Homebrew PCBs

To remove paint you just need to up the voltage - say 10kV or more. This 
could be generated by a simple car ignition coil driven from an 
oscillator. I have no idea how much paint would be removed on each 
spark. It would definitely be a case of trial and error.

Many years ago I used an engine cylinder pressure measuring machine that 
used this principle. It had an electrode that moved depending on the 
pressure from a compressed gas supply. When the cylinder pressure 
equaled the gas pressure it fired a spark, making a mark on a paper roll 
that rotated at crank speed. By varying the gas pressure you could map 
the cylinder pressures over the whole combustion cycle.

Les

On 05/01/2011 18:05, Andrew wrote
> If you want to remove paint, rather than copper directly, EDM cannot do it at all, since EDM depends on generating a spark between the electrode and the conductive metal to be removed. I suppose you could get around that by using a conductive paint, but then 1-3 above would apply, and you would add the new problem of electrically distinguishing between the paint and the copper -- I don't think there is any way you could spark all of the paint off without also sparking off at least some of the copper, and in any case, until the copper is also gone, your EDM would not be able to tell that it was finished with that spot. You could try to get around that by having it only spend a certain amount of time in each spot, but note that that is not a simple matter when the control circuitry is sensing the spark gap and adjusting the electrode to account for wear as well as for how much cutting has occurred.
>
> Whew! Just trying to describe all the problems of using EDM for this purpose has made me tired.