A Treatise on Staff Making and Pivoting | Page 6

proper position for the seat for the balance, proceed the same as for the roller, except that the foot of the gauge is lowered until it is brought sufficiently below the plate to allow of the proper clearance as indicated by the dotted lines at H. Now apply the gauge to the new staff, as shown in Fig. 10, and the taper end will locate the exact position for the balance seat.
[Illustration: Fig. 9.]
[Illustration: Fig. 10.]
As previously stated, I have taken it for granted that you preferred to finish all the lower portion of the staff while the work was held in the chuck. I have assumed that you prefer to work in this way because I have noted the fact that nine watchmakers out of every ten start with, and first finish up, the lower portion of the staff. Where this method of working originated I do not know, but it always has the appearance to me of "placing the cart before the horse." I do not pretend to say that a true staff cannot be made in this way, but it certainly is not the most convenient nor advisable. We all know that the heaviest part of the staff is from the roller seat to the end of the top pivot. Now it seems to me that it is the most natural thing in the world for a mechanic to desire to turn the greater bulk of his work before reversing it. Now if the workman has been educated to turn indifferently with right or left hand, it may make little difference, as far as the actual turning is concerned, whether he starts to work at the upper or lower end of the staff, but unfortunately there are few among us who are so skilled as to use the graver with equal facility with either hand, and it is therefore an advantage to start with the upper end, as you can thus finish a greater portion of the work more readily. You can readily see that when you come to reverse your staff and use the wax chuck, that by starting at the top of staff your wax has a much larger surface of metal to cling to, and again the shape of the balance seat is such as to secure the work firmly in the wax, while if the reverse method is employed, the larger portion of the balance seat is exposed and the staff is more liable to loosen from the motion of the lathe and pressure of the graver and polishers.
CHAPTER IV.
By the aid of the pinion calipers and the old staff, the diameter of the roller seat and the balance and hair-spring collet seats may be readily taken, but it is perhaps better to gauge the holes, as the old staff may not have been perfect in this respect. A round broach will answer admirably for this purpose, and the size may be taken from the broach by means of the calipers. In fitting our pivots, we can not be too exact; and as yet no instrument has been placed upon the market for this purpose which is moderate in price and yet thoroughly reliable. The majority of watchmakers use what is termed the pivot-gauge, a neat little instrument which accompanies the Jacot lathe, and which may be obtained from any material house. This tool, which is shown in Fig. 11, is, however, open to one objection in the measurement of pivots, and that is that it may be pressed down at one time with greater force than at another, and consequently will show a variation in two measurements of the same pivot. Some of my readers may think that I am over-particular on this point, and that the difference in measurement on two occasions is too trivial to be worthy of attention, but I do not think that too much care can be bestowed upon this part of the work, and neglect in this particular is, I think, the cause of poor performance in many otherwise good timepieces. The ordinarily accepted rule among watchmakers is that a pivot should be made 1/2500 of an inch smaller than the hole in the jewel to allow for the proper lubrication. I am acquainted with watchmakers, and men who are termed good workmen, too, who invariably allow 1/2500 of an inch side shake, no matter whether the pivot is 12/2500 or 16/2500 of an inch in diameter. Now if 1/2500 of an inch is the proper side shake for a pivot measuring 12/2500 of an inch in diameter, it is certainly not sufficient for a pivot which is one-third larger. Of course it is understood that side shakes do not increase in proportion according as the pivot increases in size, for if they did a six-inch