Re: [ATM] Polishing stroke

[Mike Lockwood <melockwo@uiuc.edu>]

Tom,

Polk, Tom wrote:
> Instead of learning to pad polishing behavior, I'm moving back to 9
> micron and pitch laps.

Sounds good.

> This is a 12.5" f/5.4., 0.72" edge thickness plate glass mirror. Is both
> TOT and MOT ok for both 9 micron and polishing? I've read somewhere fine
> grinding should be done TOT to prevent astigmatism. I have towels on my
> grinding/polishing stand to pad the mirror back.

Some also claim that MOT is the only way to avoid astigmatism.  The 
truth is either way works, but the back of the mirror must be 
supported evenly if you work TOT.

This usually means making sure the back of the mirror is flat, or a 
figure of revolution that is very close to flat (the back of the 
mirror has no astigmatism).  Then we put the mirror on top of 
something that supports it evenly (carpet, foam, etc) which sits on 
top of something else that is quite flat, which ideally is the top of 
the grinding stand.

Towels may or may not work.  They can develop creases and folds that 
can distort the mirror.  Rotating the mirror (when working TOT) every 
few minutes can help minimize astigmatism.

	Mike Lockwood


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