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Old 12-12-2011, 05:16 PM
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sopticals (Stephen)
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Join Date: Jun 2010
Location: Oamaru, New Zealand.
Posts: 226
Quote:
Originally Posted by rainwatcher View Post
I would be frightened of fracturing a 20" 19mm mirror during grinding. I guess it would be mounted on something but then you would have flexure problems.
Hi Peter, I have personally ground out the following sized mirrors using 19mm thick float glass: 18.5", 20.25", 22", 22.15", 25". No problems with fracturing, easy to grind and polish.The key with working with mirrors this thin is to have a solid flat surface for support to work on, plus to float the mirror on several sheets of wet newspaper, or artificial grass, or such like. Because float is softer than pyrex or quartz it polishes out very quickly, so in the figuring stage its a good idea to use rouge instead of cerium oxide, as the cutting action is much slower, this gives one much more control over developing the figure required. Also by using rouge one is more likely to avoid a rough (dog biscuit) finish, which can be image destroying.
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