Drilling UHMW

[hackmeister]

I was drilling some uhmw the other day using the tailstock on an engine lathe and had a difficult time getting the size hole I needed. The hole ends up being about .005-.007 undersize what the drill is (.750) I was able to make it work by using an adjustable reamer, but the finish was poor. What do you do to make a drill cut to size in this uhmw stuff?

[judleroy]

If you can use flood coolant that should help since the plastic swells alot when it gets hot and then shrinks when it cools off. I have only really had good luck with holes being accurate when I finish an undersized hole with a boring bar. Shoot for thicker chips(more
like an old telephone cord) and drill fast enough to get a similar chip. The thicker the chip the faster the heat is disipated from the material.
Judleroy

[hackmeister]

Thanks judleroy. No flood coolant on the lathe I was using. Would double drilling work? Use a drill about .030 under and then shoot for size. With most of the material gone heat should not be a problem, right?