Re: [ATM] Grit size

["David Harbour" <scarab2@cox.net>]

Richard,

I strongly urge you to use at least a 15" diameter tool, made this way; my 
largest was a 14.25" tool, though it was not a subdiameter tool, considering 
that the mirror was a 14.25 incher. However, the use of a tool at least 3/4 
the diameter of the blank is recommended to reduce to an absolute minimum 
the risks of grinding in any trace of astigmatism during the latter stages 
(more care and precaution is called for with a smaller than 3/4 diameter 
tool).

Make your tool this way:

http://www.atmsite.org/contrib/Harbour/Tool.html

Look at the first picture. Primary, 16", tool, 13.1". I got an unbelivabley 
silky fine grind. Mirror and tool in the picture are now to a nearly give 
away price; I know the man who has these; he is no longer interested in the 
project, I first saw them when I was fourteen (a very long time ago). He has 
had them well over 40 years. The primary was cast by Corning in the 
thirties, one of the test blanks leading up to the development of methods of 
casting pyrex, for the 5 meter Hale reflector. I think the last time I 
talked to him, he said he would take $200 for both. I am certain he would 
come down to $150.

Davey
N9606H


----- Original Message ----- 
From: "Richard" <cnc@cncservo.co.uk>
To: "ATM List" <atm@atmlist.net>
Sent: Thursday, March 09, 2006 11:49 AM
Subject: [ATM] Grit size


> Hi ATMers,
>
> I'll be taking delivery of a 20" Pyrex blank machine generated
> to 120" ROC. I will be taking it down to 110" ROC which is about
> a 1mm change on the Sag.
>
> Anybody care to recommend a grit size to go with a 10" or 12"
> tile tool on a machine grinder please?
>
> -- 
> Best regards,
>  Richard in the UK
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


_______________________________________________
ATM mailing list http://www.atmlist.net/