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 butting 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 butting as this is not detrimental and will not cause cutting of the teeth.