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[ATM] Richard's blanks...
I might add that the 9 inch Richard Schwartz f3.9 slumped mirror blank that I am shipping to Pakistan does not have the dimples that Bob mentions and is a very nice blank. I might have to change my mind about the usefulness of plate glass and try finishing one of Richards blanks myself. He does an excellent job of slumping the disks - I was quite pleasantly surprised at the quality. These would be a natural for finishing as a sphere and pulling to a parabolic shape.
The surface of the slumped blank will be very easy to get under control even if you have to bump up to 220 grit as a starting place. That is an enormous time savings over starting with a flat blank unless you just happen to have a diamond generator at your disposal.
Ken Hunter
Bob May <bobmay@nethere.com> wrote:
I've gotten several mirrors from Richard and all of them had
little dimples in them where some dirt or something like that was
resting on the mold when he slumped them. Those usuually took
about 6 hours or so of 320 grit grinding to eliminate, some
faster than others. I see the same basic problem happening with
your glass.
FWIW, Richard grinds the surface of themold to the ROC desired.
This tends to take out any of the high spots like you have on
your glass from the mold. In addition, your mold may have not
been well supported in the oven and thus slumped itself to the
astigmatic shape that you have from the slumping.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
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