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Hi Hamish,
Although I have previously used 22",17",11" down to 7" "subby" laps on each of the two 33" mirrors, I decided to just use the 12 1/2" lap used for polishing my recent 12 1/2" mirror (first time I used a full sized lap since early 1960's).
With the full sized lap on the smaller mirror I found I had an almost perfect sphere on coming out of the polish. From there figured if I dug out my old 7" lap it would be "easy peasy" to parabolize. Well couldn't have been easier, as it took only 3 1/2" hours to get a good parabola without any edge defects. My testing was simple, just 133 lpi Ronchi grating (bench testing) at ROC and Ronchi 133 lpi eyepiece star test to get the "jail bar" straight line (null) going through focus.
So on this second attempt at figuring this 33 I decided to "put in the yards" to remove the wide rolled edge using just the one lap (12 1/2") for the whole job. Had to go back to a sphere (or pretty close), which just seemed to happen as I removed the "shoulder" where rolled edge started. Once the edge was corrected I used the same strategy as for parabolizing the smaller 12 1/2".
Stephen
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