Machine Mirror-Making, S.I.T. Testing, and Shop Systems

Jeff Baldwin, Stockton Astronomical Society

Mirrors made not by machine.

Irrational fear of machine-caused errors, and extreme personal stubbornness.

25 cents an hour.

Nonetheless, I enjoy making mirrors the hard way, enjoy feeling the work as it happens between the mirror and the lap.

Greg Wilhite shows up, 12” f/3, needed parabolizing, too much work and stress for Greg.

Greg makes machine. I use it. I like it.

Greg and I make Ol’ Yeller.

http://www.jeffbaldwin.org/machine.htm

Learning curve, Mirror-O-Matic Logic, Carl Zambuto Logic, Bald Logic.

Slit image Test by Bill Thomas

http://yubagold.com/tests/index.php

Reasons for SIT Testing:

· Foucault Test sucks with large, fast mirrors, SIT does not care about aperture or focal ratio.

· Human subjectivity disturbs Foucault Test. SIT has no human subjectivity.

· Caustic Test and Interferometry require extremely stable rooms, time, set-up. SIT does not require room stability not mirror stability.

· Repeatability.

· Highly Precise. Collaborates with other high-precision bench testing and star testing.

· Fast, Fast, Fast. The mirror working - testing – analyzing cycle is quick. I can do 12 a day rather than 2 or 3 Caustic Tests of 1 good Interferogram.

SIT Test Jig

SIT Jig Alignment Mirror

SIT Jig Alignment Laser Target

SIT Mask for 32”

SIT Mask Router Jig

SIT Image [JPEG Repro]

Current 32” f/2.82 Tornado

Current 32” f/2.82 Millies Lacroix

Current 32” f/2.82 Profile

0.1429	1/7	0.194
0.1250	1/8	0.383
0.1000	1/10	0.605
0.0714	1/14	0.799
0.0625	1/16	0.846
0.0500	1/20	0.901
0.0385	1/26	0.942
0.0333	1/30	0.956
0.0200	1/50	0.984
0.0125	1/80	0.994
0.0111	1/90	0.995
0.0100	1/100	0.996
0.0091	1/110	0.997
0.0077	1/130	0.998
0.0061	1/165	0.999

24” f/3.7 Final Tornado

24” f/3.7 Final Millies Lacroix

Moving mirror from machine to stand. https://www.youtube.com/watch?v=bH352BlinuQ

Moving mirror from stand to machine. https://www.youtube.com/watch?v=luOQszdUmOY

From Mirror Processing Sheet Checklist

Send for aluminizing only if . . .

1. slit image test shows P-V less than 1/10 wave, less than 1/26 wave RMS, and 0.94 or more Strehl.

2. mirror smooth, no zones, no micro-ripple, smooth transition between regions.

3. no astig.

4. no tde. P-V _____ RMS _____ Strehl _____

5. sides cleaned.

6. Star test excellent.

Curve-generating attachment for Ol’ Yeller

Next Machine: 48” Lapping Machine for making large secondary mirrors for LAFFRTs as well as test flats for fringe work and autocollimation.

Figure XP, David Rose

Open Fringe, Dale Eason