious as these have been, there are two others quite as much so before the leaves are finished.
The ends are to be faced—they must be flat (that is a true plane) and receive the same finish that the leaves took, and is effected by the wig-wag; only the pinion revolves between centres, at a high speed, the grinder being brought up to the turned face. Two motions operate—one rectilinear, the other circular—the result being a compound motion which prevents the grinder from touching the same spot twice in succession. To effect this more surely, the operator gives the grinder a slight vibratory vertical motion. The polishing of the two faces is effected in the same manner as the grinding; in all cases the cutting face of the grinders and polishers being kept in a plane perpendicular to the axis of the pinion, both vertical and horizontal.
The staff and pivots being in the same condition they came from the lathe, the next step is to grind and polish them. Before, however, we treat on this process, it may not be amiss to give the general watch repairer a process by which the facing may be done on a small scale.
As a rule, when the watch repairer has to replace a pinion he selects one from the material dealer, finished in the leaves, but not on the ends or faces. The following operations are simple, and any one may finish these faces with little trouble. Having turned up your pivots and squared down the face of the leaves with the turning tool, grind it in the lathe by means of a ring of metal, the inside diameter being somewhat larger than the diameter of the staff. This ring is held between two centres, thus allowing it a vibratory motion, so that when it comes up to the face it accommodates itself to its plane, and thus has no tendency to force it out of a true flat; the ring, being larger than the staff or pivot, admits a small lateral motion, enough to effect a continuous change of surface. The same little tool may be used for polishing by substituting another polisher and using crocus and rouge. For the repairer, perhaps on general work the rouge would be superfluous. Vienna lime, used with a little slip of boxwood, brings up a very fine and brilliant polish, and in replacing new work in an injured time-piece, the steel may always be polished with great rapidity by using the lime on the gray surface left from the oil-stone dust; being quickly done and affording a very handsome finish.
To resume the consideration of the pinion, the last stage is the polishing of the circular portions. Here again the wig-wag is the most useful tool, but it operates somewhat differently, for the grinder or polisher is pressed down by the finger of the operator, the pinion being held between the centres of a small lathe attached to the wig-wag; the staff is first ground and polished as the leaves have been before, and this is the last operation performed with the pinion between centres. From this stage it is chucked in a lathe very peculiarly fitted, the mandrel being hollow; and in it is fitted what is called a pump-centre, which is movable in direction of the axis of the mandrel, and capable of being securely fastened at any desired point. On the nose of the mandrel is secured a hollow steel chuck, the two sides of which have been filed out, thus leaving an open space between the end of the pump-centre and the end of the chuck. On this end a small steel plate, extremely thin, is fastened by means of shellac, and a hole drilled in the plate capable of taking in the chamfer on the shoulder of the pivot. The pump-centre being drawn back, the pinion is introduced into the chuck, the pivot placed in the hole in the steel plate, and the pump centre is drawn forward until it forces the chamfer to fill the hole; the pivot projecting from the chuck is now ready for all the grinding and polishing processes. Here the wig-wag steps in again, and from the delicacy of the pivots is modified to suit the case; this is done by having a polisher hung in the wig-wag on centres, so it may revolve; when in operation one side of the polisher rests on the pivot, the other on a ruby placed in a screw, and which screw enables the operative to insurethe parallelism of the pivot. The ends of the pivots are next rounded off and finished in another set of tools. The pinion is now ready for use, assuming it to be of the proper gauge. In the American watches the scape and fourth wheels are generally staked on the staff pinch tight; the third and centre are staked on the pinion leaves, a rebate having been turned down on the ends, the wheel set on the shoulder, and the projecting ends of the leaves riveted down. This has not been designed as an exhaustive article on pinions; it is merely intended to open the subject as pursued in the factories. There is much more to be said; and the various processes on the small scale, as performed by the Swiss and English, together with their tools, will bear more than a general description, as they are applicable at any watch bench.
The subject will be continued, in the effort to give a full and useful article.