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

["Ken Bertapelle" <kenb@cqg.com>]

Bill,

 Thanks for the terrific reply.  I haven't yet plumbed the depths of
everything you said, but I'll study your note carefully as I get into the
further stages of my project.

Over the weekend I finished grinding with #220 (after a total of 5 hours)
and began with my next grit, which is SIC #320 microgrit.  Now for a dumb
question:  What's the micron size of #320?  Or more generally, what's the
conversion factor between microns and ordinary grit numbers?   My plan is to
grind about 3 or 4 hours at #320, then proceed to microgrit WCA 12 micron,
then WCA 3 micron, then begin polishing.  I already have these abrasives on
hand.  Is this plan consistent with your recommendation?

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.