Watch crystal sizing question/issue

[ooteenie]

Hello, 

I am working on a watch that needs a crystal. The watch has a “puck” like design ( probably not the official term. What i mean is the movement sits in the back and the crystal fits directly on that, and movement goes in from front. This whole unit then goes into the outer case, with bezel and lugs. 
 

the challenge is the crystal needs to be a specific internal diameter to fit. The existing crystal is cracked, but I was able to get measurements. The outer diameter is 28.2 mm, and the inner diameter is 27.2, and the thickness at base measures 0.5 mm as expected. All the crystal i have that are 28.2 OD are smaller than 27.2 ID. Does anyone either know a brand which would fit, or alternatively how to reduce an ID by 0.2 mm without having a lathe or other specialized tool? 
 

i thought about ordering a GS and Sternkreuz but i figured if someone knew it could save me the cost of two crystals neither of which might fit. 
 

thank you for any and all input. 

[Neverenoughwatches]

11 minutes ago, ooteenie said:

Hello, 

I am working on a watch that needs a crystal. The watch has a “puck” like design ( probably not the official term. What i mean is the movement sits in the back and the crystal fits directly on that, and movement goes in from front. This whole unit then goes into the outer case, with bezel and lugs. 
 

the challenge is the crystal needs to be a specific internal diameter to fit. The existing crystal is cracked, but I was able to get measurements. The outer diameter is 28.2 mm, and the inner diameter is 27.2, and the thickness at base measures 0.5 mm as expected. All the crystal i have that are 28.2 OD are smaller than 27.2 ID. Does anyone either know a brand which would fit, or alternatively how to reduce an ID by 0.2 mm without having a lathe or other specialized tool? 
 

i thought about ordering a GS and Sternkreuz but i figured if someone knew it could save me the cost of two crystals neither of which might fit. 
 

thank you for any and all input. 

Match up the inside diameter and reduce the outside diameter if possible.  Reducing the od is easier. 

[ooteenie]

40 minutes ago, Neverenoughwatches said:

Match up the inside diameter and reduce the outside diameter if possible.  Reducing the od is easier. 

The issue here is if I measure progressively larger crystals, the Id doesnt scale with the OD. So while a good idea, i would likely need a much larger crystal, maybe 1mm bigger OD and i would then have a very thin outer layer prone to cracking. There must be a brand that has a 0.5 mm thick rim atthe base. 

[Geotex]

Is your "puck" watch the same as the "capsule" or "module" types discussed in the thread below?  

 

[ooteenie]

That is exactly it, but not benrus branded. I have a benrus one too, but that crystal  was fine. The drawing helps in that post. I may try to grind the ledge on the crystal i have, the OD seems to be perfect, just a pesky 0.2 mm to remove. Worth a shot anyway. 

[Marc]

You could have a look here.

There's a 28.2x27.1 which may work, or a 28.5x27.2

Either would be a feasible starting point to fettle to the proper fit.