"B.B." u wrote in message
news snip---
Harold, When you wrote "Can I assume the mandrel is ½?" that last
character came out as Pi on my screen, and I have no idea what you meant
by it.

Ooops!! Sorry about that----I hit the keys in the wrong sequence, and
didn't notice. It was intended to be ½" ?----asking the size of your
mandrel. My concern is that the more slender is the mandrel, the more
likely you would experience chatter.

But, bar stock, pressed the mandrel in with an arbor press.
We're using general-purpose indexable carbide tools on all of the
lathes, but I have a fresh bit of tool steel and I'll see about making
my own tool to play with.

If you understand rake and clearances, you'd be far better off, especially
if you're using negative rake inserts. If you're using positive rake and
they're sharp with a minimal corner radius, it may not make a big
difference. Regardless of what you have, I'd strongly encourage you to
learn to hand grind toolbits while you have someone looking over your
shoulder (assuming you do have, and they understand the concept themselves),
for it will serve you well for ever. It really is nice to not have to buy
each and every special type tool that you need when it may get used only
once.

Now that we understand you're using inserts, make sure you're not running a
C5 or C6 grade, especially if the insert has looked at steel first. It's
the wrong choice for non-ferrous materials to begin with, lacking the proper
edge hardness to withstand cuts. It really does make a huge difference.


I did find (counter-intuitively) that running
on the high side of the cutting speeds helped.

All metals have what you might call a "sweet spot", where they machine
better than at other speeds. Aluminum really responds well to high speeds,
and rarely is a problem as a result, assuming you use the right tools.
Armed with that knowledge, try to run as fast as possible, which generally
yields far better finishes and improved chip flow. You risk chatter, so
you must achieve a balance for conditions at hand. You can't always use the
speed you might desire. Run as fast as possible for conditions. The
larger the area of contact your part has with the tool, the more likely
you'll have chatter. Broad tools make for difficult operations unless you
have *very* rigid machines. If you were to compare the likes of a 17"
Axelson, for example, with a 10" Southbend (not a fair comparison, but it
really proves the point) it would jump right out at you. When you run a
lathe, try to keep everything choked up as close as possible. Material short
in the chuck, tailstock quill extended only as far as absolutely needed, and
cutting tools held as short as possible. When you keep everything close, you
can usually run faster, which yields better results and shortens machining
time. That can be real critical if you're making lots of the same thing.

I'll likely settle on the heat & press method suggested by
PrecisionMachinist. Class is on monday--I'll let you know how it goes.

Good luck! Hope you can give us a good report.

Harold