UHMW

[Doggggboy]

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?

 

[Arbutus]

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!

 

[Downwindtracker2]

I have not turned any, but have drilled a fair bit. We liked using a Speedbor bit for counterboring for weld on buttons. When I used the drill press I ground negative rake onto the bits.

 

[PeterT]

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) 7 use tailstock when you can. You cant rely on metal rules of thumb.

 

[KeeponDragon]

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.

 

[David]

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.

 

[Doggggboy]

Maybe I'll just tell him the lathe is broken.
And the mill.
And my arm.

 

[ChazzC]

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.

 

[Doggggboy]

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.

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.

 

[CWelkie]

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.