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Re: [ATM] figure stroke ten inch
At 2007-09-28 19:05 -0700, Tom Fredrickson wrote:
>I'm working on a 10 inch mirror full size lap. I turned the edge and
>went to work with short coc strokes to clean it up. Now I need to add
>correction to the edge. I have been working the edge and it is going
>the wrong way. I feel I need to work the center and make it deeper.
>
>Here are my numbers in millimeters roc 2712 mm Moving source mirror D
>253.5 mm
>mask zones
>1 0 56.684
>2 56.84 80.164
>3 80.164 98.18
>4 98.18 113.37
>5 113.37 126.75
>
>Readings 0, 0.49, 0.84, 0.98, 0.98
I haven't chucked some data into Sixtests in quite awhile, but here's
the input file:
-----------------------------------
Tom Fredrickson
253.5 0.0 Mirror, obstruction diameters (mm)
Foucault
0.0 Source distance (0=moving source)
y, mm X, mm
40.08 0
69.49 0.49
89.63 0.84
106.05 0.98
120.25 0.98
*
-1.000 0 Conic targets: b, R (mm)
0.0100 Measurement std deviation, mm
2712.0 Longitudinal reading bias, mm
------------------------------------------
The zone reference numbers, y, are the RMS values of the zone inner
and outer radii (Nils Olof's method). Sixtests says the surface RMS
is 72.2 nm relative to the best-fit parabola - want that down to 20
nm to pass, so a ways to go.
Most of the error is undercorrection, with the conic constant b =
-0.414. You probably got that from the COC strokes. I'd suggest
trying one of Tex's parabolizing strokes on p. 97. One of the
"Classic methods", MOT, long stroke, might get you closer. If not,
Tex sez "Method of accented pressure", full lap, TOT, worked for him
on a 10" f/4 mirror. Last desperate go is a small tool - lotsa luck
on that one.
-- Jim Burrows
-- http://home.earthlink.net/~burrjaw
-- mailto:burrjaw@earthlink.net
-- Seattle N47.4723 W122.3662 (WGS84)
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