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Re: [ATM] figure stroke ten inch
On Sat, 29 Sep 2007 22:17:23 -0700
Jim Burrows <burrjaw@earthlink.net> wrote:
> 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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> ATM mailing list http://www.atmlist.net/
>
Thanks Jim. This is consistent with what I have seen? Have been using a
shorter W stroke MOT. But the edge has been lagging in correction (knife edge reading too small).
-- Tom
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