Re: [ATM] Ain't got no shperometer

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

A reasonably decent spherometer that you can move from one spot to the other should be able to locate gross lack-of-sphericity if the measurements change noticeably. But, iIf you are dutiful in rotating everything frequently, systematically, and somewhat randomly when you grind with finer and finer grits, then it is very, very difficult to avoid getting something very, very close to a sphere.
Grind more, worry less.
Guy

ArtfulBodger <artfulbodger@earthlink.net> wrote: Michael, David, um ... a spherometer isn't good at testing 
sphericity?  How come?  Do you mean the fact that it can't check near 
the edge of the mirror?  I'm guessing that that's what you have in 
mind, but maybe not.  Could you (or someone) elaborate, please?

David, yep, Foucault would do the job; but I only have access to a 
Foucault tester on Saturdays.  Gotta build one of those, too: it's on 
The Other List, the scary list....

About the Sharpie test, I can still do it with the finer grits, can't 
I?  25u, 12u, and like that?  I guess the mirrors should be spherical 
before then, and they were, but I'd like to check 'em again (and 
again).  Make sure they're good & round before I start polishing. Can 
I do that?

Pete

-- 
Artful Bodger
http://www.artfulbodger.net
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Guy Brandenburg, Washington, DC
My home page on astronomy, mathematics, education:
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or else 
http://tinyurl.com/r6fh2

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