I've never done it on a lathe, but I think it would be much better accomplished on a valve refacing machine. I think the material valves are made of would be more easily ground, than cut with a tool.
There is no problem doing this in a quality lathe or what I use --a Hardinge collet lathe as someone mentioned. I have a nice piece of plastic that I use on the center to apply pressure to the valve head to remove vibration. Titanium and stainless are not a problem. J.Rob
