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Shaping the Mangin mirror.
First I ground it to circular shape and then generated the convex curve with a large diamond cup wheel. After that I removed it and generated a matching concave curve on the top of the thick glass piece. I don't have photos for two of the stages. Then I reattached it with mounting tape; generated the concave curve and partially trepanned it to free as much of any residual internal stress as possible. I used a similar procedure for making the primary for the Companar, and a bit of internal stress was released when I completed the trepanning, after polishing, and the mirror went slightly astigmatic. I hope for better luck this time.
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