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UHMW

Doggggboy

Doggggboy

Ultra Member
I potentially need to turn and/or machine some UHMW plastic bar for a friend's slushy machine tomorrow.
Other than sharp tools and keeping everything cool, any tips to make this less of a gong show than I expect?
 
Not my favourite material, but here's my $0.02:
Just keep the swarf clear or there will be a spaghetti ball you will regret making.
Lower the spindle speed, take deeper cuts than normal and pull the swarf away often. If you need a lube, try Johnson's Baby Oil, it works well on plastics and smells nice too!
 
I take the time to clean metal swarf out of the tray beforehand as a precaution. Plastic swarf wrapping up on itself is bad enough, but if it picks up swarf from the tray it makes for unwanted excitement. Unfortunately the best tools to cut it (sharp cutters like for aluminum) don't really do much for chip breaking so long strings are a concern. Its safer to do some pauses when power feeding. When measuring makes sure to give the material temp stabilization as the expansion coefficient is high & easier to make errors that way. I've been trying spritz of alcohol & methanol to lubricate & cool. Seems to work well. It evaporates clean, obviously don't inhale. Careful with aggressive drilling, it can become grabby I bad things happen. I ted to use my dubbed drills like for brass for rough holes & then single point bore for accuracy. Watch out for taper as a result of stick-out (bending deflection) & use tailstock when you can. You cant rely on metal rules of thumb.
 
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Having just finished making some parts out of this stuff...everything said so far is bang on...
especially the swarf balls...jeezluz stuff is like velcro when it's whirling around...
sharper the tool the better too...I assumed "oh it's plastic, that shouldn't be difficult"...if the slightest bit of flex inducing heat occurs, a dullish tool just sort of moves the material but doesn't remove it the way you want.
 
I made some rollers from UMHW for a friend before Christmas. I used a razor sharp HSS tool and that worked amazing. Biggest swarf snarl-fest I have ever seen though so be aware of that.
 
ChazzC said:
Rig a vacuum nozzle to suck away the swarf as it forms; however, don't try to suck up a load or you'll end up needing to clear a ball out of the hose!

Can you use Acetal (Delrin)? still a pain but less so than UHMW.
Click to expand...
Possibly but I've already got the uhmw in the car. It has to be food safe. HDPE would have worked but isn't recommended for low temp applications so a slushy machine would be a problem. Delrin is foodsafe but can release chemicals at higher temps and the machines are cleaned with hot water. I think the original part is uhmw so we're going with that.
 
One consideration that may not apply to this application ... if high precision and/or consistency is required between parts. Letting the part(s) "age" for a few hours before final turning is helpful. This was learned when making go/no-go gauges. Dimensions would creep a couple thou overnight if turned to required size at one go.
 
If you are milling any of the UHMW make sure you have the piece butted up against a fixed stop. The waxy film will cause a piece in a vise to ‘slide’ during the vibrations of the cutting process.
It can be very little, but, you will wonder why you are out a several thou, because the friction hold of the vise is greatly deminished.
 
calgaryguy said:
Oh this is good info. I need to make 3 small 'pins' about 3mm in dia and about 10mm long and was going to try and use some UMHW I have but I dont mind getting some acetal rod since I only need a tiny bit.
Click to expand...
You’ll have a lot more luck making a 3mm pin out of Acetal than UHMW.
 
Thanks for all the tips guys.
I got the part made after a lot of dicking around.
Been a while since I used the lathe so I had forgotten most of what little I had thought I knew.
Started turning the 2 inch bar down to size with a fresh carbide insert and everything was going well. Had better luck with about 40 thou doc rather than 5 or 10.
Stringing off nicely and not making too much of a mess. Started turning down to the smaller stub at the end, about an inch and everything changed.
Very rough finish, mostly just pushing stuff out of the way rather than cutting. Switched to newly sharpened HSS and it all got better again.
Drilled out the center with a forstner bit with no drama and then went to bore it to size.
So much drama. First boring bar made a snarl that caught the part and ripped it out of the chuck and launched it across the shop and bent the bar.
Second attempt with a stoughter bar worked much better.
Went to part it off and it launched again. Took 1/2 hour to find. Ended up using a flush cut saw to finish.
Put in the chuck to face off the saw cut and this time it stayed in place.
Next time I'll listen to whoever it was that said to use a 4 jaw instead of a 3 jaw.
 
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