Re: ATM Mirror thickness question.

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

The basic spec for a full thickness mirror is a 1:6 ratio.  Grinders usually
don't consider a mirror to be a real thin one until the ratio gets to about
1:15 or higher.  With your mirror at 10:150, you are right there at the edge
of it being a thin mirror.
What this means is that you need to insure that the mirror doesn't flex
improperly when grinding (especially in the finer stages) and astigmitism
get ground into the glass.  Grind the backside flat and use some outdoor
(the plastic stuff) to support the mirror when it's on the bottom and when
it's on the top, don't press hard on one spot for very long - rapid turning
(10deg./stroke or so) will reduce the probablility of producing astigmitism
in the surface.  This also needs to be attended to when polishing and
figuring and you should be prepared after starting polishing to go back to
grinding to get rid of any astigmitism that you may see.
Otherwise, have fun making a mirror!  This one will be a bit more exciting
than most to do but is quite doable.
BTW, you really can't glue two pieces of glass together and expect decent
performance as the glue line will prevent the rapid passage of heat and thus
the glass will take a bit longer to settle out if it ever does.  Mirrors are
very sensitive to thermal effects and the effects change the surface shape a
lot!
Bob May
My new web space address is http://webu.wigloo.com/bobmay/ or
http://nav.to/bobmay
and my new email address is bobmay@nethere.com
Bob May