Drilling UHMW

[eric.h...@hotmail.com]

ALWAYS clamp UHMW before drilling.

I always recommend using a drill press when drilling UHMW. You get a
much better hole. However, you can get away with using a hand drill as
well. Just remember, UHMW grabs at tools. The hand drill will tend to
twist more than it does when drilling wood. Be ready for it.

1. I avoid twist drills with this material. They don't seem to make
very accurately-sized holes.
Use Forstner bits or brad-point drill bits.

2. Always remember - UHMW DOES NOT CHIP. So, if you use a continuous
drilling motion, you're going to get long stringers climbing the
shaft of the drill and getting tangled up in the chuck.
To avoid this, drill in short spurts with a little rest in between.
This will artificially manufacture a chip and prevent a mess at the
chuck.

3. You want to drill through the plastic as fast as your drill will
allow you to, especially with forstner bits that generate a lot of heat
as they rub against the walls of the hole. If you linger, you will
find that the drill bit crazes the surface of the hole, making it hard
and bumpy. This comes from the bit actually melting the plastic and
burning some of it in the process. Crazed UHMW does not slide well, so
allowing this to happen defeats the purpose of using UHMW.

4. I find I can get away with some of the more powerful bench model
drill presses as long as I'm drilling holes or using plug cutters
less than 1" in diameter. Above that, I need floor models. Above 2"
diameter, I find that I need a 1HP drill press and then I run into
problems with the arbour disengaging from the shaft.

5. Plug Cutters - I have had no problem with small plug cutters ( up to
1" diameter). They produce a plug with a nice finish as long as you
don't dawdle when drilling.
Above 1", it's a different story. The friction caused by trying to
force a tube through the plastic, complicated by the buildup of waste
in the slot ( Remember, UHMW doesn't chip and there's nowhere for
the waste to go) makes for a lousy surface on the plug.
I have found that a circle cutter works much better (up to 3"), but
you have to adapt the cutter's profile by grinding the part of the
square shaft that comes into contact with the outside of the hole. You
need to grind enough of this away to make sure that ONLY the cutting
edge is making contact with the outside wall. Since this outside edge
tends to stabilize the tool in the plastic, you will find that the
machine tends to vibrate quite a bit. Altogether, not a very good
solution.

There is another way to cut UHMW plugs that is much better. Cut an
oversized SQUARE piece, put it between centers on a lathe and turn it
down to the proper size. This is the safest method and it is the way
that I would recommend.