Re: [ATM] Grinding questions

["Bob May" <bobmay@nethere.com>]

I'd more trust the Sharpie test if it is done correctly.
Do slow strokes of the mirror and tool and verify if the black is evenly
being removed from the surface or there is a ring shape to the removal.
I'll note that rapid grinding can produce a ring structure as the heat of
the breakage of the glass off of the surface can cause sections to expand
and thus grind more than other sections until the heat is not making the
glass expand further whereupon that section then cools, losing contact with
the tool, which cools it more and other sections take up the stress of
grinding.  This is something that I've seen often in polishing more than
grinding but it does happen there also.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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