Desktop Wire-EDM
Past Work:
Three years ago I built this:
It looks nice… all the subsystems are there but it just hasn't been integrated.
The two biggest missing parts are: the pulse generator, and the controls. I'll go ahead and describe what I got up to and talk through what I'd like to try this semester to get this thing going.
Pulse Generator
This is what we're making:
When I last tried this, I did manage to see some sparking:
My last circuit looked something like this:
Which became a sort-of kludegy board:
Since then, I've thought about this every now and then, and think I understand the circuit I need a little better now.
I've had some email correspondance with Jaako Fagerlund (who is one of the few people who has made his own desktop EDM) and he had a really nice explanation of how the waveform should work:
The waveform is quite simplified in that picture, but it explains the basics very well. Looking at the upper graph you see gap voltage versus time. As the voltage is switched on, the voltage in the gap is the same as the generators output. If the gap is small enough, the dielectric breaks down and a spark is ignited. This plasma channel is of course lower resistance, so now current (lower graph) starts to flow. The gap voltage drops to basically what the plasma channels resistance times current is. In the graph this area is the lower voltage after full (open) voltage. Then after the on time pulse length is achieved, the generator switches of, the current flow stops and the gap voltage is zero until the generator once again applies a new pulse.
Based on this, this is the basic circuit schematic that I'm after:
