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13" coulter refigure problem

Started by bkhere, 11/10/2010 06:44AM
Posted 11/10/2010 06:44AM Opening Post
having trouble. central 8" of mirror shows good sphere, but is then far too flat to the edge. cannot get it to go spherical. have done mirrors but this ones got me. tried many stroke lengths and pressures. using 8" lap with 1" diamond shaped facets. Googol 64 pitch. cerium oxide. can send Ronchigram if needed. embarassing, as I have done a few of these types. help. thanks.
Bernie
Posted 11/23/2010 04:44PM #1
My first thought is that you need a larger lap. It sounds as if you have a central depression and it is going to be hard to get rid of without perhaps trying a full sized (or very close) lap. Also be sure to check the platform you are grinding on is flat, and that it does not have a depression at the center of the mirror. Also be certain to keep your palms at the center of the lap, do not hold the lap on the outside edges.