Rules and Practice for Adjusting Watches

by Walter J. Kleinlein

THEORY AND PRACTICE

[26.]Theory of Frictional Errors and the Isochronal Hairspring.

Theory teaches us in brief, that the position adjustment is made necessary principally because of frictional errors. It would therefore seem that if the watch was mechanically correct there would be little or no requirement for position alterations.

We are also advised that an isochronal hairspring is one which will cause the long and short arcs of the balance to be made in equal time and that to attain this, the center of gravity of the spring must coincide with the center of gravity of the balance and that a certain pinning point is necessary in producing this result.

Now if we have a watch of correct mechanical construction and fitted with an isochronal spring it would seem that a close rating timepiece would be assured.

[27.]How Theory Works Out in Practice and What Isochronism Consists of.

Practical adjusting, however, proves that such is not the case, for even when the construction and alterations produce watches as nearly correct as scientific methods can determine, there is often considerable variation in the position rates. A twenty-four hour test in any position may prove that the long and short arcs are made in equal time showing the spring to be isochronous and yet the position variations have not been accounted for. In this connection experience proves that a spring showing a perfect isochronal rate may have its collet pinning point changed, in relation to the pinning point at the stud and that through such an alteration, a correction in positions can be obtained, without in the least disturbing the perfect isochronal rate.

This indicates that the separation of the two adjustments which is possible in theory, does not hold good in practice, because a spring showing a perfect isochronal rate has been altered for the purpose of counteracting some position error and thereby producing a practical center of gravity of the balance and spring combined, instead of separately.

This may be further explained as creating an error in a spring which is supposed to be theoretically isochronous, with the idea of making it act in opposition to the position error and the combination thus obtained produces practical isochronism as well as a corrected position rate.

It is not suggested that these relative pinning points be altered for the purpose of overcoming position variation such as may be caused by dirt and gummy oil, damaged pivots, or balances that are out of poise. The watch should be in first-class condition and have a good motion in every position and then the alterations may be safely undertaken in accordance with the principles.