Final Figuring Of A Lightweighted Beryllium Mirror

A lightweighted Beryllium mirror, with a weight of 32 pounds and an elliptical shape of 32 inches by 34 3/4 inches, was fabricated to a flat surface. The final figuring on the mirror was accomplished using computer controlled polishing. The removal tool consisted of small Kemet pads which individually conformed to the surface and were maintained at constant pressure. This tool was rotated at constant velocity as it transversed the piece in a raster scan pattern. Control over material removal was accomplished by varying the linear velocity of the tool along its path. Velocity data for the polisher was derived from analysis of a series of sub-aperture interferograms. The abrasive elements for the polishing operation were diamond particles suspended in a slurry. The lightweighted Beryllium mirror surface was fabricated with a O.03 RMS optical path difference from flat, where λ is 0.6328