Piece of mainplate has sheared off.

[SpringMangler]

If it wasn't for bad luck I wouldn't have any luck at all.

Stripped down this old Vertex. It was all going well until I screwed in the crown wheel and the screw kept on turning. It is reverse threaded and I turned it the correct way.

First thought was that the screw had snapped but on lifting out the crown wheel I noticed that the threaded part of the mainplate had sheared off. I wasn't being heavy handed or even got to the point of giving the screw a final tighten. I managed to get the sheared piece of the screw and you can see the area and the piece in the attachment.

Is there any way to repair this or will it entail drilling, bushes etc which I am not really equipped for? Was thinking about a tiny bit of epoxy but don't know if it will hold.

Edited November 14, 2022 by SpringMangler

[nickelsilver]

There's no fix for this that won't involve a lathe at least, and some skilled work on that machine. Any type of glue will definitely not hold up, and even very careful soldering would never come close to the strength of the original material.

 

If I needed to do this, I would bore the bridge out in a faceplate in the lathe, to the diameter of the broken off tube, then (from underside) make a small additional recess a little bit larger, perhaps just 0.10mm deep. This would accept a tube of the original diameter, which has a corresponding lip on it to fit the recess, that gets pressed in. Would need a left hand tap to thread the tube*. The press fit should hold up to the stress of tightening the screw, and the lip would prevent pullout under load from winding (the winding pinion pushes up on the crown wheel while turning it).

 

*For those without a full selection of left hand taps, which is pretty much everyone, on a piece like this in brass you can take a similar left hand screw from an assortment and file 3 flats at 120 degrees and make a tap that will work fine for a use like this.

[SpringMangler]

Thanks for the quick reply and it's as I feared, way beyond my pay grade.

One for the parts bin then, or keep my eyes out for a donor or replacement movement. The movement comes from a very nice WWII watch so it's a bit of a shame.