Hi all. I have a job on which I need to achieve a 0.4 Ra surface finish on a bore. It's made out of oxygen-free copper. The bore needs to come out to Ø69.55/69.57mm and it's 104mm deep! Now I've been bought a Ø20mm solid carbide boring bar with a couple of diamond tips but I have no idea when it comes to depth of cut, surface speed, feed rates etc. Diamond turning is all new to me. Has anybody got any ideas where to start?