Re: [Emc-users] EDM from scratch

[dave engvall]

EDM of one sort or another comes up every few years. Pete 
Grundemann(sp?) put one together. His demo was to edm threads in a file.
tomp ... now in Thailand has a lot of experience in edm. 
tjtr33...atgmailcom
Someone brought a non-working commercial wire edm to Galesburg and 
almost had it working at the end of the week. This was a stepper driven 
unit made by Bridgeport but had a different label. My memory seems to be 
fading
I worked a little bit at getting something going but other pressures out 
voted the project. Still have a bunch of graphite and electrolyte around 
here someplace.


Dave

On 2/1/21 8:41 AM, Jon Elson wrote:

On 01/31/2021 07:22 PM, John Dammeyer wrote:
I found some of the earlier articles in Home Shop Machinist Issue's 
May/June 1995 and September/October 1995.   I do not have part 2 
published in July/August 1995.


However, in the 3rd part Robert Langlois describes the stepper motor 
operation in conjunction with the capacitor voltage.  His front panel 
has switches allowing combinations of 50uFd, 100uFd, 200uFd and 
400uFd in parallel.
Note that Robert Langlois is the home shop expert on WIRE EDM, which 
is a bit different from
sinker EDM, as the wire is moved fairly rapidly past the cut.  So, the 
spark generator setup is

quite different.

I met him at a couple NAMES shows in the late 1990's.

Jon


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Re: [Emc-users] EDM from scratch

[Jon Elson]

On 01/31/2021 07:22 PM, John Dammeyer wrote:

I found some of the earlier articles in Home Shop Machinist Issue's May/June 
1995 and September/October 1995.   I do not have part 2 published in 
July/August 1995.

However, in the 3rd part Robert Langlois describes the stepper motor operation 
in conjunction with the capacitor voltage.  His front panel has switches 
allowing combinations of 50uFd, 100uFd, 200uFd and 400uFd in parallel.
Note that Robert Langlois is the home shop expert on WIRE 
EDM, which is a bit different from
sinker EDM, as the wire is moved fairly rapidly past the 
cut.  So, the spark generator setup is

quite different.

I met him at a couple NAMES shows in the late 1990's.

Jon


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Re: [Emc-users] EDM from scratch

[Gerrit Visser]

Thank you Thomas, filed your excellent info for my project.

Just finishing up a shop built cnc gantry machine (uses Pathpilot), then
onto the next project which I think will be a WEDM machine.

Gerrit

-Original Message-
From: Thomas J Powderly [mailto:tjt...@gmail.com] 
Sent: February 1, 2021 12:57 AM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] EDM from scratch

Hi Gerrit

the difference between senkung and draht erodien generator

is the pulse width

in wedm 1-10uS is the entire spectrum

in sink edm 1-3000uS is the spectrum

in any edm that uses the very sort pulse,

it is important that the current shut-off be complete and very fast ( all
inductanc ein system must be watched)

if you can turn the power OFF very very quickly, you will increase the metal
removal a LOT.

the reason is

the metal removel is the expulsion of a tiny crate pool of molten material

if the thermal change ( from current supplied an heating the pool)

to the time hwne current is removed and the thermal mass of the surrounding
environment ( oil water gas )

that makes for a more IMplosive force on the hot plasma bubble channel over
the pool.

The quickness of the bubble collapse cause more of the puddle to be ejected

a slower deflating lets most of the melted material to cool back on the
surface

look for Dr. Schumakers description from AGie

i cant find it now but it was an excellent presentation of how a spark
removes material

the 9 or so pictures are a whole edm education

but try this instead

https://core.ac.uk/download/pdf/34635871.pdf

best of luck with the wedm

(btw it will be a good hole drill spark generaor if it works for wed, just
needs up to 100uS max on time )

tomp

On 2/1/21 12:53 AM, Gerrit Visser wrote:
> Another source of information about pulse generator design: 
> https://langfordw.pages.cba.mit.edu/desktopWEDM/electronics/
>
> https://www.cnc.info.pl/drazenie-metoda-domowa-moje-proby-t11692-20.ht
> ml (Google translate helps here:-))
>
> Again, my focus is on wire EDM but there must be similarities
>
> Gerrit
>
>
>
>
>
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Re: [Emc-users] EDM from scratch

[andy pugh]

On Mon, 1 Feb 2021 at 09:42, Thomas J Powderly  wrote:

(Snip the other stuff, all noted)

> a use of adaptive feed wull never apprach the needed jittery advance of
> edm, adaptive feed never reacts negatively,

That is no longer the case. LinuxCNC now supports negative adaptive
feed, introduced specifically for EDM use.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] EDM from scratch

[John Dammeyer]

I found some of the earlier articles in Home Shop Machinist Issue's May/June 
1995 and September/October 1995.   I do not have part 2 published in 
July/August 1995.

However, in the 3rd part Robert Langlois describes the stepper motor operation 
in conjunction with the capacitor voltage.  His front panel has switches 
allowing combinations of 50uFd, 100uFd, 200uFd and 400uFd in parallel.

Essentially he moves the stepper motor down (electrode) if the voltage rises 
above a pot set reference voltage and moves it up if below a second pot set 
reference voltage.  It doesn't move the motor if the voltage is between these 
two set points.

The voltage on the capacitors ranges between 0V and 100V which is divided by 20 
for a 0V to 5V value compared to the Pot values.

John Dammeyer

He also references 
Model Engineer 1976 July, August, November and 1981 October.
Strictly I.C.  1993 Aug/sept, Oct/Nov, 93-94/Dec/Jan., 94 Feb/Mar, 95 Feb/Mar 
(letters)
Home Shop Machinist 91 Jan/Feb, 91 Jul/Aug, 92 May/Jun, 94 May/Jun



> -Original Message-
> From: ken.stra...@gmail.com [mailto:ken.stra...@gmail.com]
> Sent: January-31-21 11:51 AM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] EDM from scratch
> 
> Problem solved.
> 
> -Original Message-
> From: John Dammeyer 
> Sent: January 31, 2021 2:35 PM
> To: 'Enhanced Machine Controller (EMC)' 
> Subject: Re: [Emc-users] EDM from scratch
> 
> Rats.  I'm missing #169 for some reason.
> 
> The series I was thinking about was in issues #57..#60 and with addendums in
> #64 and #68.  The #68 issue discussed dielectrics safe for the home workshop
> and the liquid mentioned may still be available in the UK.
> 
> John Dammeyer
> 
> 
> > -Original Message-
> > From: Gerrit Visser [mailto:gerr...@psgv.ca]
> > Sent: January-31-21 11:06 AM
> > To: 'Enhanced Machine Controller (EMC)'
> > Subject: Re: [Emc-users] EDM from scratch
> >
> > Issue 168, Oct 2010 is the first installment
> >
> > Gerrit
> >
> > -Original Message-
> > From: John Dammeyer [mailto:jo...@autoartisans.com]
> > Sent: January 31, 2021 1:31 PM
> > To: 'Enhanced Machine Controller (EMC)'
> > 
> > Subject: Re: [Emc-users] EDM from scratch
> >
> > Andy,
> > Check out this page:
> > http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
> >
> > Also Model Engineer's workshop had a 4 part series on building one.
> > I'll go through my archives and see if I can find them.  I'm pretty sure I
> had all 4.  An online search doesn't pinpoint which issues.
> >
> > John Dammeyer
> >
> >
> >
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> 
> 
> 
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> 
> 
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Re: [Emc-users] EDM from scratch

[Thomas J Powderly]

Hi Gerrit

the difference between senkung and draht erodien generator

is the pulse width

in wedm 1-10uS is the entire spectrum

in sink edm 1-3000uS is the spectrum

in any edm that uses the very sort pulse,

it is important that the current shut-off be complete and very fast ( 
all inductanc ein system must be watched)


if you can turn the power OFF very very quickly, you will increase the 
metal removal a LOT.


the reason is

the metal removel is the expulsion of a tiny crate pool of molten material

if the thermal change ( from current supplied an heating the pool)

to the time hwne current is removed and the thermal mass of the 
surrounding environment ( oil water gas )


that makes for a more IMplosive force on the hot plasma bubble channel 
over the pool.


The quickness of the bubble collapse cause more of the puddle to be ejected

a slower deflating lets most of the melted material to cool back on the 
surface


look for Dr. Schumakers description from AGie

i cant find it now but it was an excellent presentation of how a spark 
removes material


the 9 or so pictures are a whole edm education

but try this instead

https://core.ac.uk/download/pdf/34635871.pdf

best of luck with the wedm

(btw it will be a good hole drill spark generaor if it works for wed, 
just needs up to 100uS max on time )


tomp

On 2/1/21 12:53 AM, Gerrit Visser wrote:

Another source of information about pulse generator design: 
https://langfordw.pages.cba.mit.edu/desktopWEDM/electronics/

https://www.cnc.info.pl/drazenie-metoda-domowa-moje-proby-t11692-20.html 
(Google translate helps here:-))

Again, my focus is on wire EDM but there must be similarities

Gerrit





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Re: [Emc-users] EDM from scratch

[Thomas J Powderly]

Hi Andy

if your path is a straight line
dont use linuxcnc , just hal

use steppers to advance
use an opamp window comparator
with a too high and a too low threshold

when your measured voltage is too high advance 1 step
else dont move, just wait
if too low, turn off the power , maybe retract
no linuxcnc needed
it cuts as fast as it can automatically


in most edm (any electrode material to steel workpiece ) the optimal gap 
voltage is near 30V=

its almost 2 volts lower when roughing
and 2 volts higher when finishing


The discharge voltage Ua) varies with 'paarung' the pairing of material, 
so for carbon wheel to wolfram, its will be even less,

i have seen stable cutting al low as 18V ( do not try to go lower )
a transistorized or FET generator is way better for MMR and wear.

to cut carbidem use a carbon of copper-graphite or copper tungsten wheel

edming carbide is mostly removing the binder.

using parrafinics is better than water but requres filtering and pumps
the nature of edm grinding is the 'best' flushing in all edm realms ( 
sink, orbiting, wire, hole drill )
because the tool to workpiece junction is continuosly new (like wedm, 
but free on each side, unlike wedm )

so a bath of 'white spirits' may be enough

on AGie edm-grinders ( used mostly by sewing machine companies ) they 
used thin ( low -visc) edm oil


there is no such thing as edm oil, its merely a layer in the cracker 
tower that is removed and labeled (kerosene or edm fluid or axle grease)

get a copy of the OEL-HELD book on edm fluids

a higher supply voltge ( 80-100V=) makes it easier (and more accurate) 
for a comparator to decide wether to adance , hold still, or retract.


a use of adaptive feed wull never apprach the needed jittery advance of 
edm, adaptive feed never reacts negatively, it can only reacts 'less-ly'

the motion techniques for mills is not the motion for edm.

I did a lot of work for Union Special on such machines 
http://www.unionspecial.com/


are you using a lathe spindle as the edm spindle?

the plans that Garret Visser link to at MIT are a good idea
previous 'the garden of edm' was good but remains unfinished
https://cscott.net/Projects/FabClass/final/edesign1.html

oh, splash/spray guards are neccesary, high rpm is not


hth
I'm kneedeep in rpi-gpio driver here . is **cp same as [] ??

hahaha i have to write a lot of test code to see how the original code 
worked.

best o luck

tomp


On 1/31/21 8:28 PM, andy pugh wrote:
I have started to play around with EDM. The intention is to make an 
EDM "grinder" to profile tool steel and possibly carbide cutting tools 
using CNC-turned profiles. At the moment I am using a cobbled-together 
XY table with a couple of STMBL drives. One of the STMBL analogue 
inputs is used to measure the current through the gap. (ie using the 
voltage across the resistor that a capacitor is charged through). Then 
a PID controller tries to achieve a target current by adjusting the 
adaptive feed pin. I think that it shows promise, but only partly 
works. I am using a 50R resistor and a 1000uF capacitor. I suspect 
that this is too high on both counts. I am working at 40V and it seems 
that the tool welds to the work too readily. I suspect that I would 
get different results if I controlled to the gap voltage, rather than 
charging resistor voltage. And probably better still with some sort of 
signal processing on that voltage. What combination of R, C and V 
would be typical for a servo-controlled eroder? I imagine it might be 
different to a "doorbell" style one. Current set up: 
https://youtu.be/nxpmEFnmK-A



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Re: [Emc-users] EDM from scratch

[ken.strauss]

Problem solved.

-Original Message-
From: John Dammeyer  
Sent: January 31, 2021 2:35 PM
To: 'Enhanced Machine Controller (EMC)' 
Subject: Re: [Emc-users] EDM from scratch

Rats.  I'm missing #169 for some reason.  

The series I was thinking about was in issues #57..#60 and with addendums in
#64 and #68.  The #68 issue discussed dielectrics safe for the home workshop
and the liquid mentioned may still be available in the UK.

John Dammeyer


> -Original Message-
> From: Gerrit Visser [mailto:gerr...@psgv.ca]
> Sent: January-31-21 11:06 AM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] EDM from scratch
> 
> Issue 168, Oct 2010 is the first installment
> 
> Gerrit
> 
> -Original Message-
> From: John Dammeyer [mailto:jo...@autoartisans.com]
> Sent: January 31, 2021 1:31 PM
> To: 'Enhanced Machine Controller (EMC)' 
> 
> Subject: Re: [Emc-users] EDM from scratch
> 
> Andy,
> Check out this page:
> http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
> 
> Also Model Engineer's workshop had a 4 part series on building one.  
> I'll go through my archives and see if I can find them.  I'm pretty sure I
had all 4.  An online search doesn't pinpoint which issues.
> 
> John Dammeyer
> 
> 
> 
> 
> 
> ___
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Re: [Emc-users] EDM from scratch

[Dave Matthews]

Issues 1 - 163 might be available on some of the darker areas of the
internet if you can't find them legally.  A quick check at the Jolly Roger
one lists them.

Dave

On Sun, Jan 31, 2021 at 2:36 PM John Dammeyer 
wrote:

> Rats.  I'm missing #169 for some reason.
>
> The series I was thinking about was in issues #57..#60 and with addendums
> in #64 and #68.  The #68 issue discussed dielectrics safe for the home
> workshop and the liquid mentioned may still be available in the UK.
>
> John Dammeyer
>
>
> > -Original Message-
> > From: Gerrit Visser [mailto:gerr...@psgv.ca]
> > Sent: January-31-21 11:06 AM
> > To: 'Enhanced Machine Controller (EMC)'
> > Subject: Re: [Emc-users] EDM from scratch
> >
> > Issue 168, Oct 2010 is the first installment
> >
> > Gerrit
> >
> > -Original Message-
> > From: John Dammeyer [mailto:jo...@autoartisans.com]
> > Sent: January 31, 2021 1:31 PM
> > To: 'Enhanced Machine Controller (EMC)'  >
> > Subject: Re: [Emc-users] EDM from scratch
> >
> > Andy,
> > Check out this page:
> > http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
> >
> > Also Model Engineer's workshop had a 4 part series on building one.
> I'll go through my archives and see if I can find them.  I'm pretty
> > sure I had all 4.  An online search doesn't pinpoint which issues.
> >
> > John Dammeyer
> >
> >
> >
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
>
> ___
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Re: [Emc-users] EDM from scratch

[John Dammeyer]

Rats.  I'm missing #169 for some reason.  

The series I was thinking about was in issues #57..#60 and with addendums in 
#64 and #68.  The #68 issue discussed dielectrics safe for the home workshop 
and the liquid mentioned may still be available in the UK.

John Dammeyer


> -Original Message-
> From: Gerrit Visser [mailto:gerr...@psgv.ca]
> Sent: January-31-21 11:06 AM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] EDM from scratch
> 
> Issue 168, Oct 2010 is the first installment
> 
> Gerrit
> 
> -Original Message-
> From: John Dammeyer [mailto:jo...@autoartisans.com]
> Sent: January 31, 2021 1:31 PM
> To: 'Enhanced Machine Controller (EMC)' 
> Subject: Re: [Emc-users] EDM from scratch
> 
> Andy,
> Check out this page:
> http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
> 
> Also Model Engineer's workshop had a 4 part series on building one.  I'll go 
> through my archives and see if I can find them.  I'm pretty
> sure I had all 4.  An online search doesn't pinpoint which issues.
> 
> John Dammeyer
> 
> 
> 
> 
> 
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users



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Re: [Emc-users] EDM from scratch

[Gerrit Visser]

Issue 168, Oct 2010 is the first installment

Gerrit

-Original Message-
From: John Dammeyer [mailto:jo...@autoartisans.com] 
Sent: January 31, 2021 1:31 PM
To: 'Enhanced Machine Controller (EMC)' 
Subject: Re: [Emc-users] EDM from scratch

Andy,
Check out this page:
http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html

Also Model Engineer's workshop had a 4 part series on building one.  I'll go 
through my archives and see if I can find them.  I'm pretty sure I had all 4.  
An online search doesn't pinpoint which issues.

John Dammeyer





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Re: [Emc-users] EDM from scratch

[John Dammeyer]

HI Andy,
There's also this.
https://www.cnczone.com/forums/general-edm-discussion/
Many links are broken though.  And the Yahoo group on EDM is gone and it 
doesn't look like it was migrated to groups.io.

John Dammeyer


> -Original Message-
> From: andy pugh [mailto:bodge...@gmail.com]
> Sent: January-31-21 5:28 AM
> To: Enhanced Machine Controller (EMC)
> Subject: [Emc-users] EDM from scratch
> 
> I have started to play around with EDM. The intention is to make an
> EDM "grinder" to profile tool steel and possibly carbide cutting tools
> using CNC-turned profiles.
> 
> At the moment I am using a cobbled-together XY table with a couple of
> STMBL drives.
> One of the STMBL analogue inputs is used to measure the current
> through the gap. (ie using the voltage across the resistor that a
> capacitor is charged through).
> Then a PID controller tries to achieve a target current by adjusting
> the adaptive feed pin.
> 
> I think that it shows promise, but only partly works.
> 
> I am using a 50R resistor and a 1000uF capacitor. I suspect that this
> is too high on both counts.
> I am working at 40V and it seems that the tool welds to the work too readily.
> 
> I suspect that I would get different results if I controlled to the
> gap voltage, rather than charging resistor voltage. And probably
> better still with some sort of signal processing on that voltage.
> 
> What combination of R, C and V would be typical for a servo-controlled
> eroder? I imagine it might be different to a "doorbell" style one.
> 
> Current set up: https://youtu.be/nxpmEFnmK-A
> 
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> � George Fitch, Atlanta Constitution Newspaper, 1912
> 
> 
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users



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Re: [Emc-users] EDM from scratch

[John Dammeyer]

Andy,
Check out this page:
http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html

Also Model Engineer's workshop had a 4 part series on building one.  I'll go 
through my archives and see if I can find them.  I'm pretty sure I had all 4.  
An online search doesn't pinpoint which issues.

John Dammeyer


> -Original Message-
> From: andy pugh [mailto:bodge...@gmail.com]
> Sent: January-31-21 5:28 AM
> To: Enhanced Machine Controller (EMC)
> Subject: [Emc-users] EDM from scratch
> 
> I have started to play around with EDM. The intention is to make an
> EDM "grinder" to profile tool steel and possibly carbide cutting tools
> using CNC-turned profiles.
> 
> At the moment I am using a cobbled-together XY table with a couple of
> STMBL drives.
> One of the STMBL analogue inputs is used to measure the current
> through the gap. (ie using the voltage across the resistor that a
> capacitor is charged through).
> Then a PID controller tries to achieve a target current by adjusting
> the adaptive feed pin.
> 
> I think that it shows promise, but only partly works.
> 
> I am using a 50R resistor and a 1000uF capacitor. I suspect that this
> is too high on both counts.
> I am working at 40V and it seems that the tool welds to the work too readily.
> 
> I suspect that I would get different results if I controlled to the
> gap voltage, rather than charging resistor voltage. And probably
> better still with some sort of signal processing on that voltage.
> 
> What combination of R, C and V would be typical for a servo-controlled
> eroder? I imagine it might be different to a "doorbell" style one.
> 
> Current set up: https://youtu.be/nxpmEFnmK-A
> 
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> � George Fitch, Atlanta Constitution Newspaper, 1912
> 
> 
> ___
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Re: [Emc-users] EDM from scratch

[Gerrit Visser]

Another source of information about pulse generator design: 
https://langfordw.pages.cba.mit.edu/desktopWEDM/electronics/ 

https://www.cnc.info.pl/drazenie-metoda-domowa-moje-proby-t11692-20.html 
(Google translate helps here:-))

Again, my focus is on wire EDM but there must be similarities 

Gerrit





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Re: [Emc-users] EDM from scratch

[Gerrit Visser]

There might be some gems in this video? I have an interest (presently on hold) 
to make a wire edm so have been collecting information etc.

https://www.youtube.com/watch?v=9IWWa0xCd04=9s

There is also a Polish forum where someone describes their power supply as well 
as details on how they use LinuxCNC to run a wire edm. There might be 
similarities to what you are looking for.

Gerrit




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Re: [Emc-users] EDM from scratch

[andy pugh]

On Sun, 31 Jan 2021 at 16:06, Jon Elson  wrote:

> I made a simple EDM for tap burning type jobs a long time
> ago.  It used something like 36 V DC, 30 Ohm resistor and a
> selection of oil-paper capacitors of 1, 2, 4 and 6 uF or
> so.

A common thread here seems to be that my 1000uF electrolytic is the
wrong choice.

> Ben Fleming's pulse EDM, on the other hand is quite fast.
> Flushing of the debris is a key requirement.  Also, his
> pulser recovers quite quickly, and so fires several thousand
> discharges per second.

Lots of people seem willing to sell me a book with their secret sauce in it.

As someone who gives all my ideas away for free, this goes against the grain.

> What are you using for dielectric?

I tried tap water, but just set up steady-state electrolysis (and
couldn't find an easy way to restrain the workpiece)
So initial testing was done in air.

The only commercial EDM I ever used used what we call paraffin (and
the US calls Kerosene)  as the dielectric. It wasn't something that I
would want in my spare bedroom. Both due to the smell and the tendency
to occasionally combust in a very, very, smoky way.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] EDM from scratch

[Jon Elson]

On 01/31/2021 07:28 AM, andy pugh wrote:

I have started to play around with EDM. The intention is to make an
EDM "grinder" to profile tool steel and possibly carbide cutting tools
using CNC-turned profiles.


A fancy commercial (and patented) EDM system was described 
by a tech who worked on them.
They had a 300V supply that was capable of producing a few 
mA.  They had a lower voltage supply capable of tens of mA, 
90 V.  Then, they had a 12 V supply capable of delivering 
tens of A.  These were all or'ed together with diodes and 
controlled by a switch transistor.
After recovering from a discharge, the transistor was turned 
on, the higher voltage caused ionization of the dielectric, 
then the middle voltage supply created a discharge, and then 
the 12 V supply delivered the burning spark.  After an 
adjustable time, the discharge was cut off, and the cycle 
repeats.  I've attached a usenet discussion of that.


Also, I've attached a PDF of another EDM pulse controller 
from the web, no idea if it works.


Jon
Subject:
Re: building an edm
From:
"Ed Huntress" 
Date:
Mon, 26 May 2003 17:57:36 GMT
Newsgroups:
rec.crafts.metalworking

"steamer"  wrote in message
news:F6rAa.16980$jx2.1052...@typhoon.sonic.net...

> Spehro Pefhany  wrote:
> : control stuff? I've done it with a paper towel, a stencil and a bench
> : supply.
> --Gotta know: what voltage, amperage did it take??


A lot of different ones.

Here's the basic concept of Sodick's power supply ca. 1980. It was designed
to get around the patents of Charmille's Robofil power supply, which used a
more complex (and slightly more effective) approach.

The simplest, standard circuit (there were about four separate ones, IIRC,
for different cutting conditions) was actually three power supplies in
parallel. The first was a high-voltage, high-impedance circuit intended to
polarize a plasma channel. It was about 300 V, but I don't remember the
impedance.

In parallel to that was a 90 V, medium-impedance circuit that initiated the
plasma and got some current flowing.

In parallel to that was a high-amperage circuit that could deliver something
like 50 average amps, at around 10 - 12 volts.

The first circuit prepared the way for the second, and the second for the
third. When the third circuit fired, the plasma channel opened up and
carried an extremely dense current, which melts the little glob of metal
that each spark produces.

The sequence was repeated at about 4 kHz. At the end of each spark, the
circuit has to shut the current flow down, HARD, in order to prevent a
self-perpetuating arc. Once an arc starts, current will flow even from the
high-impedance circuits, and the workpiece will develop a weld spot and be
wrecked.

All of this has to occur with a minimum of inductive reaction. If that
sounds easy, remember that you have peak amperages of around 500 A flowing
during the discharge, if you're running at a 10% duty cycle (roughly average
in those days). Current density within the plasma channel is immense and
uncontrolled reactions ring like a bell.

Controlling the initiation of each spark is a mean-voltage sensing circuit
and a current-sensing circuit that actuates the servo and that overrides the
shut-off circuitry to prevent contact-welding. If you get contact, the
electrode often will weld to the work and blow the power supply to hell.

This is an extremely simple system by today's standards, although it was
very effective on the ordinary run of work, with ordinary projected-area
EDMing. When you have pointy electrode projections or when you're trying to
do contouring and have minute projected areas, this circuit slows down to a
crawl. Still, it's many times faster than an RC circuit under the same
conditions.

--
Ed Huntress
(remove "3" from email address for email reply)





edm.pdf
Description: Adobe PDF document
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Re: [Emc-users] EDM from scratch

[Jon Elson]

On 01/31/2021 07:28 AM, andy pugh wrote:

I have started to play around with EDM. The intention is to make an
EDM "grinder" to profile tool steel and possibly carbide cutting tools
using CNC-turned profiles.



I think that it shows promise, but only partly works.

I am using a 50R resistor and a 1000uF capacitor. I suspect that this
is too high on both counts.
I am working at 40V and it seems that the tool welds to the work too readily.

I suspect that I would get different results if I controlled to the
gap voltage, rather than charging resistor voltage. And probably
better still with some sort of signal processing on that voltage.

What combination of R, C and V would be typical for a servo-controlled
eroder? I imagine it might be different to a "doorbell" style one.

There are a few different systems for EDM.  Ben Fleming (who 
I met at a couple CNC meetings) has a line of self-published 
books out on EDM.  He has done LOTS of work with EDM, and is 
an expert.


I made a simple EDM for tap burning type jobs a long time 
ago.  It used something like 36 V DC, 30 Ohm resistor and a 
selection of oil-paper capacitors of 1, 2, 4 and 6 uF or 
so.  It was glacially slow.

See http://pico-systems.com/edm.html


Ben Fleming's pulse EDM, on the other hand is quite fast.  
Flushing of the debris is a key requirement.  Also, his 
pulser recovers quite quickly, and so fires several thousand 
discharges per second.


What are you using for dielectric?

Jon


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Re: [Emc-users] EDM from scratch

[Gene Heskett]

On Sunday 31 January 2021 08:28:13 andy pugh wrote:

> I have started to play around with EDM. The intention is to make an
> EDM "grinder" to profile tool steel and possibly carbide cutting tools
> using CNC-turned profiles.
>
> At the moment I am using a cobbled-together XY table with a couple of
> STMBL drives.
> One of the STMBL analogue inputs is used to measure the current
> through the gap. (ie using the voltage across the resistor that a
> capacitor is charged through).
> Then a PID controller tries to achieve a target current by adjusting
> the adaptive feed pin.
>
> I think that it shows promise, but only partly works.
>
> I am using a 50R resistor and a 1000uF capacitor. I suspect that this
> is too high on both counts.
> I am working at 40V and it seems that the tool welds to the work too
> readily.
>
I too have been known to do some EDM, with 50 ohms and a 2 to 10 uf 
capacitor, paper, oil filled or mylar. Electrolytics have too high an 
ESR to make a good storage cap though, damping the discharge rate and 
destroying the sparks explosive effects, hence likely your welding 
problem.

You also need a liquid medium in the gap, preferably being circulated 
somehow in order to flush away the debris which will eventually get so 
contaminated it will short out the gap.

I've cut the slots to make a coupling socket to fit the end of a small 
ball screw, by boring a piece of unhardened A2 to serve as a socket to 
insert the screw into. I also made a tapered thread at 50 tpi on the 
outside and used the same tapering technique on both the socket and 
matching nut's, doing all that machining before cutting the socket walls 
into petals so the nut, as its drawn up tight on the taper, is squeezing 
the petals and with a bit of green loctite, has been holding and driving 
the X screw in my 11x54 Sheldon for about 4 years now. This 3/4" 
diameter extension shaft locked onto the end of the 8mm ball screw and 
spinning in Torrington needles and roller washers is spun from the front 
end by a 3 phase, 2NM stepper servo drive mounted on  a slider for belt 
tension, 20 teeth on the motor, 40 on this shaft projecting out thru the 
new apron plate bolted to the front face of the carriage, reusing the 
original hand drive crank for the drive bushing in the face of the 
carriage. I used a 2NM here because it was short enough to clear the 
bed. I use the 3NM version on the much bigger Z screw. Machine moves a 
lot like Casper the ghost now.

I have also used EDM to clear broken taps, without damaging the threads 
the tap cut, quite a few times, but because that's a blind hole, the 
dielectric fluid doesn't clear the debris well so you do a lot of 
cleaning and adding new fluid.

I've had about as good a result using distilled water (its a good 
insulator and cuts as clean as using K2, and its a heck of a lot 
cheaper. To cut the petals, I made an arbor and a 3" brass disk from 32 
thou brass. And spun it at about 200 revs in my micromill which has 
since died. Connected one wire to the workpiece, the other was wrapped 
around the arbor so the currant pulse did not have to go the the spindle 
bearings as that will damage those bearings. with 2+ inches of distilled 
in a plastic tub, and at about a step a second to cut each of the 1" 
deep slots. I made 3 because the shaft was laying on the flat of one of 
the nuts installed on the shaft. EDM, unlike turning, leaves no burrs, 
beautiful cuts. About 2 hours of me standing there with a finger on the 
x jog key for all 3 slots. There is a preferred polarty, but I'd have to 
look it up again now.

> I suspect that I would get different results if I controlled to the
> gap voltage, rather than charging resistor voltage. And probably
> better still with some sort of signal processing on that voltage.
>
> What combination of R, C and V would be typical for a servo-controlled
> eroder? I imagine it might be different to a "doorbell" style one.
>
> Current set up: https://youtu.be/nxpmEFnmK-A


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] EDM from scratch

[Peter Blodow]

Andy,
I have been experimenting with EDM long time ago, say 25 years. I used a 
simple RC-circuit together with a "soft" transformer (ca.1.5 mm air gap) 
in order to forgive for the shorts and save fuses. All was mounted on my 
drill press. I gave up when I realized that without a controlled 
transistor (Lazarenko-)generator I would not get reasonable results. It 
seemed to me that developing such a generator would exceed the 
experimental effort I was willing to make, as there was no real 
application in sight. I wasn't even thinking of EMC table motion control 
at that time.


I still remember that I was using a much larger capacitor, even up to 1 
F and 60 Volts from an old IBM Printer supply I happened to have at 
hand. With an uncontrolled, deliberate discharge of this capacitor, 
about a 5-10 mm length of 10 mm² shorting cable disapeared at once, 
producing black metal vapor. Therfore, there was a second resistor (way 
below 1 Ohm) between the capacitor and the electrode to limit the short 
current and avoid sticking.

And boy, that was a messy and noisy affair!
I suppose you have read his (and other links): 
https://en.wikipedia.org/wiki/Electrical_discharge_machining

Good luck!
Peter

Am 31.01.2021 um 14:28 schrieb andy pugh:

I have started to play around with EDM. The intention is to make an
EDM "grinder" to profile tool steel and possibly carbide cutting tools
using CNC-turned profiles.

At the moment I am using a cobbled-together XY table with a couple of
STMBL drives.
One of the STMBL analogue inputs is used to measure the current
through the gap. (ie using the voltage across the resistor that a
capacitor is charged through).
Then a PID controller tries to achieve a target current by adjusting
the adaptive feed pin.

I think that it shows promise, but only partly works.

I am using a 50R resistor and a 1000uF capacitor. I suspect that this
is too high on both counts.
I am working at 40V and it seems that the tool welds to the work too readily.

I suspect that I would get different results if I controlled to the
gap voltage, rather than charging resistor voltage. And probably
better still with some sort of signal processing on that voltage.

What combination of R, C and V would be typical for a servo-controlled
eroder? I imagine it might be different to a "doorbell" style one.

Current set up: https://youtu.be/nxpmEFnmK-A





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[Emc-users] EDM from scratch

[andy pugh]

I have started to play around with EDM. The intention is to make an
EDM "grinder" to profile tool steel and possibly carbide cutting tools
using CNC-turned profiles.

At the moment I am using a cobbled-together XY table with a couple of
STMBL drives.
One of the STMBL analogue inputs is used to measure the current
through the gap. (ie using the voltage across the resistor that a
capacitor is charged through).
Then a PID controller tries to achieve a target current by adjusting
the adaptive feed pin.

I think that it shows promise, but only partly works.

I am using a 50R resistor and a 1000uF capacitor. I suspect that this
is too high on both counts.
I am working at 40V and it seems that the tool welds to the work too readily.

I suspect that I would get different results if I controlled to the
gap voltage, rather than charging resistor voltage. And probably
better still with some sort of signal processing on that voltage.

What combination of R, C and V would be typical for a servo-controlled
eroder? I imagine it might be different to a "doorbell" style one.

Current set up: https://youtu.be/nxpmEFnmK-A

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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