I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

"Karl Townsend" wrote in message
anews.com...
I need to make some new idler wheels for my wire EDM. The material is a
very hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl



Its not black, but maybe something like Tufnol. Maybe have a look at
Radiospares in their engineering materials section

http://www.rs-components.com/index.html

Bakelite? That's a likely for the car distributor, and is a high temp
and hard black plastic.

Phenolic might work well, but it's not black. It is very hard and a good
insulator, based on several years I spent building plasma physics
machines.

Micarta might also work, depending. I guess it's technically a form of
phenolic.

--
Cats, coffee, chocolate...vices to live by

On Oct 24, 11:18 am, Ecnerwal
wrote:
Bakelite? That's a likely for the car distributor, and is a high temp
and hard black plastic.

Phenolic might work well, but it's not black. It is very hard and a good
insulator, based on several years I spent building plasma physics
machines.

Micarta might also work, depending. I guess it's technically a form of
phenolic.

--
Cats, coffee, chocolate...vices to live by



Probably any of the THERMOSET plastics would work as long as they have
non-conductive fillers. Pick one with a high hardness,

Personally I like the idea of a metallic rim carrying the wire; it is
more precise and resists wear and tear better. An insulating bushing
containing the bearings would keep the magic smoke in.

Wolfgang

"Ecnerwal" wrote in message
...

Bakelite? That's a likely for the car distributor, and is a high temp
and hard black plastic.

Phenolic might work well, but it's not black. It is very hard and a good
insulator, based on several years I spent building plasma physics
machines.

Bakelite is phenolic resin and a wood-flour filler. It's probably what the
originals were made of. It can be colored black, or it can be dark brown, as
I'm sure you know.


Micarta might also work, depending. I guess it's technically a form of
phenolic.

--
Cats, coffee, chocolate...vices to live by

I find that what I "know" is limited by what I've used, sometimes - all
the phenolic (technically, phenolic laminates) I worked with that were
generically referred to as phenolic when someone wanted that were the
dark-brown with brilliant yellow dust.

So my recommendations come down to "the phenolic referred to as bakelite"

The phenolic (probably paper-based) referred to as "phenolic" in the
labs I used to work for.

And "the phenolic trademared as Micarta, of which there are many more
varieties and colors than I ever knew".

Evidently, I recommend a phenolic ;-)

Thanks Ed.

--
Cats, coffee, chocolate...vices to live by

"Ecnerwal" wrote in message
...
I find that what I "know" is limited by what I've used, sometimes - all
the phenolic (technically, phenolic laminates) I worked with that were
generically referred to as phenolic when someone wanted that were the
dark-brown with brilliant yellow dust.

So my recommendations come down to "the phenolic referred to as bakelite"

The phenolic (probably paper-based) referred to as "phenolic" in the
labs I used to work for.

And "the phenolic trademared as Micarta, of which there are many more
varieties and colors than I ever knew".

Evidently, I recommend a phenolic ;-)

You got it right. The original Bakelite is phenolic resin
(phenol-formaldehyde, IIRC) and wood flour, as I mentioned. But the
laminates, generically known as "phenolic sheet," are similar except they
have stronger reinforcement. They're layers of paper or cloth bonded with
phenolic resin. Micarta is a brand name, I think, for a high-quality line of
these laminates.

Thinking about the uses for the sheets, I suspect you're right that those
wheels on the Andrew were more likely Micarta or similar, rather than
Bakelite. The laminates are much stronger and more wear-resistant than plain
Bakelite. They've been used for timing gears on V8 car engines, because they
wear pretty well and they run quiet.


Thanks Ed.

I need to do something useful with this pile of trivia before my brain
collapses. g My pleasure.

--
Ed Huntress

On Fri, 24 Oct 2008 16:00:11 GMT, Ecnerwal
wrote:


And "the phenolic trademared as Micarta, of which there are many more
varieties and colors than I ever knew".

You can add epoxy/glass, silicone/glass and melamine composites to the
Micarta family, just to confound things a little more.

--
Ned Simmons

On Oct 24, 8:18*am, Ecnerwal
wrote:
Bakelite? That's a likely for the car distributor, and is a high temp
and hard black plastic.

Phenolic might work well, but it's not black.,,
Micarta might also work

Phenolic plastics were the first, and still the commonest,
thermosetting plastics (they take heat well).

The earliest, inventor Baekeland used with lots of
asbestos as reinforcement and filler. That is not a currently
available product.

Bakelite (Union Carbide), and Formica (General Electric) and
Micarta (Westinghouse) are all tradenames for phenolic plastics,
and nowadays use either wood-fiber (paper) or for high
performance, linen reinforcement/filler.

Can't answer the question but my last project had to switch from black
delrin to white delrin after I noticed that the black is not considered
an insulator. Must have some carbon black in it.

Karl Townsend wrote:
I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

RoyJ wrote:
Can't answer the question but my last project had to switch from black
delrin to white delrin after I noticed that the black is not considered
an insulator. Must have some carbon black in it.

Sonofabitch. I just bought a 5 foot length
of black delrin to use as an insulator. I
remember seeing the white and deciding that
the black would *look* better. On an internal
part. Jim smacks his head and pulls the M-C
catalog back out....

Karl Townsend wrote:
I need to make some new idler wheels for my wire EDM. The material is
a very hard black plastic. Maybe the same stuff you see on a car
electrical distributor. It needs to be non-conductive and be able to
have a light press fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

On Fri, 24 Oct 2008 08:21:30 -0500, "Karl Townsend"
wrote:

I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

The most economical way to produce things like this is to mold them.
However, that isn't necessarily the only way, nor the best way if you
don't happen to have the molds.

I'd make an undersized aluminum wheel, press that into an insulating
bushing made of Delryn, Noryl, phenolic or whatever, and then possibly
press that assy into a metal "tire" that would resist wear. The
resulting wheel would be non-conductive from rim to center and would
be quite robust.

On Oct 24, 10:30*am, Don Foreman
wrote:
On Fri, 24 Oct 2008 08:21:30 -0500, "Karl Townsend"

wrote:
I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

The most economical way to produce things like this is to mold them.
However, that isn't necessarily the only way, nor the best way if you
don't happen to have the molds. *

I'd make an undersized aluminum wheel, press that into an insulating
bushing made of Delryn, Noryl, phenolic or whatever, and then possibly
press that assy into a metal "tire" that would resist wear. *The
resulting wheel would be non-conductive from rim to center and would
be quite robust.

What voltage?
Especially in a dusty environment, creepage may be as important as
clearance.
(Creepage is the distance of the path from a hot lead to another
conductive surface, along the surface of the insulator.)


Dave

wrote in message
...
On Oct 24, 10:30 am, Don Foreman
wrote:
On Fri, 24 Oct 2008 08:21:30 -0500, "Karl Townsend"

wrote:
I need to make some new idler wheels for my wire EDM. The material is a
very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

The most economical way to produce things like this is to mold them.
However, that isn't necessarily the only way, nor the best way if you
don't happen to have the molds.

I'd make an undersized aluminum wheel, press that into an insulating
bushing made of Delryn, Noryl, phenolic or whatever, and then possibly
press that assy into a metal "tire" that would resist wear. The
resulting wheel would be non-conductive from rim to center and would
be quite robust.

What voltage?

On the order of several hundred volts, at very high impedance. If there's
any conductivity, the sparks won't initiate and the machine won't cut.

The actual cutting goes on at around the voltages you have with a welder --
quite low. The high initiation voltage is just to ionize the channel for the
actual current flow.

--
Ed Huntress

McMaster has micarta - they even have it in black, though I seem to
recall all the micarta I encoutered at the lab being white - but that
probably just means that the stuff we used happened to be.

I'd be wary of the metal rim that Wolfgang likes causing problems with
clearance to other parts, if the machine was designed with plastic
wheels. i.e., with a plastic wheel, the voltage is only present at the
part of the wheel with the wire on it. With a metal rim, you might get
sparks from the backside of the wheel-rim to some other part of the
machine, depending on the design.

--
Cats, coffee, chocolate...vices to live by

On Fri, 24 Oct 2008 11:47:37 -0400, "Ed Huntress"
wrote:


wrote in message
...
On Oct 24, 10:30 am, Don Foreman
wrote:
On Fri, 24 Oct 2008 08:21:30 -0500, "Karl Townsend"

wrote:
I need to make some new idler wheels for my wire EDM. The material is a
very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

The most economical way to produce things like this is to mold them.
However, that isn't necessarily the only way, nor the best way if you
don't happen to have the molds.

I'd make an undersized aluminum wheel, press that into an insulating
bushing made of Delryn, Noryl, phenolic or whatever, and then possibly
press that assy into a metal "tire" that would resist wear. The
resulting wheel would be non-conductive from rim to center and would
be quite robust.

What voltage?

On the order of several hundred volts, at very high impedance. If there's
any conductivity, the sparks won't initiate and the machine won't cut.

Ed, this assertion doesn't nearly meet your usual high standard of
editorial rigor.

"Don Foreman" wrote in message
...
On Fri, 24 Oct 2008 11:47:37 -0400, "Ed Huntress"
wrote:


wrote in message
...
On Oct 24, 10:30 am, Don Foreman
wrote:
On Fri, 24 Oct 2008 08:21:30 -0500, "Karl Townsend"

wrote:
I need to make some new idler wheels for my wire EDM. The material is a
very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

The most economical way to produce things like this is to mold them.
However, that isn't necessarily the only way, nor the best way if you
don't happen to have the molds.

I'd make an undersized aluminum wheel, press that into an insulating
bushing made of Delryn, Noryl, phenolic or whatever, and then possibly
press that assy into a metal "tire" that would resist wear. The
resulting wheel would be non-conductive from rim to center and would
be quite robust.

What voltage?

On the order of several hundred volts, at very high impedance. If there's
any conductivity, the sparks won't initiate and the machine won't cut.

Ed, this assertion doesn't nearly meet your usual high standard of
editorial rigor.

I'm not following you. What I described is the way it works. You have a high
voltage at high impedance, and that voltage ionizes the channel. When it's
ionized and current starts to flow (the "spark"), the voltage drops to a
very low value, to reflect the low ohmic resistance of the ionized channel.

In an RC relaxation circuit, like most very old EDMs used, the open-circuit
voltage is high. In a somewhat newer electronic circuit, the low- and
high-impedance circuits actually are separate. A Sodick EDM of about 1980
vintage actually has three circuits.

If there is leakage in the high-impedance circuit, you won't have enough
voltage (it will drop in the high-impedance circuit because of the parallel
resistance of the leaky element of the circuit) to ionize the channel. Thus,
no spark will be able to initiate.

Is this editorially sufficient? g

--
Ed Huntress

"Karl Townsend" wrote in message
anews.com...
I need to make some new idler wheels for my wire EDM. The material is a
very hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl


From your description, I suspect that it might be an Acetal. They are hard,
hard wearing and have a "slipery" feel to them. They are also a good
electrical insulator.
Here in Australia, it is readily available from an industrial plastics
supplier, in both shhet and rod form, but I would have no idea where you
would go for it in the US

Acetal wins. But only because its one tenth the price of micarta in the
grade I need.

Thanks for all the help ,everybody.

Karl

On Sat, 25 Oct 2008 06:18:59 -0500, "Karl Townsend"
wrote:


Acetal wins. But only because its one tenth the price of micarta in the
grade I need.


You might find something among the ceramic flanged pulleys he
http://www.cosmos-na.com/index.html
http://www.cosmos-na.com/Pulleys-Flanged-(%202%20).html

They're surprisingly inexpensive and last forever, though probably not
as cheap as a piece of Delrin.

--
Ned Simmons

On Sat, 25 Oct 2008 08:43:36 +1100, "Grumpy"
wrote:


"Karl Townsend" wrote in message
tanews.com...
I need to make some new idler wheels for my wire EDM. The material is a
very hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light
press fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl


From your description, I suspect that it might be an Acetal. They are hard,
hard wearing and have a "slipery" feel to them. They are also a good
electrical insulator.
Here in Australia, it is readily available from an industrial plastics
supplier, in both shhet and rod form, but I would have no idea where you
would go for it in the US


Correct

Any good plastics place will have acetal rod...aka Delrin....



Gunner

Whenever a Liberal utters the term "Common Sense approach"....grab your
wallet, your ass, and your guns because the sombitch is about to do
something damned nasty to all three of them.

On Oct 24, 9:21*am, "Karl Townsend"
wrote:
I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

I sell various forms of plastic offcuts on ebay.

From what you and the others say, I would agree that white delrin or
phenolic is the way to go, but you could also have a look at unfilled
Nylon in the natural form. It's quite a hard plastic and it wears
very well. I think you'll find the black delrin or the black nylon
both have carbon black in them - it's the usual way they manage to get
a black colour.

If you want to have a look at some pieces, there are pictures at;

http://stores.ebay.ca/The-Great-Indu...eNameZl2QQtZkm


If heat is a problem, delrin softens at a pretty low temperature
( say, around 300 F) - nylon's a bit more tolerant. Delrin is far
more slippery, and is known for its insulating qualities in white as
well as it's ability to be machined to extremely close tolerances.

Eric

On Sat, 25 Oct 2008 04:21:20 -0700 (PDT), eric h
wrote:

On Oct 24, 9:21*am, "Karl Townsend"
wrote:
I need to make some new idler wheels for my wire EDM. The material is a very
hard black plastic. Maybe the same stuff you see on a car electrical
distributor. It needs to be non-conductive and be able to have a light press
fit for a ball bearing.

Can somebody give me a material name and source to order?

Karl

I sell various forms of plastic offcuts on ebay.

From what you and the others say, I would agree that white delrin or
phenolic is the way to go, but you could also have a look at unfilled
Nylon in the natural form. It's quite a hard plastic and it wears
very well. I think you'll find the black delrin or the black nylon
both have carbon black in them - it's the usual way they manage to get
a black colour.

If you want to have a look at some pieces, there are pictures at;

http://stores.ebay.ca/The-Great-Indu...eNameZl2QQtZkm


If heat is a problem, delrin softens at a pretty low temperature
( say, around 300 F) - nylon's a bit more tolerant. Delrin is far
more slippery, and is known for its insulating qualities in white as
well as it's ability to be machined to extremely close tolerances.

Eric


Nylon is also rather porous, no? Or is that the "filled form"?

Gunner

Whenever a Liberal utters the term "Common Sense approach"....grab your
wallet, your ass, and your guns because the sombitch is about to do
something damned nasty to all three of them.

Gunner Asch writes:

Nylon is also rather porous, no?

Not porous per se, but has a high water absorption, 6 percent or more when
saturated vs less than 1 percent for most polymers.

On Sat, 25 Oct 2008 19:25:18 -0500, Richard J Kinch
wrote:

Gunner Asch writes:

Nylon is also rather porous, no?

Not porous per se, but has a high water absorption, 6 percent or more when
saturated vs less than 1 percent for most polymers.


How well will it absorb the dialectric in the tank?

Gunner

Whenever a Liberal utters the term "Common Sense approach"....grab your
wallet, your ass, and your guns because the sombitch is about to do
something damned nasty to all three of them.