I want to build and ''easy to make'' sinker type EDM machine. Challenge is to have as much as possible ready made components such as the ones from aliexpress/ebay. The closest to this demand is EDM project by Dominik Meffert. I really like this project, because amateur like me need this amount of simplicity to build it.
project details:
https://hackaday.io/project/181551-sinker-edm-machine/log/202201-arc-generator-circuit

BUT,
I notice there is no Voltage comparator.
Does anyone knows why and is it possible to add it (and how).

 

P.S. I mean voltage divider...

 

Hi Bogos87 and welcome to AAC.

That design of EDM probably doesn’t require a voltage divider as its control of the Z axis is done using code and also it looks like it’s just a pulsed RC output so it probably just relies on a pulsed charged capacitor/ discharge time cycle maybe? To be honest I don’t know how that design would be any good for anything other than a wire EDM or a broken tap/ drill remover as the electrode wear will be very high. It’s not possible to add a voltage divider to that design of EDM without first adding a high power current limiting resistor to the output in order to create the voltage drop necessary for the voltage divider to follow. EDIT: I've just noticed that there's some power resistors of a sort on the output so it looks like the small circuit board at the bottom of the schematic provides some sort of voltage feedback to the control board,

Cheers.

 

Thank you, edmguru.

I want to build an EDM (Electrical Discharge Machine) to create a die set for an airgun pellet mold and/or slug mold (it must be EDM because of the steel hardness, can't use CNC mill). It's a relatively small workpiece, but good precision is preferable. Surface finish is important, BUT I think the final stage of making could involve polishing with other machines or by hand. So, I want decent quality, not perfection.

My idea, if possible, is to use parts from AliExpress, such as an Arduino, a square wave pulse generator like the ZK-PP1K, a voltage divider from AliExpress ( https://shorturl.at/fwV46 ), AliExpress resistors, a power supply unit (PSU), and so on. It's not just about cost-effectiveness; it's primarily due to my limited knowledge of electronics.

Dominik Meffert's EDM project looks very straightforward to build, and that was the project I was aiming for.

I'm also open to other ideas and suggestions because I want to learn, but I'm aware of my current time limitations.

 

Hi Bogos87. You’ll need a pulse EDM in order to produce a high quality mold/ die etc as this type have the least electrode wear, also you’ll probably need to use a CNC mill or lathe at some point to produce your electrodes which are best made from copper or you could use a graphite grade specifically made for EDM. The voltage divider you have in mind won’t handle the voltage I’m afraid (only 25v) but it’s cheaper to make one anyway (100k Ohm and a 3k Ohm) as you’ll need to add a voltage adjustment to it (10k Ohm potentiometer) for gap volts adjustment during the erosion or “burn” process. The power resistors all need to be 200 Watt rated (two 100 Watt connected in parallel) and by using say three pairs of output resistors in parallel you will get three different power outputs like I do on my machines which are 3A, 6A and 10A as the total power or current output is simply a resistors in parallel calculation.

Cheers.

 

thanks,
I also almost completed Ben Flemings RC, but I guess I'll need a pulse one.
are your ''easy peasy'' and ''not so easy peasy'' both pulse type? Are the other version have stepper motor?

 

Yes both types are pulse EDM with very low electrode wear. The Easy-Peasy version is the easiest and cheapest to build depending on the quality of your machine build (X, Y and Z axis linear slides) etc. The not so Easy-Peasy version is more of a professional build and uses a stepper motor for the Z axis and the wiring for the Z axis control is a lot more complicated and expensive. Most other EDM designs use a stepper motor but I would advise you to check out the other pulse EDM machines online first before going ahead as most if not all have “issues” mainly with stability and performance which are easy to correct if you know how.

Cheers.

 

I want to build an EDM (Electrical Discharge Machine) to create a die set for an airgun pellet mold and/or slug mold

Are you talking about a mold for lead? They don't normally use a hard steel for those, but use aluminum. When you say you can't CNC a mold because it's hard steel how hard are you using? I was a mold maker for many many years before retiring. Doing sinker edm for many of the years and even most of our plastic molds weren't made from a very hard steel. Hard steel was for progressive dies, which I also made.

Look at what they are doing for bullet molding at Lee Precision - https://leeprecision.com/bullet-casting

 

Thank you for answer. I poorly explained what I need. It's not a mold for melting, it's a swaging die, or split die matrix with hardness of HRC 60. Maybe carbide. That's why I need EDM.

 

Yes both types are pulse EDM with very low electrode wear. The Easy-Peasy version is the easiest and cheapest to build depending on the quality of your machine build (X, Y and Z axis linear slides) etc. The not so Easy-Peasy version is more of a professional build and uses a stepper motor for the Z axis and the wiring for the Z axis control is a lot more complicated and expensive. Most other EDM designs use a stepper motor but I would advise you to check out the other pulse EDM machines online first before going ahead as most if not all have “issues” mainly with stability and performance which are easy to correct if you know how.

Cheers.

EdmGuru I just watched your latest video on yt ''New design of a simple pulse EDM...''
Are you willing to share a photo of the back of the circuit board (13x5 cm with IRFP250N mosfet...) So I can try to replicate the wiring? Thanks in advance.

 

Hi Bogos87. A view of the circuit board wouldn’t be much help or make much sense as there’s a few wire links involved to create the circuit also you would need to know what components are required so a schematic is really what you need. I’ve mentioned online in the past that I don’t use schematics as such I just have an idea about what I want to achieve and then draw it up in Fritzing using their PCB view layout option, which I find easy to do and then download the image as a Gerber file and convert it to G-code. Although it’s fair to say that I’ve tested certain “elements” of this circuit in LTspice XVII in order to get the correct bootstrap balance so I could no doubt draw up the complete circuit at some point, but don’t worry about the power generator side just yet as they’re just a power switching circuit and easy to make, if you follow a few basic rules, also you may find that the rest of the EDM machine build will be more tasking.

I also wouldn’t recommend making your mold dies from carbide as it’s difficult and slow to erode, and also you’ll need to use copper tungsten electrodes, and the electrode wear rate will be high.

Cheers.

 

If the material is so very hard then a mill is not the right tool. I suggest grinding, possibly with a coolant, otherwise with a very slow feed.
AND pay attention to shortbus, he does know about molds.

 

If the material is so very hard then a mill is not the right tool. I suggest grinding, possibly with a coolant, otherwise with a very slow feed.
AND pay attention to shortbus, he does know about molds.

Thanks,
that's exactly the point. As I mentioned, milling is not the way to go; grinding/polishing after EDM machining is.

 

Depending on how much material needs to be removed, grinding by itself might be an option. How smooth does a lead pellet mold need to be?

 

Depending on how much material needs to be removed, grinding by itself might be an option. How smooth does a lead pellet mold need to be?

I'm looking for unconventional ways such as EDM. Finish surface is less important. Alignment does.

So, the question is, is it possible to use ready made elements to make a sinker EDM? I think like Dominik Mefferts's design.

 

Here's the video of it working: Meffert's EDM

 

You mentioned Ben Fleming's book earlier, do you know he also has a pulse edm book? My machines mechanical picture is in that book. While I disagree with his refusal to use a stepper motor for the ram and a few other things in his design, I have to admit he has at least finished his machines. Mine is still waiting on the electronics circuit.

Where I worked we had 3 different types of machines, from different eras. The oldest were RC power supplies, then the standard pulse type and then the CNC Charmilles machines. As far as burn finishes went there really wasn't much difference in the RC and pulse finishes, the both needed to be stoned to a final surface finish. The Charmilles were much, much better and didn't need near as much bench work to get a good surface.

As far as needing carbide for a size die, are you doing this for yourself or as a business? From years of experience your in personal use, never going to wear out a die made from O-1 or 4340 prehard or stainless steel. With out a CNC edm getting to a correct size is more of an art than a science. But machining a standard type of steel you can control your diameter easier.

I don't quit understand why your swage die needs to be split? I shot air guns too and the pellet swage dies I've seen advertised were just a flat plate with holes of different diameters. the pellet is pushed through using a pin in the hollow of the pellet.

 

I should have mentioned ,since you didn't the granddaddy of DIY edm the Robert Langlois book. His has much more control than the Ben Fleming RC machine.
https://www.scribd.com/document/532780039/EDM-by-Robert-Langlois

 

Hi shortbus it's been a while how are you? I thought that the Langlois design of EDM was just an RC type so not suitable for Bogos87 to use due to high electrode wear.
Cheers.

 

@shortbus thank you for suggestions! I must admit that I already have Langlois book, but lack of free time to read it. I'll definitely start reading it.

My idea was to have a simple (simplest possible solution, due to my limited knowledge and time) of the EDM with stepper motor with pulse generator.

About the Ben Fleming: I'm in the process of completing the pcb(I know to solder elements) for RC, but I'm open for pulse version of Ben. I rejected that idea because some folks mentioned that his book for pulse have old instructions and are different than his latest pcb with solved issues. Therefore I thought it's confusing and rejected that idea. Plus, it's not stepper motor version.