ATM Too Thin?

[Anthony Stillman <atmer@flash.net>]

I've ponder this question before and each time arrived at a different
conclusion.  I've puffed up my shirt at a fellow ATM grinding a Pyrex pan
bottom and had second thoughts when I saw a photo of the first 8m Gemini
blank.  Perhaps someday I'll learn not to ridicule what I haven't yet
considered worth the effort. That aside, and in all truth, most of my
projects are driven by what materials come my way.  This is why I have a
Walter's blank.  And though unfinished, several hard hours figuring remain,
I am quite taken by its progress.  Further, holding it has turned out to be
far simpler than I believed possible.   Thus I've shed my 6:1 bias with
this project and as luck would have it, had my new 16:1 bias put to the
test almost immediately.  During a recent trip to a favorite junk store, I
came across a pane of soda-lime glass buried and damaged, and 24x28 inches.
I immediately examined it through my cross polarizers(1) and found it to be
well annealed.  But, at 5/8" thick, I was unsure.  I thought about it and
then bargained with the man until I started to consider that it might make
a fine coffee table and bought it.  Of course, a couple of days ago, while
at a neighbors garage sale, I had to ask and now, one trip to El Sobrante
later, I have a 36x60 inch piece of half inch thick annealed glass as well.

My intent is to cut these two panes up into disks and distribute most of
them to the list and at RTMC.  My objective is to get glass to people who
wouldn't ordinarily be able to afford it.  I would like to make the disks
as large as possible.  Ten and eight inch disks seem very reasonable to me,
but I would like to get input from the list before laying out a cutting
pattern.  Assuming no slumping I think 20:1 is about as thin a ratio as
this glass can go(2), but I'm open.  If someone wants something especially
challenging, I'll consider it.

What does the list think?  Ten and eight inches?  12.5 and ten inches?
Suggestions?

Anthony

PS  This post is with Mel's approval, thanks Mel.



1)  Yes they were in my shirt pocket, no I was not carrying a C compiler at
the time, yes there is room and you already know how I know.
2) Judging by the 30 inch dia. 1 inch thick (TRO) (insert hyperlink)  30:1
is reasonable for dedicated amateurs.