There are many methods for subtractive manufacturing in the industrial world. Those include milling, water jet cutting, plasma cutting, punching, laser cutting, and many more. Each has advantages and disadvantages that make one more suited to specific materials or applications than the others. Unfortunately, hobbyists generally don’t have access to many of those tools, because they’re often big, expensive, and messy. Electrical discharge machining is one such method, and Jake Wachlin has managed to use it to make circuit boards at home.
Electrical discharge machining (EDM) can be done with any conductive material, so it’s well-suited to metals. It works by creating rapidly recurring sparks between a tool electrode and the work piece. As those sparks make contact with the work piece, a small amount of material is chipped away. Clean cuts in metal can be achieved by repeating the process in a controlled manner. Wachlin’s project uses that process to cut traces into blank copper-clad circuit boards.
To do so, he started with a 3D printer to be the base of the CNC EDM machine. He used inexpensive mechanical pencil lead for the tool electrode, which is readily-available and is actually made from graphite — a material that’s perfect for use as an EDM electrode. That is connected to a high voltage power source. The blank circuit board work piece is submerged in a bath of distilled water, which helps to keep the cuts clean. By applying voltage between the tool electrode and work piece at the proper times as the tool moves, he was able to get nice trace cuts.
This technique offers a number of advantages over traditional at-home PCB milling. It’s much faster, it’s cheaper as special end mills aren’t required, and it can be done with a weak machine because no pressure is actually put onto the tool. The biggest challenge is that the tool electrode has to very lightly touch the work piece, which is difficult when circuit board blanks aren’t very flat. In the future, some sort of feedback would be needed to maintain the proper Z-height of the tool electrode.