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SudoHalt

Replacing Mineral Crystal with Acrylic? Which Size?

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Hey there,

I accidentally cracked the crystal on my Mondaine watch, and I would like to replace the original mineral crystal with Acrylic. The Original crystal is friction fitted into a plastic gasket.

On my vernier calipers, the Original crystal measured at 38.2mm. I have a simple Crystal/Back Cover Press to insert a new crystal, but I assume this approach would be best for replacing with Mineral or Sapphire.

  • Can I use a Crystal Press to friction fit acrylic crystals? Is there a difference in the approach when the new acrylic crystal is flat, low-domed, or high-domed?
  • I am somewhat confused as to the size of the replacement Acrylic Crystal... Do I go with the same size? If not, how much larger?

Thanks!

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You can press an acrylic crystal with a tension ring. For example GS Diver Tite. I would go with a 38mm or 38.1mm. Because if you dont you will never be able to press it in since it expands when pressed and in some case tension ring slips out.

GS Lo/Hi dome can be compressed in using a brass jaw type crystal remover. In this case you will need to go 38.4mm because the jaws grip the crystal and it compresses it then when set into the bezel or case the jaws are released expanding the crystal to set in the case.

flat crystals will need to be glued and any acrylic crystal can be glued except tension ring crystals.

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4 hours ago, SudoHalt said:
  • Can I use a Crystal Press to friction fit acrylic crystals? Is there a difference in the approach when the new acrylic crystal is flat, low-domed, or high-domed?

Yes, with the correct dies. See attached STK document about fitting "snap-in" crystal with a press as opposed to a jaws tool (crystal lift).

8836_Sternkreuz R19 Snap In Glasses Pages 12 to 29.pdf

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Wow thanks a lot!

I got a bunch of homework to do on this... based on what I am understanding, the Acrylic crystals with tension rings could be press-fitted with the crystal press given that we use the correct size of dies, and those crystals would do fine without that plastic gasket, isn't it?

What I am confused about is the plastic gasket that was used to friction-fit the mineral crystal in place. Do I remove it before fitting the acrylic crystal? If yes, then I believe that I have to measure the new diameter of the "dial compartment".

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I have actually went over that guide. However I am still confused about the sizing choice of acrylic crystal if the watch was designed originally to go with Mineral Crystal.

What I am trying to say is... which one of these is true?

  1. I can fit the acrylic crystal into the case using the gasket that came with the original mineral crystal. Could the crystal gasket break or wear out during the assembly of the acrylic?
  2. I need to remove the original gasket and fit the acrylic crystal without a gasket. I have heard that Acrylic crystals could provide decent waterproofing without a crystal gasket.

 

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Hi  If you are going to replace the mineral crystal with an acrylic one without the gasket it is possible but you will need to measure the case seating of the watch and what ever the measurement is add 0.01 but you will need a claw insertion tool and pick up table to do that and also probably some glue/sealant to put round the case, Usually somthing like Minicol UV curing cement to ensure water resistance.

May I ask what is the reason for the change as the minerals are harder and scratch resistant,  acrylics pick up lots of marks but they can be polished out in in most cases.

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Thanks guys! For now that sounds good to me. I will post back here if I have any questions or trouble.

I am considering Acrylic crystals because they are more shatter resistant than both mineral crystals and Sapphire. Yes, acrylic crystals are brittle, so when you drop them they could develop a crack, but Acrylic crystals don't shatter and fall apart when they crack.

It is nowhere as hazardous when cracks happen as fragments will not fly around when a crack happens, and they can maintain a slight degree of splash resistance.

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2 hours ago, SudoHalt said:

I am considering Acrylic crystals because they are more shatter resistant than both mineral crystals and Sapphire. Yes, acrylic crystals are brittle, so when you drop them they could develop a crack, but Acrylic crystals don't shatter and fall apart when they crack.

It is nowhere as hazardous when cracks happen as fragments will not fly around when a crack happens, and they can maintain a slight degree of splash resistance.

Really? I have not see any reports or mineral glass crystals shattering so terribly. The expected use of a dress watch should not involve such potential destructive shocks.
I would not replace a mineral glass with acrylic, but I would replace it with sapphire, because scratching is the actual, common and annoying occurrence.

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Ok  you have your reasons and i stand by that, but I agree with jdm I have not seen a mineral shatter except under extreem circumstances like being dropped onto a hard surface, but I have also seen acrylics crack under the same circumstances.  Cheers.

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52 minutes ago, rodabod said:

I've actually had a sapphire shatter before, never mind a plain mineral glass. That's why acrylic are almost always used for military watches.

Actually mineral glass is more resistent to impact than sapphire. That's why is still fitted to some true diver's watches, a choice that raisises criticism by some.

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4 hours ago, jdm said:

Actually mineral glass is more resistent to impact than sapphire. That's why is still fitted to some true diver's watches, a choice that raisises criticism by some.

That's interesting to know. CWC use plain mineral glass on their divers, but it is very, very thick.

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