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Polishing Query

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Posted by Robert May on July 18, 2002 18:00:12 UTC

If you were polishing the mirror on pads, that "crater" appearance is normal when the pads aren't well flattened when they got applied.
If you were on pitch, you need to do a warm press to get the pitch to good contact with the glass everywhere. When you polish, do a W stroke that is at least 1 1/2 the distance of the waves and also the length of the same. This should quickly get rid of the zones and then you need to work with varying stroke lengths to eliminate the tendency to produce zones of other radii.
To do a good warm press, put the lap into hot water for about 1 minute and then pull from the water and immediately put the mirror on top and let sit for a half hour and then check to see if all the pitch is in contact with the glass. If not then do it again until you have that complete contact. Bubbles in the center of a pitch block are acceptable as they are not over 50% of the block's surface.

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