A while back I asked for advice about screwcutting with carbide inserts. The consensus was that I was (a) going way to slow and (b) not helping myself by using crappy (Banggood) inserts. Upped speed a bit, got new inserts (JB cutting tools) and all went well.

I don't do much lathe screwcutting, but I needed to make a non-standard (41×1.5 mm) male thread recently. I thought I would have a bash at pushing carbide, so I cranked the lathe up to 550 (as fast as I dared go with a 4mm relief) and plunged 0.4, 0.4, 0.3, 0.2 mm straight in on the cross slide.

I was pleased by that, straight off the machine without cleaning the crests.

This lead me to start some experiments with carbide inserts. What I am finding (with CCMT 08 inserts) is that that I get a good finish if I take a 1.5mm cut at about twice the rpm recommended for HSS, but weirdly the finish doesn't seem to depend on surface speed – when facing (surfacing) I see no difference in finish across the diameter of the piece although the cutting speed is going from whatever to zero. Does that make sense?

I know all this stuff is documented for industrial machinery, but it ain't quite the same game at home.

Robin.

Edited By Robin Graham on 26/02/2019 23:34:40

Edited By Robin Graham on 26/02/2019 23:35:14