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Fitting a pocket watch crystal - which tool


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Sometimes a special transparent (such as hypo gs) cement can be/was used for fitting certain types of glass on certain types of cases/bezels.

First of all those claw like lift tools do NOT work on mineral glass. They work on acrylic which is more elastic than mineral.

You're supposed to press fit it (if it fits that is). As I said, some jeweller's cement might be necessary if it's a bit smaller or if for some reason it wiggles around or rotates/moves around.

You would have to use a watch glass press for this one if it's a tad larger.

Edited by Chopin
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I got two sizes of glass just in case.

The bezel has an overhand/lip so I though the crystal would need to be compressed/distorted to fit?

P4250016.thumb.JPG.6b892611464d69ebb0401f3e8afaf1ed.JPG

 

I've got one of these...

press.thumb.jpg.dde3a612d90f412e7f74323601147d7e.jpg

 

It a cheap 'n' nasty.

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35 minutes ago, p2n said:

I don't know what the original was - it was missing when I got the watch.

You need to fix with cement, glass won't work as "friction fit" without a nylon gasket, as it will break.

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Yes that is the one. I would say you could also use acrylic but I'm guessing the original one, given the age, may have used glass.

Careful not to buy one that is TOO small. Just enough so that it'll fit in there.

Edited by Chopin
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Aren't some of these old crystals fitted by heating the bezel?  Maybe I dreamed it up, but I thought pocket watches with mineral crystal glasses required the bezel to be heated in order to expand the opening to accept the crystal.

I haven't done many pocket watches so forgive me if I'm leading us astray here.

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9 hours ago, RyMoeller said:

Aren't some of these old crystals fitted by heating the bezel?  Maybe I dreamed it up, but I thought pocket watches with mineral crystal glasses required the bezel to be heated in order to expand the opening to accept the crystal.

I haven't done many pocket watches so forgive me if I'm leading us astray here.

Not dreamed up at all, that is exactly how they should be fitted.

Do NOT try to press it in, it will just break, particularly if it is a bevelled edge crystal.

You could use a smaller crystal and cement it in but this is a compromise for an under-cut bezel; the degree of the compromise depending on whether the crystal has a bevelled or 90 degree edge.

The correct approach is to use a bevelled edge crystal that is slightly too big to drop in, heat the bezel so that it expands, drop the crystal in place and when the bezel cools down and contracts it should be a nice snug fit so that the crystal doesn't rotate in the bezel.

crystal fit.pdf

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TBH I've always just used a small electric hot plate. Lay the bezel on it and keep trying the crystal until it fits, then switch off and let it all cool down slowly. I've never measured the temp.

However, a quick Google search turns up this site;

https://www.engineeringtoolbox.com/linear-thermal-expansion-d_1379.html

If I'm using it right then it looks as though heating a brass bezel from 20C to 200C should give you just over 1mm expansion across the diameter of a 35mm bezel aperture.

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I really hate to admit this but I have found that a bead of lock tight glue works better than GS Cement for glass crystals that are not friction fit. I do agree with Mark on his recommendation (now doing the "I'm not worthy" hand gesture), however, i have tried all of these glues and the lock tight glue works and also cleans up nice if you have a future issue. I would recommend getting a acrylic crystal and fitting it with your cheap tool. I bought a GS Tool which works like a charm.

Sent from my GT-N5110 using Tapatalk

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I did try with a hot plate - not sure what temp it got to but it was too hot to touch. I think the crystal I got is a little too large so ordered the next size down.

 

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  • 4 years later...

I would think that you should be able to leave the  glass "crystal" on the bezel letting them both get hot together.  Glass has a very low coefficient of thermal expansion in comparison to most other materials.  This may reduce the risk of cracking as the temperature of the glass quickly changes when dropped into the hot bezel. The difference and rate of change may be to high for the glass.  When the glass drops in, turn off the heat and let them both cool very slowly.  Not sure about an actual crystal crystal.  If anyone knows about this, I would appreciate their correction or corroboration.

Thanks

Shane

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