Need Help!- cutting UHMW polyethylene

[rardoin]

Anyone with experience cutting UHMWPE. Speeds and feeds info would be appreciated before I gum up or burn up carbide. I will be outside profiling a part and performing .75" deep pocketing. Discoloration of the piece is not a problem so coolant is OK if advised. Any info would be greatly appreciated.

RCA

[cadman@teluspla]

We do quite a bit of UHMW . you can treat it like Nylatron,
make sure your carbide is very sharp, I think virgin carbide is best.
If you are inside a pocket coolant is best, you will find the chips sort of clump if left in the slot. I find it best to use a smaller mill and pocket mill rather than slot mill.
you might be tempted to use a 60 deg. helix, if you do make sure that you can hold on to the part, if you get to agressive it will pull out of your vise
due to its slippery nature.
Just my 2 cents

[Geof]

Micrograin carbide high helix tools for aluminum work well, but they have to be new. A tool that has touched metal will not perform as well.

Use the same rpm that would be used for aluminum and take healthy cuts, maybe two or three times the chipload that would be used for aluminum, and as mentioned make sure your part is clamped well.

As far a clamping goes just relying on friction to hold UHMWPE is dicey, it is very slippy and not very rigid so it will pull out of vise jaws. Some kind of keying is necessary to hold it under aggressive cutting. For blocks if possible prep the part with a dovetail step and use custom jaws which form a mating dovetail so the material is gripped and held down.

When working with sheet material held down with bolts it is sometimes handy to have a sheet of 1/8" or 1/4" aluminum over the top and machine through it. This spreads the bolt pressure over a larger area and stops corners lifting under the action of the cutter.

[rardoin]

Thanks to both of you for such an in depth and quick reply. I really did not consider the "slickness" of the material as relates to fixturing, good points to consider. My only experience with UHMWPE has been in manual turning operations and clamping in the 3 jaw chuck was not a problem. Since I am working on round stock I have already prepared Al jaws which will grip about 1.5 in in depth of a 4 in diameter stock. Hopefully this will be adequate.

Thanks, RCA