Andy,
I have been experimenting with EDM long time ago, say 25 years. I used a
simple RC-circuit together with a "soft" transformer (ca.1.5 mm air gap)
in order to forgive for the shorts and save fuses. All was mounted on my
drill press. I gave up when I realized that without a controlled
transistor (Lazarenko-)generator I would not get reasonable results. It
seemed to me that developing such a generator would exceed the
experimental effort I was willing to make, as there was no real
application in sight. I wasn't even thinking of EMC table motion control
at that time.
I still remember that I was using a much larger capacitor, even up to 1
F and 60 Volts from an old IBM Printer supply I happened to have at
hand. With an uncontrolled, deliberate discharge of this capacitor,
about a 5-10 mm length of 10 mm² shorting cable disapeared at once,
producing black metal vapor. Therfore, there was a second resistor (way
below 1 Ohm) between the capacitor and the electrode to limit the short
current and avoid sticking.
And boy, that was a messy and noisy affair!
I suppose you have read his (and other links):
https://en.wikipedia.org/wiki/Electrical_discharge_machining
Good luck!
Peter
Am 31.01.2021 um 14:28 schrieb andy pugh:
I have started to play around with EDM. The intention is to make an
EDM "grinder" to profile tool steel and possibly carbide cutting tools
using CNC-turned profiles.
At the moment I am using a cobbled-together XY table with a couple of
STMBL drives.
One of the STMBL analogue inputs is used to measure the current
through the gap. (ie using the voltage across the resistor that a
capacitor is charged through).
Then a PID controller tries to achieve a target current by adjusting
the adaptive feed pin.
I think that it shows promise, but only partly works.
I am using a 50R resistor and a 1000uF capacitor. I suspect that this
is too high on both counts.
I am working at 40V and it seems that the tool welds to the work too readily.
I suspect that I would get different results if I controlled to the
gap voltage, rather than charging resistor voltage. And probably
better still with some sort of signal processing on that voltage.
What combination of R, C and V would be typical for a servo-controlled
eroder? I imagine it might be different to a "doorbell" style one.
Current set up: https://youtu.be/nxpmEFnmK-A
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