In article , Ed Huntress says...

"jim rozen" wrote in message
...

Some of the postive rake, uncoated carbide inserts (with
formed-in chipbreakers) were *too* sharp when I was
turning nylon parts for a second job. It was common
practice to go and deliberately break the edge, with an
arkansas stone to prevent the material from chipping out
at high speeds and feed rates.

An Arkansas stone? On carbide? I'd think it would gouge the stone, no?

Yes. We kept one stone just for doing this, in the toolbox.
I know it sounds crazy but at the speeds and feeds we were
turning annealed nylon 6,6 it would tend to form tiny
pits on the surface when brand new tooling was installed
and you could either a) reduce the speeds and feeds for about
20 parts, or you could knock the brand new edge off the
insert. After 20 parts the insert was broken in and would
not show the problem.

As for the positive rake, positive rake for what? Steel? Aluminum? And do
you keep a separate set of zero-rake tools for brass? Or is one supposed to
just cross his fingers that he doesn't have a crash?

In this case it was a production environment - and nothing but
nylon 6,6 was in the machines. When they did profile aluminum
jaws the chip bins had to be cleaned out because all the chips
were sent out for recycling, they were used for injection molding
feedstock.

I'm not arguing with you. I'm arguing with the idea of using carbide as your
basic tool material for hobby machining. I've used a lot of carbide over 30
years, and I wouldn't do it. Not on my South Bend, and not on a Chinese
lathe.

As per my other posts, I agree with this. I do have some lathe
holders that run TPG221 inserts, only for turning hard parts
that HSS won't touch. They get used on occasion, at home.
But mostly I run with three tools in the toolpost, a positive
rake turning tool, a grooving tool, and a 60 degree threading
tool. All made from 3/8 HSS blanks. The QC station of the
toolpost typically either gets a HSS cuttoff tool, or a HSS
bokum type boring bar.

I've been meaning to try to find some tpg221 HSS inserts, and
also some uncoated carbide ones as well, but the need hasn't
been very pressing.

Jim

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