General Information about UHMW
eric.h...@hotmail.com
Ultra-High Molecular Weight Polyethylene is a member of a group of
plastics called polyolefins. This family includes all polypropylenes
and polyethylenes. UHMW has the following specific benefits;
1. It is relatively soft - you can carve it with a knife
- it's easy on tools (we recommend that you use carbide tools
wherever possible)
- It will not scratch most other plastics or hardwoods
- if used as a cutting board, it will not tend to dull knives.
2. It has an extremely stable and closed molecular structure
- It will not react to most chemicals
- you cannot glue it (more on this later)
- it will not absorb water, unlike most other plastics.
- it is non-toxic
3. It has a slight tendency to "grab" when you are using tools on
it (because it is so soft)
- you have to clamp it when drilling
- you should clamp it if you are routing (ESPECIALLY if you are
plunge routing)
4. It has an extraordinary resistance to compression (at least 20 Tons
per square inch)
- you cannot nail UHMW unless you drill a pilot hole the diameter of
the shank of the nail
- DO NOT attempt to use power nailers, either air-powered or the
ones with the explosive charge, to nail UHMW. The nail will either
ricochet or jam in the tool, causing a potentially fatal buildup of
pressure within the tool.
- Whether using screws or lag bolts, you must drill a pilot hole at
least as large as the central shaft or you will break it off in the
plastic. (As long as you do this, UHMW will self-tap)
5. UHMW is very slippery
- it is the third most slippery plastic available (Teflon and acetal
are slipperier but much more expensive)
-UHMW makes an excellent linear bushing (fancy name for a sliding
surface). That's why woodworkers like it for their jigs.
- UHMW will even make an excellent bushing for an item that turns,
BUT only if the item revolves at a low rpm (I would think 50 rpm or
less)
6. It absorbs no water - Normal plastics do absorb water. That's
why nylon bushings squeak when they get wet. They absorb water, expand
and start binding against the shaft.
- UHMW absorbs ZERO water. This makes it ideal for water
applications like fence hinge busings, etc
7. UHMW does not chip like wood does
- UHMW has no grain, so it does not chip normally. This becomes
important when you are drilling or turning it.
8. UHMW does not have a lot of structural strength
- This plastic is slippery, not strong. You should always fasten a
UHMW piece to a piece of wood or steel, especially if it is a thin
piece. You can occasionally get away without the supports if the UHMW
is above ½" in thickness. It depends on the application.
- NEVER try to use UHMW to make a shelf unless it is attached to
wood.
9. UHMW does not bond to any glue
- This can be very useful, as you can use UHMW as a facing material
for any gluing jig without gluing the jig to the material you want
glued. The wood glue, once dried, will peel right off.
10. Since UHMW is a cast plastic, formed under pressure, the
thicknesses along the surface can vary as much as 10%. You may have to
surface plane pieces to get perfectly smooth sides.
11. Standard UHMW will not give any glossier finish than a semi-gloss.
Certain types of UHMW, like anti-static UHMW, may achieve a finish
closer to gloss.