How to insert a mineral glass crystal in a Pocket watch?

[Endeavor]

Yes, I've broken the old (scratched) mineral glass crystal of an open face pocket-watch

However not while taking it out but when attempting to insert it. I wasn't sure whether it was an acrylic or a mineral glass crystal and I used a press like as one would use to remove/insert an acrylic crystal. It came out fine and it didn't seemed to be glued; 43.1mm in diameter.

Still not sure whether it was mineral glass or acrylic, I attempted to insert the crystal using the press in the same "acrylic-insert" way but the crystal shattered into a 1000 pieces ..... now I knew it was a glass crystal

CousinsUK has a 43.1mm open-face mineral glass crystal but what is the safest way to re-insert these mineral glass crystal? Since there wasn't any glue, are these a kind of "snap-in" crystals?

Anybody with some tips & tricks?

Love to hear ....... thanks !

Edited October 28, 2022 by Endeavor

[Marc]

Heat up the bezel so that it expands then drop the crystal into place. As the bezel cools it contracts and grips the crystal.

[Endeavor]

Thanks Marc

Sounds logic, but don't you get the risk of that the crystal cracks due to the heat?

And than the other obvious question, how hot is hot enough? An hair-drier on "max" or a paint-stripper gun?

Edited October 28, 2022 by Endeavor

[Marc]

I suppose in theory the glass could crack through thermal shock but I've never had one go yet.

As to how hot, the hair drier will make no impact what so ever. A paint stripper gun would probably do it but I suspect might be awkward.

An electric hot plate works very well. You have good control over how hot it gets, and you can lay the bezel down on it leaving both hands free to manipulate the crystal. I have always heated up the bezel keeping the crystal at room temp, dropping the crystal into place once the bezel had expanded enough. However, it occurs to me that you could rest the crystal on top of the bezel while you heat it. Providing the rate of expansion of the bezel is significantly greater than the glass you could just heat until the crystal drops down into the bezel. As the glass would also be getting hot there will be less thermal shock, reducing the risk of breakage.

[Endeavor]

Sounds pretty okay to me

I guess you haven't seen my wife's hair-drier , but to avoid screwing up here $$$ hair drier, I have to go for my own el-cheapo paint-stripper

Not sure yet whether to leave the crystal cool and heat the bezel (since you never experienced a problem), or heat both until the bezel drops over

Anyhow, thanks for your help. Need to order one (or two?) crystals from CousinsUK and that may take a while .....

I'll be back !

[Endeavor]

@Marc; the watch-crytal has arrived (CousinsUK).

Inserting the crystal went actually much easier than I thought. I've a paint-stripper heating gun with 2x postions; 1 & 2.

My approach was to heat the "glass-ring" on the lowest position "1" for about 30-40 seconds ........ if that didn't work, I always could give it some more "whack" ("Gie it Laldy" for our Scottish friends ) , either longer on position "1" or go to position "2".

One thing I had to take into considerations; the PW has a silver-case and the hinges are "silver-soldered", so I didn't want to heat the "glass-ring" too high. I didn't want the silver-solder to melt.

Anyhow, my first attempt with about 40 seconds on the lowest "1" level of my "paint-stripper" turned out to be good enough for the crystal to drop in.

I did let the ring and the crystal cool down and all seems fine !! The crystal seems fully fixed with no heat-cracks !!

Thanks for your help !!

 

Edited November 10, 2022 by Endeavor

[Marc]

@Endeavor it's great when it just works

[KarlvonKoln]

I have a little coffee mug warmer that gets just hot enough.   I leave the bezel sitting upon it for a few minutes (since the warmer doesn't get very hot very quickly).  Then I use a little suction cup to pick up the crystal and place it in.  Sometimes it needs coaxing to pop into place but usually, if I've measured right, it settles in.  And when the bezel cools the crystal is snug.

[gpraceman]

I tried the heat gun approach, but that didn't work for me.  Then I remembered that we had a hot plate stored away.  Pulled that out.  With the heat gun I had to use a steak knife to keep the bezel from blowing away.  With the hot plate, I just set the bezel on it, keeping my hands free.

First try with medium heat didn't work.  Second try with medium high heat for about 5 minutes worked.  I kept the crystal at room temp and used a loop of tape to set the crystal down onto the bezel once it was hot.  Then I left it alone while it cooled.  The gold got tarnished from the heat.  However, some Never-Dull was able to remove that. 

[ManSkirtBrew]

On 10/28/2022 at 10:45 AM, Marc said:

However, it occurs to me that you could rest the crystal on top of the bezel while you heat it. Providing the rate of expansion of the bezel is significantly greater than the glass you could just heat until the crystal drops down into the bezel.

I don't have any knowledge to add specifically about inserting glass crystals, but this reminded me something my dad taught me while we were fixing cars and using a torch to remove stubborn nuts:

Yes, both the nut and bolt expand as you heat them, but so does the space between them.