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"Need Smoothest Possible Surface on Copper"

An ongoing discussion beginning back in 2000 ...


Q. How do I get the smoothest copper surface (better than 0.1 micrometers)?

k. Shambrook
- Sebastopol, California


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

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


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.

W. Carl Erickson
- Rome, New York


thumbs up signI'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, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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.

larry hanke
Larry Hanke
Minneapolis, Minnesota


Q. Sir,

I would like to know the operating parameters range (spindle speed, tool feed rate, depth of cut) to get better quality parameters (figure error, average roughness) on Diamond Turning Machine, i.e; the range of spindle speeds under which the cutting should be done...same for depth of cuts & tool feed rates.

Response for above query will be appreciated.

Santosh Kandregula
machinist - Visakhapatnam, Andhra Pradesh, India


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.

Hariharan Ramamoorthy
- Chennai, Tamil Nadu, INDIA

February 19, 2009

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.

Jim Thompson
diamond turning tools - Charlotte, North Carolina

June 5, 2012

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

Andy Simonson
- Indianapolis, Indiana, USA

March 30, 2013

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.

Theertha Kumar
- Bangalore, Karnataka, India

Copper polishing for optical use

October 25, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am getting some oxygen free copper blanks that have been diamond point turned for optical use. These are small, one 8 mm dia. and the other 25 mm dia. They are for parabolic reflectors. I need to have the diamond cutting edges smoothed so that the parts when coated by a UV reflectance coating, will work with negligible scatter down to 194 nm. Will copper polishing accomplish this and if so, can you direct me to a company that does this?



Vern Bangerter
product designer - Orem, Utah, USA

November 7, 2016

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.

tony kenton
AF Kenton



Morse Taper machining in Copper

February 5, 2018

Hey guys,
anyone who can help?
I need to turn a Morse Taper on solid copper. Can anyone recommend cutting tools, speeds, feeds, etc.?
Would very much appreciate any help.

daniel charleston
toolmaker - melbourne victoria australia

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