From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


The thing that you have to remember is that when grinding two same sized
discs, the one on top turns concave while the one on the bottom turns
convex,  This can be negated by applying pressure very unevenly to the two
but normally, this is what happens. I'd go make another tool with some
fresh tiles (you probably have plenty of tiles and plaster if you bought
from original sources rather than a mirrormaking supply) and bed them in
with the 120 grit, trying to get the ROC to where you want it to be.  Don't
worry about getting 100% of all of the tiles to be fully ground on the
surface as a few tiles that aren't fully grinding will still work just
fine.  As you go down through the grits, make an occasional measurement for
the ROC and adjust the mirror to be on top or on the bottom depending upon
your results. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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