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

by Ward L. Goodrich

Referring to what was said in a previous chapter on wheels being merely compound levers, it will be seen that as we gain motion we lose power in the same ratio. We shall also see that by working the rule backwards we may arrive at the amount of force exerted on the pendulum by the pallets. If we multiply the circumference of the escape wheel in inches by the number of its revolutions in one hour we will get the number of inches of motion the escape wheel has in one hour. Now if we multiply the weight by the distance the barrel wheel travels in one hour and divide by the first number we shall have the force exerted on the escape wheel. It will be simpler to turn the weight into grains before starting, as the division is less cumbersome.

Another way is to find how many times the escape wheel revolves to one turn of the barrel and divide the weight by that number, which will give the proportion of weight at the escape wheel, or rather would do so if there were no power lost by friction. It is usual to estimate that three-quarters of the power is used up in frictions of teeth and pivots, so that the amount actually used for propulsion of the pendulum is very small, being merely sufficient to overcome the bending moment of the suspension spring and the resistance of the air.

It is for this reason that clocks with finely cut trains and jeweled pivots, thus having little train friction, will run with very small weights. The writer knows of a Howard regulator with jeweled pivots and pallets running a 14-pound pendulum with a five-ounce driving weight. Of course this is an extreme instance and was the result of an experiment by an expert watchmaker who wanted to see what he could do in this direction.

Usually the method adopted to determine the amount of weight that is necessary for a movement is to hang a small tin pail on the weight cord and fill it with shot sufficient to barely make the clock keep time. When this point has been determined, then weigh the pail of shot and make your driving weight from eight to sixteen ounces heavier. In doing this be sure the clock is in beat and that it is the lack of power which stops the clock; the latter point can be readily determined by adding or taking out shot from the pail until the amount of weight is determined. The extra weight is then added as a reserve power, to counteract the increase of friction produced by the thickening of the oil.

Many clock barrels have spiral grooves turned in them to assist in keeping the coils from riding on each other, as where such riding occurs the riding coils are farther from the center of the barrel than the others, which gives them a longer leverage and greater power while they are unwinding, so that the power thus becomes irregular and affects the rate of the clock, slowing it if the escapement is dead beat and making it go faster if it is a recoil escapement.

Clock cords should be attached to the barrel at the end which is the farthest from the pendulum, so that as they unwind the weight is carried away from the pendulum. This is done to avoid sympathetic vibrations of the weight as it passes the pendulum, which interfere with the timekeeping when they occur. If the weight cannot be brought far enough away to avoid vibrations a sheet of glass may be drilled at its four corners and fixed with screws to posts placed in the back of the case at the point where vibration occurs, so that the glass is between the pendulum rod and the weight, but does not interfere with either. This looks well and cures the trouble.

We have, heretofore, been speaking of weights which hang directly from the barrel, as was the case with the older clocks with long cases, so that the weight had plenty of room to fall. Where the cases are too short to allow of this method, recourse is had to hanging the weight on a pulley and fastening one end of the cord to the seat board. This involves doubling the amount of weight and also taking care that the end of the cord is fastened far enough from the slot through which it unwinds so that the cords will not twist, as they are likely to do if they are near together and the cord has been twisted too much while putting it on the barrel. Twisting weight cords are a frequent source of trouble when new cords have been put on a clock. The pulley is another source of trouble, especially if wire cords (picture cords) or cables are used. Wire cable should not be bent in a circle smaller than forty times its diameter if flexibility is to be maintained, hence pulleys which were all right for gut or silk frequently prove too small when wire is substituted and kinks, twisted and broken cables frequently result from this cause. This is especially the case with the heavy weight of striking trains of hall and chiming clocks, where double pulleys are used, and also leads to trouble by jamming and cutting the cables and dropping of the weights in tower clocks where a new cable of larger size is used to replace an old one which has become unsafe from rust, or cut by the sheaves.

Weight cords on the striking side of a clock should always be left long enough so that they will not run down and stop before the time train has stopped. This is particularly the case with the old English hall clocks, as many of them will drop or push their gathering racks free of the gathering pinion under such conditions and then when the clock is wound it will go on striking continuously until the dial is taken off and the rack replaced in mesh with the gathering pinion. As clocks are usually wound at night, the watchmaker can see the disturbance that would be caused in a house in the “wee sma’ hours” by such a clock going on a rampage and striking continuously.

Oiling Cables.--Clock cables, if of wire and small in size, should be oiled by dipping in vaseline thinned with benzine of good quality. Both benzine and vaseline must be free from acid, as if the latter is present it will attack the cable. This thinning will permit the vaseline to permeate the entire cable and when the benzine evaporates it will leave a thin film of vaseline over every wire, thus preventing rust. Tower clock cables should be oiled with a good mineral oil, well soaked into them to prevent rusting. Gut clock cords, when dry and hard, are best treated with clock oil, but olive oil or sperm oil will also be found good to soften and preserve them. New cords should always be oiled until they are soft and flexible. If the weight is under ten pounds silk cords are preferable to gut or wire as they are very soft and flexible.

In putting on a new cable or weight cord the course of the weight and cord should be closely watched at all points, to see that they remain free and do not chafe or bind anywhere and also that the coils run evenly and freely, side by side; sometimes, especially with wire, a new cable gets kinked by riding the first time of winding and is then very difficult to cure of this serious fault. Another point to watch is to see that the position of the cord when wound up will not cause an end thrust upon the barrel, which will interfere with the timekeeping if it is overwound, so that the weight is jammed against the seatboard; this frequently happens with careless winding, if there is no stop work.