In executing ordinary repairs to clocks and watches, there is nothing of such an intricate or difficult character that it cannot be undertaken by any one possessing some skill and dexterity in handling delicate tools. On the other hand, it would be folly for the same person to attempt to make a clock or watch without having studied the art as a trade, and being provided with all the necessary and expensive outfit.
It will be best to begin with clocks, as their works are on a larger scale and more easily understood.
As far as the "going" part of clocks is concerned - and that is the part liable to injury and wear - the ordinary 8-day English house-clock may be taken as the type.
The interior of such a clock is shown in side section in Fig. 212: a rope is coiled round the barrel A, 16 times for the 8 days, and the barrel is fixed to its arbor B, a prolongation of which is the square winding pin that comes out on the face of the clock. The dial plate or face is fixed by small screws a or by sockets and pins b, to some 4 or 5 legs c which join the front and back plates of the clock frame; frequently the dial is provided with a special set of legs of its own. On the arbor B also rides the great wheel C, which is connected with the barrel by the ratchet D. The great wheel drives the centre pinion d on the arbor of the centre wheel E, which is prolonged outside the dial plate and carries the "minute" or long hand e.
The centre wheel makes 1 revolution in an hour, and the great wheel 1 in 12 hours, by being provided with 12 times as many teeth as the centre pinion. The centre wheel drives the second wheel F by its pinion /, and that again drives the escape wheel G by its pinion g. If the pinions fg have each 8 "leaves" (the teeth of pinions are so called), E will have 64 teeth and V 60, in a clock whose escape wheel revolves once in a minute, so that the seconds hand may be set on its arbor prolonged to the face of the clock. The arbor h of the pallets of the eacapement H goes through a large hole in the back plate near i, and its back pivot turns in a cook j i k screwed on to the back plate.
From the pallet arbor at i descends the crutch it, ending in the fork I, which embrace the pendulum J, so that, as the pendulum vibrates, the crutch and pallets necessarily vibrate with it. The pendulum is hung by s thin spring m from the cock k so that the bending point of the springshall be just opposite the end of the pallet arbor, and the edge of the spring as close a: possible to the end of that arbor.
Of the "motion work" of the clock, the first thing to notice is the minute hand, which fits on the square end of a brass socket fixed to the wheel K, and sits closely but not tightly on the projecting arbor of the centre wheel-Behind this wheel comes a bent spring, which should be set on the same arbor with a square hole in the middle, so that it turns with the arbor. The wheel is pressed against this spring, and is kept there by a cap and a small pin through the end of the arbor: consequently there is sufficient friction between the spring and the wheel to carry the hand round, but not enough to resist a moderate push with the finger for the purpose of altering the time indicated. This wheel K, usually called the minute wheel but is really an hour wheel, drives another L having the same number of teeth, and a pinion attached to it; this pinion drives the 12-hour wheel M, also attached to a large socket or pipe carrying the hour hand, riding (to relieve the centra arbor of extra weight) on an intermediate socket fixed to the bridge N, which is screwed to the front plate over the minute wheel K.
A heavy weight 10, which drives the train, and gives the impulse to the pendulum through the escapement, is generally hung by a catgut line passing through a pulley attached to the weight, the other end of the cord being tied to some convenient projection in the clock frame or seat-board, to which it is filed by screws through the lower legs.
It is a common practice to make the cases of house clocks 6 ft. high; this is a great waste of space and materials. The rase need Only be long enough to give the pendulum full play, if the size of the barrel is diminished, or the great wheel is increased in diameter, or the weights are hung on a treble instead of a double line, at the same time increasing the weights in a progressive ratio to overcome the additional friction.
Fig. 213 represents a front view of the clock minus its face, thus exposing the repeating or rack striking movement. On the pipe of the hour wheel A the minute hand is set. B is the reversed hour wheel with its pinion a, driving the 12-hour wheel 0, on whose socket is fastened the snail 6, belonging to the striking work exclusively. The hammer c is raised by the 8 pins in the rim of the second wheel in the striking train; it does not quite touch the bell d, or it would cause a jar in striking. The spring D is arranged both to drive the hammer against the bell when the tail E is raised, and to check the hammer just before reaching the bell, so that the blow on the bell is due to the hammer having acquired sufficient momentum to carry it a little beyond its place of rest. Occasionally one spring is used to impel the hammer and another to check it; the latter may be replaced by a piece of vulcanised rubber tied round the leg where the hammer shank approaches it. To reduce the chattering of a heavy hammer, make it lean forward so as to act partially by its weight.
As a rule, the pinion of the striking wheel has 8 leaves; and as a clock strikes 78 times in 12 hours, the great wheel will revolve in that period if it has 78 teeth instead of 96, which the great wheel of the going part has for a centre pinion of 8. The striking wheel drives the wheel above it once round for each blow, and that wheel drives a fourth e, on which is a single pin f, 6, or any integral number of turns for 1 turn of its own; that again drives a fan fly to moderate the velocity of the train.
The reversed hour wheel B is so adjusted that, within a few minutes of the hour, the pin in it raises the lifting-piece g so far that the latter disengages the click A out of the teeth of the rack •*, which, helped by a spring k near the bottom, immediately falls back as far as it is permitted by its tail / coming into contact with the snail b. It is so arranged that the number of teeth which pass the click is proportionate to the depth of the snail; and as there is one stop in the snail for each hour, and it goes round with the hour hand, the rack always drops just as many teeth as the number of the hour to be struck. This drop makes the noise known as "giving warning." The clock is not ready to strike till the lifting-piece has fallen again: for as soon as the rack was let off, the tail of the gathering pallet n, on the prolonged arbor of the third wheel o, was enabled to pass the pin p of the rack on which it was pressing before, and the striking train began to move; but before the fourth wheel e had made half a revolution, its pin / was caught by the end of the lifting-piece, which is bent back and goes through a hole in the plate, and when raised stands in the way of the pin /, so that the train cannot go on till the lifting-piece drops, which it does exactly at the hour, by the pin on the wheel e slipping past it.
The train is then free. The striking wheel begins to lift the hammer, and the gathering pallet catches up the rack, a tooth for each blow, till it has returned to the place at which the pallet is stopped by the pin p coming under it. The lifting-piece is prolonged to E, where a string is hung to it; this is the proper place for such a string when it is wanted for the purpose of learning the hour in the dark. It is generally put on the click h; but in this case, if held too long the clock will strike too many, and if the string accidentally sticks in the case, the clock will go on striking till it is run down. The click r only exists in clocks which strike the quarters. The lever $ controls the striking: if pushed up to s i, the other end will meet a pin in the rack and prevent the striking.