RE: [ATM] Sand-blasting a mirror blank

["Thomas" <tomjan@ozemail.com.au>]

How about an osilating arm with a diamond wheel equiped grinder on the
end? The arm's length is the ROC that you want, swing the arm and rotate
the blank. Move the pivot point towards the blank as you grind away the
surplus material. This should work out cheaper than the sand
blasting......

A couple of safety points, this should be done wet to minimise dust, be
aware of the shock hazards inherant to the idea (water and electricity
don't mix well), and wear a good quality dust mask.

Clear skies,
Thomas Janstrom
http://www.tjanstrom.com
http://www.norsewines.com.au
"Your nobody untill you've been ignored by your seventh cranio-facial
nerve."


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of N1XLP
Sent: Tuesday, 23 November 2004 10:55 PM
To: atm@atmlist.net
Subject: [ATM] Sand-blasting a mirror blank


I am currently in possesion of a 24"x5" fused silica, 135 lbs, mirror
blank that has the wrong curve on it. 

The current curve is around f/1 (the sagitta is about 1") and I would
like to "shave" down the outer zones for the overall shape to come down
to about f/5 (target sagitta of .33"). 

I have found a local sand blasting outfit that will do the work for me
(quoted me $100 over the phone)and I am wondering about some of the
issues with doing this before I start blasting.

I cant see grinding this out by hand. I would have Popeye arms in no
time. :-)

Can anyone enlighten me on the techniques, issues, and/or pitfalls? 

TIA!

-Phil
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