EDM How-To Book
by
Ben Fleming
Electrical Discharge Machining. Although this magical metal working system has been around for decades, you won't find it in but a few home shops. But you can build one. And you, too, can do magical things!
Here you get a book loaded with detailed how-to, practical
tips, and further design ideas. And it's all proven. No pie-in-the-sky.
This works. One look at the file, and you know.
The system here uses a simple RC (resistor-capacitor) power supply. Pros will tell you that it's not as good as a digital supply because it erodes graphite electrodes rapidly. That's true. But electrodes have been improved so much over the years, that erosion isn't nearly as bad as it once was. The RC system is simple to build and works well.
The few, homebuilt systems around usually use stepper motors to drive the ram into the work. Ben will show you how to use a airplane trim servo (almost $150) to do the job. But if you're handy with tools, (and if you're not, why are you reading this catalog?) he'll show you how to build one for far less money. Ben's servo system is quite simple.
The
power supply is made up of three transformers, two large resistors, and easily
obtained electronic components soldered to a printed circuit board he got
at Radio Shack. And he'll show you step-by-step how to put it together.
A tank of kerosene and electrical sparks sounds dangerous, and it can be. But as long as the sparks occur deep in the kerosene where no oxygen exists, there can be no fire. (I would still have a fire extinguisher handy, no matter what.)
Details of the system are best described by Ben himself in excerpts from the book, and by his illustrations.
Great
book. High quality. Unusual information. It's unlikely that I'll build
the system... too many other irons in the fire, but I'll certainly have
a copy in my reference library. Get a copy. I think you'd be foolish not
to. 5-1/2 x 8-1/2 softocover 168 pages
No. 1584 ... $19.95
"[There are] several moneymaking reasons to build an EDM for small shop use. One is the precision removal of broken taps and drills. It is possible to burn a broken tap, drill, or an easy out from a piece of aluminum without touching the previously formed threads. Other practical applications are, the squaring of corners in milled pockets, or burning odd shaped blind and through holes in pieces.
For example, let's say a seven-sided hole is needed in a piece of hardened steel. Machine a seven-sided electrode and then burn it through the workpiece. With a ram EDM, it is a walk in the park. For the artisan, carve your initials or a design on the end of an electrode (negative or positive) and then burn it into the workpiece. The EDM opens up a completely new world of machining capabilities; your imagination is the only limit, so go for it! This book will show you how you can have EDM capabilities in your shop for a minimal amount of time and dollars invested...."
"Many of you may have attempted to delve into the mysteries of the EDM generator and control circuits... The large EDM manufacturers certainly are not going to tell you anything about generator/control circuit design. I know that from personal experience as one EDM company engineer told me, 'the kind of information you are seeking is proprietary and only actively worked on by about 20 people in the U.S.'
This book is, in part, an attempt to fill the EDM knowledge void. In this book I will give you hands on, step-by-step information needed to build a simple, low cost, automated EDM system."
"Electrical Discharge Machining (EDM) is a process that uses electrical discharges from an electrode to erode an electrically conductive material. As a result, it is possible to erode or 'burn' the shape of the electrode into the workpiece. The following drawing is a of a typical EDM system... comprised of a generator, also known as a power supply, a servo system, a dielectric tank, and filtration system...
The workpiece is placed in the dielectric tank and affixed to a metal plate in the tank. The tank is filled with a hydrocarbon dielectric fluid (such as kerosene), which ionizes in the presence of an electrical field. The dielectric fluid breaks down electrically (i.e. conducts), after a short ionization period, assuming the electrical field intensity is high enough. The electric field is created by applying a voltage between the electrode and the workpiece (known as the gap).
The breakdown of the dielectric fluid is much like the breakdown of air when a large voltage is supplied from the coil in an automotive ignition system to the spark plug. However, since in EDM the gap is typically held to only a few thousandths of an inch, the applied voltage does not need to be very large for an EDM 'spark' to occur. Typical operating gap voltages for EDM machines are in the range of 25-5OVDC though the ionization voltage may be quite a bit higher.
The servo system maintains the appropriate separation of the electrode and workpiece as determined by the operator setting the desired gap voltage on the EDM generator... As each spark is discharged from the electrode (the cutting tool) to the workpiece, a small amount of metal is vaporized and a crater is left in the workpiece. The dielectric fluid quickly cools the vaporized metal. The solidified metal partials, known as swarf, are removed from the work area by the circulating of the dielectric oil, and the filtering system traps the metal partials.
The EDM burning process is repeated thousands of times each second. As the workpiece is eroded away by the repeated discharges, the electrode descends under the servo system control. As a result of millions of electrical sparks melting small quantities of metal, it is possible to erode various shapes into any material that will conduct electricity Even some semiconductor materials may be machined via this process. Generally speaking, the hardness of the workpiece has little effect on the burn; this is one of the biggest advantages of the EDM process...."
"I anticipate that there will be more machinists with minimal electronic experience attempting to building the EDM, than there will be electronics persons with minimal machining abilities. Assuming this is most likely the case, I have opted to give a detailed step-by-step description of how to build the control system and generator. If you are a metal working person with minimal electrical/electronic skills you should be able to successfully complete the project if you can follow written instructions closely, perform sound electrical connections on a P.C. board, be able to read and understand simple electrical schematic diagrams, and understand how to use a VOM/multimeter." "To remove broken screws, bolts, studs, etc. in many cases, it is not necessary to burn the complete broken item out. I have, on occasions made a six-sided hex electrode and then burned a hex shape in the broken part. Once deep enough, insert a standard hex key and remove the part...."
"One job I did for a customer that really saved the day for him and put money in my pocket, was burning blind 1/4" keyways in 48 (existing) commercial tool holders with 3/4"bores. The holders were hardened and the blind keyways made conventional machining extremely difficult. I made an electrode of the required size and length. The parts were positioned horizontally and the electrode was extended into the tool holder's bore. Instead of making the cut down to the 6 o'clock position, I chose to move the servo up toward the 12 o'clock position. This made flushing much easier, as the swarf fell out of the cut area. To accomplish this, I rewired the servo to cut going up, instead of down. It is nice to understand the design of the machine so that these kinds of changes are made with ease..."
"A 24 cylinder diesel engine shipboard was down with a broken head bolt. The service person tried to remove the bolt, he ended up with an easy-out broken off, then he attempted to drill it out, yes, a broken drill bit was also in the mix. With a EDM and small servo heads, such as you have built, it is possible to perform the operation in a remote location..."
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