Recasing an Elgin 760

I purchased this Elgin movement and dial some time ago on EBay.

No doubt it was originally in a solid gold case that has gone to off to the melting pot. So I decide to try casing it in a modern case (in particular one of the ones sold by Otto Frei intended for a Swiss ETA movment).


Now this has been done before, see this posting:

With this very same movement and dial, so I knew it could be done.

First some very careful measurements both of the case and of the movment



From these measurements I determined that it was necessary to set the dial back 0.5mm from the surface in the case in order for the stem to line up. I also determined that with that setback there would still be plenty of clearance for the movement in the back of the case. (This Elgin movement is really quite slender compared to a modern ETA).

When "SQLguy" did this he used a tension ring to fill in the gap. My initial plan was to turn a brass ring to fit the gap and then gold plate it with a Pen Plater. However I then hit upon the idea of making the spacer out of black Delrin. So I turned a suitable ring and gave it a try:



I liked the end result the black plastic is basically invisible behind the case's reflector ring.

My original plan was to fabricate a new movement ring to fit the movement to the case. Unfortunately this particular case comes with a combined movement ring and rear gasket and while I felt confident in my ability to create a movement ring, with this case design I figured I was stuck using the ring that came with the case. As you would expect, with the Delrin spacer in place the movement ring needs to be shortened by that same 0.5mm:



So in a classic case of spending 100x as long to make the tooling as to actually do the job, I fabricated a mandrel to hold the somewhat soft movement ring securely on my lathe. I then ground the back side of a 1/4" lathe tool to make a suitable knife:


Once all that was done, it was a very easy process to pare that 0.5mm off about 0.1mm at a time.


After the slicing the movement ring is now flush with the back of the case:


I had planned to use a Stem Extender to adapt the tap-9 Elgin Stem to the tap-10 crown that came with the case. But Borel sent me the wrong thing -- the extenders I got appear to be tap-10 on both the male and female sides. I may yet make that change, but in the meantime it turns out that the crown that came with the movement fits this case tube just fine. (But probably lacks any waterproofness). And I had also ordered a couple of spare stems from Borel (the original stem was about 1 mm too short). So for the moment this is the result: