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Rough Grinding Time

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Posted by Bill Wetterau on November 15, 2002 02:09:25 UTC

I'm working on my second mirror ever, hoping to make a 16" f5. My first attempt was an 8" which turned out to be about f7.5 when finished. On my first attempt, I was down to about the correct sagitta after about 2 hours of 80 grit grinding. I calculated the volume of glass to remove for the 16" mirror would be about 13 times as much for the 8" mirror. I'm already well over 13 times as many hours on the 16" mirror and still have a ways to go to get to the 0.2" sagitta I calculated. I'm curious - is the time required roughly proportional to the volume of glass which needs to be removed,or is something else going on here? I think I have been relatively consistent in technique and am using abrasive from the same lot as the first mirror. Is there any rough rule of thumb aboout how grinding time changes with mirror size (assuming all other variables are kept fixed)?

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