Part 1 (2/2)

1. _General Method of Obtaining Results._

Only since the introduction of the compensation balance which received its most substantial early experiments as recently as the year 1859, has it been possible to control the variation in pocket timepieces which is caused by changes in temperature. Previous to this introduction it was not uncommon for the best watches to vary as much as two or three minutes with changes of forty or fifty degrees Fahr.

Through experiment and improvement in the quality and application of balance materials, such advancement has been made, that this variation has been reduced to seconds and temperature adjusting is now quite universal in the production of medium and high grade watches.

In the large factories, girls and young men of very little previous experience are frequently taught to make the alterations and to do the testing, while men of experience in watchmaking handle only the more intricate cases such as ”stoppers” and radical rates that may require investigation of the inner workings of the movement. The simplicity of the adjustment naturally becomes more apparent with experience and the general alterations consist merely of transferring the balance screws in opposite pairs, either forward or backward one or more holes, according to the extent of the correction desired.

As these alterations are quite positive the adjustment can be undertaken with considerable certainty of obtaining results in every instance.

The repairer will not find as much daily necessity for understanding temperature adjusting as he will for being thorough in Position adjusting. The subject is covered, however, for the benefit of those who may desire practical experience in this branch of adjusting and also for those who desire a general knowledge of the details.

2. _How to Place Screws When the Rate is Either Slow or Fast in Heat Compared to Cold._

If a watch rates slow in heat compared to cold it is necessary to s.h.i.+ft screws in opposite pairs out toward the cut or free end of the rims; because when the metals expand the hairspring becomes weaker and produces a loss in time. During this period the free ends of the balance rims, carrying the transferred weight are forced toward the center and produce a gaining rate which compensates for the loss caused by the weakened spring.

As the metals contract in cold the free ends of the balance are drawn outward from their true form and the concentrated weight of these screws near the ends reduces the fast rate in cold and in principle works both ways in its action on the rate.

Should the circ.u.mstances be just opposite, or the rate be fast in heat compared to the rate in cold, it will be necessary to move the screws away from the free end of the rims. In doing this, less weight will be carried toward the center as the free ends curl inward and as a result, the rate in heat will become slower and the slow rate in cold will be reduced.

3. _Composition of and Distortions of Compensation Balances._

Compensation balances are generally made of one layer of bra.s.s and one of steel, with the bra.s.s on the outside consisting of about three-fifths of the total thickness and the steel on the inside consisting of about two-fifths. These metals are firmly soldered together and the distortions in changes of temperature are as follows.

In heat both metals expand, which infers that the rims become longer as well as wider and thicker. Bra.s.s expands more than steel and because of its attachment to the steel it cannot continue to lengthen in its true circular form, due to the fact that the steel does not become enough longer to maintain the true curve, and the result is that the free ends of the rims are forced inward.

In cold the bra.s.s, contracting more than the steel, pulls the rim outward at the free end which is just in reverse of the operations in heat.

The end of the rim which is attached to the balance arm always moves in the opposite direction from the free end, or outward from the center of balance, when the free end moves in, and inward when the free end moves out. In comparison, however, this movement is negligible as will be noted later in the results obtained in moving screws in that direction.

4. _Tests and Experiments._

It is generally understood that the purpose of the compensation balance is to act in opposition to the error caused princ.i.p.ally by the hairspring. The steel hairspring having no compensating qualities, either grows stronger or weaker with changes in temperature. When it becomes longer, wider and thicker in heat, experiments seem to prove that the increased width and thickness are not in proportion to the increased length, for if they were, the spring would actually be stronger; while timing proves that it is weaker because of the loss in time. In cold the shortening factor seems to dominate because of a gain in time.

In a series of tests with steel springs on uncut steel bra.s.s balances, the temperature error in the extremes of 40 degrees and 90 degrees Fahrenheit was found to be from eighty to one hundred and sixty seconds. With the same balances cut the error was reduced from seventy to one hundred and thirty seconds in each instance, without any correction of the balance screws.

A former test with palladium springs on the same balances, previous to having been cut, showed a considerably reduced error, indicating that the steel springs were mainly responsible for the temperature variations.

The above tests were in actual practice and results are given as noted, regardless of scientific or established formula relating to the cubic measurement of metals in changes of temperature.

5. _Effect of s.h.i.+fting Screws to Different Locations._

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