From: dan otto 
To: atm{at}shore.net
Reply-To: dan otto 


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You must not have searched in the right place there are many discussions
about this in the archive.  http://astro.umsystem.edu/atm/search.html

Look for casting, melting ...

I don't think anyone has been sucessful at making their own blank but there
is a lot of information about why it didn't work.

"Michael D. Crawford"  wrote:

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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You must not have searched in the right place there are many discussions
about this in the archive.  http://astro.umsystem.edu/atm/search.
html">http://astro.umsystem.edu/atm/search.html;
 
Look for casting, melting ...
 
I don't think anyone has been sucessful at making their own blank but
there is a lot of information about why it didn't
work."Michael D. Crawford"
<crawford{at}goingware.com>
wrote:
I would find it hard to believe that you could
save money on even a 20" blankby casting it yourself. You
need a kiln you can get very hot and keep hot forquite some time,
and cool down at a precisely controlled rate. The equipmentfor
that is likely expensive.Where you might save money
would be if you made a number of blanks. Once youhave all the
equipment then casting a single blank should be cheap. So if
youneeded, say, ten 20" blanks I could imagine saving some
money. You could payfor the equipment by selling some blanks, but
then it might be less effort tojust 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? TheCentral Maine Astronomical
Society sometimes has blanks for sale. I personallylusted after a
full-thickness pyrex blank they had, but wasn't able to buy itat
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.
CrawfordGoingWare Inc. - Expert Software Development and
Consultingcrawford{at}goingware.comTiltin" target="new">http://www.goingware.com/crawford{at}goingware.comTiltin
g at Windmills for a Better
Tomorrow.
 Do you Yahoo!?
The">http://us.rd.yahoo.com/search/mailsig/*http://search.yahoo.com">The
New Yahoo! Search - Faster. Easier. Bingo.
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