[ATM] Is it possible?

[Ralph <wolfteacher@gmail.com>]

Hello all,
I am new to ATM. My first experience was throwing a 6" ebay mirror in
a tube and being surprised at what I could see. My second experience
is involving getting an old 10" ebay mirror recoated and we will see
how that does.

But my post currently involves the following challange. I went out and
bought an old 20" porthole ($28 total cost to me). I cut off the
bronze frame and was pleased to find a nice chunk of 3/4" glass that
was 16.5" in diameter. It is in prettys good shape with some surface
scratches that I'm sure will grind out. No large internal bubbles
although there are a few small ones near the surface... i am hoping
these will grind out as well.

Do you all think I have half a chance of successfully grinding this
into a thin mirror if I use a cell with lots of points of support? I
don't mind making it a long focal length to keep the center from
getting to thin... This will be my first experience at making a
telescope mirror. Am I being too ambitious trying to tackle a 16.5"
thin mirror for my first experience? I think this is a motivating
factor. How many hours will it take? 100?

What is the lowest f-ration anyone would recommend this getting ground
into? Have others had success grinding thin mirrors from 3/4" glass?

I know I have alot of questions,
Thanks,
Ralph
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