EDM How to Book
5 1/2 x 8 1/2 Paperback 161 pages
Price $19.95 Buy Me
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Electrical Discharge Machining (EDM), sounds very expensive and high tech, but you can build this affordable tabletop machine from surprisingly common components, most of which are available from Radio Shack. No exotic parts or special tuning required, and no circuit boards to etch.
The basic idea is to move an electrode very close to the work piece, and repeatedly produce a spark between the two while flushing out debris with a dielectric fluid. You first create an electrode in the shape you want out of copper, brass or graphite. It is then fed slowly down into the metal workpiece while maintaining a precise spark gap. The electrical discharges blast little bits of metal away while a fluid cools and flushes away particles. This is called “Sink” or “Ram” EDM and it can produce impossible shapes in metals too hard to machine any other way, and it doesn't create heat and ruin the temper of your workpiece.
Check out the sample shapes sunk into a hard file blade and also a small hole cut through a carbide tool. The electrodes used are shown above the parts. The most obvious use is for removing broken taps and drills without damaging the part. People have called these “metal disintegrators” and this space age process can actually be done on your workbench with a machine costing a few hundred dollars.
Most people mount the Ram assembly on a mill or drill press for convenience, but there are no forces or deflections to deal with and the ram itself handles the 
electrode travel, so so you could use simple brackets to mount it anywhere you want, for instance on top of an engine block to remove a broken stud. This design is easier to build because it uses a simple servo motor to power the ram instead of a stepper motor and the driver circuitry that goes with it. You can build a simple ram mechanism from parts as shown, or save some time and buy an aircraft trim servo to perform that function.
This is a truly useful piece of equipment that can pay for itself quickly, you might even create a small business around it. Let your imagination run wild with this amazing process!!