Peter Fairbrother wrote:
Any hints for turning pure copper?

I tried a medium positive rake, very sharp tool, fine feed, and high
speed,
but that broke the tool (and the expensive workpiece) when it dug in,
and a
negative rake doesn't cut, it just rubs (and probably work-hardens
too).

Lathe is about as tight as I can get it, overhangs as short as
possible. I'm
turning the soft state, but I could perhaps heat-treat it somehow if
that
would help.

I can't work-harden the piece first though. Neither can I use much
tool
pressure - it's a diffusion-brazed assembly of thin pieces.


Thanks,


--
Peter Fairbrother

Like the other guy said, 0 degrees rake, basically a flat top tool.
Any positive rake will hog in, as you've found out. I've turned a lot
of commutators and usually take off about .005" at the most with that
interrupted cut. I haven't had to use any coolant. I use HSS and use
a diamond hone on the tool to polish before using it. Feed slowly and
don't get in a hurry and the finish comes out just fine. A round-nose
tool helps, too. Make sure it's dead on center, too high or low is as
bad as having rake.

If you've got bucks and need the finest finish, use a diamond. I saw a
picture of a copper drum that was turned with a diamond for some
special optical purpose, looked like a mirror.

The only heat-treat possible with copper is to anneal it.

Stan