Re: [ATM] Astigmatism

["Mitchell R" <funnybone101@embarqmail.com>]

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Che Ers
Sent: Wednesday, January 23, 2008 12:36 PM
To: ATM Mailing List
Subject: [ATM] Astigmatism

Hi,

Is a 7" or 8" X 0.75" blank at a greater risk of ground-in astigmatism than
a 1:6 thickness blank? If yes, how? And how would one avoid it (except, of
course, by getting a full-thickness blank : )? Focal ratio would be more
than 7.

Thanks,

Zain

     Technically yes it is. The thinner you go the more a blank flexes under
grinding and polishing pressure. 6:1 is the old ratio which works fine but
is not necessary. If you support the mirror/tool (which ever is on the
bottom) with soft rubberized foam/newspaper, etc and don't used overly heavy
pressure you should be fine. Rotate them often. A blank in the size you
mentioned is barely considered "thin" by what a lot of people have pulled
off. I've seen a few 16" mirrors out of .75" plate glass on the net, a 7" or
8" should be no problem. Good luck!

Mitchell  




 
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