Machining Plastic
 

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

Machining Plastic
 

In article ,
"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


I know nothing of Acetal or UHMW (until reading this message, not even
the fact that they existed) but I can tell you with certainty that the
UV resistance of PE (Either HD or LD "flavors") is pretty much
nonexistent. They'll both "brittle up" and start to crumble in short
order. Depending on the thickness, coloring (if any), exact amount of
exposure, intensity of the UV source, and so on, they may start showing
signs of problems in just a few hours, or they may stand up for a few
days, but they *WILL* disintegrate into a worthless scattering of
plastic dust in far less time that what you're likely to call
"acceptable" for your application.

Nylon also gets a bit weird when left in the sun, but not in every case,
so I would presume there are variations (probably from additives aimed
specifically at altering UV characteristics) within the overall
type-designation "nylon" that have at least some UV resistance.

--
Don Bruder - --- Preferred Email - SpamAssassinated.
Hate SPAM? See http://www.spamassassin.org for some seriously great info.
I will choose a path that's clear: I will choose Free Will! - N. Peart
Fly trap info pages: http://www.sonic.net/~dakidd/Horses/FlyTrap/index.html

Machining Plastic
 

Don Bruder wrote:
In article ,
"Ge
offrey W. Schultz" wrote:
snip I know nothing of Acetal or UHMW (until reading this message, not even
the fact that they existed) but I can tell you with certainty that the
UV resistance of PE (Either HD or LD "flavors") is pretty much
nonexistent. They'll both "brittle up" and start to crumble in short
order. Depending on the thickness, coloring (if any), exact amount of
exposure, intensity of the UV source, and so on, they may start showing
signs of problems in just a few hours, or they may stand up for a few
days, but they *WILL* disintegrate into a worthless scattering of
plastic dust in far less time that what you're likely to call
"acceptable" for your application.

It depends on the additives.
I've got an around 10 year old poly-tunnel, which is ~0.5mm polythene sheet
covering aluminium hoops.
Works well, the plastic has not become brittle enough to tear even in
relatively high winds.

Machining Plastic
 

My choice from these would be UHMW. Best machining of the group and at least
in my very limited experince doesn't seem to break down when used outside.

Use a VERY SHARP HSS cutter and a cold air gun if you have it or an air hose
if you don't. The problem here is melting on the cutter, so slow the rpm's
down if you get that. All plastics don't hold their shape well, UHMW is no
exception, light cutting and clamping forces help. Also water can absorb and
change dimensions on UHMW, I think.

My knowledge here ain't perfect. Maybe others would care to comment.

Karl

Machining Plastic
 

Best plastic for a bushing would be Nylon or Delrin.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.



"Geoffrey W. Schultz" wrote in message
7.77...
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

Machining Plastic
 

In article ,
Ian Stirling wrote:

Don Bruder wrote:
In article ,
"Ge
offrey W. Schultz" wrote:
snip I know nothing of Acetal or UHMW (until reading this message, not even
the fact that they existed) but I can tell you with certainty that the
UV resistance of PE (Either HD or LD "flavors") is pretty much
nonexistent. They'll both "brittle up" and start to crumble in short
order. Depending on the thickness, coloring (if any), exact amount of
exposure, intensity of the UV source, and so on, they may start showing
signs of problems in just a few hours, or they may stand up for a few
days, but they *WILL* disintegrate into a worthless scattering of
plastic dust in far less time that what you're likely to call
"acceptable" for your application.

It depends on the additives.
I've got an around 10 year old poly-tunnel, which is ~0.5mm polythene sheet
covering aluminium hoops.

"Polythene"? (Tries to figure out why that rings a bell... And fails...
I've heard of the stuff before, but I can't remember where or in what
context)

Idunno what you've actually got, but if it has survived 10 years in
sunlight, I'm certain beyond any possibility of doubt that it's
something other than Polyethylene.

Whether high or low density, polyethylene is notorious for
disintegrating in sunlight - 6 months, tops, is all the longer a piece,
especially a thin sheet, of it can be reasonably expected to last when
directly exposed to sunlight. If it lasts beyond that, it's a safe bet
that, whatever it is, it ain't PE.

--
Don Bruder - --- Preferred Email - SpamAssassinated.
Hate SPAM? See http://www.spamassassin.org for some seriously great info.
I will choose a path that's clear: I will choose Free Will! - N. Peart
Fly trap info pages: http://www.sonic.net/~dakidd/Horses/FlyTrap/index.html

Machining Plastic
 

"Roger Shoaf" wrote in message
...
Best plastic for a bushing would be Nylon or Delrin.

I'm not convinced either of them would be the best plastic, but each of them
are available as bushing material and would be a good choice, assuming
either variety that was chosen was of that nature. Nylon so found is black
in color as I recall, and has graphite included in its makeup for lubricity.
Delrin is available with Teflon included (Delrin AF), which makes it a
superior bearing over typical acetyl, but I have no clue about either's
ability to resist UV, which, for sure, is death on white acetyl plastic,
albeit a slow one in some cases. Delrin AF is a light milk chocolate color
and is a pleasure to machine. Likewise, the black nylon machines better
than the ivory colored stuff. Apparently the graphite helps lessen the
stringiness for which nylon is so well known. If the piece in question
can be covered by anything that would shield it from UV, I'm of the opinion
that material choice would not be so critical.

Harold

Machining Plastic
 

On Wed, 12 Nov 2003 14:02:57 GMT, "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

Delryn, aka acetal, machines very nicely. Don't know how UV stable
it is. It (and nylon) will absorb moisture a little with
consequent slight dimensional change.

Another possibility might be Noryl.

Machining Plastic
 

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

Machining Plastic
 

I have a KISS wind generator wind generator that develops vibration at
certain wind speeds. T

Balance it more carefully.

The problem is that there's a PVC fitting that goes
over a 2" stainless schedule 40 support pipe that is loose fitting.

Are you _sure_ that's the problem? This is a support pipe, not a running fit,
right? Oscillations are supported by springy supports, not by loose fitting
ones.

I want
to machine one with a sleeve bearing on a lathe and make it out of plastic.

If that's what you want to do we can help.

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.


Use the web engine to find your stock, then show the catalog page for machining
data there.

Acetal is Delrin, right? That's the one you want. All the others melt during
machining. Delrin is pretty stiff and strong. A good all around engineering
plastic. UV grade is black.



Yours,

Doug Goncz (at aol dot com)
Replikon Research, Seven Corners, VA

1100 original posts at:
http://groups.google.com/groups?as_e...uthors=dgoncz@

Machining Plastic
 

Don Bruder wrote:
In article ,
Ian Stirling wrote:

Don Bruder wrote:
In article ,
"Ge
offrey W. Schultz" wrote:
snip I know nothing of Acetal or UHMW (until reading this message, not even
the fact that they existed) but I can tell you with certainty that the
UV resistance of PE (Either HD or LD "flavors") is pretty much
nonexistent. They'll both "brittle up" and start to crumble in short
order. Depending on the thickness, coloring (if any), exact amount of
exposure, intensity of the UV source, and so on, they may start showing
signs of problems in just a few hours, or they may stand up for a few
days, but they *WILL* disintegrate into a worthless scattering of
plastic dust in far less time that what you're likely to call
"acceptable" for your application.

It depends on the additives.
I've got an around 10 year old poly-tunnel, which is ~0.5mm polythene sheet
covering aluminium hoops.

"Polythene"? (Tries to figure out why that rings a bell... And fails...
I've heard of the stuff before, but I can't remember where or in what
context)

I think it's a more commonly used in the UK synonym for polyethylene.


Idunno what you've actually got, but if it has survived 10 years in
sunlight, I'm certain beyond any possibility of doubt that it's
something other than Polyethylene.

Whether high or low density, polyethylene is notorious for
disintegrating in sunlight - 6 months, tops, is all the longer a piece,
especially a thin sheet, of it can be reasonably expected to last when
directly exposed to sunlight. If it lasts beyond that, it's a safe bet
that, whatever it is, it ain't PE.

It is, it's all in the additives.
Polythene tape of a similar thickness is translucent, "white", and degrades in
a few months.
This has a fairly pronounced yellow cast, due to the UV blockers.

Machining Plastic
 

For UV resistance select from........

Abs
Acetal (delrin)
Noryl
Nylon
PBT
Polycarbonate Glass Filled
all above in color black

PEEK - if you have LOTS of money, ie 1993 per foot, 2" dia, $231.88,
unless you would like a "sheet", which is only 12" x 48" x 2" thick,
sit down........$7163.20
Acrylic (UF-3, UF-4, Solar Shield)
Polycarb (Tuffak XL, Hyzod SR)
Poly-Teak Board
PVDF (Kynar)
Starboard
Starlite 6000
UHMW
Ultem 1000

source was a Laird Plastics selection guide

Someone else can please narrow down the other factors.

michael

Machining Plastic
 

Hey Geoff,

Have you considered Micarta or Bakelite? Works pretty well, and
machines OK too.

Take care.

Brian Lawson,
Bothwell, Ontario.

Machining Plastic
 

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

Machining Plastic
 

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.

If you select to use Nylon you should slit that
bushing lengthwise. Moisture and/or temperature
changes will otherwise change the fit and could
grab the shaft. The slit allows for expansion. HTH
--
SATOR AREPO TENET OPERA ROTAS
Have 5 nice days! John
******************************
--- ILN 000.000.001 ---

Machining Plastic
 

Based upon input from this forum, rec.rec.boats.cruising and all of the
pointers that were provided, I decided to go with black UHMW. As
described on some web sites it's the "poor man's teflon" with a very low
coefficient of friction, good UV stability and machines well. On top of
that, a 3"x1' piece of rod UHMW is only $11. I ordered it yesterday
from MSC and it'll be here today.

I've opted to simply machine the UHMW to form the sleave bearing surface
rather than purchase a sleave bearing and mount it in the housing. I'll
let you know how it turns out,

Thanks again for all of the help!

-- Geoff


John wrote in :

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.

If you select to use Nylon you should slit that
bushing lengthwise. Moisture and/or temperature
changes will otherwise change the fit and could
grab the shaft. The slit allows for expansion. HTH

Machining Plastic
 

Getting back to METALWORKING ...

Is there a *reason* you're not making this out of bronze or steel?
Just because there was a plastic piece there *before* doesn't
necessarily mean you gotta have one now.

It seems that about half of you wear concerns and UV deterioration
problems would go away with a good bronze or steel sleeve bearing.
(Might help solve the vibration issue too.)

My two cents.
- Carl

"Geoffrey W. Schultz" wrote in message
7.77...
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

Machining Plastic
 

Geoffrey W. Schultz wrote:

However, I really don't have any experience machining plastic,

The most critical factor is a scary sharp cutter. Certain carbide
inserts work quite well if they are uncoated and of the
positive/negative type e.g. TNMP-321. You can hone these on a fine
diamond hone. Otherwise, a carefully honed HSS cutter.

Nylon
UHMW

I would choose one of those.

Comments on the machining qualities, UV resistance, and overall strength of
these would be greatly appreciated.

Could you avoid the UV resistance problem by placing a thin walled
stainless shield over the bearing area? Attach it to the mast but have
it not in contact with the bushing.

Ted

Machining Plastic
 

This is going on a boat in salt water. Steel would rust and there would
be a big glavanic corrision problem at the stainless/bronze interface.

-- Geoff

"Carl Hoffmeyer" wrote in
:

Getting back to METALWORKING ...

Is there a *reason* you're not making this out of bronze or steel?
Just because there was a plastic piece there *before* doesn't
necessarily mean you gotta have one now.

It seems that about half of you wear concerns and UV deterioration
problems would go away with a good bronze or steel sleeve bearing.
(Might help solve the vibration issue too.)

My two cents.
- Carl

"Geoffrey W. Schultz" wrote in message
7.77...
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

Machining Plastic
 

Actually, Geoff, it used to be that good turnbuckles were made with
stainless screws and bronze bodies (or vice versa). The reason is that
stainless galls badly against itself (as many of us know, although we may
not know the word for it other than, "!#$%&*?!" .) Stainless against bronze
runs freely and happily and is a much better quality device. Unfortunately,
they cost more and looked strange, and are now, I think, gone from the
market.

Galvanic doesn't become a real issue unless the two pieces are immersed.
Above deck, there may be a little salt around, but it mostly gets washed off
by the rain, I suspect.


--
Jim Woodward
www.mvFintry.com


..
"Geoffrey W. Schultz" wrote in message
4.17...
This is going on a boat in salt water. Steel would rust and there would
be a big glavanic corrision problem at the stainless/bronze interface.

-- Geoff

"Carl Hoffmeyer" wrote in
:

Getting back to METALWORKING ...

Is there a *reason* you're not making this out of bronze or steel?
Just because there was a plastic piece there *before* doesn't
necessarily mean you gotta have one now.

It seems that about half of you wear concerns and UV deterioration
problems would go away with a good bronze or steel sleeve bearing.
(Might help solve the vibration issue too.)

My two cents.
- Carl

"Geoffrey W. Schultz" wrote in message
7.77...
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

Machining Plastic
 

Jim,

I wish that you'd tell that to the stainless screws installed in aluminum
pieces aboard BlueJacket. Those that weren't treated with TefGel are
corroded. Since this is going to be a bearing surface I didn't want any
corrosion increasing the CoF.

-- Geoff

"Jim Woodward" jameslwoodward at attbi dot com wrote in
:

Actually, Geoff, it used to be that good turnbuckles were made with
stainless screws and bronze bodies (or vice versa). The reason is
that stainless galls badly against itself (as many of us know,
although we may not know the word for it other than, "!#$%&*?!" .)
Stainless against bronze runs freely and happily and is a much better
quality device. Unfortunately, they cost more and looked strange, and
are now, I think, gone from the market.

Galvanic doesn't become a real issue unless the two pieces are
immersed. Above deck, there may be a little salt around, but it mostly
gets washed off by the rain, I suspect.

Machining Plastic
 

Jim,

I was also under the impression that the Anodic voltage difference between
two metals should be kept below .15 V in harsh environments. Bronze has an
Anodic voltate of 0.25 to 0.33 (average 0.29) and 300 grade stainless has a
range of 0.0 to 0.15 (average 0.075). This gives a difference of about
0.22V, which is outside of what I thought was acceptable.

-- Geoff

"Jim Woodward" jameslwoodward at attbi dot com wrote in
:

Actually, Geoff, it used to be that good turnbuckles were made with
stainless screws and bronze bodies (or vice versa). The reason is
that stainless galls badly against itself (as many of us know,
although we may not know the word for it other than, "!#$%&*?!" .)
Stainless against bronze runs freely and happily and is a much better
quality device. Unfortunately, they cost more and looked strange, and
are now, I think, gone from the market.

Galvanic doesn't become a real issue unless the two pieces are
immersed. Above deck, there may be a little salt around, but it mostly
gets washed off by the rain, I suspect.

Machining Plastic
 

Geoff --

Bronze and stainless turnbuckles are not my imagination. They are mentioned,
favorably, in Understanding Rigs and Rigging, Richard Henderson,
International Marine, 1991 and in Rod Stephens' chapter in Desirable and
Undesirable Characteristics of Offshore Yachts, John Rousmaniere, ed. W.W.
Norton, 1987. (I assume you know of Stephens -- Henderson wrote the USNA -
Annapolis official textbook on boats, among many other things.)

Turns out, they are not gone from the market. Some current Navtec
turnbuckles are stainless and bronze (the web site isn't clear, but the
paper catalog is).

As for stainless screws into aluminum, I'm with you. As a whole, however, we
don't have much in the way of alternatives for attaching things to masts,
particularly where the mast alloy can't be welded, so you frequently see it.
As you say, one of the pastes will help. Best solution is to through bolt
with plastic washers, but doing that on a mast or boom can require
imagination, good hands, and luck.

So, again, I would seriously consider a bronze bushing here......

--
Jim Woodward
www.mvFintry.com


..
"Geoffrey W. Schultz" wrote in message
4.17...
Jim,

I wish that you'd tell that to the stainless screws installed in aluminum
pieces aboard BlueJacket. Those that weren't treated with TefGel are
corroded. Since this is going to be a bearing surface I didn't want any
corrosion increasing the CoF.

-- Geoff

"Jim Woodward" jameslwoodward at attbi dot com wrote in
:

Actually, Geoff, it used to be that good turnbuckles were made with
stainless screws and bronze bodies (or vice versa). The reason is
that stainless galls badly against itself (as many of us know,
although we may not know the word for it other than, "!#$%&*?!" .)
Stainless against bronze runs freely and happily and is a much better
quality device. Unfortunately, they cost more and looked strange, and
are now, I think, gone from the market.

Galvanic doesn't become a real issue unless the two pieces are
immersed. Above deck, there may be a little salt around, but it mostly
gets washed off by the rain, I suspect.

Machining Plastic
 

In article , Geoffrey W.
Schultz says...

I wish that you'd tell that to the stainless screws installed in aluminum
pieces aboard BlueJacket. Those that weren't treated with TefGel are
corroded. Since this is going to be a bearing surface I didn't want any
corrosion increasing the CoF.

Hmm. Are you sure it was the SS, and not the
aluminum, that was going bad? I think that
aluminum will corrode badly in salt air in
very short order.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

Machining Plastic
 

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

Machining Plastic
 

I just wanted to let you know that I machined the part earlier this week
and was VERY happy with the finish that I got. It's a smooth as a baby's
bottom. I had to cut 2" pipe threads also, and they turned out perfect
also. Taking larger cuts of .100 to .150 worked great using a very sharp
HSS cutter,

-- Geoff

Based upon input from this forum, rec.rec.boats.cruising and all of the
pointers that were provided, I decided to go with black UHMW. As
described on some web sites it's the "poor man's teflon" with a very low
coefficient of friction, good UV stability and machines well. On top of
that, a 3"x1' piece of rod UHMW is only $11. I ordered it yesterday
from MSC and it'll be here today.

I've opted to simply machine the UHMW to form the sleave bearing surface
rather than purchase a sleave bearing and mount it in the housing. I'll
let you know how it turns out,

Thanks again for all of the help!

-- Geoff