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RE: Grinding Mirrors

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Posted by Robert May on June 12, 2000 17:13:29 UTC

The supprising thing is that it actually costs about as much to make a mirror as to just buy one. What is happening is that the cost of handling the glass is so high and the time it takes to produce a mirror on a production line is so low (grinding a 6" is on the order of less than half an hour!) that a mirror can be ground and polished on a production line and then aluminized for about what you can do yourself.
What you do get when you grind yourself is the pride of having done it yourself. The best way is to go find the astronomy club near yourself and let them help you do the job. The tools for testing and the experience of doing it are all there ready for you to take advantage of. You can probably buy a piece of pyrex there for less than somewhere else. At the SDAA mirror making group, the cost of a 8" blank is $47.50 and a weekly charge of $2 for the room, supplies and experience. After that, it will cost you for the aluminizing of the mirror. Prices vary there depending upon what type of surface you want.
If you are really interested in low price on the next mirror, a plate glass (the only problem is a somewhat slower equilibrium time) mirror will drop the price a bit. Any glass shop can provide a 3/4"=1" thick piece of glass that big and basically round. You may want to get the glass square and make it round yourself with a coring tool which is easy to make and use. About 16:1 is about as thin as you should go for easy grinding and polishing.

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