Machining plastics

[bfk]

I'm looking for tips on machining plastics. I know acetal is said to be easy to machine, but what little things will make it easier, or less expensively destructive?
And how about UHMW, nylon, or even HDPE. I suspect that there could be a problem with melting, but I'd rather benefit from your experience than end up with a bunch of tools with baked on plastic.
Part of the reason is that I mentor the high school robotics team in town and they now have a mill (LMS 3990) and an Emco Maximat 7 (gifted from the university, and needing checked out), and it might be safer to have them experiment on plastic rather than metal as a first step. But I might be totally wrong about that.

Brian

 

[KMoffett]

One issue that you might run into with slick plastics, is material holding.

Ken

 

[mmcmdl]

Flood coolant is your friend . Or just blast air or even a spray mist to clear your chips . If you're trying to feed too quick for your rpm's , you may run into trouble .

 

[Metal]

Another thing I've found is uncoated, really sharp tools with one flute (on the mill) really does the job
You need to manage the long, long, long, stringy chips so they don't tangle up on everything though

 

[GoceKU]

I've machined plenty of nylon and is not difficult at all, lots of chips, i've even used worn out brazed carbide tools still cuts well, sharp radius HSS tool leaves best finish.

 

[ch2co]

I guess I never thought about it. I just blindly started with some nylon and it cut pretty well and then tried delrin and was very impressed
with how easy it was to mill or turn. No special tooling, just watch out for taking too deep a cut because it will melt on you. Neither tend
to produce chips, just long tangling threads that get wound around everything.

 

[Ulma Doctor]

delrin is forgiving with a wide range of tooling and is just beautiful to machine on a lathe or mill.
if you work delrin too hard or generate excessive heat in it's working, formaldehyde will be released from the acetal and a strong smell will be noticed.
i have used sharp and well radiused tooling with great success.

Nylon is similar but sharp generously radiused tools seem to finish nylon nicely.

i don't have enough practical experience to share an intelligent opinion on tooling for HDPE or UHMW.

sharp tooling is a good thing for most plastics in my experience

 

[Asm109]

Once you try machining HDPE you will never want to do it again. It just doesn't cut clean.

 

[uncle harry]

Once you try machining HDPE you will never want to do it again. It just doesn't cut clean.

Polypropolyne (sp ?) is similarly evil. I use it primarily because I got a potload of it for an hour's worth consulting and an hour round trip.

 

[mksj]

Similar experience to Ulma Doctor. HDPE or High Density Polyethylene, there are lots of cross linked (high density) variations, often seen it in medical practice as a mating surface in joint replacement UHMWPE and HXLPE. Very durable and tough stuff. I mostly have machined delrin on the lathe and mill, using very sharp uncoated cutters at fairly high speed. Comes out with a very nice finish. Polyethylene is softer and deforms more, and may be stringier, you also may get more deflection in the work piece and if you advance the cutter too quickly at low speed it could catch. I was planning on machining some HDPE for mill covers on either side of my vice, so will see how that machines.

I also would be very careful of turning some plastics on a lathe, I recall one case were an individual was practicing on some heavy wall PVC pipe, it deformed while turning and got caught up on the cutter, made a real mess. Also some plastics like acrylics will shatter and also the heat from the cutter will melt the plastic and can be catastrophic. Lexan or polycarbonate will not shatter, but it requires the right cutters and speeds. My vote would be for delrin using very sharp cutters, I recently did some work with delrin and the finished milling was absolutely smooth.