Question Box

From Horology magazine, November, 1937

Question Box

Tightening Cannon Pinions

Editor HOROLOGY, 
Dear Sir:

Recently I happened to pick up a copy of a July 1936 issue of HOROLOGY. I was much impressed with the article on Systematic Repairing and the explanations on the cannon pinion friction. In my opinion that article would be complete if recommendations of tools used in tightening a cannon pinion were given.

I would also like to know something about the hollow center pinions which were not considered in that article. To get the right friction on the pin which goes through the center has always troubled me. I have been using the triangular punch for tightening the pinion on the pin. For the center friction I roll the pin between two coarse files. Some watchmakers insert a bristle of a brush in the center. What would you recommend?

L. D.

Answer: The use of the triangular punch for tightening a cannon pinion cannot be too strongly condemned. Aside from the mutilation of the pinion the friction thus created is never lasting or smooth. Even if these three nicks should survive long enough to be pushed on the post, the first few times the hands are set they will wear off. For tightening an ordinary cannon pinion there is nothing better than the cutting plier illustrated in Figure 2. The edges of this plier are very thin enabling one to get into the narrow groove of a small pinion without burring the square sides of the groove. Of no less importance is the adjustable stop screw, an absolute assurance that the pinion will not be cut in two. In addition one should always insert a round steel broach in the pinion while tightening it.

The hollow center pinion, a cross section of which is shown in Figure 3, needs a somewhat different treatment. The insertion of a bristle or rolling the pin between files is unmechanical and is not recommended, even if it does work after a fashion. In case the center pin is badly damaged or hopelessly small nothing short of a new pin will do. It is possible, however, to place the pin in the staking tool on a flat stump and tap it with a flat punch as shown in Figure 4. After it is thus flattened it may be stoned to size either in the lathe or by holding in a pinvise on the filing block.