"jim rozen" wrote in message
...
In article , Harold and Susan Vordos says...

It's taken this many exchanged for the fact that he is using a negative
rake
tool, not a positive rake one, to surface. At this point I'm beginning
to
question the ability of the instructor. I can't imagine a poorer
combination if I tried-------a chip welded negative rake insert on
aluminum.
Changing to a HSS tool, properly ground, one would experience an
astonishing
level of improvement.

Oh. I missed that. Though, if he's using coated carbide, he
probably would effective have a negative rake tool even if it were
in a positive holder for tpg inserts.

I agree---the coated inserts are likely a poor choice, but there are no
good
choices when it comes to negative rake and aluminum. It screams for
positive rake for good performance. Positive rake, with a proper
chip
breaker. There is little to be gained by using negative rake for
aluminum.

Is there *anything* to be gained, ever?

I can envision a large object made of 7075-T6. Longer insert life. Still,
it would work fine with positive rake. I was just trying to leave the door
open ever so slightly for those that may swear negative is better. I've
never found it to be, but it works wonders when machining ductile or good
gray iron. Much better tool life. That's assuming the operator has
enough on the ball to know that it screams for a C2 grade of carbide.
That's more important than the rake angle.

He could have made 100 of those flywheels with a HSS tool ground
with only three grinds, and a proper mandreal and pusher block,
in one day.

Yep! I can't help but wonder how well equipped the instructor is at this
point. I can't think of a bigger disservice to anyone learning to machine
than to not instruct them on grinding (proper) cutting tools. Until one
understands cutting tool geometry, it's almost impossible to make decisions
to improve operations when things aren't going well. I consider myself to
be one very lucky person in that when I was trained, there was almost *no*
insert tooling, and each operator had to grind his own tools. It's
something that has served me very well. I rarely rely on inserts,
although I do use them. Mostly for roughing, however.

Harold