Re: [ATM] Grinding the back flat

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

Any ol' chuck of glass or iron will do a good job grinding on the
backside.  My "traditional" method is to use a pipe end cap for
grinding to dig a hole in the glass and this also works well for
flattening the backside of troublesom pieces of glass.  For a
flatness check, just put some cheap paint on a piece of plywood
or such material that is basically flat and rub the glass over
the paint.  High spots on the glass will pickup the paint and
show where you need to grind some more.  A perfect surface will
be one that most of the surface picks up the paint.  This should
get you well within a thousandth of an inch which will be good
for a back surface.  For something better, finding another thick
piece of glass will do the last little bit of flatness.  I'll
also note that you can stop at 25 micron grit as this is going to
be more than fine enough.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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