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