Need Smoothest Possible Surface on Copper

A. Hi. Copper is diamond-turnable. Look into diamond turning.

A. We diamond cut copper plate and sheet but do not come close to a 0.1 micrometer RMS (ISO # N3) surface finish, (our customers do not require it).

One could possibly achieve this, using a new, round diamond tool and by taking a series of very light passes at different pass angles, but doubt this would be practical. It will be important to know if the copper object is cylindrical, or flat, as the tooling would differ.

Either form, however, should be capable of being smoothed to this finish by burnishing with either a hardened, polished wheel on a lathe, or passing between rolls, ground and polished to at least this level of smoothness. Some metals suppliers are equipped to roll copper to mirror-like finishes, then interleave a special paper to protect the surface for shipping, as another possibility. The ISO texture would have to be negotiated, of course, and will cost extra.

I'd certainly agree that we're talking completely in the abstract here, Mr. Erickson, since we have no information on size, shape, speed, etc., etc.. But I am told that Large Optics Diamond Turning Machines achieve 0.028-0.030 micrometer RMS. Only "book knowledge" though.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2001

A. I have not tested to verify surface finish quantitatively, but several years ago I looked at diamond turned copper surfaces for optics by scanning electron microscopy. I would believe that those surfaces approached a 0.1 micron finish. (I wish that I had the microscopes then that we have now.)

Back then, there was a 3M Optics plant in Santa Rosa, CA - not too far from Sebastapol - that did the diamond turning that I worked with. Maybe some inquiries there would turn up some local talent that could help you.

Good Luck.

A. Dear Mr. Santosh,

I am also finding it difficult to maintain good surface finish on our Copper (Slip Ring) turning of our Alternator Rotors. We are using Sandvik grade insert DCMW diamond turning insert @ 2000 - 3000 RPM with feed rates from 0.04 to 0.07. The total material removal is about 0.70 mm and we are doing this in 2 passes.

Can someone help me in getting a good surface finish. We are currently getting only Rz8 and we need Rz2 or RZ4. Please help us.

A. Mr Hariharan Ramamoorthy, are you using a DCMW carbide insert tipped with Polycrystalline (black) diamond or tipped with a Monocrystilline (yellow) synthetic diamond, or tipped with a Natural (clear - colour) diamond?

Monocrystalline & Natural diamond tips give extremely low RMS values, but you must have a very rigid turning machine & take extremely small cuts in very slow passes. The diamonds are easily chipped under too much material removal.

A. If you have a good diamond turning milling machine, good technique, and a really good single crystal diamond tool 10 angstroms RMS (.010 microns) is achievable. It is routinely accomplished in the industry

A. We are also manufacturing rotor alternators, I'll use Korloy tnmg 0.4 insert (pc 9030), 2800 to 3100 rpm, 0.08 feed, 2 passes, finally using scrub pad for polishing 3 to 5 second. I'll get Rz4.

A. I remember trying to polish similar parts for another company using mass finishing processes; however, they did not work out. There are too many variables and the results were inconsistent. I suggest you go with an automated system.