Labor Day 2026

I finally assembled my primitive Electric Discharge Machine (EDM) and got it working this weekend.  

I became interested in EDM about 5 weeks ago when Crucible Production decided to have parts sent out to have wire EDM done to achieve a smooth surface finish.

The spark EDM is able to create holes and cavities in any conductive metal that would be impossible to create with any other method.  Another plus is that the electrode does not make contact with the work and does not exert any forces on the work.

One of the first devices that I stumbled across was the Zadig Machine in the March 1968 Popular Science magazine.  This device uses mains voltage plugged into the wall and it is risky to use.  This device would never see the print in a magazine today.  With 120 volts from the wall, the circuit sees a maximum of 180 volts.  If you are careless this device will bite you!

This device is a good starting point to build a demonstration unit and to understand how the voltage and current change as the spark gap changes.

Next I came across Benjamin Flemings' Homebuilt EDM website.  Fleming also wrote two books on this subject:  Build a Pulse EDM, and  The EDM How-To Book  .  I also found Robert Langlois' book Build An EDM.   Both authors use a resistor-capacitor circuit to deliver the powerful spark for eroding the work.  

For my machine I added a 5 amp fuse for safety.  I used two 200-watt incandescent lamps for my resistors.  I used a 1000 microfarad capacitor for the reservoir and current smoothing cap, and I used a 200 microfarad cap (two 100 microfarad caps in parallel) for the spark capacitor.  There are no bleed off resistors in this device, so you must manually discharge the circuit after cutting the power to it.

I am going to continue developing the EDM into Version 2.0.  I want to build a spark circuit like the one described by Robert Langlois in his book, but I am not going to use the analog spark sensing and motor control circuit.  For driving the ram, I will use an Arduino or Raspberry Pi Pico controller to sense current and voltage and automatically maintain the spark gap by driving a stepper motor to move the electrode up or down.

This morning I began eroding coins - a penny and a nickel.  I started with purified water as my dielectric fluid and that seemed to work acceptably well.  Later I tried tap water, but that did not work very well - it had too many ions and contaminants in it.  Finally I used distilled water and this seemed to work best of all.  In the video below you can see the swarf and metal fragments darkening the dielectric fluid as the machining progresses.  Version 2.0 will use paraffin (lamp oil), and the paraffin will be filtered to keep swarf and contaminants low.

The first completed job was a hole burned through a 1992 US nickel (about 2 mm thick) using a brass electrode with a square cross-section.  This work took about two hours and I had to manually guide the tool the entire time.