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19mm * 10 Inch Mirror

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Posted by Ian McKernan on August 8, 2002 05:18:41 UTC

Hi! My current obsession is polishing a 10 inch mirror out of 19mm plate glass. Its actually a bit thinner than that now since i ground a lot of glass off ( i made a few stuff ups ) by overshooting sagitta and taking out some scratches. Im going to make a 9 point cell for it.Overall it seems to have gone pretty well as a project.

One of the other guys in our group is doing a 5 inch out of the same stuff and he trepanned out his own blank from a small slab using a homemade cutter in a drill press with lots of 80 grit. 19mm is about the thickest plate i could from a local window maker, and after a lot of shopping around it cost about 40% of what a pyrex blank would have. It grinds and polishes faster than pyrex, and didn't have the cast in ripples and bumps that some of the other group members full thickness (50mm) 10" pyrex blanks did. Also, not having to grind the back flat means i can easily see through the back which makes finding pits/scratches and checking the contact on the tool easier.

The problems ive had have all been to do with me learning the techniques and repairing my own mistakes, not with the glass thickness, although i have been carefull to keep things turning to try and avoid astigmatism.

Have fun!

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