Interesting about acetyl being non-hydroscopic. Although I'll take your
word for it, we have constant problems in wet areas where acetyl was
used and the material degraded. It usually shows up as stress cracks as
though the material has swollen slightly. I've even had some parts
explode from internal stresses when used in hot water.

Koz (who is responding late because he was ghawn)

Dennis J Brown wrote:

Acetal is NON-HYDROSCOPIC I don't even have to gry it to injection mold it.
Nylon IS.
"Koz" wrote in message
...


Whichever you choose, the material will need to have a UV stabilizing
additive. Generally this is simply carbon and turns the material black.
I would probably choose black UHMW (some people call it UHMWARCB for
Ultra high molecular weight abrasion resistant carbon black, but that's
a mouthfull). This assumes that the piece is a bushing and takes no
actual loads itself, except to fill a gap. UHMW will tend to cold flow
a little when it gets hot and is used as s structural member of some
kind. Machines beautifully though.

Delrin (acetal) is probably a good choice too. Delrin is often used in
bearings (as is UHMW) but tends to be slightly higher in yeild strength
when warm so may be more structurally stable. The negative about delrin
is it can absorb some water and swell and can also crack. UHMW is
almost impossible to crack (until it breaks down from UV)

koz

Geoffrey W. Schultz wrote:



I have a KISS wind generator wind generator that develops vibration at
certain wind speeds. The problem is that there's a PVC fitting that goes
over a 2" stainless schedule 40 support pipe that is loose fitting. I


want


to machine one with a sleeve bearing on a lathe and make it out of


plastic.


However, I really don't have any experience machining plastic, I've been
looking at www.mscdirect.com under Raw Materials/Plastic Material/Rods


for


3" material. To keep costs under control I'm looking at the following:

Nylon
Acetal
UHMW
LDPE
HDPE

Comments on the machining qualities, UV resistance, and overall strength


of


these would be greatly appreciated.

-- Geoff