DIY electrochemical machining drill (ECM drill)

[MarkusWiener]

Hello,

I want to build an ecm(electrochemical machining) drill. I got the inspiration from the following article and video:

**broken link removed**

All I want is a drill for very small workpieces(the size of a fingernail). I'm thinking about using a 20 Amp current at most so a computer power source would be enough unless some of you guys has a better idea. But I'm concerned about the short-circuit danger. So how do I design a short-circuit detection circuit that would immediately turn off the power in case it happens?

Btw, the power outlets in my apartment are not grounded(yes, for real) I don't know if this is relevant for the short circuit protection.

Thanks for any help, Markus

 

[Sceadwian]

This is not a drill, it doesn't work like a drill and has nothing to do with the word drill =)
Is your workpiece conductive? If it's not you're dead in the water from the start, what exactly are you trying to do? What is your workpiece size, the tool you intend to use and the size of the hole you're trying to make?

 

[bychon]

What you need is a device with controlled current. It's called, "constant current", but the current isn't constant, it just has a limit. It's like, you can't get more than 12 volts out of a car battery, no matter how you try. With a constant current supply, you can't get more than the amps you told it to stop at. Pages 8 and 10 of the attachment give basic drawings of how to use this chip for constant current limiting. Are you up to building a circuit that attaches to the voltage supply and protects it, constantly, no matter what you do to mess up?

 

[MarkusWiener]

This is not a drill, it doesn't work like a drill and has nothing to do with the word drill =)
Is your workpiece conductive? If it's not you're dead in the water from the start, what exactly are you trying to do? What is your workpiece size, the tool you intend to use and the size of the hole you're trying to make?

The example given is not a drill but the same principle can be used to make one. Of course the workpiece would be of metal.

This is just for hobby purposes I neet to make holes into small delicate pieces of metal.

 

[MarkusWiener]

What you need is a device with controlled current. It's called, "constant current", but the current isn't constant, it just has a limit. It's like, you can't get more than 12 volts out of a car battery, no matter how you try. With a constant current supply, you can't get more than the amps you told it to stop at. Pages 8 and 10 of the attachment give basic drawings of how to use this chip for constant current limiting. Are you up to building a circuit that attaches to the voltage supply and protects it, constantly, no matter what you do to mess up?

The problem with ECM is that you always need a small gap between the workpiece and the tool, otherwise you will have a short circuit and the electrochemical reaction will stop. The ideal tool should have a detector that gives a beep in case of contact so that you know it and can take corrective measures(reestablish the gap).

The thing is not only protecting the voltage supply but also the tiny workpieces. In case of short-circuit they will overheat and I want to avoid that(I don't want to burn my fingers either).

 

[Sceadwian]

If the bit never touches the surface and electricity was used to cause the surface erosion rather that a sharp edge on a surface... I'd hardly consider them the same principles being in use for the material removal.

 

[MarkusWiener]

What you need is a device with controlled current.

I took a look at the lm317 but they recommend a maximum current of 1.5 Amp, right? This would be too little, for ECM I need more Amps, I guess 20 Amps would be minimum(up to maybe 100 Amps).

 

[MarkusWiener]

If the bit never touches the surface and electricity was used to cause the surface erosion rather that a sharp edge on a surface... I'd hardly consider them the same principles being in use for the material removal.

You have a point. How would you call such a device then?

 

[Sceadwian]

An ECM tool. The tooling itself is nearly an artform. The wear characteristics and the exact material and solution are still in development for specific needs.

 

[bychon]

Sceadwian seems to be leading you in the right direction. I'll let him do the 20 to 100 amp supply and how to have it notify you if a short happens.

 

[Sceadwian]

The 5 volt line of a typical high wattage (350W or so) supply will be current limited to around 35 amps. The supply will shut itself down automatically if more is drawn. The current your setup uses will depend on the electrode and the solution conductivity and the electrode itself.

 

[MarkusWiener]

The 5 volt line of a typical high wattage (350W or so) supply will be current limited to around 35 amps. The supply will shut itself down automatically if more is drawn. The current your setup uses will depend on the electrode and the solution conductivity and the electrode itself.

So a computer power supply would have this characteristic? I'm still worried, suppose the current that is flowing through the electrolyte is just 20 amps, then a short happens and the current rises above that. There would still be some time lapse between the actual short-circuit and the shut down of the power. I don't know if this would be enough to overheat the metal piece. Should I still consider making an additional short circuit detector? Does there exist something like this prepackaged, like the lm317 mentioned above, a simple short-circuit detector circuit?

 

[Sceadwian]

Markus, you'd be hard pressed to do better than the short circuit detection of an ATX power supply. I wouldn't be paranoid about it try it and see if it works for your needs, the cost is so low it's almost a no brainer. Don't over think the project till you've done some tests to see if it's even feasible. How do you plan on making the tools themselves? If it's made out of the wrong metal it will tend to plate with whatever metal is being removed, or worse form a smut of badly plated oxidized metals that will mess up it's conductivity.

 

[MarkusWiener]

Markus, you'd be hard pressed to do better than the short circuit detection of an ATX power supply.

Hi Sceadwian,

thanks for the advice. You are right, I'm probably paranoid and overthinking it. Will any cheap ATX power supply do it? There are some very cheap no name brands.

As for the tools, since all I want to do is to bore a hole I'm just thinking about using a small iron nail for it.

 

[MarkusWiener]

One thing I forgot. My wall outlets are not grounded, so if I use an ATX power supply I usually connect it to a voltage stabilizer which has 3-pin outlets. But I'm not sure if the 3rd pin on the stabilizer is really grounded, I know that some stabilizers have a virtual ground but I'm not sure if it is the case with mine.

The big question is: does the power supply need to be grounded for it's short-circuit or over current protection to work?

 

[Sceadwian]

If your house doesn't have a ground then there is no way the voltage stabilizer can have a ground, in fact the voltage stabilizer might not actually be doing anything if there is no ground wire, unless you've dug a 10 foot long steel pole directly into the earth and are using that as a grounding wire, or it's grounded through something like the houses metallic plumbing (not a good idea generally)

You should not be attempting ANY of this without a proper ground no matter what method you use for short circuit protection. The short circuit protection of the ATX power supplies output should be maintained even if there isn't a third prong ground, however because there isn't a third prong ground in case of some other fault elsewhere if the power system the ATX supply itself could possibly fail, as pretty much any device that is designed to work with a dedicated ground would.

Suffice to say, do everything in your power to get yourself a true earth ground. Large conductive metal steak(s) into ground with low gauge wire as the leader. Make SURE that your stabilizer has that wire as it's earth ground and then everything after that can be considered properly grounded. If your stabilizer shows direct conductivity between it's neutral and earth input prongs I'm guessing it might be worth throwing it out =)