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CNC Polishing

I need to finish a titanium part that is a 16mm diameter disc, with a concave sphere on one face of the part. The tolerance on the sphere is a surface profile of .025mm. The surface finish called out on the sphere is Ra .10 um.

Due to the tight tolerance, I am looking for a way to control the material removal/distortion that would result from polishing. I can get the finish to Ra .4 as machined. One thought I had was to look into a coated tool that could be used in a lathe, with the matching radius on it. Does anyone have any experience with anything like this?

Any alternative suggestions would also be appreciated.

Thanks.

Brian Blackwell
Engineer - Charlton City, Massachusetts
2007

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First of two simultaneous responses --

For a trouble free and quality job, you would need a round lapping device (similar to the ones used by prescription lens manufacturers) or a half million dollar diamond turn. They cut with a real diamond tool, run over airfloating pads and are super precise (their final finish rivals a lapping machine but with much less distortion).

Guillermo Marrufo
Monterrey, NL, Mexico
2007

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Second of two simultaneous responses --

Alternative suggestion is that you consider a mass finishing system. Titanium is a tough SOB and there will be no noticeable material removal in hours of processing; therefore, if you are looking for a reasonable polishing time cycle, look into a centrifugal system.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2007

I would suggest SPDT. An experienced diamond turner should be able to hold your finish somewhere near the 100-200 angstrom level. For a better finish, I have seen titanium post polished after diamond turning allowing for <100 angstrom finishes. the spherical profile should also be an easy target to hit on a diamond turning machine.

Matt Zabko
- Keene, NH, USA
June 14, 2008