A lot of work for an old alarm clock-repairing a “cannon pinion”

Can you spot the new tooth and the split in the gear?  The new tooth is in the 12 o’clock position and the gear was split around the 8 o’clock position.  I repaired this gear with a torch and some very fine files.

This gear is called the cannon pinion, it fits on the same shaft as the minute hand, and it drives the gear that turns the hour hand.  If the gear splits, as this one did, the minute hand will continue to move and tell the minute, but the hour hand will be stationary.

The most delicate part was  brazing on the tooth.  The gear is small enough that you have to keep your head very close the the part to see what you are doing and you have to be very aware of where the flame is.  The company says that this torch puts out 6,000 degrees at the tip (I’ll take their word on that) and I don’t want to test that out on my face.  Not a good time for a sneeze.  When I brazed it on, I cut the tooth over sized, and then I filed it down to the correct dimensions.

It turned out very well, and these don’t split that often, but when they are this small, the work can be a little delicate.