A Treatise on Staff Making and Pivoting | Page 5

ascend to the same height between the plates, as shown at c in Fig. 6. If the plates were united at the back like a book and spread somewhat at the front, the oil would ascend the higher as the two sides approach one another, as shown at d, Fig. 6. If a drop is placed somewhat away from the intersecting point, of the glasses, as shown at m it will, if not too far away, gradually work its way to the junction, providing the glasses are level. If, however, the glasses are inclined to a certain extent, the drop will remain stationary, since it is drawn in one direction by gravity and in the other by capillarity. When a drop of oil is placed between two surfaces, both of which are convex, or one convex and the other plain, as shown at g, it will collect at the point n, at which the surfaces nearest approach one another. We now see very clearly why the hole jewel is made convex on the side towards the end-stone and concave on the side towards the pivot.
[Illustration: Fig. 6.]
Particular pains should be taken to polish those portions of the pivots which actually enter the jewel hole and to see that all marks of the graver be thoroughly removed, because if any grooves, no matter how small, are left, they act as minute capillary tubes to convey the oil.
If the hole jewel be of the proper shape, the end-stone not too far from the hole jewel and too much oil is not applied at one time, the oil will not spread nor run down the staff, but a small portion will be retained at the acting surface of pivot and jewel, and this supply will be gradually fed to these parts from the reservoir between the jewel and end-stone, by the action of capillarity.
Having examined into the requirements of the pivot and its jewel and having gained an insight into what their forms should be, we are the better able to perform that portion of the work in an intelligent manner.
CHAPTER III.
Our wire has been roughed out into the form of a staff, has been hardened and the temper drawn down to the requisite hardness and we are now ready to proceed with our work. As I said before, we have now arrived at a point where many authorities differ, i. e., as to whether the finishing of the staff proper, should be performed while the work is held in the chuck, or whether a wax chuck be substituted. We will take it for granted that you have a true chuck and that you prefer to finish all the lower portion of the staff while held in the chuck.
Before we proceed with our work it will be necessary for us to make some accurate measurements, as we cannot afford to do any guess work by measuring by means of the old staff. I have used a number of different kinds of calipers and measuring instruments for determining the various measurements for a balance staff, but have met with more success with a very simple little tool which I made myself from drawings and description published some years ago in THE AMERICAN JEWELER. This simple little tool is shown in Fig. 7, and has been of great service to me. It consists of a brass sleeve A, with a projection at one end as shown at B. This sleeve is threaded, and into it is fitted the screw part C, which terminates in a pivot D, which is small enough to enter the smallest jewel. The sleeve I made from a solid piece of brass, turning it down in my lathe and finishing the projection by means of a file. The hole was then drilled and threaded with a standard thread. The screw part C, I made of steel and polished carefully.
[Illustration: Fig. 7.]
To ascertain the proper height for the roller, place it upon the tool, allowing it to rest upon the leg B, and set the pivot D in the foot jewel. Now adjust, by means of the screw C until the roller is in its proper position in relation to the lever fork. This may be understood better by consulting Fig. 8, where A is the gauge, C is the roller, E is the lever, F is the plate and G is the potance.
[Illustration: Fig. 8.]
Now in order to locate the proper place to cut the seat for the roller, remove it from the foot of the gauge and apply the gauge to the work as shown in Fig. 9. The foot of the gauge resting against the end of the pivot, the taper end of the gauge will locate accurately the position of the roller seat. In order to locate the