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

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

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

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

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 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

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

"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

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

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

"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

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 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.

On Fri, 24 Oct 2008 23:48:48 -0400, Ned Simmons
wrote:

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.

And Cycolac. Back when telephones had dials, some of them were made
of Cycolac. Tough stuff. I think it's a form of ABS.

"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

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 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 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 01:33:18 -0400, "Ed Huntress"
wrote:


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

Yes! I was questioning the assertion of high voltage and
particularly that of very high impedance.

You apparently know a lot more about EDM than I do. I thought they
were all RC circuits as described in Langlois' book. Those devices
were neither particularly high voltage nor particularly high
impedance.

"Don Foreman" wrote in message
...
On Sat, 25 Oct 2008 01:33:18 -0400, "Ed Huntress"
wrote:


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

Yes! I was questioning the assertion of high voltage and
particularly that of very high impedance.

You apparently know a lot more about EDM than I do. I thought they
were all RC circuits as described in Langlois' book. Those devices
were neither particularly high voltage nor particularly high
impedance.

I wrote most of McGraw-Hill's old book on non-traditional machining; I was
the EDM editor at _American Machinist_; and I was the US Marketing and Sales
Manager at Sodick. I also gave Mitsubishi's East-coast lectures on wire EDM.
When we were hard-pressed at Sodick, I took off my tie and made board-level
repairs to power supplies.

sigh But, as with many other things, my knowledge is becoming something
that's mostly of historical interest. Hell, *I'm* becoming something that's
mostly of historical interest. Just ask my wife. d8-)

As for the high voltage, that was just one way to do it. If you have
patience, you can get sparks started with lower voltages, and the very
earliest EDMs had only one capacitor bank, which compromised several things,
including the time between sparks. But when Agie came up with sophisticated,
heavily researched power supplies during the '70s, the Japanese,
particularly, developed some work-arounds that kept them from violating
Agie's patents (more or less -- but that's another story g) while
competing with them on performance. Sodick's approach was common, although
they did it particularly well for the time.

Early wirecut machines tended to have pretty high initiation voltages. I
think the Andrew was in that category, but I'm not dead sure. It was a good
machine and an excellent buy at the time. It also was one of the few
American-made wirecut machines ever.

--
Ed Huntress

Early wirecut machines tended to have pretty high initiation voltages. I
think the Andrew was in that category, but I'm not dead sure. It was a
good machine and an excellent buy at the time. It also was one of the few
American-made wirecut machines ever.

Mine measures -206 volts when you turn the burn on but haven't touched metal
yet. I'm not sure I remember correctly, but I think he said up to 50,000
pulses per second while cutting. Apparently the voltage is very high for a
few microseconds at the beginning of each pulse.

Karl

"Karl Townsend" wrote in message
anews.com...
Early wirecut machines tended to have pretty high initiation voltages. I
think the Andrew was in that category, but I'm not dead sure. It was a
good machine and an excellent buy at the time. It also was one of the few
American-made wirecut machines ever.

Mine measures -206 volts when you turn the burn on but haven't touched
metal yet. I'm not sure I remember correctly, but I think he said up to
50,000 pulses per second while cutting. Apparently the voltage is very
high for a few microseconds at the beginning of each pulse.

Karl

Yeah, that's the way. The high voltage ionizes a channel in the dielectric
for the current to flow through, (the "spark"), which occurs at low voltage.
I think the typical voltage during the spark is around 15 - 18 V.

--
Ed Huntress

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 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.

On 2008-10-25, Don Foreman wrote:
On Fri, 24 Oct 2008 23:48:48 -0400, Ned Simmons
wrote:

[ ... ]

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

And Cycolac. Back when telephones had dials, some of them were made
of Cycolac. Tough stuff. I think it's a form of ABS.

Hmm ... that must have been Ma Bell's 500 series phones. I know
that the 300 series had aluminum (or brass) dials painted black. I
don't know if I ever *saw* a 400 series phone.

But I have some of these still around here -- even some
connected where I don't need to initiate calls. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Sat, 25 Oct 2008 12:49:02 -0400, "Ed Huntress"
wrote:

But when Agie came up with sophisticated,
heavily researched power supplies during the '70s, the Japanese,
particularly, developed some work-arounds that kept them from violating
Agie's patents (more or less -- but that's another story g)

What was Agie's approach? Those patents are expired now.

Sodick's approach was common, although
they did it particularly well for the time.

What was Sodick's approach?

What was Agie's approach? Those patents are expired now.

Sodick's approach was common, although
they did it particularly well for the time.

What was Sodick's approach?

Don,

I bought a booklet that is a copy of all WEDM patents though the '90s. Too
technical for me. If you're interested, I'll mail it to you.

Karl

"Don Foreman" wrote in message
...
On Sat, 25 Oct 2008 12:49:02 -0400, "Ed Huntress"
wrote:

But when Agie came up with sophisticated,
heavily researched power supplies during the '70s, the Japanese,
particularly, developed some work-arounds that kept them from violating
Agie's patents (more or less -- but that's another story g)

What was Agie's approach? Those patents are expired now.

Sodick's approach was common, although
they did it particularly well for the time.

What was Sodick's approach?

I'm hoping you just want a general description, and not design info, because
I've long since forgotten it and some of the details were secrets that I
never knew. But here's the general pictu

Let me first describe the EDM spark cycle as consisting of three stages. The
first is ionization and polarization of molecules of liquid dielectric. As
the molecules become polarized they start to flow; this flow, called
"streamers," starts heating the liquid channel according to the IR drop. The
second stage is low current flow via the streamers, within this "channel,"
that vaporizes the dielectric and then ionizes the resulting gas, forming
the low-resistance channel that allows high current flow in the third stage.
The third stage is an extremely high rate of current flow through the
ionized gas, originating in a low-impedance circuit of the power supply.
This is the spark that does the eroding of the workpiece.

Agie's breakthrough power supply design (it had a name -- Robo-something or
other), which came along in the mid-'70s, used an oscillator to produce a
string of pulses at the beginning of a spark cycle. These were fairly high
voltage, high impedance pulses, but the voltage was much lower (IIRC) than
that of other EDMs of the time. The pulses apparently were very quick and
effective at starting the ionization of the liquid and they could be
reliably controlled. The control is the key to producing a high duty cycle
and, thus, high cutting rates at relatively low rates of current flow in the
later stages of the cycle.

Sodick and others used an advanced version of earlier power supplies,
without the oscillation. (That part was an Agie patent.) They had a separate
circuit for each of the three stages: high voltage, high impedance; medium
voltage, medium impedance; and low voltage, low impedance. They used
transistors to switch each of the stages *off* at the appropriate time in
the cycle. Timing circuits for each stage were adjustable, although not all
of it was user-adjustable. Switching these circuits *on* was not actually
under direct electronic control; the physics of the process determined when
they turned on.

I think you can see in general how these circuits apply to the three stages
of the cycle. With this system you had pretty good control, although the
physics of the process limited what you could do electronically. Further
advances in power supply design, since the '70s, could be thought of as
efforts to "force" the physical dynamics to conform to desired timing,
voltage, and current flow, and to do it with the highest possible
predictability and reliability.

If you're interested in improving the RC relaxer circuits used in home-built
EDMs, there is an earlier stage of commercial development that holds more
promise and *could* be within the realm of a hobbyist who's knowledgeable
about electronics. Before these power supplies I've described came along,
the standard approach was an RC circuit with an electronic switch -- first
tubes, then switching transistors -- to turn off the high current flow. This
made EDM much faster, allowed finer finishes, and improved the process a
great deal over the earlier, plain RC designs.

To understand how and why they worked is another story. I'll just point out
the physics involved. The elemental RC power supply is a current source, a
series charging resistor, a capacitor, and a second series resistor, which
is the EDM channel itself, with the electrode and workpiece forming the
terminals, and the channel being the resistor material. The key to the
process is that the resistance of this "resistor" drops with changes in
voltage, due to the ionization of the channel. It starts out behaving like a
low-value capacitor, in other words, and then it becomes a resistor as
current starts to flow.

The storage capacitor is charged through the charging resistor until the
voltage on the capacitor is high enough to start the ionization process at
the electrode-workpiece interface. Then the cap discharges through the
channel, eroding the workpiece in the process. The whole process depends on
getting all the values -- charging resistance, capacitor size, and
electrode-workpiece gap -- in the proper balance for the process to proceed.

The limitation of this simple circuit results from the resistance of the
cutting channel immediately dropping to a very low value. If the value of
the charging resistor is too low (and you want it to be as low as practical,
because its value determines cutting speed -- lower value means faster
cutting), and if the channel resistance becomes too low from high current
flows, the spark doesn't stop; it becomes a continuous arc, and you've just
turned your EDM into a welding machine that wrecks the workpiece and the
electrode. This is the dreaded "arc" that was the bane of EDMs before
fancier transistor-controlled power supplies came along. A simple hobbyist
machine must be run at very low cutting rates to prevent this from
happening. That means that the charging resistor must have a higher value
than you might prefer, and it also places limits on the size of the storage
capacitor, because a big one will allow the EDM channel's resistance to drop
through the floor.

I hope you're following all this. I haven't tried to explain it for years.
g If you're with me, you can see how a switching transistor (or vacuum
tube) in the circuit can be used to great benefit if it switches off the
current flow under direct control, using something as simple as a 555 timing
circuit that's triggered by the high current pulse at the start of the cut.
It allows low charging-resistor values, larger storage capacitors, and high
current flow rates, and it keeps the sparks from turning into arcs.

In theory. In practice, it works pretty well, but not perfectly. The famous
old Elox EDMs (vacuum tubes) and the iconic Charmilles D20 (transistors) of
the 1960s were practical and effective machines that made EDM the practical
process that it is today.

Two more things: Notice that I'm not distinguishing between wirecut and
ram-type EDM power supplies. The differences are in the values of the
circuits more than in the concepts. Wire EDMs can be a little more brutal on
the power supply end because electrode wear is not a problem. You toss the
wire after it makes one pass.

The other thing to note is that EDM has developed from experience, not from
theory. The companies involved threw things at the wall until something
stuck, and then tried to figure out later why it worked. It's led to some
screwy theories that seem to contradict each other over time. The Swiss were
particularly good at buggering the story up. g The point being, don't get
too hung on the theories. And face the fact that EDM has been developed by
people who had well-equipped labs and lots of financial incentive, not by
hobbyists. It really doesn't lend itself to easy, low-cost experimentation.

Oh, I should mention that I haven't looked at the hobby designs for at least
five or more years. so someone may have hobby-level designs incorporating
transistors. If so, I wouldn't try to re-invent them, if my object was to
build a homemade EDM that worked and actually cut things.

Good luck, if that's what you have in mind.

--
Ed Huntress

Oh, I should mention that I haven't looked at the hobby designs for at
least
five or more years. so someone may have hobby-level designs incorporating
transistors. If so, I wouldn't try to re-invent them, if my object was to
build a homemade EDM that worked and actually cut things.

Good luck, if that's what you have in mind.

I got a second "parts machine" with my EDM. The spark supply boards in this
one are an earlier generation design and not compatible with my machine.
They would be perfect for a homebuilt unit. there are sixteen boards for 32
power levels (each board can be 1/2 on). Free for the asking.

Karl

On Sun, 26 Oct 2008 08:40:43 -0500, "Karl Townsend"
wrote:


What was Agie's approach? Those patents are expired now.

Sodick's approach was common, although
they did it particularly well for the time.

What was Sodick's approach?

Don,

I bought a booklet that is a copy of all WEDM patents though the '90s. Too
technical for me. If you're interested, I'll mail it to you.

Karl

If it is of no use to you I would like a look at it. Reading patents
can be like swimming thru peanut butter but I do have some experience.

Thanks!

On Sun, 26 Oct 2008 10:35:32 -0400, "Ed Huntress"
wrote:


"Don Foreman" wrote in message
.. .
On Sat, 25 Oct 2008 12:49:02 -0400, "Ed Huntress"
wrote:

But when Agie came up with sophisticated,
heavily researched power supplies during the '70s, the Japanese,
particularly, developed some work-arounds that kept them from violating
Agie's patents (more or less -- but that's another story g)

What was Agie's approach? Those patents are expired now.

Sodick's approach was common, although
they did it particularly well for the time.

What was Sodick's approach?

I'm hoping you just want a general description, and not design info, because
I've long since forgotten it and some of the details were secrets that I
never knew. But here's the general pictu

Let me first describe the EDM spark cycle as consisting of three stages. The
first is ionization and polarization of molecules of liquid dielectric. As
the molecules become polarized they start to flow; this flow, called
"streamers," starts heating the liquid channel according to the IR drop. The
second stage is low current flow via the streamers, within this "channel,"
that vaporizes the dielectric and then ionizes the resulting gas, forming
the low-resistance channel that allows high current flow in the third stage.
The third stage is an extremely high rate of current flow through the
ionized gas, originating in a low-impedance circuit of the power supply.
This is the spark that does the eroding of the workpiece.

Agie's breakthrough power supply design (it had a name -- Robo-something or
other), which came along in the mid-'70s, used an oscillator to produce a
string of pulses at the beginning of a spark cycle. These were fairly high
voltage, high impedance pulses, but the voltage was much lower (IIRC) than
that of other EDMs of the time. The pulses apparently were very quick and
effective at starting the ionization of the liquid and they could be
reliably controlled. The control is the key to producing a high duty cycle
and, thus, high cutting rates at relatively low rates of current flow in the
later stages of the cycle.

Sodick and others used an advanced version of earlier power supplies,
without the oscillation. (That part was an Agie patent.) They had a separate
circuit for each of the three stages: high voltage, high impedance; medium
voltage, medium impedance; and low voltage, low impedance. They used
transistors to switch each of the stages *off* at the appropriate time in
the cycle. Timing circuits for each stage were adjustable, although not all
of it was user-adjustable. Switching these circuits *on* was not actually
under direct electronic control; the physics of the process determined when
they turned on.

I think you can see in general how these circuits apply to the three stages
of the cycle. With this system you had pretty good control, although the
physics of the process limited what you could do electronically. Further
advances in power supply design, since the '70s, could be thought of as
efforts to "force" the physical dynamics to conform to desired timing,
voltage, and current flow, and to do it with the highest possible
predictability and reliability.

If you're interested in improving the RC relaxer circuits used in home-built
EDMs, there is an earlier stage of commercial development that holds more
promise and *could* be within the realm of a hobbyist who's knowledgeable
about electronics. Before these power supplies I've described came along,
the standard approach was an RC circuit with an electronic switch -- first
tubes, then switching transistors -- to turn off the high current flow. This
made EDM much faster, allowed finer finishes, and improved the process a
great deal over the earlier, plain RC designs.

To understand how and why they worked is another story. I'll just point out
the physics involved. The elemental RC power supply is a current source, a
series charging resistor, a capacitor, and a second series resistor, which
is the EDM channel itself, with the electrode and workpiece forming the
terminals, and the channel being the resistor material. The key to the
process is that the resistance of this "resistor" drops with changes in
voltage, due to the ionization of the channel. It starts out behaving like a
low-value capacitor, in other words, and then it becomes a resistor as
current starts to flow.

The storage capacitor is charged through the charging resistor until the
voltage on the capacitor is high enough to start the ionization process at
the electrode-workpiece interface. Then the cap discharges through the
channel, eroding the workpiece in the process. The whole process depends on
getting all the values -- charging resistance, capacitor size, and
electrode-workpiece gap -- in the proper balance for the process to proceed.

The limitation of this simple circuit results from the resistance of the
cutting channel immediately dropping to a very low value. If the value of
the charging resistor is too low (and you want it to be as low as practical,
because its value determines cutting speed -- lower value means faster
cutting), and if the channel resistance becomes too low from high current
flows, the spark doesn't stop; it becomes a continuous arc, and you've just
turned your EDM into a welding machine that wrecks the workpiece and the
electrode. This is the dreaded "arc" that was the bane of EDMs before
fancier transistor-controlled power supplies came along. A simple hobbyist
machine must be run at very low cutting rates to prevent this from
happening. That means that the charging resistor must have a higher value
than you might prefer, and it also places limits on the size of the storage
capacitor, because a big one will allow the EDM channel's resistance to drop
through the floor.

I hope you're following all this. I haven't tried to explain it for years.
g If you're with me, you can see how a switching transistor (or vacuum
tube) in the circuit can be used to great benefit if it switches off the
current flow under direct control, using something as simple as a 555 timing
circuit that's triggered by the high current pulse at the start of the cut.
It allows low charging-resistor values, larger storage capacitors, and high
current flow rates, and it keeps the sparks from turning into arcs.

In theory. In practice, it works pretty well, but not perfectly. The famous
old Elox EDMs (vacuum tubes) and the iconic Charmilles D20 (transistors) of
the 1960s were practical and effective machines that made EDM the practical
process that it is today.

Two more things: Notice that I'm not distinguishing between wirecut and
ram-type EDM power supplies. The differences are in the values of the
circuits more than in the concepts. Wire EDMs can be a little more brutal on
the power supply end because electrode wear is not a problem. You toss the
wire after it makes one pass.

The other thing to note is that EDM has developed from experience, not from
theory. The companies involved threw things at the wall until something
stuck, and then tried to figure out later why it worked. It's led to some
screwy theories that seem to contradict each other over time. The Swiss were
particularly good at buggering the story up. g The point being, don't get
too hung on the theories. And face the fact that EDM has been developed by
people who had well-equipped labs and lots of financial incentive, not by
hobbyists. It really doesn't lend itself to easy, low-cost experimentation.

Oh, I should mention that I haven't looked at the hobby designs for at least
five or more years. so someone may have hobby-level designs incorporating
transistors. If so, I wouldn't try to re-invent them, if my object was to
build a homemade EDM that worked and actually cut things.

Good luck, if that's what you have in mind.

Thanks for taking the time to write this, Ed.

I've thought about doing a "hobby" EDM for years but I don't really
need one. I now have a friend with a real EDM! I was able to follow
your clearly-written treatise with no difficulty.

I would definitely "re-invent" hobby level design for myself. Some
stuff found on the web is quite good but some of it is abysmally bad
design tinkered into existance. I do have some degrees in EE and a
bit of experience in design and as a research puke. I also have a
benchstock of suitable transistors --like 800-volt 50-amp MOSFET's
courtesy of my son the silicon peddler.

In a sort of EDM experiment some years ago, I was surprised to
discover how high the conductivity was of "distilled" water from
Wal-Mart. I was also surprised at how much the inductance of leads
affected rise time of immersed sparks as observed on a scope. I had
my apparatus on the mill so I could use the quill feed (with dial
indicator) as a calibrated part of my experiment.

"Don Foreman" wrote in message
...
On Sun, 26 Oct 2008 10:35:32 -0400, "Ed Huntress"
wrote:

snip


Good luck, if that's what you have in mind.

Thanks for taking the time to write this, Ed.

I've thought about doing a "hobby" EDM for years but I don't really
need one. I now have a friend with a real EDM! I was able to follow
your clearly-written treatise with no difficulty

Good. If I lose that, I'll have to look for other work. g


I would definitely "re-invent" hobby level design for myself. Some
stuff found on the web is quite good but some of it is abysmally bad
design tinkered into existance. I do have some degrees in EE and a
bit of experience in design and as a research puke. I also have a
benchstock of suitable transistors --like 800-volt 50-amp MOSFET's
courtesy of my son the silicon peddler.

In a sort of EDM experiment some years ago, I was surprised to
discover how high the conductivity was of "distilled" water from
Wal-Mart. I was also surprised at how much the inductance of leads
affected rise time of immersed sparks as observed on a scope. I had
my apparatus on the mill so I could use the quill feed (with dial
indicator) as a calibrated part of my experiment.


If you do give it a try, you'll find that your experience with stray
inductance tends to get multiplied in an actual machine. It's a real
problem, and some of the older machines won't work at all if you ground the
machine chassis. This leads to some surprising jolts. g You may find that
you have to tune out the inductance by adding some experimentally derived
capacitance.

FWIW, I think that water dielectric is more problematic for a homebrew
machine than oil dielectric is. The water is quickly re-ionized and needs
some kind of attention, like a deionizing filter.

--
Ed Huntress

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.