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Vacherin

Making a display back window in a plain back

Question

I have a few generic cases that I could chuck up in the lathe and machine a recess in the back with tapered sides. The idea is then to heat the back, put the glass in the freezer, and shrink fit it. Can I just use mineral glass (ie, from a window!). I have never worked with glass other than cutting panes for house windows (not easy!). I guess I can grind the glass while super glued on a mandrel, using a dremel while the glass rotates?

What sort of taper angle should I aim for? Any idea what thickness of glass I should use?

I have access to a surface grinder with a magnetic table. I was thinking that if the glass was thick when I fitted it I could take off a mm, then hand polish using silicon carbide powder on a glass block.

Is this all impractical?

I did consider making a screw back from scratch, but was not sure how to cut the thread, and I still would need to know how to fit the glass.

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Round mineral glasses are available in all sizes for little money.
Thickness starts at 0.8mm afaik. 
They are glued in or pressed using a gasket.
Window must have 90 deg edges. 
A too thin back can be an issue, test before cutting!

Frank

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I think if you try to shrink fit it it will break, if not upon installation then down the road from being under tension. As above, a gasket or glue are the usual ways to install. Be wary when cutting away the inside of your back as you get toward the tapered sides you will lower the level of the glass, possibly crashing into the movement. On one odd customer request I once added a pressed in stainless ring to the opened back which blended in and added the necessary height.

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Another option would be to cut it to fit a low dome acrylic crystal.you could install it with a crystal lift.nice tight fit.you might even be able to install one in the back of the case with no machining of anything..I have never tried it.but it might just work

Edited by yankeedog
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Nickelsilver that is an amazing picture thanks! I have not thought about the crystal hitting the movement. That looks like an attractive way of getting round that problem. Yankeedog I did see an Omega on here that someone had simply fitted a crystal to the back of.

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On ‎12‎/‎17‎/‎2018 at 9:02 PM, nickelsilver said:

Here's the one with the added ring. Customer had a case he wanted to use for sentimental reasons and fit a vintage monopusher chrono in. Not the best pic but only one I have. Movement was old enough to be pin setting you can see the added pin next to crown. fe146f414188838a99088d445e65d485.jpg&key=9060778ac461341f882b6a1b170bbe0fdebd1657667f16670a13dcbf7e7ac507

 

 

Sorry, did you make that case back?  That looks incredible!  I guess, thinking about it looking at that picture, it's a case of machining a case back and then slotting a crystal into it.  I also suspect it's one of those where it's easy to explain but difficult to do well/right!

I have a watch for which I have been considering how good it would look with a clear back, hence my interest!

Cheers

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1 hour ago, MattWatch said:

Sorry, did you make that case back?  That looks incredible!  I guess, thinking about it looking at that picture, it's a case of machining a case back and then slotting a crystal into it.  I also suspect it's one of those where it's easy to explain but difficult to do well/right!

I have a watch for which I have been considering how good it would look with a clear back, hence my interest!

Cheers

The customer wanted to keep as much of the original case there as possible, as I recall this was the last case from a family watchmaking endeavor in the 80s. I opened it up and added the ring the crystal is fit into, it's press fitted into the back and the crystal if fitted in with a gasket. The movement they wanted to fit was significantly thicker than what was originally fitted. It probably would have been about the same work to make it up entirely from scratch.

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