Nick,
For parting AND facing (don't get the first letters muxed ip), the most important part is to get the saddle locked, plus the topslide (compound) if you are parting.
Without it being rigid you will be getting tapered cuts and putting side strain on the tooling. At one time, it was thought that having an angled face on the front of the parting tool would help enormously. But people were finding that it was snapping the blade off because it was putting a side load on the tip. The cutting face must be square to the blade and the blade has to be square to the job. I don't suffer from any of those problems because my toolpost is invariably always spot on square. Just drop the holder on, and the tip is square to the job.
The reason why rear parting SEEMS to work better is a bit of a conundrum. All sorts of theories have been come up with, but all can be disproved one way or another. My personal view is that the chips fall away rather than get jammed on the tip. But again, that is just a personal view.
I have never had to do it because I don't have any trouble parting at all, and never have had, even with smaller less rigid machines, just a little more care has to be taken the lighter you go with machinery or the smaller the parting tool. I regularly part off brass up to 1/2" diameter using a 0.025" (0.6mm) wide parallel tool.
Your heavy machine should be able to part off under power at a high speed on non ferrous, and a fairly fast hand feed with nasty ferrous materials.
A square, very sharp tool, on centre or a couple of thou above to allow for tool flex, lubrication and cooling, and a steady CONTINUOUS feed is always the way I tackle parting. Depending if it is a fast or slow feed, and of course material, I sometimes omit the lube and coolant. Brass, bronze, cast iron and some of the leaded steels, I don't bother. For ali and stainless, then definitely used.
John
