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

HSS is not as critical as to how it's applied, but when it is a concern,
one
selects tool steel high in cobalt, which offers tougher conditions at
elevated temperatures. Any HSS will work for aluminum, especially if
you
understand chip breakers and rake angles.

It'll work fine even if he doesn't have a chipbreaker - but has a
sharp tool with even reasonable postive rake. I'm suprised this
wasn't more of an issue here - my experience with *coated* carbide
inserts is that they actually work pretty poorly for aluminum,
especially so for small depth cuts. Coated inserts have a honed
edge so the coating will adhere well - but that feature effective
turns them into negative rake tools for small depth cuts.

Jim


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.

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.

For the most part, I rarely grind a rake angle without incorporating a chip
breaker. The sole exception is parting tools, where I use the radius of the
wheel to grind the top of the tool, generating a small amount of positive
rake, but improving chip flow tremendously. As you likely know, too much
rake on a parting tool encourages hogging, a serious problem on light duty
machines.

Chip flow is usually a serous consideration when machining aluminum. I
don't like to generate strings, so by grinding a chip breaker, rather broad
and somewhat deep (according to need) I can usually end up with small broken
curls, the ideal chip. Cutting pressure is at a minimum.

Harold