Build an EDM Machine

8 1/2 x 11 Paperback 56 pages

EDM, or "Electrical Discharge Machining" is an almost magical process that uses an electrical spark to erode or eat away metal, and it doesn't care how hard the metal is. This is sometimes the only way to remove a broken tap or drill from an expensive aluminum part. The EDM process has many other uses, because it can cut holes in metals too hard to machine. Did you ever wonder how they drill holes in solid carbide to make a nozzle for your sandblaster? You can also cut unusually shaped holes in all metals, but it won't compete with a drill to cut round holes in soft metals because its very slow.

You won't find one of these in the hardware store, and you couldn't afford one for home use if you did. This is one of those industrial processes that costs many thousands of dollars, yet the concept is fairly simple. Sooner or later some clever person will always figure a way to make a homebuilt version, and apparently someone did.EDM Front Panel

This is a collection of six construction articles originally published in Home Shop Machinist magazine. The instructions are clear and abundantly illustrated, but you will need some basic skills in electrical assembly. You don't have to be an electrical genius, but you must know how to read schematics and solder things together. You can mount all the components and solder "point to point", or use the template given and etch your own circuit board.

Most of the work is in the electrical controls. The actual mechanical parts consists of a stepper motor that drives a screw and lowers the electrode as it wears away. These parts are mounted on a bracket that is soldered together. You don't even have to machine or weld anything but it may be easier if you have these capabilities.

The finished machine works like this to remove a broken drill.. You clamp the portable electrode driver assembly over the workpiece and center it on the offending drill. You will need to flood the area with a dielectric fluid (distilled water or anti freeze will work) You can just siphon the fluid slowly out of a jug, and contain it with a dam built up from clay. The electrode will sizzle like frying bacon and erode the metal away as the electrode is slowly lowered.

You will make many new friends if you have one of these machines, and there is a real possibility of using it to make money. You can send out flyers to auto repair shops and other business. They would be thrilled to pay $50.00 to save a $500 cylinder head from the scrap bin. 

Chapter 1 - Introduction and Box Construction

EDM Head

Start with some basic theory and see pictures of several homebuilt units. You can make an enclosure or  salvage one from something else. You get a good explanation of the project ahead, a bill of materials and sources for parts.

Chapter 2 - The Spark power Supply

See how to mount your components and connect them together. The instructions are very easy to read and even give basic information on soldering and assembly techniques. Includes tips on how to increase the current to build a more powerful machine.

Chapter 3 - The Stepper Motor Driver Board

You can mount the components on a perfboard and connect the wires or use the template supplied and have a circuit board made. You can even buy a kit and etch the board yourself. Great instructions should make this a fun project. I think you can purchase a ready made generic driver board if you don't want to build one?

Chapter 4 - Installing The Stepper Motor and Board

Mount the driver board in the enclosure and hook it up to the front panel. This article also gives you a great lesson in stepper motor construction and how they work.

Chapter 5 - The Head and EDM Operation

The stepper motor is mounted on a bracket and turns a fine threaded screw to lower the electrode. These instructions show you how to use brass plates and solder everything together. They went out of their way to avoid welding or machining. You can get the basic idea and alter the design to suit your fabrication skills and equipment.

Chapter 6 - Other Odds and Ends

This article explains the circuitry and operation in great depth and shows you how to adjust and troubleshoot it. It talks about safety and shows how to make a fancy variable speed aquarium pump for the dielectric fluid.

Removing a Broken Stud

Finally, an excellent example with picture of the machine in use. It is being used to remove a broken stud from a snowblower engine with minimal dissassembly.