arw01 wrote:
What do you guys DO with the UHMW Poly?

I've picked up my pieces from a local scrap place that buys from a
plastics distributor their left overs. But only one piece was used as
a sled runner and it is too flexible for that.

Alan

To Alan;

UHMW (Ultra-High Molecular Weight) Polyethylene is a very slippery
plastic that is usually used to reduce friction on sliding services
when you make jigs for woodworking. In appropriately sized pieces, it
makes good cutting boards because it does not absorb water like other
plastics do. Since it does not absorb water, it does not absorb blodd
on cutting boards, which makes them more sanitary when you wipe them
down.
As an aside, for anybody that has ever wondered why Nylon bushings
squeak, it's because they absorb water. When they absorb water, they
expand and jam against the shaft they are on. UHMW will not absorb
water and therefore will not squeak.
Back to the lesson - UHMW is also valued by woodworkers because it
repels ALL Glues, including polycyanate and epoxy glues. I once asked
an industry expert how to glue UHMW pieces together and he replied,
"Use screws." (If you ever want to have some fun at a woodshow, take a
couple of pieces of UHMW over to those guys that claim to have a glue
that glues anything to anything and ask him to demonstrate on your
pieces. It drives them crazy.)
UHMW also has ENORMOUS crush resistance at room temperature (
approx 20 tons/square inch). So you cannot drive a nail through it
unless you drill a pilot hole, and you must drill pilot holes for all
screws or you'll snap them off. (UHMW will self thread with a pilot
hole)
UHMW does not have a lot of structural strength. If you're going
to use it as a fence for your table- or bandsaw or for your router,
either you need a really thick piece of you have to screw it to a piece
of wood of metal.
Woodworkers like UHMW because they can use all of their
woodworking tools on it and it's really soft to cut and easy on their
tools (You can literally carve it with a knife)

.. Some specific cautions-

1. UHMW DOES NOT CHIP. Engrave this on your skull because it's
extremely important. If you're drilling wood, the wood normally chips.
UHNW doesn't. It tends to wrap around the spindle of the drill if
you're using a Forstner bit, so don't be surprised when it does. I
find that if you drill a bit at a time and then raise the drill bit,
you will get chips that fall away from the work area normally.
2. If you are drilling large holes with a forstner bit, you want
to move the bit through the plastic as fast as possible. If the drill
bit spends a lot of time in the plastic, the plastic will start to melt
and you will get crazing on the inside of the hole.
3. When you lathe UHMW, it does not chip. So if you're doing deep
cuts you want to cut a bit, pull the tool back, then cut a bit. Then
you'll get small chips that won't start wrapping around your spindle.
4. Table-sawing - Some thicker pieces of UHMW will start to curl
back into themselves on long cuts, which will tend to bind the saw.
You can prevent this by putting small wedges in the end of the boards
to keep them open.
5. Bandsawing - See # 4 above in spades. A friend of mine put an
impressive kink in his bandsaw blade when he tried to crosscut a 7"
diameter piece by grabbing either end and pushing it through the blade.
He made it about 3/4's of the way through when the ends of the plastic
came together, grabbed the blade and stopped it dead in about 1/10th of
a second. If you have to resaw by bandsaw, use wedges.
6. Routing. - No special problems because routers make their own
chips. I advise against using router mats because the plastic is so
slippery.
7. Surface planing/jointing - Again, no special problems.


A special note of caution. If UHMW ignites, it smells like candles
buring, but the drippings are NOT wax. They will burn through your
skin right to the bone and keep buring until the fuel is exhausted.
Hurts like hell and you're talking 3rd degree burns. So be careful.

Hope that helps.

Eric