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Default Design Q: O-rings as wipers? Fuzzy O-rings?


I know o-rings are used in hydraulics as seals, wipers.
But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4" id,
with the id smooth but unpolished, and not a great material, like alum...
no flashing.

I see two possibilities: o-ring material itself with a square xsection, in
a groove around the 3/4 material. But the corners would have a radius,
unless I could find o-ring stuff with a square xsection and also for
square/rect rod.

Square xcection o-ring material can be found here
http://www.epm.com/square_cut.htm
but round bar/rod, not sq or rect. bar.


Or, on the END of the 3/4 bar, take a nominal 3/4 sq pc of some compressible
(but hopefully low-frcition) material, and screw it to the end end of the
3/4 bar, the tension of the screw (and washer/plate) squeezing out the wiper
material for a suitable "fit" on the inner wall of the tube.

Compressibility (rubber) and low friction *seem* to be mutually exclusive
properties, but not sure.
Some kind of leaf spring steel/brass wiper could do as well, altho I
wouldn't want stuff too mechanically fragile.

Or just screw some felt/cloth to the end of the 3/4 bar???

The logic, rationale behind this is that the 3/4" bar needs to slide freely
but be reasonably low tolerance (.005 to .010), which could allow grit to
jam it in the tube. Ergo the wipers. A square fuzzy o-ring for rect. mat'l
would be ideal.

Idears, leads?
--
EA


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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sun, 24 Mar 2013 12:53:38 -0400, "Existential Angst"
wrote:


I know o-rings are used in hydraulics as seals, wipers.
But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4" id,
with the id smooth but unpolished, and not a great material, like alum...
no flashing.

I see two possibilities: o-ring material itself with a square xsection, in
a groove around the 3/4 material. But the corners would have a radius,
unless I could find o-ring stuff with a square xsection and also for
square/rect rod.

Square xcection o-ring material can be found here
http://www.epm.com/square_cut.htm
but round bar/rod, not sq or rect. bar.


Or, on the END of the 3/4 bar, take a nominal 3/4 sq pc of some compressible
(but hopefully low-frcition) material, and screw it to the end end of the
3/4 bar, the tension of the screw (and washer/plate) squeezing out the wiper
material for a suitable "fit" on the inner wall of the tube.

Compressibility (rubber) and low friction *seem* to be mutually exclusive
properties, but not sure.
Some kind of leaf spring steel/brass wiper could do as well, altho I
wouldn't want stuff too mechanically fragile.

Or just screw some felt/cloth to the end of the 3/4 bar???

The logic, rationale behind this is that the 3/4" bar needs to slide freely
but be reasonably low tolerance (.005 to .010), which could allow grit to
jam it in the tube. Ergo the wipers. A square fuzzy o-ring for rect. mat'l
would be ideal.

Idears, leads?


A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress
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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Mar 24, 1:11*pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress


That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.


Dan

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Default Design Q: O-rings as wipers? Fuzzy O-rings?

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress


That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
================================================== =

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?
--
EA



Dan



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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sun, 24 Mar 2013 16:35:24 -0400, "Existential Angst"
wrote:

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress


That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
================================================= ==

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.

--
Ed Huntress


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Default Design Q: O-rings as wipers? Fuzzy O-rings?

"Ed Huntress" wrote in message
...
On Sun, 24 Mar 2013 16:35:24 -0400, "Existential Angst"
wrote:

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress


That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
================================================ ===

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.


Hmmm, perty hard.

Hey Ed, is yer email workin?
--
EA



--
Ed Huntress



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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On 3/24/2013 1:35 PM, Existential Angst wrote:
wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress


That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
================================================== =

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?

It tends to "cold flow" when compressed, so I would say that using it in
compression might require replacing it often.

BobH
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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sun, 24 Mar 2013 17:09:03 -0400, "Existential Angst"
wrote:

"Ed Huntress" wrote in message
.. .
On Sun, 24 Mar 2013 16:35:24 -0400, "Existential Angst"
wrote:

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress

That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
=============================================== ====

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.


Hmmm, perty hard.


Yes, but as Dan knows, it's slippery as a greased pig -- slipperier,
actually. It makes a great unlubed bearing surface -- like Teflon on
steroids.

As long as you don't have a lot of interference, it shouldn't have any
trouble with roughness. It's pretty exceptional material. It won't
handle much heat, though: 180 deg. F for continuous duty.

Try it, if you can get your hands on a sample piece.


Hey Ed, is yer email workin?


Yup. Delete the "3" from the phony one. 'Just one "s" in the "huntres"
part.

--
Ed Huntress
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Default Design Q: O-rings as wipers? Fuzzy O-rings?


"Ed Huntress" wrote in message
news
On Sun, 24 Mar 2013 17:09:03 -0400, "Existential Angst"
wrote:

"Ed Huntress" wrote in message
. ..
On Sun, 24 Mar 2013 16:35:24 -0400, "Existential Angst"
wrote:

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress

That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
============================================== =====

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?

I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.


Hmmm, perty hard.


Yes, but as Dan knows, it's slippery as a greased pig -- slipperier,
actually. It makes a great unlubed bearing surface -- like Teflon on
steroids.

As long as you don't have a lot of interference, it shouldn't have any
trouble with roughness. It's pretty exceptional material. It won't
handle much heat, though: 180 deg. F for continuous duty.

Try it, if you can get your hands on a sample piece.


Hey Ed, is yer email workin?


Yup. Delete the "3" from the phony one. 'Just one "s" in the "huntres"
part.

--
Ed Huntress


The UHMW could be a thin sheet so it bends more than it compresses.

But I am confused about one thing; if you can screw this wiper to the end of
the inside rod, couldn't you just seal up that end of the outside tube? Afer
all, if the end of the inside rod ever protrudes, the wiper will not seal
anything.

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Default Design Q: O-rings as wipers? Fuzzy O-rings?

Ed Huntress fired this volley in
:

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


UHMWPE is both compressible and elastic -- A LOT compressible, but not a
lot elastic. FWIW, you can usually let the compression-set between
fixed-spacing parts determine the elastic point for you, since it will
deform under pressure, then stop with some elasticity left to recover
back a few tenths.

LLoyd


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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sun, 24 Mar 2013 12:53:38 -0400, "Existential Angst"
wrote:


I know o-rings are used in hydraulics as seals, wipers.
But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4" id,
with the id smooth but unpolished, and not a great material, like alum...
no flashing.

I see two possibilities: o-ring material itself with a square xsection, in
a groove around the 3/4 material. But the corners would have a radius,
unless I could find o-ring stuff with a square xsection and also for
square/rect rod.

Square xcection o-ring material can be found here
http://www.epm.com/square_cut.htm
but round bar/rod, not sq or rect. bar.


Or, on the END of the 3/4 bar, take a nominal 3/4 sq pc of some compressible
(but hopefully low-frcition) material, and screw it to the end end of the
3/4 bar, the tension of the screw (and washer/plate) squeezing out the wiper
material for a suitable "fit" on the inner wall of the tube.

Compressibility (rubber) and low friction *seem* to be mutually exclusive
properties, but not sure.
Some kind of leaf spring steel/brass wiper could do as well, altho I
wouldn't want stuff too mechanically fragile.

Or just screw some felt/cloth to the end of the 3/4 bar???

The logic, rationale behind this is that the 3/4" bar needs to slide freely
but be reasonably low tolerance (.005 to .010), which could allow grit to
jam it in the tube. Ergo the wipers. A square fuzzy o-ring for rect. mat'l
would be ideal.

Idears, leads?

Since you want to keep dirt out I think your application would benefit
from a dense felt wiper. McMaster Carr used to sell felt in various
densities and probably still does. Cut a square of this stuff and use
a slightly smaller square of some type of stiff material held against
it with screws threaded into the end of the 3/4 bar. If the sliding
element is going to operate without lubrication, especially if the
tubular component is aluminum, you may run into problems with galling.
If you have room I would suggest making several plastic short
cylindrical pieces from acetal or UHMW. Press these plastic parts into
shallow flat bottom bores in the 3/4 bar. UHMW, while not as hard as
acetal, is an excellent material for this application. Delrin AF, a
teflon filled acetal plastic, would work better than UHMW, and is
easier to machine because it is a little harder. I know McMaster Carr
sells Delrin AF.
Good Luck,
ERic
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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Mar 24, 5:06*pm, Ed Huntress wrote:



Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.

--
Ed Huntress


It has some give. Milk jugs are made of polyethelene, and UHMW poly
is similar. Maybe slightly harder , but not much harder. We used
UHMW poly tape on the missile to prevent fretting of the graphite
epoxy where the seals contact the missile skin.


Dan

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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sun, 24 Mar 2013 19:03:59 -0700 (PDT), "
wrote:

On Mar 24, 5:06*pm, Ed Huntress wrote:



Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?


I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.

--
Ed Huntress


It has some give. Milk jugs are made of polyethelene, and UHMW poly
is similar. Maybe slightly harder , but not much harder. We used
UHMW poly tape on the missile to prevent fretting of the graphite
epoxy where the seals contact the missile skin.


Dan


I've only run my fingers over it and watched it perform as a bearing,
but the reports on its properties suggest it's pretty unusual stuff,
in terms of lubricity and other physical and mechanical properties.
How does it cut?

--
Ed Huntress
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Default Design Q: O-rings as wipers? Fuzzy O-rings?

Not O-Ring - but Washer, being square with a round hole.

Martin

On 3/24/2013 11:53 AM, Existential Angst wrote:
I know o-rings are used in hydraulics as seals, wipers.
But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4" id,
with the id smooth but unpolished, and not a great material, like alum...
no flashing.

I see two possibilities: o-ring material itself with a square xsection, in
a groove around the 3/4 material. But the corners would have a radius,
unless I could find o-ring stuff with a square xsection and also for
square/rect rod.

Square xcection o-ring material can be found here
http://www.epm.com/square_cut.htm
but round bar/rod, not sq or rect. bar.


Or, on the END of the 3/4 bar, take a nominal 3/4 sq pc of some compressible
(but hopefully low-frcition) material, and screw it to the end end of the
3/4 bar, the tension of the screw (and washer/plate) squeezing out the wiper
material for a suitable "fit" on the inner wall of the tube.

Compressibility (rubber) and low friction *seem* to be mutually exclusive
properties, but not sure.
Some kind of leaf spring steel/brass wiper could do as well, altho I
wouldn't want stuff too mechanically fragile.

Or just screw some felt/cloth to the end of the 3/4 bar???

The logic, rationale behind this is that the 3/4" bar needs to slide freely
but be reasonably low tolerance (.005 to .010), which could allow grit to
jam it in the tube. Ergo the wipers. A square fuzzy o-ring for rect. mat'l
would be ideal.

Idears, leads?

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Default Design Q: O-rings as wipers? Fuzzy O-rings?

Ed Huntress fired this volley in
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How does it cut?


Like butter on a saw. Like strings of spiderweb on a lathe!

It's important to take as heavy a cut as you can afford to without
springing the work out of the chuck. This, only because if you take
light cuts, you end up with a rat's nest of 'stringies' that will rapidly
interfere with the work. The heavy cut will produce a chip than can be
readily cleared.

Also, don't expect to take your last cut just moving swarf. All the
polyolefins have a tendency to spring away from the tool tip -- even if
it's razor-sharp of the correct rake. So you must take a deep enough cut
to overcome that resiliancy, and get the tool tip into the work and
cutting. Once in and cutting, the stuff cuts cleanly and easily.

Lloyd


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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Mon, 25 Mar 2013 06:11:51 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ed Huntress fired this volley in
:

How does it cut?


Like butter on a saw. Like strings of spiderweb on a lathe!

It's important to take as heavy a cut as you can afford to without
springing the work out of the chuck. This, only because if you take
light cuts, you end up with a rat's nest of 'stringies' that will rapidly
interfere with the work. The heavy cut will produce a chip than can be
readily cleared.

Also, don't expect to take your last cut just moving swarf. All the
polyolefins have a tendency to spring away from the tool tip -- even if
it's razor-sharp of the correct rake. So you must take a deep enough cut
to overcome that resiliancy, and get the tool tip into the work and
cutting. Once in and cutting, the stuff cuts cleanly and easily.

Lloyd


Hmm. I'll have to try some. I have a possible application, too.

Thanks, Lloyd.

--
Ed Huntress
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Default Design Q: O-rings as wipers? Fuzzy O-rings?

"anorton" wrote in message
news

"Ed Huntress" wrote in message
news
On Sun, 24 Mar 2013 17:09:03 -0400, "Existential Angst"
wrote:

"Ed Huntress" wrote in message
...
On Sun, 24 Mar 2013 16:35:24 -0400, "Existential Angst"
wrote:

wrote in message
...
On Mar 24, 1:11 pm, Ed Huntress wrote:



A square on the end of your rod, made of UHMWP:

http://en.wikipedia.org/wiki/Ultra-h...t_polyethylene

You shouldn't need to lubricate it.

--
Ed Huntress

That is exactly what I would do. You can get UHMW poly from either
MSC or Grainger. I got a little from MSC to have some around.
============================================= ======

Haven't read ed's link yet, but does it have any "give" to it, is it
compressible at all?

I'll let Dan comment on that, since he has some. Its measured hardness
is pretty high, though, like typical thermoplastics: Shore D 80.

Hmmm, perty hard.


Yes, but as Dan knows, it's slippery as a greased pig -- slipperier,
actually. It makes a great unlubed bearing surface -- like Teflon on
steroids.

As long as you don't have a lot of interference, it shouldn't have any
trouble with roughness. It's pretty exceptional material. It won't
handle much heat, though: 180 deg. F for continuous duty.

Try it, if you can get your hands on a sample piece.


Hey Ed, is yer email workin?


Yup. Delete the "3" from the phony one. 'Just one "s" in the "huntres"
part.

--
Ed Huntress


The UHMW could be a thin sheet so it bends more than it compresses.


That's a good insight. A block of UHMW poly would seem ok, but as a wiper,
you'd then have to machine the size pretty accurately. And then how long
would it last at that dim?

So give, springiness, flexibility would seem to be a requirement in any kind
of wiper -- even literally a spring pushing the wiper mat'l to the surface,
if the wiper mat'l itself is not flexible.

So a thin sheet has promise, in principle, altho it would remain to be seen
if the "concavity" of the bending sheet would accommodate both pushing and
pulling, or if the concacity could change with pushing/pulling.
Also, it would seem that two sheets would be necessary, to accommodate the
wiping of opposite faces, independently. Which can be finagled, with a
spacer between the two sheets.

This is food for thought.


But I am confused about one thing; if you can screw this wiper to the end
of the inside rod, couldn't you just seal up that end of the outside tube?
Afer all, if the end of the inside rod ever protrudes, the wiper will not
seal anything.


This was a simpliification of the app, for illustration of the problem. The
actual geometry is a little more complicated, but not by much: a rect
slider in a channel (actually, a tube with a long wide-ish slot in one
face), but the jamming issue is very similar.
--
EA





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Default Design Q: O-rings as wipers? Fuzzy O-rings?

wrote in message
...
On Sun, 24 Mar 2013 12:53:38 -0400, "Existential Angst"
wrote:


I know o-rings are used in hydraulics as seals, wipers.
But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4"
id,
with the id smooth but unpolished, and not a great material, like alum...
no flashing.

I see two possibilities: o-ring material itself with a square xsection,
in
a groove around the 3/4 material. But the corners would have a radius,
unless I could find o-ring stuff with a square xsection and also for
square/rect rod.

Square xcection o-ring material can be found here
http://www.epm.com/square_cut.htm
but round bar/rod, not sq or rect. bar.


Or, on the END of the 3/4 bar, take a nominal 3/4 sq pc of some
compressible
(but hopefully low-frcition) material, and screw it to the end end of the
3/4 bar, the tension of the screw (and washer/plate) squeezing out the
wiper
material for a suitable "fit" on the inner wall of the tube.

Compressibility (rubber) and low friction *seem* to be mutually exclusive
properties, but not sure.
Some kind of leaf spring steel/brass wiper could do as well, altho I
wouldn't want stuff too mechanically fragile.

Or just screw some felt/cloth to the end of the 3/4 bar???

The logic, rationale behind this is that the 3/4" bar needs to slide
freely
but be reasonably low tolerance (.005 to .010), which could allow grit to
jam it in the tube. Ergo the wipers. A square fuzzy o-ring for rect.
mat'l
would be ideal.

Idears, leads?

Since you want to keep dirt out I think your application would benefit
from a dense felt wiper. McMaster Carr used to sell felt in various
densities and probably still does. Cut a square of this stuff and use
a slightly smaller square of some type of stiff material held against
it with screws threaded into the end of the 3/4 bar. If the sliding
element is going to operate without lubrication, especially if the
tubular component is aluminum, you may run into problems with galling.
If you have room I would suggest making several plastic short
cylindrical pieces from acetal or UHMW. Press these plastic parts into
shallow flat bottom bores in the 3/4 bar. UHMW, while not as hard as
acetal, is an excellent material for this application. Delrin AF, a
teflon filled acetal plastic, would work better than UHMW, and is
easier to machine because it is a little harder. I know McMaster Carr
sells Delrin AF.
Good Luck,


Alum is one pita when it comes to sliding. I have indeed made what you
described, in various forms, and the ultimate "sliding solution", esp.
inside alum tube, may be to make the slider itself out of some
plastic/polymer (nylon, delrin, some of the stuff mentioned here), which
would certainly solve the galling/friction issue, but jamming could *still*
occur, ergo proly still the need for some kind of wiper.

I mentioned felt/cloth, altho that seems sort of a brute-ish force solution,
but mebbe ultimately the only solution.
I like anorton's idea, in part because I think such a material would have a
much longer lifespan than felt or cloth.
But felt is def'ly a consideration, I'll check out McM.
--
EA




ERic



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Default Design Q: O-rings as wipers? Fuzzy O-rings?

On Sunday, March 24, 2013 9:53:38 AM UTC-7, Existential Angst wrote:
I know o-rings are used in hydraulics as seals, wipers.

But what about in a dry environment?

Imagine a 3/4" sq bar freely sliding inside a square tube, nominal 3/4" id,
with the id smooth but unpolished...


Sounds like a place for an oversize leather washer. It'll conform, and
if you get it wet it'll seal. And if you run it with a charge of carbide
grit or metal polish, the inside of that tube stops being unpolished
after a while.

If I wanted a sliding fit, I'd consider drilling sockets in the bar, and
gluing buttons of delrin into 'em. For big loads, screw delrin plates onto
the bar faces.
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