I agree with you in most respects.

COMMON carbide inserts are NOT very suitable for small lathes. It's true
that negative rake carbide (or even HSS) tools do NOT work well except
in rigid machines. It's also true that small low powered machines cannot
make the BEST use of carbide.

There are, however, families of small uncoated inserts, mostly
triangular, that are VERY sharp, have considerable relief, NO rake, cut
with minimal pressure, and work well at most any speed. I use these
regularly, on a 6" Atlas, and even on my old round-way Unimat SL. While
the rake is zero (flat on top), these cut with less pressure than most
positive rake tools (which are less sharp). I can take as heavy a cut,
with as good a finish, with these carbides as I can with HSS ... even on
the Unimat!

I also use these, and a variety of more common carbide inserts on a 10"
Logan. This heavier machine is more forgiving of the commonly available
carbides inserts. It still doesn't like negative rake tools much, however.

The advantages of the carbides are that they stay sharp longer than a
HSS bit in the same service. I find this especially advantageous in
turning soft but abrasive plastics. It is also useful when one has to
turn hard materials. The inserts work reasonably well with almost all
materials, but there is no advantage when turning softer steels, brass, etc.

Disadvantages include problems with interrupted cuts, the inability
(easily) to custom grind odd shaped tools, and higher cost (considerably).

That said, I use HSS for perhaps 90% of my turning needs. The carbide is
less versatile, and more expensive. On a small lathe, carbide is NOT
the best choice for general work. But, to say it's NOT suitable at all
for use in a small lathe, even a Unimat, is just plain WRONG!

Dan Mitchell
==========

Ted Edwards wrote:

I'm not going to waste my time plowing through *all* the used hay in
this thread such as:
"Ya have to have a really rigid machine to use carbide." I use it on
a Chinese 3-in-1 for the vast majority of my turning. I use HSS when I
want a special shape cutter.
"Carbide can't be as sharp as HSS." I use uncoated carbide TNMP-321
inserts. When I want them *really* sharp, I hone the edges on an
Easy-lap diamond hone.
"You need to turn at really high speed to use carbide." You *may* run
carbide at much higher speed than HSS but you don't *have* to. I run it
at whatever speed I feel comfortable and my machine can handle.
There's more but I suggest you try it for yourself.

Ted