ATM 16" BVC figuring progress

["Herb Kasler" <h.kasler@worldnet.att.net>]

Hello again,

Well, my latest figuring strategy seems to have worked pretty well. I made
that 10" star lap and dug away at the center for 20 minutes. In addition to
producing innumerable sleeks (arrgh!), my calculated maneuver left me with
the following numbers. The difference on the Ronchi test from the previous
figure was noticable, but quite subtle.

Dia: 406.4
S. dist: 3175
xbias: 3152
sigma: 0.075
c. obstr: 90 mm

zone mm    offset mm
60                4.79
85                5.99
105            7.42
125            8.29
140            9.43
155            10.44
165            11.33
175            12.05
185            13.13
193            13.88
198            14.62


I now get Strehl = 0.839, and there is no conic with a better fit.
Apparently I took the center down just a bit too much relative to the 40-60%
zone. Again using the target function, I find that I should be able to
improve my figure considerably from here by taking down an annular region
from 40-70%, peaking just outside of 50%, by maybe 40 nanometers. This I
will attempt to accomplish by pressing yet another, smaller, inverse star
into the center of my tool, so that the full-contact zone is a ring centered
on a radius of 105 mm. Then I'll apply it with short strokes for maybe three
minutes.

But first, I guess I'd better repeat those measurements on a different
diameter, to be sure that's really what I need to do. In any case, though,
I'm definitely getting close now!


LAter,
Herb.