Part 12 (1/2)

1. Excessive side friction of pivots because of being too large in diameter.

2. Train wheels and pinions being of incorrect proportion and causing irregular motion and affecting the vertical positions mostly.

3. Centrifugal force, which would cause the balance rims to spring outward in the longer arcs of vibration and thereby produce an abnormal slow rate in the horizontal positions where the arc of motion is always longest. This is due to the balance rims being too heavy in proportion to the arms or center bar.

When either of these three conditions are found there will be others among the same lot of watches, but as a rule they are only found on older watches made before correct proportions were firmly established.

Train depthings can often be improved if the workman is equipped with a rounding up machine and knows how to use it. Otherwise the watch can be sent to the factory for correction and the only alternative of the repairer is to cut the spring to the slow point, or counterpoise, with the intention of eliminating expense and getting as good results as can be expected for the financial returns that are to be received.

74. _How to Locate Defective Gearings._

Defective gear or depthing of wheels can be detected in two ways, one by observing the engaging surfaces of the wheel teeth and another by testing the engagement of wheel and pinion.

If the gearing is correct, observation will show that the engaging surfaces of the wheel teeth are smooth and either dark or possibly polished from wearing away of the plating. If the gearings are not correct the engaging surfaces will have cuts or ridges crosswise which have been produced by the pinion leaves.

The cause of this cutting is due to either a faulty construction of the teeth or to the fact that the pitch circle of the wheel is too small while that of the pinion is too large.

Testing the gearing in the watch is accomplished by placing the engaging wheel and pinion in the watch so that they are free to turn without engaging with any other wheel. A piece of ivory or celluloid several inches long and about the diameter of a piece of peg wood should be pointed at one end and this end should be held between the upper pivot and oil cup of the jewel, with enough pressure of the left hand to cause friction in turning the pinion. The larger wheel should then be turned in the direction in which it revolves when running; this is accomplished with a piece of peg wood held in the right hand.

If the gearing is perfect there will be smoothness as the wheel and pinion turn and if it is imperfect there will be a b.u.t.ting effect in the action. Should there be a slight intermittent stepping action due to drop of the wheel teeth on the pinion leaves it should not be mistaken for b.u.t.ting as this is not detrimental and will not cause cutting of the teeth.

Watches that have below standard train gearings require considerably stronger mainsprings than do those which have correct gearing and they will seldom take a reasonably good motion without a strong spring.

A safe way to judge gearings if in doubt is by the motion and the engaging surfaces of the wheel teeth. If the motion is steady and the teeth are not cut by the pinion leaves they may be considered as satisfactory. If the motion is steady for a time and then suddenly drops off there is generally something wrong in the gearing. The wheel and pinion in error can be determined by noting at what particular intervals the motion decreases. In nearly all instances this condition will cause a gaining rate in the vertical positions because of the fact that the vertical arcs are shorter and comparatively more easily affected than the horizontal arcs.

CHAPTER XV

TIMING AND FINAL REGULATION

75. _Mean Time Screws and Timing Washers._

In the general overhauling of watches, changing staffs, retruing and repoising of balances it is often necessary to make corrections of several minutes per day in the mean time.

For this reason and for the convenience of the future some manufacturers have provided from two to four mean time screws in the balances. A complete revolution of these screws either in or out, generally corrects any variation that may be required and frequently considerably less is all that is required in bringing the watch to time.

It is of course necessary that these screws be turned in opposite pairs as well as equal distances and that they be fitted with enough friction to prevent looseness and not too tight to cause bending of the pivots when they are turned.

If properly used for the purpose for which they were intended they are of inestimable value to the repairing fraternity in producing results.

The manufacturers of some watches do not supply mean time screws with the balances and the repairer is obliged to depend entirely upon timing washers for fast corrections, for it is, of course, not to be expected that repair shops will carry an a.s.sortment of all different kinds of screws such as the factories are able to maintain.

Occasionally a jeweler or watchmaker will be found who has strenuous objections to the use of timing washers in any sense, but unless they are supplied with a large a.s.sortment of the various makes and weights of screws and are willing to use the extra time required for properly changing the screws it is difficult to see just what legitimate alternative they can adopt. Investigation of this point disclosed the fact that the method employed by some watchmakers was to spread the regulator pins, which would of course make the mean time slower but would certainly destroy the adjustment to positions and make it practically impossible to obtain results from the regulator.