[ATM] Final figuring advice?

[BERNARD KOSICKI <kosicki@verizon.net>]

I'm into final figuring of an 8" f/5.3 mirror.  This is my first mirror so I'm feeling my way along.

The situation I'm in now is that along one axis, the PV error is about 1/12 wave. 
(I'm using FigureXP to do the analysis).

However, if I rotate the mirror 90 degrees and test again, the PV error along this axis is not as good - 1/6 wave.

The shape of the Surface Error is the same in both axes (which is good), but the magnitude is different, obviously.

I'm only been using a full size tool, and don't want to start trying any subdiameter tools at this point.  

I've used a series of different modified W strokes to take care of high spots so far (an extension of what Tex discusses).  This has worked for me until the last session created this imbalance between axes.

I can imagine using this method to work only on the angular part of the mirror that is still high, but would appreciate any guidance as to what experience others have had with this.  Up to now, I haven't tried to restrict a session to one axial region only, and would like to know if others have had success doing this.

My goals are
- getting to about 1/10 wave in both directions
- avoid any "lumpiness" in the figure (the mirror looks very smooth now in the F tester- no apparent lumps).  

Avoiding lumpiness is the reason I've been sticking with only W strokes (I also slightly rotate the mirror slightly (about 10-15 degrees) during each stroke to keep things smooth- this has seemed to work much better for me at keeping it smooth than not doing these rotations)  

BUT its been difficult  (but just about possible) to satisfy all the constraints I've placed on myself in a single session
-integral number of W strokes for symmetry (last session was 1 W) 
-one mirror rotation per full W (full = both left and right overhang)- again for symmetry
-keeping the mirror positioned properly on the tool to address the high spots

Is there a site that discusses some of this, and how to modify W strokes to get at only one angular zone without causing   "lumps"?  I haven't found any references yet.

I'd appreciate your advice, especially those of you who have used this method successfully.

Thanks,
 
Bern K.


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