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Fitting a watch crystal


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Hello again. Following my request for help finding a watch back the only option seems to be fitting a low dome crystal instead so the back becomes see through, curtesy of philipk5

My question is how much bigger than the actual size of the hole should a watch crystal be to ensure a tight fit but still fit in.

The diameter measures 27.8mm and as it's only a cheap watch which I want to fix as usable for my son but I don't want to spend loads of money buying a range of sizes.

Any advice would be appreciated.

Thanks, Mike

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I have always heard that it should be the same size as the opening, But in my adventures I have found that the same size is sometimes a bit small.Sometimes spot on.If you go the next oversize its usually a safe bet.

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If you still find it loose and you need it to stay put.....on a cheap watch....just a tiny bit of super glue applied to a well cleaned oil free case..three or four tiny spots..so you wouldn't notice it.and the crystal will stay in place .

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If the internal diameter of the case measures 27.80mm then a 28.00 low dome acrylic should be able to be fitted using a "claw". It needs to be tight enough to provide some sort of seal and not fall out but not so tight it won't fit!!.

If you use any sort of adhesive it will make removing the acrylic somewhat difficult in the future (probably next week when a proper case back turns up). 

Also make sure that the crystal doesn't foul the stem &/or pushers and any moving parts.

Photos of your watch front & rear may remind someone they have something in their scrap bin?

Hope this makes sense, and helps keep another watch in use.

Cheers

Phil.

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A simple cheap alternative would be to make a case back from a CD (Compact Disc)

I have a habit of stringing up CD's in the garden. After they have weathered the coating comes off and they are clear but not as transparent as a watch crystal. Also the ones I have had are 2 part laminates which easily separate after weathering. I have used these in the past for emergency crystals in cheap watches.

In this case you could use a new CD. Cut out a circle which fits tightly into the case. Cut another circle which fits over and to the overall diameter of the case and glue the 2 together. Alternatively just cut a circle which fits the overall diameter of the case and glue it on but glue it all around so to seal it. Trim if necessary with a file, sandpaper etc.

It should not scuff up as quickly as a crystal. I use scissors to cut after the CD has delaminated ie one half but I use my scroll saw to cut a full thickness CD

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3 hours ago, Alaskamick said:

Hi JerseyMo, It's a snap back.

you may than have to measure the inner dimension of the crystal if there is a lip.  Either way it goes I would not recommend the use of any adhesive.  

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   the use of glue, on the crystal, will reduce the value of any watch!  if you must use it,  use epoxy,  on the bezel, because it can be removed easily  with 200 degrees farenheight.    there are many instructions on proper "crystal replacement".  vin

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If you have the dimensions I can have a crystal custom made to any profile or flat, costs are at most two euros.

I also have abundance of desent european quality vintage NOS flat crystals at low price.

Cutting is done with grinding stones.

To alter one and make fit yourself. Use a razor blade to shave off the circumference down to a perfect fit. 

The art of perfect fit is patience.perfect fit gathers no or minimun dirt. 

The diameter is to be 2/100 of a millimeter larger for tight fit.

If polymer try heating the case , insert the crystal, keep under press, raise tempto get the polymer melt fit. 

A good press insertion dose a lot of good for flat crystals.

Regards joe

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