This place reserved for photo of completed system doing its first cut.
OK, so what is it?
This site is a build log of a homebuilt EDM, which stands for Electrical Discharge Machine or Electrical Discharge Machining. The purpose of this website is to provide information to someone thinking about building one of these, as well as enjoying the contact with others that already have one.
In 1770, Joseph Priestley first noticed and recorded the destructive effects of an electrical discharge on metals, and there is an 1889 patent recorded by Benjamin Tilghman for a process called "Cutting Metal by Electricity", but nothing came from these efforts.
Modern EDM as we now know it probably was invented during World War II by a Russian husband and wife research team, Boris and Natalya Lazarenko who were given the task of studying what could be done about the destructive arcing that ruined switch contacts in electric circuits. They realized that this destructive power to pit metal could be used to machine and form metal surfaces as well as destroy it, and they designed a circuit that could be used to provide that kind of electrical power. Eventually, EDM has evolved over time and came to be used to make the rocket engine fuel injectors for the Saturn booster of the Apollo program.
Basically, an EDM is a machine that uses electricity to zap tiny pockets of metal over an extended period of time to cut and form any metal that can conduct electricity - that's ANY metal. Steel. Carbide. Titanium.
This build is based on the work of Ben Fleming, whose book, The EDM How-To Book was instrumental. I met Ben at the 2011 CNC Workshop, where he was demonstrating his machines. While there, I read his book and bought a PC board that he sells to implement his RC type EDM machine. More information from a homebuilt EDM community can be had at the yahoo group here.
The heart of the RC type machine uses a resistor-capacitor circuit to provide a sawtooth type wave of energy across the gap. The other major type is a pulse EDM, which uses more sophisticated electronics to control the shape and timing of the pulse. Most high-end or industrial machines today are the pulse type, which have the advantage of cutting faster with less wear on the electrode. Ben has been working on a pulse machine as well, and will be finishing a new book later this year on that, which he also demonstrated at the show. After talking to him about his experience though, he said that the higher quality of available electrodes now allow them to wear much slower than before, and if you don't mind it taking a little longer, the simplicity and capabilities of RC machines has much to recommend their use. Some of the pulse machines include RC capabilities as well because the RC methods can provide a very fine finish.
This will be a "sinker" or "ram" type EDM, where an electrode of a desired shape is lowered into the metal to be cut, resulting in a pocket the shape of the electrode. Another type is a "wire" EDM, where a charged wire is moved through a piece of metal, much like a wire foam cutter. Since the wire is thin and also erodes, it must be fed continually past the metal as it cuts. Movement of the wire is usually controlled by a computer like a 2 axis CNC machine.
To cut some metal with it, we need to make an electrode whose shape and form will be mirrored onto the cut metal. We need to place an electric potential across that electrode and the metal to be cut and maintain a gap in between. In order to keep the electric potential low, we will flood the gap with an electrolyte that makes an ionization path easy to form, which can also be made to flush away debris from the tiny craters that are formed.
What this translates to is a machine with three main subsystems - 1. generate, shape, and monitor the proper electrical power across the cutting gap, 2. raise, lower, and maintain the electrode gap, and 3. pump, flush, and filter the electrolyte. The building process for each of these three subsystems are on the left hand side menu. The last page is for demonstration of cutting and pictures of example work.
(Note: If you want to see any of the photos on this website in a larger format, you can. If you are using Firefox or Internet Explorer, right-click on the photo and select "view image..." If you are using Chrome, right-click on it and "open image in new tab...")