I first played around with EDM about 50 years ago in the mid 1960s but did not have much succes. I was mainly interested in removing broken taps etc at the time

I was a tool/mold make and ran them for ~13 years. Worked at GM's wiring plant. After around 1883 I worked on just about every wiring connector mold they had at one time or another. Even made so new molds that they couldn't get made fast enough on the "outside'. I have a small machine shop and build things for myself. EDM is one of those things that unless you've ever used one you can't really imagine how much they can do. Slow, but sometimes the only way to do something.

I have one of the build plans in a back issue of Model Engineer, that I sent to the UK to buy.

Yeah, I agree with you about the comparator in his schematic, and he made it worse in the pulse plans. I tried to explain to him with no avail. He has it set up so the "window" is high not low. Then he used some caps to keep voltage in the comparator to try and keep the motor from running during the cap recharge. In the relaxation version he had three separate resistors instead of a potential divider, he did that to only use one pot to set the 5V window. That's when I came up with the diode in the block #7 comparator to do that and only use one pot. Got a lot of flack by other members on his forum for trying to get him to understand why it was better.

 

Worked at GM's wiring plant.

Packard?

 

Yep, when I started there it was Packard ,then changed to Delphi Packard. Pretty much a 'ghost town' today. Even though products are still sold under the Delphi name, just not made in the US.

 

After around 1883 I worked on just about every wiring connector mold they had at one time or another.

Are you really that old??

 

EDM is one of those things that unless you've ever used one you can't really imagine how much they can do. Slow, but sometimes the only way to do something.

Wire EDM = Instant Punch and Die maker.

 

I just spotted the error when I came back to the thread and corrected it to about 50 before I read your comment.

Edit. Just noticed that I wrote this last night but did not click on the "Post reply" button.

Les

 

Are you really that old??

I feel like it some days.

 

Wire EDM = Instant Punch and Die maker.

Your so right about WEDM. Never got the chance to run them but the company had a few. Instead of having to rough machine parts, then heat treat and then grind to finish size, they just kept preheat treated steel in stock. Ground it to the required thickness then wired to finish shape and size. EDM doesn't care how hard the metal is. It isn't "instant" but is much faster than the old way, all considered.

 

Hi SB,
After reading your post #21 I had a look back at Ben's schematic and my version. It looks like we disliked the same thing in his design. I have attached a PDF of my schematic. The current mirror part that provides the constant current to the resistor chain for setting the window level and window width did not work very well but it was good enough. I too have a small workshop with a Seig X3 mill and a Chester DB-10G lathe. I also have a stick welder and a mig welder.

I've done it again. I wrote this this morning but fogot to click the reply button.

Les.

 

Hi Les. I just printed out your schematic and will study it. Thanks for sharing.

You would probably not like what Ben did in the pulse machine either. Instead of high side mosfet switching he uses low side. This on itself wouldn't be bad but he also tied the high voltage common to earth ground. With the positive side of the circuit always "live" when on and the common tied to earth, there is a very big possibility of touching any earthed part of the machine and getting a shock. To my thinking not good. But like the comparator, I was ridiculed for even bringing it up.

 

I too have a small workshop with a Seig X3 mill and a Chester DB-10G lathe. I also have a stick welder and a mig welder.

I've got a Bridgeport, a 9" Southbend lathe, a 12" Logan with a 5" bed , and a Chinese 14" short bed lathe. An 18" metal cutting band saw with blade welder, a 12" homemade metal cutting band saw , a Chinese horizontal band saw. A couple of drill presses, and a life times worth of precision measuring tools and hand tools. A stick welder, Mig, small Tig and torch set up. I do sheet metal work and build cars and motorcycles too.

 

1. Schematics PDF's with thumbnails. They scale and become readable at higher magnification.

2. You can also use designators like R101, 201, 301 for different sections.

Aside:
In the mid 70's, a high school classmate used the autoshop and dropped a 307 V8, I think, into the middle of a Corvair (was a rear engine, air cooled car). His transmission shaft kept breaking until he managed to have an cooling port EDM'ed into the drive shaft.

 

Nice setup. I'm envious.

Les.

 

ith the positive side of the circuit always "live" when on and the common tied to earth, there is a very big possibility of touching any earthed part of the machine and getting a shock. To my thinking not good....

and to my thinking, also not good ... besides, if one's gone through all the trouble of designing the rest of the circuit, why not do a little extra work and implement high-side switching for safety purposes?

 

Nice setup. I'm envious.

Les.

I got most of them at good prices by just keeping my eye's out and waiting for the right deal. Forgot to put down a surface grinder in the list.

Looked at the schematic. Seems like I don't know enough about electronics. Mine is much simpler. I did notice you have a current mirror and you have mentioned current in my circuit, by current are you meaning 'amperage'? Even Ben's like mine and any machine I've run is voltage based, not amperage.

And I see your using a brushed motor too like Ben does. To my way of thinking that's another wrong thing, steppers are the way to go, The movement is less than 0.001 inch at a time, the gap distance. His use of a brushed gear motor caused them a lot of problems, guys started to make slip clutches for the drive lead screw to keep from breaking things. Never could understand his refusal to use steppers. And with the price of ready to run stepper drivers today it's just not worth not using steppers. Also his use of the two color Led's to tell whether the ram is going up or down, just don't get it.

 

1. Schematics PDF's with thumbnails. They scale and become readable at higher magnification.

2. You can also use designators like R101, 201, 301 for different sections.

Aside:
In the mid 70's, a high school classmate used the autoshop and dropped a 307 V8, I think, into the middle of a Corvair (was a rear engine, air cooled car). His transmission shaft kept breaking until he managed to have an cooling port EDM'ed into the drive shaft.

Thanks, one of the reasons I drew it as two different things is it will be two different boards. One for the high voltage/power and the other for the logic. Didn't even consider the fact it would cause confusion in a discussion. And didn't know any better, since it's my first foray into a design. But will try to do better with the next drawing.

Used to love those Corvair's, especially the second generation, the body style was way ahead of it's time. Built a rail type dune buggy using a turbo charged Corvair engine, that sucker was fast.

 

I zoomed up your original schematics and converted to .PDF for you. Not super but maybe will help.
Hope so.
And as long as I was posting bad images, here is one of my '65 Corsa Ragtop 140 from 1970. Fun little ride.

 

I've got a Bridgeport, a 9" Southbend lathe, a 12" Logan with a 5" bed , and a Chinese 14" short bed lathe. An 18" metal cutting band saw with blade welder, a 12" homemade metal cutting band saw , a Chinese horizontal band saw. A couple of drill presses, and a life times worth of precision measuring tools and hand tools. A stick welder, Mig, small Tig and torch set up. I do sheet metal work and build cars and motorcycles too.

Logan 9" w/VFD
Lagun 9"x42" 3-axis CNC all A.C. servos
Delta drill press 2hp
Imperial 20" gap-bed lathe (resto project, unfinished)
Craftsman MIG (p.o.s.)
Acetylene torch
Mendel 3D printer
1889 power hacksaw

Soon to purchase @ scrap value from my employer going out of business :
Miller 252 MIG
Eastwood TIG200
Northern Plasma375
Gearhead drill press

First project after that acquisition will be a multipurpose CNC table. Plasma, router, and if I can figure a DIY way, waterjet.

One thing I don't have, but would love to have, is an EDM. Here's a preemptive big THANK YOU for figuring all this out and documenting your journey so that I and others can follow in your footsteps.

 

Hi SB,
My workshop is already full. As well as the metal working tools I have a 12" saw table and a sliding cross cut saw that takes up quite a lot of space and also a floor mounted drill press. Amperage is basically just another name for current. Amps are the unit of current. There needs so be a high enough voltage across the gap for the insulatiom of the dielectric to break down. (Before that point the gap has a very high resistance no almost no current is flowing through the gap.) When the dielectric in the gap breaks down the gap has a low resistance so a large current flows which produces a lot of heat in a small space which vaporises a tiny amount of metal. The power in the gap is the product of the voltage across the gap and the current through it. The energy in each spark is the product of power and the duration of the spark. I think I have document somewhere that gives a very technical explanation of what happens. I will try to find it and post it or a link to it. Going back to my comments about adding a resistor in parallel with the two diodes in series with the gap. A perfect silicon diode would have close to 0.6 volts across is even with only a few microamps of current. So with no parallel resistor you could have about 1.2 volts due to leakage current through the dielectric. With a parallel resistor of say 100 ohms the voltage would be almost zero. When the dielectric breaks down the current would be many tens or hundreds of amps so the voltage across the two diodes would rise to around 1.5 volts. It is this change that you are trying to detect to step your logic onto the next step. The diode you are using to set the difference between the lower and upper thresholds of the window detector may not have any current trough it (And therefore no voltage across it) This is because the input leakage current to the op amp/ comparator is very small and can be positive or negative. I think you are hoping for about 0.6 volts across this diode. Try measuring this when you build the circuit. My circuit is quite simple when you break it down to blocks. Everything to the left of the output of IC2B is the active rectifier which allows the input to be either positive or negative so I can just reverse the polarity of the main spark power supply. The current mirror provides a constant current through the two variable resistors R11 and R12 to set the lower threshold and the difference between the lower threshold and upper threshold. The voltage across these resistors is the product of their resistance and the current through them. As the current is constant the voltage across them just depends on the resistance they are set to. This way there is no interaction between their settings. IC3 a & B form the window comparator. IC6 just acts as a DPDT switch to select between manual and automatic feed. IC4 is just an H bridge motor driver. The motor drives a very fine thread (Like the 40 TPI thread on a micrometer.) via a reduction gearbox.
Edit. I have fut the file I mentioned in my Dropbox account. Here is the link to it.
https://www.dropbox.com/s/orf5r85puwtzzhv/oh_Important_facts_about_spark_erosion_en.pdf?dl=0

Les.

 

@strantor, forgot to list my plasma cutter in my list. Thought it would be more useful than it really is. Also have a sandblast cabinet. And forgot about the Miller portable spot welder. Only paid $10 for it because that's what the guy was asking. My Mig is a Miller 235 with the spot weld add on. Both the plasma and the Mig were store demonstrators that they sold me for like 1/3 the new price when Miller came out with newer models. Like I said earlier, I keep my eyes open.

A while back there was some guys trying to make a DIY water jet using a pressure washer. Don't remember where I saw it though. I watched it for a while but have too many ongoing project to start another one.

Feel free to use this EDM circuit if you want and comment on what is being said. I plan on putting it out there into the DIY EDM community when it's working. Not for sale, but to just help people that want one. One that is more than just a toy.