EDM Machine (Not the musical type)

Electrical Discharge Machining (EDM) is the process of machining features into any conductive material using electrical sparks to erode the workpiece. As there are very few things that can withstand the heat of plasma, it works on practically any material that is conductive no matter how hard or tough it is. And because it uses sparks, there is no cutting force to speak of which means it can achieve very tight dimensional tolerances and high surface quality. See the picture below where this process was used to drill a 0.2" hole through a 0.5" carbide end mill. 

The goal of this project is to build a wire EDM, which can be thought of as a "hot wire" styrofoam cutter for metal. Currently the focus is on the control algorithm and power supply design to optimize arc properties for a better cutting speed. The current iteration is a sinker or hole-popper type EDM, the electrode can only move in one axis relative to the work piece. The power supply is a very simple setup of a variac, rectifier, capacitor and a heating element as a current limiting resistor. The variac is used to set the voltage and therefore the amount of energy delivered by the spark to the workpiece. The electrode is driven forward until a "breakdown" occurs and an arc is struck. The voltage is monitored to determine the arc gap and determine when to advance or slow the electrode to maintain the arc. Some care must be taken not to let the electrode fully make contact with the work; this can cause the electrode to weld to the work piece, requiring operator intervention. 

Thus far, only brass tube electrodes have been used, which are readily available as surplus on eBay and work very well for burning out broken taps. The next test is to machine an electrode to "burn" a torx profile into a work piece, which is a good test of dimensional accuracy and how arc properties change as surface area is increased. Professional machine use an "orbit" technique which moves the electrode along a helical path to only engage part of the electrode at any given time. Another constraint is that the electrode wears down as it burns, requiring dressing of the electrode to return it to the desired shape. A three axis motion platform is also high on the list of next steps.