From: "Michael D. Crawford" 
To: atm{at}shore.net
Reply-To: "Michael D. Crawford" 


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{at}goingware.com

       Tilting at Windmills for a Better Tomorrow.

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