Either of the two following methods can be adopted in the place of that above explained: Support the winding square end of the barrel-arbor in an eccentric runner; let the opposite end run in a small coned hole in the end of a steel runner, which must be polished and hardened so as to prevent the corners of the square that receives the stop-finger from wearing it away; now apply coarse rouge until the fault no longer exists and follow with fine rouge to complete the polishing.
If not provided with an eccentric runner, it will be sufficient to take a tight-fitting key, drive it on with a blow of a hammer and file a point at the tapped end so as to be in the axis of the barrel-arbor. Having attached a ferrule to this key, place the whole between the runners and proceed as explained above.
524. To Renew a Worn Winding Square. The best plan is to make an entirely new arbor; but when this cannot be done, as, for example, on the ground of expense, the following method of repair may be attempted: Direct the blow-pipe flame on to the square while holding the body of the arbor in a pair of pliers, so as to prevent its being over-heated; and round off the corners of the square, leaving the diameter no greater than is necessary for strength, and tap it with a screw-plate. Now drill a hole at the end of a piece of round steel of somewhat greater diameter than the original square, and form an internal screw by means of a tap made in the same hole of the screw-plate as was used for the arbor; the end of the tap should be tapered and with good cutting edges.
If the arbor is the full length allowed by the case, reduce the length slightly and screw on the small steel spindle, tapped to the right depth. It must not be screwed quite down to the ratchet, although intended ultimately to come into actual contact. After having thus tested it, form the square, which will naturally be rather larger than the original, and cut a deep groove with the graver at the point where the square is to be broken off, but, before breaking it, harden and let down to a blue or violet temper; then smooth, polish, and screw finally on to the arbor. If this last operation does not result in the square breaking away, grip the spindle in a vise, and, taking the square in a pair of long-nosed pliers, break it with a sharp blow. It only remains to finish off the end in a screw-head tool.
THE MAINSPRING.
525. A free and uniform action of the mainspring is one of the primary conditions that have to be satisfied for ensuring a continuously good rate.
526. To make the eye in a Mainspring. Every watchmaker knows that this is commonly done by means of a mainspring punch; but in its absence a hole can be made by hammering a pointed punch one or more times through the end of the spring after it has been softened, and, after filing away the projecting metal, the hole is broached out or enlarged with the point of a graver and finished with a rat-tail file, taking care that the corners are rounded off so as to avoid the risk of cracks.
527. To reduce the height of a Mainspring. This and the following method are only to be resorted to when a new spring cannot be obtained.
Introduce the spring into a barrel of less height than itself and wear the steel away by rubbing it on a hard surface charged with oilstone dust, keeping it constantly rotated between the fingers. When the reduction is sufficient remove the spring and draw-file it, so as to round off the two edges; then clean the entire surface.
528. Selecting a Mainspring: Adapting it to a Fusee. The spring that is characterized by the most uniform uncoiling and the least difference between the force exerted when fully and only partially wound up will generally secure the most constant rate. In selecting one for a going-barrel watch, or in adapting to a fusee, the adjusting rod, shown in Fig. 246, and described in article 530, is used.
THE FUSEE.
529. At the outset, we would state the three characteristic properties of a fusee that have led to its adoption and retention in high-class watches and marine chronometers: 1, it equalizes the motive force; 2, it enables us to use a tapered mainspring, in which the uncoiling takes place in the most advantageous manner possible; and, 3, it secures a longer period of going.
530. To Adjust a Fusee to Its Mainspring. Set the barrel and fusee in position in the frame, with the mainspring and chain carefully hooked in their places, and the former set up about half a turn, and grip the fusee square in the clamp, d n, of the adjusting rod, shown in Fig. 246; then wind up the mainspring by rotating this lever with the hand until arrested by the stopwork. Now slide the weight m, which is held by friction and a light spring, along the rod until a point is reached at which the lever just neutralizes the force of the mainspring, so that the whole rests in equilibrium when left to itself. Rotate the rod backwards by half turns at a time. If equilibrium is maintained to the end, the fusee is well adjusted. But when this is not the case, it will be found that the weight of the lever is too great or too small; showing that the radius of the fusee is either too small or too great. Adjust the lever so that it balances with the radius of the fusee, which is thus shown to be most deficient, and at all other points along the thread of the fusee more metal must be removed to an extent indicated by the experiment.
When not provided with a fusee engine, it is a common practice to use the ordinary lathe, and an equaling file smoothed on its two faces; or a templet might be adapted to the T-rest of such lathe.
If the irregularity observed is but slight, it is advisable not to touch the fusee; because, in the great majority of cases, an equipoise can be arrived at by altering the degree to which the spring is set up. Thus, if the weight is too heavy for the lower coils of the spring, set it up more, so as to increase its tension; in the converse case, of course, it must be let down. By trying several springs, especially if they are of different manufacture, it will very often be found possible to secure a sufficient degree of uniformity without there being any occasion to re-cut the fusee.
CHAIN.
531. To Ease a Chain. When the links are rusty or not sufficiently supple, the chain should be placed in oil and left there for some hours at least. Round off the edge of a boxwood block, cut a groove across this edge, and clamp the block in a vise; then place the chain like a saddle in the groove, so that it hangs down on either side. Applying oil liberally to the wood, take an end of the chain in each hand, and pull it backwards and forwards in the groove, renewing the supply of oil at intervals. When perfectly flexible, the chain must be cleaned with benzine, or, after soaping, wash it in water and leave for some minutes in alcohol. After being dried, it is dipped in fine oil and dried in a clean linen rag free from fluff, pressing the rag against the edge. A chain treated in this manner will be found to remain supple for a long time, and it will not be liable to rust.
532. Riveting a Hook, Etc. When riveting either a hook or link to a chain, it is very necessary that the end of the rivet be cut or filed quite square; for, otherwise, the blow of the hammer will bend the rivet, so that the chain will not be square on the barrel, neither will the riveting be firm.
WHEELS.
533. To Rough Out a Wheel. The sheet brass having been prepared in the manner indicated in article 103, one face is smoothed with a file, followed by oilstone dust; the plate is then set up in the lathe, to true the other face with the slide rest. On the smoothed face trace out the rim and the crossings. These latter can best be marked out on the dividing plate, or grammaire, already explained in article 343.
After drilling the small holes, a, c, etc., Fig. 247, at the corners, cement the wheel to a plate that is perforated to permit the use of the pump center, and remove the metal between the crossings by first turning the sinks indicated by the shaded disc s with the slide rest, and subsequently cut the groove i i. Now center the wheel in the lathe, and trace the arcs a c with a fine graver, moving the face-plate backwards and forwards in the manner referred to in article 364.
Remove the wheel from the plate, and finish off the spaces with a file. Two files will be needed for forming the angles; one a flat barrette file, with the corner beveled off and smoothed to nearly a right angle, to go against the rim of the wheel; and the other a taper file, with faces of the same curvature as the inside of the rim, its two edges being inclined at rather more than a right angle and smoothed carefully. If these simple precautions are not taken, there is a risk of cutting through the arms or making them too narrow.
Many of the details in the following article, although specially relating to a balance, will be found applicable to the construction of other wheels.
534. To Make a Plain Balance. The round plate of which the balance is to be made must be hammered with the greatest possible care, and of a thickness but little greater than that of the finished balance (103). Smooth one face and cement it either to a perforated plate through which the pump center can reach the balance (if the universal head is to be used), or on the chuck of an ordinary lathe, or on the wax chuck C, Fig. 233. Hollow the middle portion with the slide rest cutter or hook tool, according to the kind of lathe used; but, whichever it be, it must be very well set, and only remove a small portion at a time. The application of an excessive pressure will produce a kind of rolling action, which will induce a tendency in the arms to bend. Remove the metal between the rim and boss until its thickness is diminished by about a third; smooth this surface carefully, finishing with a piece of charcoal. The disc is now ready for crossing out.
Place it on the dividing plate (see article 343) to mark out the three arms, and remove the metal between them, either in the lathe, as explained above, or by drilling a series of holes parallel to the arms and rim. These holes should be so arranged that they can be enlarged with a fine-pointed graver (while the balance rests on a flat wooden block or is cemented to it), and a turn with a sharp edged broach, or the passage of a thin rat-tail file should be sufficient to separate the useless metal. As a rule, the series of holes is drilled with the disc held against a wooden block, but the burrs produced on the under side by the drill prevent it from being maintained flat, unless they are removed after each hole is drilled, and this might occasion a distortion of the disc. It would, perhaps, be better to cement the rough balance to a sheet of zinc; the color of the shavings would suffice to indicate whether the hole was through.
The arms and rim must be made smooth and even with nicely formed crossing files, the edges of which are smoothed to the most convenient angle, as already indicated.
In filing the crossings the balance should rest against a small block in the vise, and they are rounded while resting in a groove at the edge of a similar block, specially shaped for the purpose. This block is also useful as a support in finishing the angles between crossings and rim.
The under face of the balance is smoothed with oilstone dust; and the arms by drawing the polisher along them while the balance rests on a flat block; it is then cleaned and fitted on a very true arbor, as A, Fig. 233. This should pass through the center hole of the balance without play after a broach has slightly enlarged it, and the balance is clamped by a cap and three screws, j. It only remains to set the arbor in the lathe and polish the rim, first turning it to a half oval if desired. In the latter case the rim, after being smoothed, is polished first with coarse rouge on hard pith, and subsequently with fine rouge on softer pith.
535. If the arms of a balance are found to be too long, so that they curve, the rim must be lengthened by hammering with the greatest possible care; the inside and outside of it must then be trued on an arbor of the form A.
The boss at the center will be found thicker than is desirable; its height can be reduced with the balance merely adjusted on a smooth taper arbor, but it is necessary to observe that the balance and arbor must not be adjusted to each other by pressing or by rotating the balance with the rim held in the fingers. It must be pushed on or off the arbor by applying pressure at the center of the boss on one side or the other with a piece of hard wood resting firmly against the T-rest, while you cause the arbor to rotate.
Instead of the form of arbor shown at A, a screw arbor might be used, with its cone pressing against a cap, but the balance must always be carefully adjusted on the arbor, and this latter must run perfectly true.
536. To Make a Number of Identical Wheels. If it is desired to make a number of brass wheels of the same size and shape, the workman will find it much to his advantage to employ the punching machine. By adopting the following method he can make his own punches and bed-plates.
With a view to secure same length in the matrices that are used for forming the crossings, without augmenting the difficulty of construction, proceed thus: Each of the pieces V, V, Fig. 248, consists of two parts: 1. The star-piece, a c b d, of three, four, five or six arms, according to the number of crossings of the wheel. 2. The collar, V. The star-piece is of the same length as the collar, and is made in the wheel-cutting engine in the same manner as the leaves of a pinion. The punches, of which one is shown at P, are fitted by hand to the recesses of the star-piece, and then cemented in position; the whole is then chucked in the lathe and turned as one piece, so that its diameter is slightly greater than the interior of the collar. Now harden the star-piece, and temper it to a blue color. When cold harden the collar V v, and temper it to the same degree, but, while expanded by the heat in tempering, introduce the cold star-piece and drive it home. By proceeding in this manner, no subsequent hand fitting will be required. V n must not be hardened.
Tools for punching the crossings of wheels are sometimes made on this system in which the disc of brass is fixed to a support that can be made to revolve by quarters of a revolution at a time, and a single punch serves to remove the metal by four separate operations. But as a rule it is better to use four punches together.
537. To Repair Wheels. When the teeth of a wheel are damaged, the only possible remedy is to provide a new one. If, however, a single tooth is broken, the following method can be adopted, on an emergency, for inserting a new one:
538. To insert a new tooth in a wheel. Cut a small notch in the rim of the wheel, shown at a, Fig. 249, which should be dovetailed if possible, and the two sides spread out slightly from the upper towards the under side, as indicated at c c. Cut a small piece of well-hammered brass, of the form B, so that the part d d fits exactly into the notch in the rim. Now invert the wheel and grip it near to a in a pair of long-nosed pliers, which must be held in the vise. Moisten the inner faces of the notch with soldering fluid and, placing B in position, put particles of solder round its edge; holding the lamp beneath the nose of the pliers, the solder will presently melt, and a drop of the fluid should be added to facilitate its running into the joint. Cool the wheel and wash thoroughly, first with water and subsequently with alcohol.
It only remains to file both faces smooth and level with the rim of the wheel; then shape the tooth carefully.
By introducing B from the side opposite to that which is visible in the watch, and sloping the faces d d, to a less degree than a, the inverted wheel will present a recess to receive the solder; so that, on looking at the upper surface, at which the edges fit very closely, the joint will be scarcely visible.
539. To true a wheel. When the teeth are found to be in good condition, but the wheel does not run true, or one or more of its arms are strained, the fault can be corrected, in a case of absolute necessity, as follows:
Remove the pinion from its wheel. Enlarge the central hole in the lathe and rivet or solder in it a brass ring that is slightly thicker than the wheel, and perforated with a smaller hole than that required for the riveting. Now center the wheel from its circumference; increase the central hole with the slide-rest cutter, and turn down the two faces of the ring level with the wheel. Rivet the pinion in its place, after testing the truth of its riveting neck, when the wheel should be found to turn both true and flat.
If the wheel under repair is likely to be subjected to much force, at least two small notches should be left in the enlarged hole in the wheel to receive corresponding projections in the brass ring.
540. If the crossings of a wheel are broken and the wheel cannot be replaced, it must be chucked in the lathe and the arms turned out with a graver, the inner edge of the rim being at the same time turned circular, and a step turned on this edge where the metal is to be left of half its original thickness.
Take another wheel of the same size and thickness, or a plain disc, and turn it of the same diameter as the outer ridge of the step; reduce its thickness at the edge by one-half and a disc will thus be obtained with a ridge round the edge corresponding exactly with that of the wheel, and the one will fit in the other. They are, of course, soldered in this position, care being taken to prevent the solder from reaching the teeth, and the old wheel will thus be provided with a new interior.
If the disc is made to fit closely on the upper side, a wedge-shaped ring being left to receive the solder in the manner explained in article 537, the joint will be scarcely perceptible on the exposed face, even with a glass.
In repairing delicate wheels in any way it is a good precaution to cement the rim to the edge of a hole in a brass plate, so that only the arms or other part to be operated upon is exposed.
541. To Make a Stem-Wind Wheel. We will suppose that the old wheel is available as a pattern; if it is not, the several dimensions must be ascertained by calculation in accordance with the laws of depths.
Prepare a thick plate, and drill a central hole, fitting a steel pin into it as shown at o d, Fig. 250. The diameter of d must be exactly the same as that of the pump-center in the universal head. Fit the wheel-blank R to the pin o without play, and cement it to the plate. Remove the pump-center and insert d in its place, clamping the plate P firmly against the face-plate by the dogs. By using well-sharpened gravers or cutters, the wheel may be rapidly shaped.
The pin might be forced in from the under side to the level of that face of the plate; and if it were perforated as shown by the dotted lines, it might be centered by means of the pump. Or the plate P might be made circular and centered from its circumference.
542. To cut the teeth on the circumference the wheel need only be fixed on the chuck of the wheel-cutting engine as usual by means of the steel cone. The crown teeth are cut while the wheel is firmly cemented to a pin-chuck like that used in turning it.
Other keyless wheels can be made on the same principle, and such modifications as may be necessary experience will suggest. Sufficient information in regard to wheel-cutting has already been given in 397 and following articles.
PINIONS.
543. To Make a Pinion. At the present day pinions of all sizes can be obtained of the material dealers, so that it is very seldom that a watchmaker is obliged to make one for himself.
In an emergency, however, he can adopt the following method for making one out of the ordinary drawn steel; but it should be added that, in all probability, some practice will be needed before success is arrived at. Cut a length of steel wire of suitable diameter about two-thirds as long as the files that are to be used for shaping the teeth. Turn it down to form the axis, leaving a block near each end equal in length to the required pinion, as if three pinions were to be made on the same staff. Then cut and round leaves on all, keeping the file always in contact with a leaf of each pinion. By proceeding thus the sides and roundings of the leaves will be maintained parallel to the axis, and there will be no risk of the pinion being barrel-shaped, as is nearly always the case when a short pinion is held in the fingers or rested on a block in the vise.
Proceed in the same manner in smoothing and polishing, using pieces of some close-grained wood, such as walnut.
It is much easier to make the pinion of the required form by means of a revolving cutter in the lathe, if the workman is not provided with a special tool for the purpose: the arrangement of the lathe is described in article 402.
In some factories the leaves are cut in two operations: a cutter with plain fine saw teeth divides the circumference into the requisite number of equal parts, the leaves being subsequently made of the correct shape by a special cutter, the method of making which has already been very fully explained in articles 417-435.
544. To Determine the Size of a Pinion. The following table is usually employed for this purpose. See also 562 and the following articles.
To give the approximate diameter of a pinion, the pinion caliper should include:
| For | 16 | leaves, | 6 full teeth; that is to say, measuring the distance between the two external faces; |
| ” | 15 | ” | rather less than 6 teeth, or 5 teeth, and just beyond the point of the sixth; |
| ” | 14 | ” | 6 teeth, measuring at the points. |
| ” | 12 | ” | 5 teeth, measuring at the points (or rather 4½ teeth); for a clock-wheel, 5 full teeth; |
| ” | 10 | ” | 4 full teeth; for a clock-wheel, 4 squared teeth; |
| ” | 9 | ” | rather less than 4 full teeth, or 3 full teeth to the point of the fourth; |
| ” | 8 | ” | 4 teeth, measured at the points, minus a quarter of a space; |
| ” | 7 | ” | rather less than 3 full teeth; for a clock-wheel, 3 full teeth, plus a quarter of a space; |
| ” | 6 | ” | 3 teeth, measured at the points, or rather more; for a clock-wheel, 3 full teeth. |
It is important to notice that these measures can only be regarded as a first approximation, and it is only by actual trial in a depth-tool that we can be certain that a pinion is correctly sized. By taking the measures in a micrometer, or other accurately divided gauge provided with a vernier, the work of selecting will be much abridged; but how long will it be before the generality of watchmakers will make use of these convenient appliances? The well-known wheel and pinion sector, although convenient, is not equal to them in point of accuracy, and is affected by an error in measuring a chord, not a true diameter of the wheel or pinion.
545. To Increase or Decrease a Pinion. The pitch circle of a pinion may be increased by reducing the thickness of the leaves in such a manner that their flat faces are continued further on to the rounding; conversely, a pinion may be decreased by carrying this rounding farther down towards the base of the leaf.
546. To Decrease a Pinion Without Removing the Wheel. Some watchmakers recommend that the wheel be removed from the pinion, and, after the necessary reduction has been effected and the leaves re-polished, again riveted on the pinion-neck. Very few workmen, however, can do this well, so that after the operation the wheel is seldom found to run true. If a new pinion cannot be procured, the old one must be reduced.
When a pinion that is too large is replaced by one that is smaller, it is necessary to take care that the hole in the wheel is well centered and not too large; in either of these cases it must be enlarged and bushed after being centered by the circumference.
547. To Polish Pinion Leaves Mechanically. It was formerly the custom to polish the leaves of a pinion, holding it on a block or between two fingers and traversing a strip of metal with oilstone dust backwards and forwards in each space for the smoothing, and a similar strip of walnut wood (with rouge) for polishing.
This method has long been abandoned in factories, where all pinions are polished in a machine.
We will proceed to explain a simple arrangement for polishing pinions in the ordinary lathe, but it is advisable first to describe one form of tool that is actually in use on the large scale for this purpose. The two only differ in their dimensions.
548. Pinion-polishing Machine. A frame B B, Fig. 251, supports at its upper end an H-shaped piece, of the same form as the cutter-holder in an ordinary wheel-cutting engine; but the arbor, instead of carrying a cutter, is provided with a wooden drum R. On the base of the frame is a plate P, which can be fixed by the screw E, and carries a second plate p to serve as a bed for the slide, which supports the pinion to be polished freely between two brackets a, a. The plate p can be set a little oblique and clamped by the screw v.
The machine acts as follows: Present a corner of a pinion-leaf to the circumference of R (which is caused to revolve by a cord passing round the pulley n n), the axis of the pinion being not quite at right angles with that of the drum, in order that the groove formed in the soft wood may resemble the thread of a screw, and so cause the pinion to revolve. When the groove is of sufficient depth, apply rouge if operating on a small pinion, and emery for a large one: after a few turns of R, the slide carrying the pinion being at the same time moved backwards and forwards, the pinion will be found to be polished. A better surface can be obtained by using flour emery.
The steel wheels of keyless work can be polished in the same manner.
549. The spindle of the screw E passes through a rectangular slot in B in order that the slide and its support can be moved parallel to the axis of R.
The grain of the wood must be at right angles to the axis of rotation of the drum, and a wood that is non-fibrous is preferable. It must evidently not be too hard, and, if too soft, the thread formed on its circumference will get rough, and often will suddenly change position. When the entire surface has been worn it must be re-turned smooth and cylindrical. The larger a roller is, the quicker it will polish and the less it will wear. Moreover, it will render a proportionately less amount of motion of the slide necessary. The root of the walnut tree is especially sought after, but, when this cannot be obtained, other woods can be used.
In factories where clock pinions are made, thin discs are employed in place of the drums. They are at least a decimetre (4 inches) in diameter, and very narrow at the edge, and can be re-turned with a graver when worn without being removed from the tool, if a T-rest be fixed in some convenient position.
The screw d is for limiting the descent of the drum, but some workmen prefer to dispense with it, and, instead, hold the frame C C in the hand, pressing it gently against the pinion. They urge that the wood is never of the same degree of hardness round its circumference, and therefore must of necessity wear irregularly; by holding C C in the hand the pressure on the pinion can be more evenly adjusted, as it is possible to feel at once whether the drum is polishing or scratching.
The inclination of the slide to a plane at right angles to the axis of R is measured by the pitch of the screw formed on the drum. But in practice no special precautions are taken, and it is only necessary to incline the slide slightly to the right or left, until the pinion is found to revolve freely.
The drum may be from two to three inches in diameter, and, in order to ensure the same degree of hardness throughout the entire circumference, it is a good plan to make the drum of a series of wedges cut so that the grain in all radiates from the center. Beautiful polished surfaces are obtained in this manner.
550. To polish a pinion in the ordinary lathe. Various methods may be adopted, but the following is one of the commonest:
Support the pinion between the two centers b, d, of the pinion-carrier shown in Fig. 252, the form of which will be evident without explanation. Rest this carrier by the portion M against the T-rest, pressing it against the drum at the same time with one finger. Rotating the drum first by hand, make the pinion cut a groove varying the inclination until it is found to be correct, and, when sufficiently deep, charge with polishing material, and rotate it with wheel, at the same time moving the pinion-carrier backwards and forwards endwise. A little experience will give the requisite skill.
If the pinion is not held at a sufficient inclination it will scrape and will not revolve. If too much inclined, only the roundings of the leaves will be polished, the sides being left untouched. A well-formed groove will last for a long time.
551. To Tighten a Cannon Pinion. If it is simply slack it will be sufficient to increase the diameter of the set-hands arbor as described in article 336. But if the cannon pinion is in the habit of working off this arbor when setting the hands, the arbor can be tapered a little downwards; or proceed as follows:
Drill a hole in the square that receives the minute hand in the position shown at a, Fig. 253, and also indicated by dotted lines at c s; now turn a groove round the arbor, also shown by dotted lines, at the point n, to correspond with the hole a. Insert a pin in this hole, filing it off smooth with the surface at the side at which it enters, and nearly level at the other side, to be hammered over just sufficiently to prevent the pin from working its way out. The cannon pinion will now be found to turn with the requisite degree of friction, and without any tendency to work up. It will last all the longer if both the pin and the groove in which it works are polished.
SET-HANDS SQUARE.
552. To Make a Set-Hands Nut. This is a small square nut pinned to the pivot of a solid cannon pinion that projects beyond the top-plate in some watches after passing through a hollow center pinion. This construction has been latterly discontinued, but it may be well to explain the mode in which such a nut can be renewed when necessary.
Take a rod of soft steel of a diameter half as large again as that of the square to be made. Drill a hole along its axis rather less in diameter than the set-hands arbor and cut off the ends a little longer than the square is required to be. Put this nut on an arbor and turn it flat on each end (although still a little long) and truly cylindrical. Having inserted a loose fitting coned brass wire of oval section into the nut, hold it on its side on an anvil. With a sharp blow of the hammer cause the cylinder to assume an oval form, so that the round hole is as seen at A, Fig. 254, this being the section of the end of the set-hands arbor itself. If the work has been carefully performed up to this point, the steel nut should now pass a short distance on to the arbor on applying a moderate pressure, and it will suffice to slightly alter the form of this latter in order to ensure a perfect fit. As there should be no shake, it is advisable that this adjustment be made after the nut is hardened.
File the two faces d and f parallel to each other and to the axis of the oval, reducing the total thickness very nearly to the amount ultimately required, then holding the nut in the pincers by these two faces firmly, but without scratching them (or it may be held by a rod fitted to the oval hole), form the square, removing all the metal that is beyond the two vertical lines in the figure. Then set it on an oval arbor and turn the corners down to the exact diameter required; pass the graver over the two ends so as to adjust the length. It will then be easy to finish off the square and round the lower end, holding the nut on a steel rod in a pin-vise. Drill the hole for a pin after marking its two ends on the nut as explained in article 518, then, holding the nut so that it rests on its lower face, form a recess with a chamfering tool held in its axis; the form of this can be modified if required with the rounded end of a rod and oilstone dust.
Harden the square and temper it to a blue color; then smooth its faces and ends, and fit the square to the set-hands arbor. The hole for the pin must now be made through this arbor, taking care not to allow the square to rise out of its place during the operation. It only remains to polish the recess formed in the nut with a rod rounded at one end and rotated with a ferrule, and finish off the corners with a burnisher and rouge; the lower end is finished in the same manner as the head of a screw.
553. We have here considered the case of a new arbor, but, if fitting a nut to one that is already drilled, proceed as follows: Make the nut rather longer than necessary and drill a hole higher than the point at which measurement shows it ought to be; then remove metal from the lower face until the two holes coincide. The work is simplified if the nut be made of the correct height at once and, instead of drilling a hole, a slit be formed as in the head of a screw, the bottom of which must correspond with the lower edge of the hole in the arbor.
554. To fit the Set-hands Arbor to the Center or cannon pinion. We have pointed out in article 364, the objections to hammering the set-hands arbor so as to secure sufficient friction to make it hold in either of the pinions through which it passes in the ordinary form of watch. Tracing a spiral line on its surface is not much better, as the metal thus caused to project soon wears off. A better method is explained in article 337, but, when only a slight increase of diameter is needed, the following will suffice:
Roll the arbor on a hard flat wood surface with a file of medium cut, applying considerable pressure so that the arbor is forced against the file. If the pressure is sufficient and maintained long enough, a dead rough surface will be formed on it which will increase its diameter so that it will retain a small quantity of oil. It is well to roughen the surface rather more than necessary, subsequently passing a burnisher lightly over it until the arbor fits the pinion with sufficient friction.
As to the making of a set-hands arbor, it will present no difficulty to a watchmaker of even average skill in turning and filing.
PIVOTS.
555. The Play Of Pivots. It may be accepted as an approximate rule that the play of escapement pivots in their holes should be as follows:
In the cylinder escapement, about one-sixth the diameter of pivot.
In the duplex escapement, about one-tenth the diameter of pivot.
In the lever escapement, about one-eighth the diameter of pivot.
A large hole causes the pitching of the depths to vary with position, and a deficient play renders the escapement more sensitive to thickening of the oil.
The depth of a pivot-hole or the length of its cylindrical acting surface may be taken to vary inversely with its hardness. Thus a ruby hole is made less deep than one of brass.
556. To Replace the Pivot of a Hollow Pinion. It often happens that the pivot of a hollow center pinion is so deeply cut that it cannot be re-polished, in consequence of the careless manner in which too many examiners finish the center holes (461). If the pinion itself is found to be still in good condition, it can be made serviceable as follows:
Cement the pinion, with its wheel attached, firmly to the chuck of a lathe after having removed the two worn pivots, and, when it is accurately centered, increase the hole by means of a drill that is a trifle larger than the original pivots (see article 282); in the hole thus enlarged and carefully smoothed insert a close fitting steel tube that has been hardened and tempered to a blue color, which must be smoothed and run true. The portion of this tube that projects on either side is then adjusted to the proper length, and it only remains to polish the pivots.
If only one pivot requires renewal, ascertain whether there would be sufficient hold with the hole enlarged through half its length, and proceed as already explained.
We have assumed that the shoulders of the original pivots can be made to serve again, but it often happens that the shoulders do not possess sufficient substance, in consequence of the hollows being cut too deep. In such a case it is hardly necessary to observe that the hole must be drilled larger, so that, after the tube has been adjusted, new shoulders can be turned on it.
557. To Redress a Bent Pivot. For this purpose some workmen merely use a pair of pliers or tweezers; others place the pivot in a slot of the Jacot tool, and press on it with a burnisher that has little or no cut, at the same time causing the staff to rotate. Either of the two following methods may be adopted:
Drill a number of straight holes in a plate exactly at right angles to its surface. Now introduce the pivot into a hole that it fits with very little play, and redress it by causing the staff to rotate, at the same time holding the plate in the hand. Caution is necessary since there is some risk of bending the pivot too far.
558. Pivoting a Cylinder, etc. This operation will not present any difficulty if the several heights are properly taken. See also the articles on Beaupuy files (240), and on compasses for measuring heights, etc. (243).
559. Polishing Pivots in the Lathe. Pivots are as a rule polished by metal polishers provided with suitable materials, and held in the hand; in Fig. 255, however, is given the design of a machine by which this work can be accomplished when the pivoting is done in the chuck-lathe, the pivot itself being free and unsupported by a runner.