Harold and Susan Vordos wrote:
I'm totally unfamiliar with the inserts of which you speak, but I'm somewhat
familiar with carbide grades. If the inserts you are using are, indeed,
intended for use on stainless, as Dan suggested, they're the wrong grade for
steel and would likely present premature tip failure, even if only on a
small scale. Surely enough to create poor cutting conditions. A change to
the right grade alone would be quite helpful. Considering you're taking a
light cut and feed, a C6 would probably serve you well. You're most likely
using a C2.

It is Cermet NX2525 - the only grade that the company I
bought them from had in stock with a finishing chip breaker.
They had no carbide inserts with finishing chip breaker.

Besides, Mitsubishi carbide lists FS as suitable for almost
any material so I don't see that as a problem:
http://www.mitsubishicarbide.com/mmu...on_turning.htm

I can't see the relevance of the grade - whether some carbide,
coated carbide, cermet.. As long as it's continuous cut,
there shouldn't be much of a difference, except in
lifetime of the insert. For me, it is pretty much the grade
that the company I buy them from has in stock - UTI20T,
US735, UC6010, NX2525 are some of the turning inserts I
have - and I have used them for all work with aluminium,
steel, stainless steel, Hastelloy etc.. Yeah, not optimal, but
works - my volumes are low enough that I can't get 10 pcs of
inserts of various optimal grade/chipbreaker for all different
materials. Just use one for all. The different materials
listed above are for different geometries of inserts,
WNMG, SNMG etc. - whatever they had to sell from stock.

I get absolutely no technical advice - I just pick from
catalog a code for insert, and the sales person tells
me on the phone the price and availability. Oh well, it
is like that in almost all companies - they only know the
price, but not technical stuff - so I just live with it.
At least, they have a reasonable catalog.

The CNMG-FS insert shows no physical damage after cutting a short
while with the huge chatter. The chips produced are very short
and shiny, not discoloured by heat.

I did try the height around, so it is not a simple mistake
of having the height totally wrong. The CNMG inserts have
same outside dimensions as the CNMG-FS.

Oh well, lesson learned - stay away from FS chipbreaker.
Still, really strange effect.

Kristian Ukkonen