Re: [CAD_CAM_EDM_DRO] Re: EDM machine

marble here wrote:

> I my self am making his EDM I just started looking for
> the caps Now are you saying the the should be lower
> instead of 100ufX150volts . So if one used 50uf X XXv
> would make a better spark

Sheesh! I'm using between 30 and 40 V with caps ranging
from 1.5 uF to 20 uF. I get the best results around 3 - 6 uF,
although progress is slow. I've been using it only to burn out
taps in aluminum workpieces. This is the archaic R/C EDM
technique. A plain rectified and filtered (but not regulated)
DC power supply feeding the EDM capacitor bank with a
resistor sized so a shorted electrode won't burn up the power
supply. If I use the larger capacitors in the bank, it really starts
blasting everything to bits, and the electrode is badly rounded
off very quickly. At the lower cap values, the electrode survives
quite a while, but progress is pretty slow. I am not using a
flowing fluid, as my electrode is some .040" or so brazing rod.
I have been using alum-tap (a light, somewhat oily, tapping
fluid) as the EDM fluid. It works quite well, although it is
marked flammable. I got quite bold about letting the 'pit'
go dry, until the EDM process was spitting yellow sparks all
over the place. I only had one flash of the Alum-Tap, a little
orange puff of flame about 1/4" diameter, and a small
'putt' sound. I have a fire extinguisher handy in case the
whole thing goes up! I haven't found any water that is pure
enough to not electolyze.

Perhaps a FET switch to turn the current on and off would be
a good thing to try. I wonder how this is done commercially.
From what I've heard in these discussions, it seems like there
is a fixed off time, in the uS range, and when the EDM current
reaches a threshold, the juice is turned off for the preset duration.
Has anyone built something like this? It doesn't sound that
hard for the experienced electronic experimenter.

Jon