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The Home Built EDM Machine

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Excerpts from The EDM How-To Book

[ ] Mount the control transformer T3 in place with two 6-32 screws. The black primary wires should face the power transformers.
[ ] On the secondary side of the transformers T1& 2, clip both black center tap wires off close to the transformer case, and save these wires.
[ ] The rectifier (D1) is held securely on the back panel with a 6-32 screw; see photo. To aid in heat dissipation and to assure good contact, sand all the paint from the case in the area that will have contact with the rectifier. Apply Radio Shack (276-1372) or similar, heat-sink grease for good thermal contact.
[ ] Note which terminals are AC and DC on the rectifier; these markings may not be visible once the rectifier is mounted.
[ ] Install the AC switch (SW1), the fuse holder (F1), and the AC power cord grommet in the rear panel.

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[ ] Cut the female end off a Radio Shack (61-2859) AC power cord. Strip the covering back about five inches, exposing the three inner wires.
[ ] Cut and save a two-inch length from the end of the black (or blue) wire.
[ ] Strip the black and white (some are blue and brown) wire ends back 1/2" exposing the bare wire. Strip the green wire back about 1/4".
[ ] Thread the cord through the panel grommet, and tie a knot to act as a strain relief (if a strain relief is used, the knot is not necessary).
[ ] Secure the green wire under a screw holding the transformer in place.
[ ] Solder the hot side, the black wire (or blue) of the line, to the fuse terminal.
[ ] From the remaining terminal of the fuse holder (F1), solder an insulated jumper, (using the previously cut black transformer center tap wire), to one of the terminals on the AC switch.
[ ] The (black) primary wires from each transformer connect in parallel. With the transformers T1&2 mounted in the box, pull the black primary wires forward; make sure the wires from each transformer are not crossed. Select the left most wire from each transformer; twist these together. Select the remaining two primary wires and twist them together.
[ ] The (black) primary wires from transformer T3 connect

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Chapter 12
Dielectric tank overview and construction

A well designed dielectric tank and filter system do several things:
1. It contains the dielectric fluid around the workpiece.
2. Provides a method to accurately secure the workpiece.
3. Circulates clean filtered dielectric fluid to the gap.
4. Electrically isolates the electrical discharge from other parts of the machine
5. Provides a rapid method for filling/draining and storing the dielectric fluid.
For serious EDM work, a tank needs to have a pump, filters, and a work holding plate. The photos and descriptions in this section are of a (rather large) tank that has proven to be of a very versatile design. After 8 years of use in portable, as well as stationary applications, there are few, if any, changes that I would make to the design.

I can not over stress the importance of have a good dielectric filtering and flushing system for your EDM. A good flushing system will make a poor EDM generator look good, a poor flushing system will make a good EDM generator look bad. The dissatisfaction with many home built EDM machines I think stems from a poor dielectric cleaning and flushing system.

Use ideas presented here and build a good dielectric tank to suite your particular needs. Before getting into details of how it is built, I would like to suggest a possible alternative.

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The product line is called Toteline, and they come in various sizes and colors. The tank shown in the photos in this section is a Toteline model 814-308. The outside dimensions are 25 3/4 X 15 3/4 X 7 5/16. If this tank is too large for your application, their web site lists several smaller size tanks. I recommend staying with the 814 series of tanks, which have four flat walls, making it easy to mount the filtering system.

Grainger Industrial supplier (www.grainger.com) carries Toteline products. Unfortunately, they do not list the 814 series; instead, they have the 780 series which has curved shaped walls on the ends. It is possible to use the 780 series tanks, but some changes will need to be made in order to mount the filtering system. The Granger stock number (for a tank similar to the Toteline model # 814-308) is 4TH05; price approximately $20 (2005). You should also know that Granger does not sell to the public, so purchase would need to be through a business.

Using the Toteline model #814-308 permits a respectable 12X15 work plate; a two-filter filtering system, along with associated plumbing; and a dielectric pump; all of which, may be housed inside the tank. Using this in-tank design, filters maybe changed without spilling dielectric fluid outside the tank. For a portable EDM system, having virtually everything contained inside the tank has some real advantages during use, as well as storage. Given these advantages, this system is not for everybody; some have space concerns and elect to use a smaller tank and/or position the filter/s and pump external to the tank; it's your choice.

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Chapter 14

EDM techniques and methods

The following section, as far as I know, is unique to all EDM plans I have seen. Most plans for EDM machines tell you how to build a very complicated machine, and never give any real hands on application information. What good is an machine if you really don't know how to use it. In the next few pages, I hope to give you some insight into ways you can use your EDM for fun and to actually make money.

Electrode materials

The most commonly used electrode materials are graphite and copper. In the U.S. the primary material is graphite, in Europe I understand copper is widely used. The EDM machine described in this book burns nicely with graphite, copper, and brass electrodes. With this generator, I personally prefer graphite. About 90% of my EDM work is with graphite as the electrode material. The wide availability of graphite and copper make these materials an excellent choice for everyday applications. When graphite is used, it must be of the type manufactured specifically for EDM applications. Carbon welding rods, motor brush material, and other forms of graphite are very poor choices; their use will be disappointing at best. The largest manufacturer and suppliers of commercial grade EDM graphite is POCO.