RE: ATM 21" f/6 report: status and questions

["Jeff Arnold" <scoper10@hotmail.com>]

Ken:

#320 is around 35 micron ( Texereau, pg. 29, second edition)......I'd get 
some 20 micron after you're done with the #320 before going on to #12 as the 
#320, if that's carbide, can leave larger pits that the equivalent aluminum 
oxide micron grits. Using 20 micron would just be a little finer but leave a 
very fine finish free of any large pits.  The 12 micron then would smooth 
further, etc...... Using 12 micron after #320 may take you awhile to be SURE 
ALL previous pits are gone. Some may also recommend stopping at 5 micron. If 
you're careful, 3 micron is ok, just remember to keep the tool/mirror at the 
same temperature and stay very clean - scratches can be easy with 3 micron - 
but since you have some - use it.

Jeff with .02 $



>question:  What's the micron size of #320?  Or more generally, what's the
>conversion factor between microns and ordinary grit numbers>Thanks again, 
>and clear skies.
>
>- Ken
>
>-----Original Message-----
>From: owner-atm@shore.net [mailto:owner-atm@shore.net]On Behalf Of Bill
>T.
>Sent: Friday, October 06, 2000 11:13 PM
>To: atm@shore.net
>Subject: Re: ATM 21" f/6 report: status and questions
>
>
>
>Ken,
>
><snip>
>
>I'd go from 220 grit right to either:
>--25 micron then 9T (9 micron, with talc)
>or
>--30 micron, 20 micron, 9T
>
>You can also do 20, then 9, but you'll need to spend a lot of time at 20. 
>Of
>course sequences with more grit steps will work, too, with more cleanups.
>Before advancing grits be sure to scrutinize all parts of the mirror with a
>strong magnifier, a strong cross light, and an eagle's eye. The outer 1/2"
>can be more of a problem on large mirrors than small, so spend a lot of
>inspection time there. If you swap positions, you should be able to get
>through all the grits after 220 in no more than 5 or 6 hours with a large
>safety margin.
>
><snip>
>
>Bill T.
>
>

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