Tid-Bit 17 - 6-Jaw "Bezel" Chucks
Over the years I have fielded quite a few questions about holding gears so that one can work pivots. This is why I wrote the previous Technical Tid-Bit in this series – “Gear Holding Techniques”. But, as I discuss gear holding techniques with students and other clock repair folk the focus usually ends up on holding gears that don’t have much arbor sticking out past the gear hub. An example of such a gear is shown in Figure 1.
Figure 1 – Minute arbor from a Vienna regulator – an example of a gear where there is very little arbor protruding past the gear to chuck up in a lathe
One option that I have seen before is to chuck up the pivot on the end where there is not enough arbor. While this can probably be done with larger pivots, at the least it will scar the pivot. More often it results in an arbor with a pivot on one end, and a broken stump on the other. To make it fairly clear, I do not recommend chucking up on a pivot.
Which leads to the subject of this Tid-Bit – “6-Jaw Chucks”, or, as they are some times called, “Bezel Chucks”. The rest of this Technical Tid-Bit focuses on the chucks I think are most usable, and how I set up the lathe to use them.
Bezel chucks were so named because they have jaws that were designed to hold the bezels of pocket watches – allowing a repair person to repair the groove that held the crystal. A repair person could also use them to chuck up the back of a pocket watch and polish out small dings and scratches. For those purposes bezel chucks are very functional. Unfortunately, the typical bezel chuck from the 1800’s or the early 1900’s has very shallow steps in the jaws, which really are not deep enough to hold most clock gears (see top jaw profile in Figure 7). OK, maybe they can hold a French clock gear if the jaws are still in really good shape, but only because the French gears were fairly thin and small. But even with French gears, the early bezel chucks are hard pressed to hold well enough to let you work pivots. I have included a couple of pictures of a classic bezel chuck in Figures 3, 4 and 5.
Figure 2 shows how I set up my lathe to use a 6-jaw chuck to turn pivots.
