Re: [ATM] Rough grinding, focault test

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

The posts are on the archive system so they aren't lost.
The foucault test isn't done until you have a fully polished
surface.  The grain of the ground surface won't reflect the light
correctly to be able to do the Foucault test.  The best you can
do in this regard is the flashlight test (described on my
mirrormaking article on my pages) which can get you to about 1/2"
of the true ROC of the mirror.  For a Newtonian mirror, this is
more than accurate enough.  For more accuracy (I'm working with a
guy who wants some surfaces to less than 0.1" so he is polishing
the surface and then doing a Foucault test to get the exact ROC
of the surface.  If you're off, you then go back to 12 micron and
grind some more for the ROC you want and then polish it again.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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