Re: [ATM] Ain't got no shperometer

["Francis J. O'Reilly" <foreilly@bestweb.net>]

Pete,

A spherometer cannot verify sphericity (?) It can measure the depth of a
hole, that's about all. It cannot come near to measuring with the accuracy
necessary . It measures in ten thousandths, mot ten millionths.

Further, it does not check the entire curve, just very discreet spots on the
curve.

Try a foucault test.

Regards,

Francis J. O'Reilly
----- Original Message ----- 
From: "ArtfulBodger" <artfulbodger@earthlink.net>
To: <atm@atmlist.net>
Sent: Tuesday, November 27, 2007 1:05 PM
Subject: Re: [ATM] Ain't got no shperometer


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


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