Hi Everyone:
I'm working on a 32" f/5 BVC mirror. Right now, my focus is on getting the back of the blank prepared so as to minimize the chances of developing astigmatism as I grind and polish the face. The back has already seen a very coarse degree of flattening--it is my understanding that BVC blanks are pregenerated by slumping on a mold, and that afterwards, the convex back side is ground (very roughly) flat. I want to clean up the back side by grinding it flat through #220.
All of that is no problem. My question is about wedge--specifically, how much wedge is acceptable in a blank of this size? Using a caliper, I find that there is about 0.015" difference between the thickest and thinnest points around the edge of the blank. Is 0.015" of wedge across a 32" blank acceptable, or should I be trying to cut down this wedge before grinding the back of the blank flat?
Thanks for any advice.
Doug Hudgins
Dumfries, VA
I'm working on a 32" f/5 BVC mirror. Right now, my focus is on getting the back of the blank prepared so as to minimize the chances of developing astigmatism as I grind and polish the face. The back has already seen a very coarse degree of flattening--it is my understanding that BVC blanks are pregenerated by slumping on a mold, and that afterwards, the convex back side is ground (very roughly) flat. I want to clean up the back side by grinding it flat through #220.
All of that is no problem. My question is about wedge--specifically, how much wedge is acceptable in a blank of this size? Using a caliper, I find that there is about 0.015" difference between the thickest and thinnest points around the edge of the blank. Is 0.015" of wedge across a 32" blank acceptable, or should I be trying to cut down this wedge before grinding the back of the blank flat?
Thanks for any advice.
Doug Hudgins
Dumfries, VA
