Complete a EDM circuit

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Hi!

I have some questions about an EDM circuit I've been thinking about.
I want to build an EDM machine, and I don't have experience enough to finish a circuit that's needed so I've been thinking I can use some existing stuff and put it together.

So I thought this could be a good place to start motor pulse controller.
And I have a variable PSU with 90v at 4.5 amps.

I changed the controller a little bit, I checked what pins on their implemented chip the pwm was coming from, then removed it and hocked up an Arduino to those pins so that I can control both the frequency and the pulse width.

Then I have a quite capable start I think.
Now here comes a few questions regarding this setup.

  1. One thing I noticed while testing the output of the controller with my oscilloscope was that if I don't have a motor connected then the pulse isn't working, and I guess that's because the motor acts like a pull down resistor.
    So the question is, since there will be some power on the output, what resistor should I use? or am I misunderstanding it completely?
  2. Provided that this works as it should there is still one big thing missing as I understand it, that's some protection for when the circuit will short, so if the wire touches the workpiece I need to be sure that the complete circuit or PSU doesn't burn.
    And on top of that I guess I the controlling software would need to know that this happened to so that it can stop moving, or back of a little.
    Is there a good way to add this protection?
  3. The last question, quite simply, am I forgetting something? :)
 

shortbus

Joined Sep 30, 2009
10,045
As some one who has been working to design my own EDM power circuit for over 10 years, I can feel your frustration. I to thought to use a PWM to control the pulses, but the more I've learned about electronics the farther I've moved away from that idea.

To use the PWM module for what your doing, instead of driving the electrode voltage directly from it, use it to switch a mosfet. What is called a low side switch, there are to kinds of mosfet type switching circuits, high and low side. High side is better for EDM but much harder to make it work. It's better because the gap ciruit would not be 'live' when not burning the part. With a low side switch the circuit would be live any time the machine is on.

There is much to learn about EDM. There are many DIY books on them but not all are created equally, and I have bought them all, or at least all I have been able to find.
The ones that are promoted most are the two by a man named Ben Fleming. But to my way of thinking they are popular only because he promotes them, not because they are good. His designs will work with some tweaking but they are not the way real machines work. I ran real EDM machines for many years, so I have some experience with an EDM. Ben has a web forum about his machines, and I have been active there over the years. But since I wanted a higher class machine I've not built his. For his books and forums, Google Ben Fleming EDM

Then there is to my thinking the best book on DIY EDM. If your going to buy just one book I would suggest buying the one by a man named Robert Langlois. It is a book sold by Home Shop Machinist magazine. It is made up of a series of articles that was in the magazine, then put out in book form. Instead of just telling you "do this because I said"(like Fleming does) it explains why you do it. And if you want a more powerful EDM it gives the information on how to change the design to do it. This is where I started my journey to a home EDM and the one book I go back to. To EDM you don't need a pulse EDM, the R-C type will work, and was the first type made. And it was the main one for many, many years.

If you really want an EDM start with the R-C type, and expand from there. If I had done that I would have a working EDM right now. I've had the mechanical part of my machine done for years before I started to design my own circuit, in fact a photo of it is in one of Fleming's books. Just giving you my experience

https://www.amazon.com/Build-EDM-Electrical-Discharge-Machining/dp/094165351X The book is also on Ebay from time to time.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Agree, one of the first DIY books I bought was the one by R. Langlois and although it can be improved with today's electronics it is a good basis.
It uses principles used in older style Industrial EDM m/c's.
Max.
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
As some one who has been working to design my own EDM power circuit for over 10 years, I can feel your frustration. I to thought to use a PWM to control the pulses, but the more I've learned about electronics the farther I've moved away from that idea.

To use the PWM module for what your doing, instead of driving the electrode voltage directly from it, use it to switch a mosfet. What is called a low side switch, there are to kinds of mosfet type switching circuits, high and low side. High side is better for EDM but much harder to make it work. It's better because the gap ciruit would not be 'live' when not burning the part. With a low side switch the circuit would be live any time the machine is on.

There is much to learn about EDM. There are many DIY books on them but not all are created equally, and I have bought them all, or at least all I have been able to find.
The ones that are promoted most are the two by a man named Ben Fleming. But to my way of thinking they are popular only because he promotes them, not because they are good. His designs will work with some tweaking but they are not the way real machines work. I ran real EDM machines for many years, so I have some experience with an EDM. Ben has a web forum about his machines, and I have been active there over the years. But since I wanted a higher class machine I've not built his. For his books and forums, Google Ben Fleming EDM

Then there is to my thinking the best book on DIY EDM. If your going to buy just one book I would suggest buying the one by a man named Robert Langlois. It is a book sold by Home Shop Machinist magazine. It is made up of a series of articles that was in the magazine, then put out in book form. Instead of just telling you "do this because I said"(like Fleming does) it explains why you do it. And if you want a more powerful EDM it gives the information on how to change the design to do it. This is where I started my journey to a home EDM and the one book I go back to. To EDM you don't need a pulse EDM, the R-C type will work, and was the first type made. And it was the main one for many, many years.

If you really want an EDM start with the R-C type, and expand from there. If I had done that I would have a working EDM right now. I've had the mechanical part of my machine done for years before I started to design my own circuit, in fact a photo of it is in one of Fleming's books. Just giving you my experience

https://www.amazon.com/Build-EDM-Electrical-Discharge-Machining/dp/094165351X The book is also on Ebay from time to time.

Thanks for your very detailed answer!

The sad thing about this, is that I've been thinking about this and reading other threads for info, starting to get confident that I had an idea that might work but looks like I was wrong.
Actually nothing sad about that, that's learning I guess! :) And thankfully there are places like this which can point you in the right direction.

So I guess I need to read some more about this, what is level of experience needed to understand say the Robert Langlois book?

The thing you wrote about not using the controller to drive the controller makes me think.
Do you mean I should use the controller to control another mosfet with the voltage it provides or do you mean I should forget about it completely?
And what is the reason for this, seems to me I would just switch the voltage again.

Just one question though, isn't the basics of EDM a high voltage with a frequency that is brought close to the opposite pole that makes a spark jump between?

Since I got your answers I found some videos where they use pwm for EDM, so it makes me wonder a little why it would be a bad option.
Isn't R-C type basically an analog way of producing the frequency?
 
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Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Okay thanks!

If i where to pursue the pwm idea anyway.

It seems like i have much of the parts already available, i can control the motors from the same mcu that does the pwm for the pulse module i linked before, and thereby stop the movement when the pulse is low or if there is a short (not sure how i would do this yet, possibly by reading the voltage on an analog pin, obviously with something keeping the voltage in a good range for the pin).

Another positive thing with this for me is that i have no problems writing a software for it so that i can control the frequency and stuff from a gui instead.

So to try to narrow it down from this point of view there's just a few things i need to solve, as i can see right now.
There will be more later but lets start with this.


Say my very basic setup looks like this, an arduino provides the pwm for the pulse module i linked which outputs a 90v pulse.
The arduino also controls the motors for both movement and wire feed.

The positive wire from the pulse module is attached to the wire, and the negative to the workpiece.

Could i here wire the negative wire to an analog pin on the arduino to see when there is voltage flowing caused by a short and after that have some sort of protection so the short doesnt destory the module?

And as i said the pulse module doesnt output a correct pulse right now if no motor is connected, is there a good way to solve that?

To me it seems as though solving those small issues would give me a compelete setup, am i wrong about that?
 

shortbus

Joined Sep 30, 2009
10,045
You keep mentioning 'wire', so your wanting to make a wire EDM? Not a sinker EDM? They take different power supplies, that are not interchangeable. But a wire EDM can work somewhat with a R-C supply. Not trying to dash your hopes here, just like many things in life, you need to walk before you run. If you Google "EDM thesis", there is a lot of information out there. One circuit to avoid though is the one called, "Garden of EDM". That guy never completed it and it has a lot of dangerous information in it like high voltages that even industrial EDM's don't use.

Your pulse module out put needs some type of load between the positive and negative to complete the electrical path. With out that there will be no output. Using any micro controller in an EDM circuit makes it another step harder. The spark gap produces a high frequency signal that will need to be separated in some way(galvanic separation) from the micro. The computer controls in an industrial machine are in a Faraday cage plus the other isolation.

The R-C power supply works by charging a (C)capacitor bank through a (R)resistor to a voltage that will then jump the gap which is a smaller R value. This charge/discharge sets the frequency of the circuit.

Your description of the + and - output from the power source is backward. If done with the work negative, it will take more off of the electrode with each spark than it takes from the work part. And the electrode does go through a certain amount of wear, even with it as the negative.
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Sorry if i was unclear about wanting an to build a wire edm.

I just watched an interesting video where a R C circuit is pretty well explained

He basically has exactly what im after but not using a pwm.

So since i already have a PSU i would "only" need to setup the rest, so maybe that would be a good way to start?
 
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shortbus

Joined Sep 30, 2009
10,045
Maybe you should give a list of what you have already bought. It's getting confusing, you know what you have and I don't. On second thought along with your parts, maybe a block diagram would help to. I'll try to explain the way I understand what your trying to do. I'll try to help you in anyway I can.

1. You say you are feeding a Arduino pwm pulse into a pwm module. From the link you gave to the module, it seems to have a built in pulse generator in it. Did you modify the module to use the pulse output from the micro? The pwm module as built uses a pot to control the pulses out to the motor. Putting pulses into where the pot would go won't work.

2. You say you have a variable power supply, PSU. To me that sounds like it would be a switching type. If it is it won't work as an EDM power supply. It needs to be a linear PSU, meaning a transformer, bridge rectifier, and a large output/smoothing capacitor. A switcher PSU has problems in this type of thing. They don't like to be shorted out, that will happen in an EDM, shorting will cause a switcher to shut down the output. They don't have enough 'headroom' to supply the pulses. The large cap in a linear PSU is what give it the 'headroom' to keep the sparks happening, and small shorts don't effect them or shut them down.

The basic power supply and and what the guy is explaining in the video is what in the Langlois book. Lanlois also had a series of build articles in Home Shop Machinist magazine on using the power supply in the book to make a wire EDM. A how to of building the mechanical parts of the wire machine. The build series was back in the 1990's. Maybe their web site would sell the back issues, or scanned copies of the articles? http://www.homeshopmachinist.net/
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Hi again and thanks for your answer.

I will try to put together a block diagram and post it here.
What is the preferred way of doing this, is there some easy way to draw it and post it here or does people just draw images and post them?

But the things I currently have is basically
The motor module (slightly modified to be controlled from an Arduino)
A PSU (that wont work in this case)

1. I have removed the micro controller from the module and to the same pins that the old micro had it's pwm and ground I hooked up the pwm and ground from my Arduino, so the potentiometer part of the module isn't used at all. I did this because by using just the potentiometer I only had control over pulse width but I wanted to be able to change the frequency to and it seems to be working so far.

2. You are right, it's a switching power supply. so then I have to buy or build a linear PSU instead of the one I have, seems doable.
 

cmartinez

Joined Jan 17, 2007
8,220
What is the preferred way of doing this, is there some easy way to draw it and post it here or does people just draw images and post them?
Normally you'd draw the images in your pc, and then upload them in your post.
You can use any software you like (I like using AutoCAD, for instance) and then capture a screenshot and upload it as a jpg or png file.
Other people like using special software for drawing electronics diagrams, so that the circuit can also be later run in a simulator. You'll find that LTspice is favored by most members here. And it's free!
 

shortbus

Joined Sep 30, 2009
10,045
As far as a transformer, you don't have your location in your information profile. So it makes it harder to give ideas, but I agree with Max about new ones. But a good appropriate used one will work fine. I was talking online with a guy that took a transformer out of a public address(PA) system amplifier to use in his. It's all in the output voltage and amperage. I'm building a sinker so I need more amperage, than your wire. I was able to find some servo motor power supplies and one of them had a 20Amp transformer in it. It was a 70VAC output, then when you multiply by 1.41(the rectifier constant) it ends up at ~99V DC which is perfect for an EDM.

In a nut shell, the differences between a sinker and wire power supply(or spark generator which is the common and some what preferred term) is the sinker has more amps with a slower frequency and the wire has lower amps at a higher frequency, with the voltage the same. Biggest reason for this is the sinker electrode has more area compared to a wire. If you put the sinker power into a wire, you would need to move the wire speed so fast(to keep it from burning in half) that it would be even more wasteful of wire. And EDM wire is expensive. Even when using a low amperage, the wire moves at a few meters a minute, to keep it from breaking. All EDM is one if not the highest cost machining operations, but many times it's the only way to machine certain things.
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Thanks again.

Sorry i will update that, im in sweden.

Can you think of any good way of replacing the r/c part from the video with pwm, or does it need to be completely different?

I can see how it is expensive, but as you some stuff needs it.

I have built both a 5 axis and a 3 axis cnc but none of them would be capable of the level of detail i need for some parts.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I would think apart from the challenges mentioned above. A wire EDM requires a interpolated X & Y axis that has to be controlled by the EDM process, the sinker usually just needs a simpler Z axis control.
Max..
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
I would think apart from the challenges mentioned above. A wire EDM requires a interpolated X & Y axis that has to be controlled by the EDM process, the sinker usually just needs a simpler Z axis control.
Max..
Thanks
Ive read that there should be no movement when the pulse is low and if there is a short.
Is that what you mean by controlled by the EDM process?

Im still trying to find out how i could use pwm instead of rc, any suggestions on that?
 

shortbus

Joined Sep 30, 2009
10,045
Ive read that there should be no movement when the pulse is low and if there is a short.
Is that what you mean by controlled by the EDM process?
He explained it in the link you gave. Pretty sure your over complicating this. The pulse, not really PWM works in a sinker because of the higher amperage and lower frequency. Don't think the movement is anywhere near as fast as the frequency of the actual discharges in the gap. And the wire speed through the gap definitely is. The only time movement would stop is when the circuit 'shorts' out. In a sinker the electrode retracts to clear the short. With a wire one of two things happen, the programed movement stops or the wire breaks, depending on how severe the short is. A window voltage comparator is used in both the sink and wire to decide movement.

Are you planning to use the Arduino for movement? There was talk some time ago of people adapting Mach3 to workin X and Y only for wire paths. Wasn't interested in wire so didn't keep up with it.
 

Thread Starter

stellanhaglund

Joined Mar 31, 2017
23
Thanks!

Do you know of any circuit that shows the use of a pwm instead of the r/c part?
That's my main concern at the moment once I have the basics of the circuit it will be easier to think in terms of how I should program it and such.

Is it still a linear psu with a mosfet setup instead of the r/c part?

I will do the movement myself with arduino or stm32 setup, I don't like mach3 at all so I will do my own small software for this.

EDIT

I just ordered the Langlois book.
So I will start with the r/c type as you said @shortbus.

I also contacted the home shop machinist about the back issues.
 
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