Re: ATM where can I purchase a 12.5" f/20 mirror

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

I'll bet a dozen wets at 320 grit will get you most of that depth.  Starting
at 40 grit is something that I'd only do for a short FL surface on a large
mirror.  The depth of the cracking from the grit will be much more than that
depth and you will have to remove a lot of glass in order to get where you
want to be for depth and have a crackfree surface.
I find that using larger grits to be not worth the effort unless you stop
way short of the final curvature as the glass is so strongly affected by the
high pressures of the larger grit forcing the cracks deep into the glass.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net