Chapter 4 SOME PRACTICAL METHODS OF CORRECTION

16.Example of Maintaining a Pleasing Appearance of the Balance.

In altering the location of screws during the temperature adjustment it is often possible to either mar or improve the appearance of the balance. As a demonstration of this point the correction made in regard to Fig. 3 is analyzed. The balance had twelve screw holes in each rim, with the space between the first and second holes from the arms equal to double the space between any other two holes. There were seven screws in each rim, equally divided as per cut Fig. 5, which indicates screws in the first, second, fourth, sixth, eighth, tenth and twelfth holes.

Fig. 5

A correction of the rate could have been obtained by shifting the screws in either the sixth or eighth holes forward three holes. Or those in either the first or second holes could have been shifted to the ninth holes and those in the fourth holes might have been shifted to the ninth holes with good results possible in either instance.

Moving one pair of screws under any circumstances however would have caused a massing of three pairs of screws at some point and a vacant space of three holes at another point which would not present a very good appearance for high grade work. Therefore the alteration made was to move the screws from the second to the third holes, fourth to seventh, and from the eighth to the ninth holes as indicated by the positions shown in Fig. 6.

Fig. 6

Examination of the fourth column Fig. 3, which gives the result of the second test will show that the desired correction was obtained with a better appearance of the balance than would have been possible if only one pair of screws had been shifted.

In following the logic of the alterations made we must consider that the screws moved from the second to third holes made no correction, due to the fact that the balance rims remain almost stationary at this point, the alteration being for appearance only, those moved from the fourth to the seventh holes were estimated for a correction of seven or eight seconds only, for the reason that the alteration did not carry them beyond the center of the rims where the greatest curvature takes place. The screws moved from the eighth to the ninth holes however were estimated for the full correction of four or five seconds which is to be expected through shifting a normal pair of screws from one hole to another beyond the center of the rim on sixteen or eighteen size balances. In moving a pair of screws one hole between the first quarter and the center of the rims, a correction of from two to three seconds can be expected and from the center to the cut the difference for one hole is generally four or five seconds, while an alteration between the arm and the first quarter seldom yields any correction.

The matter of appearance should at all times be respected, for it is just as easy to obtain results in most instances and also have a well-appearing balance. There is also less disturbance of the poise usually in moving several pairs of screws a short distance than there is in moving one pair a longer distance.

17.Correction Varies When Screws are Above or Below Normal Size and Weight.

Normal corrections can only be realized when normal screws are shifted. Some balances have one half, or quarter head screws which of course will not produce a correction as great as will be obtained by shifting regular screws. Sometimes platinum, or other extra heavy screws will be found in balances and these will produce a correction almost double that of ordinary screws of the same size.

18.Over or Under Compensation.

On some occasions it will be found impossible to maintain a pleasing arrangement of the screws because the temperature variation will make it necessary to mass all of the screws either in the holes nearest the cuts or in those nearest the arms.

This is due to either over or under compensation of the balance. Over compensation is caused by too large a proportion of brass in the rims, which causes them to curve inward too far at the free ends in heat and outward too far in cold. When the extent of this error is so great that the rate is still fast in heat, with the screws massed in the holes nearest the arm, a correction can be obtained by fitting heavier screws in the holes adjacent to the arms and lighter screws in the holes nearer the free ends.

When the rate in heat is slow with the screws massed at the free ends of rims the balance is under compensated, which is caused by too large a proportion of steel compared to the proportion of brass in the rims. This prevents the free ends of rims from curving inward far enough to carry the weight the proper distance toward the center of balance. A correction for this can be obtained by fitting heavier screws in the holes adjacent to the cuts and lighter screws in the holes toward the center of rims.

In changing the weight of screws as stated above it should be remembered that the gross weight of all screws must remain the same or the timing will be seriously affected. It is also important that the poise be tested whenever a considerable degree of alteration is made, as this will assist in obtaining an accurate rate.

19.Special Corrections for Over or Under Compensation.

Balances having the extreme degree of over or under compensation will seldom be found in high grade watches. In any instance, however, it is possible to obtain a better distribution of the screws by fitting either a larger or a smaller hairspring. For instance, we will assume a case of under compensation in which the screws have all been massed at the holes nearest the cuts. If the spring has seventeen coils, a correction of from five to ten seconds can be obtained by selecting and fitting a spring of the same make that will have eighteen coils, and the correction obtained will permit of shifting one or two pairs of screws back toward the arms.

In case of over compensation a spring of the same make, one coil smaller, will permit of shifting one or two pairs of screws toward the free ends of rims.

In a series of tests it was demonstrated that by duplicating or changing springs of the same make and size, on balances that had previously been compensated, there was very slight difference in the temperature variation of the watch. Also by changing pinning points or breaking out one-fourth to one-half of the coil around collet and adding weight to the balances to correct the mean time the difference in the variation was almost negligible.

On the other hand it was found that by replacing the springs with others of larger or smaller size, variations of from three to ten seconds were noted in all instances.

In selecting and fitting a spring that will be one coil larger or smaller, it should be noted that the inner coil of the original spring and that of the new spring are approximately the same distance from the collet. For if there was considerable space between the collet and inner coil of the original spring, and the new spring was colleted quite close, there might be the addition of an extra coil in the inside only. This was found to produce only a very slight correction, compared to that obtained by the addition of a complete outer coil. These tests indicate that the proportion of strength of the spring in the temperatures varies with any appreciable change in length while slight changes make practically no difference.

20.Example Demonstrating that Temperature Variation is not Always Due to the Balance and Spring.

Fig. 7 No. .................... Make...................

HEAT -10 -10 + 4 + 4 + 1 + 1

NORMAL - 6 + 4 + 5 + 1 + 4 + 3

COLD +12 +18 + 1 - 4 + 7 + 3

28 8 2

The following example is submitted to show that temperature variation is not always due to the balance and spring, and that the general condition of the watch may be responsible. The second column of Fig. 7, indicates an error of twenty-eight seconds slow in heat with all screws assembled in the holes nearest the free ends of the rims.

Examination proved that the motion of the balance in cold was reduced to about one-fourth of a turn. In heat the arc of motion was at least one full turn. This difference in motion was sufficient to prove that there was some binding in the train.

A very close fitting of the escape pivots was found and this undoubtedly caused binding of the pivots in heat due to slight expansion. Expansion of the stone would also tend to close the hole, and while the degree of temperature would hardly have any bearing on this point it is sufficient to show in what direction the tendency would be. The fourth wheel end shake was very close and probably caused binding of the wheel in cold, due to greater contraction of the bridge than of the fourth pinion. Furthermore the mainspring was only 0.02 of a millimeter narrower than the space in the barrel box. This no doubt also caused binding through greater contraction of the barrel than occurred in the mainspring.

The above defects were remedied and the rate was found to be eight seconds plus in heat as per third and fourth columns Fig. 7.

This made it necessary to shift several of the screws away from the cut, in almost the same position in which they were before the alteration which caused the close assembling of the screws was made. The final rate was two seconds slow in heat as shown in fifth and sixth columns.

The variation of thirty-six seconds between the second and fourth columns was entirely erroneous, and was due to condition of the watch irrespective of the balance and hairspring. Should the variation with the screws assembled have been by chance within the limits of allowance the watch would undoubtedly have been a very unreliable timepiece. The errors in the watch would no doubt have been corrected during the position adjustment later, but the large error in temperature which would have been introduced by wrongly moving the screws, would have prevented reliable timing until possibly at some future period a test in temperature would have been made and the screws replaced in the proper positions.

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