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View Full Version : Working with Copper... Any tips?



flyboy771
08-09-2006, 09:04 PM
I've been lurking here for a little while now, but haven't posted before. I work in the Physics dept machine shop at my university (as an apprentice, basically) and one group needs made a small (aprox 3/4" dia) copper wire holder for an electrical experiment. I've never machined copper before, and have heard it's a royal pain (ie, deflects before it cuts, won't hold shape, breaks taps, etc).

What can I do about it? Are there any useful techniques for working with copper on either the mill or lathe? I don't know *exactly* what it is, other than it's pure copper. Not an alloy to the best of my information.

Thanks
-Mike

HWooldridge
08-09-2006, 09:36 PM
I've machined a lot of copper based alloys with an older lathe and a lantern post tool holder. I can't speak to carbide for the application but sharp HSS bits leave a very fine finish and cut without trouble. I have been told that milk is a good drilling/tapping fluid but have personally always used WD40.

LarryinLV
08-09-2006, 09:51 PM
Copper heats up pretty quick and expands while machining. You might experiment a little with the machine you're using to get the cutting edge where you need it, i.e., on center, hi/lo.

It's probably electrolytic tough pitch copper (ETP) which is good for electrical conductivity(next to silver) but a bit of a hassle to machine, although I second HSS and a light touch. Watch for buildup on the tool

It could be free machining copper (if you get lucky) where a bit of sulfur is added to get it from a machinability rating in the cellar up to about that of brass, which is very good.

edited to add tapping comment: If you need to tap don't go beyond 75% thread and you shouldn't break any taps.

ASparky
08-09-2006, 11:54 PM
I am guessing OFHC copper (Oxygen Free High Conductivity) which is nearly pure copper. I have worked with the stuff a bit. Three tips.

One It likes sharp tools think knife cutting off not hard edge scraping.

Two it work (and age) hardens so it loves to dig in. If you have been meaning to adjust jibs etc to remove play now is a good time to do so.

Three a little lubricant helps a lot. Get and use a little of one of the miracle tapping fluids - it works wonders. Ditto on the lathe or mill, a little cutting fluid helps. Dont bother with a high flow to try and cool it it is a waste of time and tends to make the copper stick around and clog things, so just enough to lubricate the cut and minimise the effects of any rubbing.

Rustybolt
08-10-2006, 10:33 AM
four; fast speeds and lite feeds will keep it from heating up and a lot of cutting fluid.

flyboy771
08-10-2006, 01:24 PM
Thank you. We'll see how things go today. Yesterday, one of the other guys in the shop made a duplicate of the original piece (which was a real mess) that turned out OK. So that's one down, one to go.

YankeeMetallic
08-10-2006, 05:08 PM
Yes. Let us know how it went and what methods gave you the best results.
I had to make several oil-impregnated bronze (oilite) bearings for a customer a few weeks ago. I couldn't find anything in my books about machining Oilite so I used methods for brass. It machined nicely and I kept .0005" internal tolerance. I used mist coolant which was a mistake. The coolant and the oil in the bronze made the chips stick like glue to my lathe. I had to soak them in 409 and then scrape them off with a plastic scraper. Next time they get machined DRY!
I have some small parts parts to make out of copper as well so I am looking forward to your report.