Watch crystal internal diameter question

[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. 

Bumped myself, didnt see subforum so i moved this there