"Gunner Asch" wrote in message
...
On Mon, 12 Dec 2005 22:48:37 -0500, "Bob Chilcoat"
wrote:

I may actually never have tried to machine actual cast iron before
(except
for drilling and tapping a few holes). I have machined plenty of mild
steel, however. I guess that's a different animal. I'm not sure what
this
is, but I'm willing to concede that it's probably cast iron. The
Browning
taper-lock hub, OTOH, is almost certainly a powdered metal part. It is
clearly molded with mold parting lines and fine detail. Not sand cast or
what I've ever seen from cast iron. That's what led me to believe the
sheave was PM too. Live and learn.

Sintered or pressed metals often behave far differntly, even when of
the same material..due to compression when molding and heat treating
effects.

I turned something once that I KNOW was cast iron..and got chips. My
customers turn powderd metal every day..and get fines.

Iron-based PM usually produces gritty powder. Decent quality cast iron tends
to produce small, partially-formed chips. There is a *lot* of PM in consumer
products these days (even the bevel gears on angle-head grinders), and less
cast iron.

But it varies all over the map. If you get your hands on some infiltrated,
double-pressed, or HIPped PM, it may turn like wrought metal -- although
it's likely to be harder than hell. And some cast irons turn curly chips.
Low-grade CI can turn into powder. We used to keep a bucket of the powdery
turnings from cheap CI for fire extinguisher, to dump onto magnesium fires.

Ordinary, run-of-the-mill, press-and-sinter ferrous PM tends to machine into
powdery stuff. Whether it's hard depends on whether it was chilled or
quenched, or just allowed to cool in air.

--
Ed Huntress