Machining Powdered Metal - ugh!

I just spent a couple of hours making an Ebay Browning two-groove sheave a bit smaller (4.75" pitch diameter to 4.25" PD) for the HF $99.99 air compressor pump I bought. Surprise! These aren't cast iron any more; they're apparently some sort of powdered metal. Hard -- high-speed tool bits just rolled over and died. Fortunately, I had some carbide bits that worked fine, but this stuff doesn't produce a nice curly chip. It reverts to powder when cut. Anyone need a pound or so of iron (steel?) powder? Great for experiments with magnets. Glad that's over. Now to clean up the Myford... and my clothes and me. I'd better not get anywhere near an MRI before I bathe. I'd get sucked right into the magnet.

These aren't cast iron any more;

Cast iron never produces a curly chip. However, you should be able to cut it with HSS.

CI _can_ produce short curly chips.

Disregarding the skin which _can_ be hard. Depending on the alloy and the speed of cooling down (or tempering after casting).

Nick

Never say never. :-)

Actually there's so many types of cast iron that this statement isn't true. It depends on the cast iron type and heat treatment. I've actually produced some pretty good sized curls in really good quality cast iron. Cheap cast iron on the other hand will usually powder up.

Wayne Cook Shamrock, TX

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.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

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

If anyone in So. Cal is interested..I may be able to get ya a tour of a metal powder plant in Anaheim

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Yes they've been making the hubs out of powdered metal for a few years now. I've not seen a pulley made that way yet but just give them time and they will.

If the powder was dark gray then it was probably cast iron.

Wayne Cook Shamrock, TX

Wayne is correct. Just because "I" never machined a different type of cast iron doesn't mean none exists. LOL

One of my first high school metal shop projects was to make a flywheel weight for my Suzuki trials bike. I had found a 5 lb barbell weight while delivering my paper route. Took it to the shop and started hogging away on that chunk of cast iron. Mostly getting little chips I asked the teacher how to speed it up. Slow down the lathe and increase the pressure. That worked. Took a couple days to get the contour just right so it would fit in the side cover. It cameout nicely balanced and the bike was much more fun to ride

Be sure to let us know your experience with this pump. Bob