Re: ATM About making a glass blank

["Michael D. Crawford" <crawford@goingware.com>]

I would find it hard to believe that you could save money on even a 20" blank
by casting it yourself.  You need a kiln you can get very hot and keep hot for
quite some time, and cool down at a precisely controlled rate.  The equipment
for that is likely expensive.

Where you might save money would be if you made a number of blanks.  Once you
have all the equipment then casting a single blank should be cheap.  So if you
needed, say, ten 20" blanks I could imagine saving some money.  You could pay
for the equipment by selling some blanks, but then it might be less effort to
just convince your boss to give you a raise.

May I suggest you find a low-cost blank at a swap meet or through a club?  The
Central Maine Astronomical Society sometimes has blanks for sale.  I personally
lusted after a full-thickness pyrex blank they had, but wasn't able to buy it
at the time.

On the other hand, I heard (probably on this list) that the Mt. Wilson 60"
mirror was cast from wine bottles.  I think bottle glass would work fine, but 
you would want them all to be the same kind of glass, and not a mix of 
different types because you wouldn't be able to get them to blend evenly when 
melted, which could cause warping from thermal expansion and contraction.

Mike
-- 
Michael D. Crawford
GoingWare Inc. - Expert Software Development and Consulting
http://www.goingware.com/
crawford@goingware.com

       Tilting at Windmills for a Better Tomorrow.