Finishing of precision generated metal optical components Page: 4 of 7
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FIG. 5a. Interferogram taken with same set-up FIG. 5b. Machining marks: By blocking the
of Fig. 2 except showing the effects of diamond reference bean the effects of the machining
tooling marks near the center. marks present in other interferograms are now
Roundness um 0.32
Max. slope angle on part X 10-6 40
- Part surface error um 1.11
,a arar - 4 Max. displacement at target um 9.5
FIG. 6. Knife edge test of energy distribution in TABLE 1. As machined Copper clamshell figure
the focal spot of the as machined copper ellipse. error summary
The approach in polishing was to run a small ring-shaped tool using a fast stroke going from edge to
center varying stroke position and spindle speeds and reduce the strong slope changes resulting from dia-
mond turning without altering the basic figure. This was accomplished within 4 days time including testing.
The fringes had been smoothed out enough to show a few other problems such as out of roundness and
asymmetrical areas (Fig. 7a., 7b).
In the course of correcting these problems, I created some of my ewn. I used some overly flexible tool-
ing and wound up with flat spots and zones. I did not vary the speed randomly or often enough, also the
stroke positions should have been more random. These problems can be corrected by the use of a rigid full
size tool to average and bridge the errors.
The surface quality approached the original cleanliness of the machined surface. The background condi-
tion was not as good, by that I mean micro-sleeking. I feel the surface can be polished as clean as a
diamond turned surface. We hope to determine whether or not the damage threshold level is raised to equal
diamond turned surfaces in our future studies.
Some of the data on 1.5-inch samples show promise especiallly the Nomarsky photographs of diamond
turned polished copper samples. The surfaces appear as smooth as diamond turned surfaces. (2) The only
problem is eliminating the micro-sleeking. The reflectivity at 10.6 um was as high as 99.34 measured at
Kirtland AFB (Table 2). Scatter levels were not as good due to the micro-sleek structure, the lowest total
integrated scatter at 0.63 em was 0.5%. At 1.06 mm the reflectivity dropped somewhat in comparison to
diamond turned parts (Table 2,3)
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Baker, P.C. & Sonderman, J.B. Finishing of precision generated metal optical components, article, August 1, 1975; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc866559/m1/4/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.