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Re: [ATM] Spherometers and sphericity
Guys (and ladies if there are any on the list):
I must be seriously out of touch. I never do any testing of the surface
whatsoever until I am fully polished out. I made an exception to this rule
a couple of months ago when I went to Guy Brandenburg's telescope workshop
in at the Community Center in Chevy Chase, DC. I put my 12.5 inch f/7 mirror
on Guy's test stand after I had about seven and a half hours of polishing
completed. (Before I brought it to the shop) The mirror came up as slightly
corrected the edge was perfect (pounds his chest). I was dissapointed as I
always aim for a sphere first then go for the correcrtion after polishing. I
the correction was due to my spending 1/2 hour more time with the mirror on
top then the tool on top, I have now put another seven hours of polishing
into the mirror. I think I'll be good to go.
I adopt Guy's comment, Grind (polish) more, worry less.
Francis J. O'Reilly
----- Original Message -----
From: "Bob May" <rmay@nethere.com>
To: <atm@atmlist.net>
Sent: Wednesday, November 28, 2007 6:40 PM
Subject: Re: [ATM] Spherometers and sphericity
> Any furrow that you may dig with a piece of grit will go away
> with the next wet, providing that the grit is the same size as
> you have ben using on the mirror at that time. If the grit is
> larger, you need to clean up the stand and do the test again.
> I'd advise against the pencil testt on finer grits due to the
> grits that may be in the lead of the pencil - they don't size the
> lead so that we can do that test!
> I'll do the Sharpie test all the way down to the five micron
> level as the ink is quite thin on a Sharpie pen )black color,
> permenent ink_ so it will easily wear away. I'll note as others
> have is that the Sharpie test really isn't all that great for
> this purpose as it indicates more where the grit is grinding.
> Bob May
> Due to the large volume of SPAM thaat I'm getting, add an open
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> your post~
> rmay at nethere.com
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> http: slash /bobmay dot astronomy.net
> Replace the obvious words with the proper character.
>
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