The Modern Clock / A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair

by Ward L. Goodrich

On common clocks the crutch is simply riveted on its collet and bent as required to set the clock in beat, but for a first-class clock a more refined arrangement is usually adopted. There are other plans, but perhaps none so thoroughly sound and convenient as the following. The crutch itself is made of a piece of flat steel cut away so as to leave a round boss at the bottom for the fork, and a round boss at the top to fit on a collet on the pallet arbor, a part projecting above to be embraced between a pair of opposing screws. On the collet is fixed a thin brass plate with two lugs projecting backwards from the frame, these lugs being drilled and tapped to receive the opposing screws in a line. The boss of the crutch lies flat against this plate, and is held up to it by a removable collet. The collet may be pinned across or fitted keyhole fashion, in either case so as to hold the crutch firmly, allowing it to move with a little stiffness under the influence of the screws. With this arrangement the adjustment to beat may be made with the utmost delicacy by slacking one screw and advancing the other, taking care that in the end they are well set home so as to make the crutch practically all one piece with the arbor. Milled heads are most convenient for these screws, and being placed at the top they are easily got at. The crutch should always be fitted with a fork to embrace the pendulum rod, as this ensures the impulse being given directly through the center, and with the same object the acting sides of the fork should be truly square to the frame. A slot in the pendulum rod with a pin acting in it is never so sure of being correct, as, although the surfaces may be rounded, it is very unlikely that the points of contact will be truly in the plane of the axis of the rod. The slightest error in this respect will tend to cause wobbling of the bob, although, to avoid this, great attention must also be given to the suspension spring, the pin on which it hangs, and the pin and the hole at the top of the pendulum rod. All these points must be in a true line, and the spring symmetrical on both sides of the line in order that the impulse may be given exactly opposite the center of the mass, otherwise wobbling must occur, although perhaps of an amount so small as to be difficult of detection, and this is not a matter of small importance, as it has an effect on the rate which could be mathematically demonstrated.

The frames of many regulators are made too large and heavy. In some cases there may be good reasons for making them large and heavy, but in most instances, and especially when the pendulum is not suspended from the movement, it would be much better to make the frames lighter than we frequently find them. Very large frames present a massive appearance, and convey an idea of strength altogether out of proportion to the work a regulator is required to perform. They are more difficult and more expensive to make than lighter ones, and after they are made they are more troublesome to handle, and the pivots of the pinions are in greater danger of being broken when the clock is being put together than when they are moderately light.

In a clock such as we have under consideration, where the frame is not to be used as a support for the pendulum, but simply to contain the various parts which constitute the movement, the thickness of the frames may with propriety be determined on the basis of the diameter of the majority of the pivots which work into the holes of the frames. The length of the bearing surface of a pivot will, according to circumstances, vary from one to two and a half times the diameter of the pivot. The majority of the pivots of our regulator will not be more than .05 or .06 of an inch in diameter; consequently a frame 0.15 of an inch thick will allow a sufficient length of bearing for the greater portion of the pivots, and will also allow for countersinks to be made for the purpose of holding the oil. If thin plates are used one or two of the larger pivots should be run in bushes placed in the frame, as described in [Fig. 155].

The length and breadth of the frame, and also its shape, should be determined solely on the basis of utility. There can be no better shape for the purpose of a regulator than a plain oblong, without any attempt whatever at ornament. For our regulator a frame nine inches long and seven inches broad will allow ample accommodation for everything, as may be seen on referring to [Fig. 157].

Fig. 154.

The plates are made of various alloys: cast-brass, nickel-silver, and hard-rolled sheet brass. It is difficult to make plates of cast-brass which would be even, free from specks, etc., but cast plates may very well be made of ornamental patterns and bushings of brass rod inserted, or they may be jeweled as shown in Figs. [154], [155], [156]. Nickel, or German silver, makes a fine plate, but it is difficult to drill the small holes through plates of four-tenths of an inch in thickness, on account of the peculiar toughness of the metal, so that bushings are necessary. The best material where the holes are to be in the plates is fine, hard-rolled sheet brass; it should have about 4 oz. of lead to the 100 lbs., which will make it “chip free,” as clockmakers term it, rendering it easy to drill; the metal is so fine and condensed to that extent by rolling, that the holes can be made with the greatest degree of perfection. The many improvements in tools and machinery have effected great changes and improvements in clock-making. It once was quite a difficult task to drill the small holes in the plates with the ordinary drills and lathes; now we lay the plates after they are soldered together at the edges (which is preferable to pinning), on the table of an upright drill, and with one of the modern twist-drills the task is rendered a very easy one. After the pivot holes are drilled, we run through from each side a round broach, finished lengthwise and hardened, which acts as a fine reamer, straightening and polishing the holes exquisitely. A little oil should be used on the reamer to prevent sticking. The method of fitting up the pivot holes invented by LeRoy, a French clockmaker of some note, is shown in [Fig. 154]. It is a sectional view of the plate at the pivot hole. It will be observed that, instead of countersinking for the oil, the reverse is the case. A is a hardened steel plate counterbored into the clock plate B, and held in its place by the screws. There should be a small space between the steel plate and the crown of the arch for the oil. After the clock has been put together it is laid down on its face or side, a drop of oil is put to the pivot end, and the steel plate immediately put on; and the oil will at once assume the shape of the shaded spot in the drawing, being held in the position at the center of the pivot by capillary attraction, until it is exhausted by the pivots; the steel plates also govern the end play of the pinions. The pivot ends being allowed to touch the plates occasionally, the shoulders of the pinions are turned away into a curve, and, of course, do not bear against the plate, as in most clocks.