"Harold and Susan Vordos" wrote in message
...

"Peter Fairbrother" wrote in message
...
Jerry Foster wrote:

What is the material?
[..]

"Peter Fairbrother" wrote
I'm doing facing cuts and the tool is grabbing because the rake is
too
positive (I think. There's a graunchy noise and the feed goes slack
for
a
bit. Worse near the center, I'm not sure why. Chinese minilathe, 0.5
mm
cut, brazed carbide tool on cast iron).

Cast iron. Grey, fine-grained, not scrap.

[..]
It's not really practical to change or regrind the tool. I'm dead on
center height, and wondered whether changing the height might make it
better
by changing the effective rake somehow?

If so, which way? And why? I tried to work it out but got confused,
and
came up with two different answers.

What I really wanted was a quick rundown on how changing tool height
might
change the effective rake, and why. I'm sure I've read something about
it,
but I can't remember where.


--
Peter Fairbrother


Changing tool height has a bit of an affect on rake, but very little. You
generally can't change the height of the tool enough to make much of a
difference. It has a profound affect on front clearance, however,
especially on small diameter cuts. If you're experiencing the tendency
to
hog, reduce the front clearance a little, which will lower the hogging to
some degree. You can achieve a delicate balance where the feed rate is
just slightly less than the amount of clearance, so the tool isn't
dragging,
but if it hogs, it bumps into the cut below the tip and stops the advance.
That's not a great way to go, but on a light machine it can be a useful
dodge. Good luck.

Harold



One more thing. Cast iron responds fairly well to negative rake, so if
you're having trouble with hogging and chatter, consider reducing your rake
to 0 degrees. I wouldn't go negative on a light duty machine, but no rake
would likely be quite useful.

Harold