Repairing a worn Elgin 780

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This is a manual-wind movement, and without regular cleaning and oiling manual wind movements suffer the worst. This one has had a hard life.

The watch is an Elgin B.W. Raymond Durabalance model 780. The barrel arbor's two holes, one in the main plate, and one in the barrel bridge, are the only unjeweled holes in this 23 jewel movement. They can be unjeweled because any friction there doesn't affect timekeeping at all - the only time the barrel arbor turns in those holes is while winding the watch. Unfortunately, though, if those holes are dry and dirty, the winding can cause a lot of wear.

This is the hole in the barrel bridge. You can see where the barrel arbor wore through the plating down to brass, and then continued to take a big bite out of the bridge. This caused the ratchet wheel to bind against the top of the plate, causing difficult winding, and also let the barrel tip over and interfere with the center wheel. A bushing to make the hole round and in the right place again, to upright the barrel, is called for.

First, I centered the main plate's unworn barrel arbor hole on a wax chuck (a small faceplate, covered with shellac and warmed to hold the part). To make sure it centered well, I made a wobble stick out of a piece of pegwood. This has a point that sits in the hole and a notch that sits on the T-rest. It multiplies any error to make it easy to see at the free end of the stick. If the hole is not centered perfectly, the free end wobbles around in a circle. (Click for full size photo)

Once the main plate is centered I screwed on the barrel bridge, which automatically centers the correct location for the new hole. I verified this with the microscope, and could see what was left of the oil sink running true. Next step is to bore it to make an oversize and correctly-centered new hole. (Click for full size photo)

Next I removed the barrel bridge, turned a piece of brass to a slight taper and parted it off, and set up the bridge in the staking set. With a liberal dose of Loctite and a few taps it's permanent.

Replacing the bridge on the main plate automatically recenters the bushing, and it is turned down flat.

Now the barrel bridge is mounted on another wax chuck (it's nice to have more than one) and centered with a pegwood against the bushing's outer taper. This again centers the correct hole location. Turning the bottom flat, drilling, boring almost to size and then reaming to size is straightforward. (Click for full size photo)

The work is complete. To remove shellac from the parts, I placed them in a jar of rubbing alcohol, put that in boiling water until it was nice and warm, and swirled. The heat is not strictly needed, but the parts have to sit overnight in alcohol without it.

Of course, now I cleaned and reassembled the movement, being quite sure to correctly oil the barrel arbor (and the shocking number of cap jewels in this movement too). The barrel is upright, has correct end and side shake, and the winding is smooth.


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