I am a home shop machinist. I have a SB 9" lathe. I am interested in
using carbide inserts and making my own tool holders. I know that HSS
is easier to work with but I still want to experiment with carbide. I
have been doing my homework but have a few questions and need some
clarification on a few points.

1. Any insert with a "N" in the second position is a negative insert.
Any insert with any letter other than an N in the second position is
a positive insert.

2. I am assuming that the positive and negative are refering to back
rake.

3. Negative inserts if kept horizontal, really have no back rake on
their own and also no end clearance or side rake. Positive rake
inserts if kept horizontal, really have no back rake on their own just
end and side rake.

3.5 Negative inserts are more economical because both sides can be
used.

4. Tilting down a negative rake insert gives end clerance and
negative back rake. This is why they are called negative inserts when
really they have no back rake on their own.

5. Tilting up a positive rake insert *should* give end clerance and
some positive back rake would seem to be the ideal situation for a
small lathe. However this creates an interesting paradox, all of the
sources that I could find, seem to want to operate a positive rake
insert perfectly horizontal. This would make it a zero back rake tool
(neither positive or negative). Why does everyone want zero back rake?

6. I found a source suggesting using a TNMP insert. The chip breaker
goes clear out to the edge of the insert. Tipping this insert down 5
degrees gives you 5 gegrees end relief and 5 degrees positive back
rake. I think that this insert has chip breakers on both sides so it
could be turned over and used again. DOes anyone know for sure? I
think that this is the best way to go. Has anyone tried this?

7. What effect does the tip radius have. I beleive that the larger
the raduis the smoother the surface finish on turned work. However,
the larger the radius the more power required.

Any help would be greatly appreciated. Thank You