(John Albers) wrote in message om...
I took a couple of old HP deskjet 40V DC wall warts and wired them in
series to produce 80V DC. I checked this with a DVOM and I am getting
80V DC output. According to various sources the break down voltage of
air is around 20V per .001 inch.

Nope. The breakdown for short gaps in air (Paschen's Law) is:

Volts = 30,000(cm) + 1,350

....in other words, you get no spark at all for voltages below 1.35KV,
and then the voltage rises like this:

Gap (millimeters) Voltage
0 1400
0.2 1900
0.4 2600
0.6 3200
0.8 3800
1.0 4400




For even better equations see:

HIGH VOLTAGE HANDBOOK
http://home.earthlink.net/~jimlux/hv/hvmain.htm

I have a block of wood (pine) with a
notch in it holding two machine screws facing each other to create a
spark gap. Using a piece of .001 inch brash shim stock, I adjusted the
gap to be .001 inch. I am thinking that if 80V is supposed to jump a
.004 inch gap, then 80V should have no problem jumping a .001 inch
gap.

I am not getting a spark. Should I be getting a spark with this set
up?

Nope. As I understand it, in EDM the electrodes actually touch
together. Since they're not perfectly smooth, they touch in one
or two tiny spots. The discharge then blasts a crater in both
electrodes, the capacitor charges back up, and a spring pushes the
electrodes back into contact for a repeat performance.

And isn't this always done immersed in an insulating liquid? I'd
think you'd want to prevent the parts from welding themselves
together. A liquid would cool and quench out the arc, and also
prevent new arcs until the two electrodes were pushing together
hard enough to squeeze out the liquid from between the highest
solid points.