Electro Arc
Your Guide to EDM Terminology

EDM has become a common method used across industries with a number of sub-categories including MDM.  This list of EDM terms can help you understand all of the aspects of EDM.  Many of these terms are interchangeable with MDM terms:

Ammeter (Amp Meter) – A measuring instrument for electrical current.

Amp (amperage) applied – Amperage selected on power supply controls.

Amp (amperage) average – Amperage shown on the amp meter.

Arc (Arcing) A damaging flow of electricity (pulsating yellow flash) between electrode and workpiece.
Incorrect term for EDM machining (sparking).

Average current – (see average amp)

Blind Hole (cavity) – A cavity with no flush holes.

Burning – A synonym for EDM Machining.

Capacitor – An electrical component that stores a charge.  Used occasionally to intensify the spark.  (Wear on Electrodes will result).

Carbon – The raw material used to make graphite.

Center Flushing – Flush hole through the center of electrode..

Conductor – A material which will carry electric current.

Coolant – See dielectric.

Copper Graphite – Graphite infiltrated with copper.

Copper Tungsten – A blend of copper and tungsten.

Core – A non-machined area of the cavity created by the flush hole(s) in the electrode.

Corner Wear – Wear on the corners of the electrode parallel to the direction of machining, and proportional to the distance machined.

Crater – Small cavities in the workpiece created by the individual sparks.

Cut – Synonym for machining with the EDM process.

DC Arcing – see arc.

Deionization – Bringing the sparkgap back to a nonconductive state.

Depth finder – An electronic circuit which automatically stops the electrode .0001″ before it touches the workpiece without the high voltage on.  Used during “setup” for setting an accurate depth.

Dielectric – A fluid which insulates the sparkgap between the electrode and the workpiece until a high voltage ionizes the sparkgap and makes it a conductor.


Dither – See vibrator

Discharge – see spark

Dual powersupply – Two identical power supplies in one single cabinet, used to inform the operator when the electrode makes contact with the workpiece, usually with light or an acoustic signal.

Duty Cycle -“on time” +”off time”


EDM Grinding – This procedure is accomplished by mounting a rotating electrode wheel parallel to the direction of the servo.

Electrode – The “cutting tool” in the EDM process, always made of a conducting material.

End Wear – The linear wear at the end of an electrode after EDM machining.

Flashpoint – The temperature at which a flammable material will ignite.  An important factor in selecting a dielectric. 

Filtering – Removing the solid particles created during the machining from dielectric.

Flushing – The single most important Factor in EDM machining.

Flush Hole – A hole to facilitate flushing through either the electrode or workpiece.

Flush Pressure – The necessary pressure to insure an even flow over the “area of contact” between the electrode and the workpiece.

Flush Tank – Also called flush plate or flush pot, a box-like fixture mounted on the worktable. The flush hose connects to the side of the box and the workpiece is clamped either directly or on a subplate, on top, allowing the workpiece and into the empty space of the box.

Gap (spark gap)  – The distance between the electrode and the workpiece during machining.

Gap Voltage – The average voltage in the sparkgap during machining. (meter reading).

Frequency – The number of discharges (sparks) per second.

Graphite – An easy machineable electrode material with high heat resistance and good electric current transfer.

HAZ (heat affected zone) – Also called the “recast layer”.  The depth of the heat penetration altering the parent material’s metallurgical structure due to the EDM process.  Magnitude usually from .0002″ to .008″ depending on the material and the energy per pulse.

Hunting – Excessive reciprocating movement of the servo during machining caused by shorts in the stopgap.

Injection flushing – A synonym for pressure flushing.

Ionization – A breakdown of the resistance in the dielectric flowing in the sparkgap, when a voltage of sufficient magnitude is applied between electrode and workpiece.

Ionization Channel- The path of the positive and negative ions linking the electrode and the workpiece at the moment of ionization.

Microsecond – One-millionth of a second (.000001 seconds) (usec).

Multilead–One power supply with multiple independent power leads.

Nanosecond – One billionth of a second (.000000001 seconds)

Non-directional – A finish having no specific direction to its surface pattern.

Normal Polarity – Negative polarity.  A designation no longer used, as the polarity depend on the application, and as such a polarity (positive or negative) can only be normal in relation to a given application.

No Wear – No wear as such does not exist, but generally speaking, wear less than one percent is called “no wear”  range, a deposit or plating can occur so the electrode actually grows, but as this phenomenon is unpredictable it has no practical value.

Oil through Chuck – A sealed adjustable chuck for tubular electrodes which allows a flow of dielectric fluid through the chuck to the electrode.

“On Time” – Duration of the applied amperage during one pulse cycle measured in nanoseconds.

“Off Time” – The time in microsets between the applications of open gap voltage.

Overcut – The dimension the finished cavity is larger than the electrode. (2 x sparkgap).

Redressing – Removing the worn part of an electrode, bringing it back to its original shape.

Recast Layer – See HAZ.

Reverse Polarity – see normal polarity.

Servo – The electro-mechanical mechanism which automatically maintains the proper spark gap during machining.

Spark -controlled discharge between electrode and workpiece.

Sparkgap – The distance between the electrode and workpiece during machining.

Spark Erosion – Synonym for EDM.  Mainly used outside the U.S.

Split Lead – See Multi lead.

Stepped Electrode – An Electrode constructed in two or more concentric tiers, to be used for through-hole machining,  The first smaller portion is used for the roughing, and the larger subsequent tiers are used for the medium to finishing machining.

Trepanning Electrode -An electrode constructed like a cookie cutter.  Used to machine through holes, this way increases the machining speed by minimizing the amount of workpiece material to remove.

What is the History of Electro Arc and EDM?

When you search for the term “metal disintegrator” you will likely find ‘Electrical discharge machining’ as a result.  That is because the technological breakthrough that led to metal disintegrating machines was spearheaded by a team including Harold Stark who went on to patent the idea for AC metal disintegrators and started the world’s first metal disintegration machine factory in Detroit Michigan.  This process is metal disintegration machining (MDM).

You may have heard Electrical discharge machining, EDM for short, called spark machining, arc machining, and spark eroding.  This is a non-conventional group of machining which now includes electrochemical machining, water jet cutting, and laser cutting.  This process is limited to use with ferrous alloys because it requires the base material to be electrically conductive.  A solution for high-accuracy, complex machining applications provides an efficient alternative where other methods are impossible.  Using an electrical current, spark discharge erodes the workpiece using dielectric fluid as an electrical insulator. There are three main forms of EDM, wire EDM, die sinker EDM, and hole popping EDM.  

EDM is usually associated with the wire EDM machine method which was developed between the 1960s and 70s to make dies from hardened steel.  This EDM process uses wire wound between two spools of wire creating two electrodes, the tool-electrode, and workpiece-electrode, which are separated by dielectric fluid. With increased voltage, the fluid produces an electric arc. The wire moves in a controlled pattern and sparking occurs between the wire and the workpiece.  This method removes excess material with automated technology similar to CNC providing high accuracy and precision.  Commercial wire EDM capability has continued to advance substantially over the last few decades.

Joseph Priestly originally discovered the erosive effect of electrical discharges in 1770.  Die sinker EDM was invented independently by two groups.  In 1943 two Russian scientists Boris and Natalya Lazarenko were exploring methods to increase the lifespan of tungsten breaker points. Their research led to the discovery that erosion could be precisely controlled if the electrodes were immersed in dielectric fluid. This allowed the invention of an EDM machine tool for processing hard materials like Tungsten. This tool became known as a resistor-capacitor (R-C) circuit for EDM.  

During this time, without knowledge of the experimentation taking place in Russia, a team of American scientists consisting of Harold Stark (the founding president of Electro Arc), Victor Harding and Jack Beaver were also developing a method to remove broken drills and taps from aluminum castings.  This team was tasked by their employer with finding a solution because tools were being broken off in expensive aircraft parts.  Initially constructing machines from electric etching tools, they were unsuccessful.  After trying compressed air, they added fluid to the machines, combined with spark repetition allowing them to cut through metal quickly and efficiently while the coolant flushed away metal particles created in this process. Their research was able to produce 60 sparks per second, a breakthrough in technology at the time. Machines initially developed by this team were used during World war II and the trio patented the system for removing broken bolts, taps, and drills as well as an electronic-circuit servo system that maintained proper spacing between the electrode and the workpiece.

This led Harold Stark to develop Electro Arc’s Metal Disintegrator line of metal disintegrating machines which are still produced by Stillion Industries today (Stillion Industries purchased Electro Arc in 2019).  This technology was key in the development of vacuum tube EDM machine tools capable of producing thousands of sparks per second (electric discharge machining) in the 1960s.  Die sinker EDM machines are traditionally used to create three-dimensional shapes.  EDM provides an advantage because the process is predictable and accurate, making it easy to reproduce, but it is slower than other methods.

Hole drilling EDM is a specialized hole-making machine sometimes called a “hole popper” which is used to create the pilot hole necessary for wire threading. Using thermal energy rather than mechanical force, these machines cut through extremely hard materials such as titanium, carbide, carbon graphite, and high alloy steel.  These machines work on the same principle as wire EDM machines.  Instead of wire, these machines use a tool that works like a drill bit, no physical contact takes place between the tool and the workpiece, the electrical discharge is conducted to rapidly cut the metal.  This process is ideal for extremely small holes, as small as 0.010”. 

In his book, ‘Electrical Discharge Machining’ Elman C. Jameson mentions working with Victor Harding and Harold Stark during the origination of the EDM process in the United States.  EDM became popular in Japan as a result of damage from the war.  This new method was key in rebuilding after the destruction of their infrastructure.  On the other hand, The existing equipment and workers in the US caused a delay in the acceptance of EDM technology in the US.  Electro Arc metal disintegrators are an appealing option because they do not require special training for operators as other EDM machines require.

Electro Arc Metal Disintegrators made in Michigan since 1947

Electro Arc is the original manufacturer of Metal Disintegrators based in Michigan.  The company’s founder, Harold Stark patented the AC metal disintegration process in 1942 and opened Electro Arc’s doors in 1947.  Stillion Industries purchased Electro Arc in 2019 and carries on the quality name that Electro Arc metal disintegrators have become synonymous with.

Electro Arc Metal Disintegrators Last a Lifetime

You can see one of Electro Arc’s original paper promotions above, featuring the following models: 

Model 2-S – Still one of our most popular portable models!  This basic metal disintegrator now features our Arc-er Head and portable design which make it perfect for use in small shops.

1-S (See below) – The model 1-S was the largest table top metal disintegrator offered by Electro Arc initially.  

2-SA – The model 2-SA was one of the first tabletop metal disintegrators offered by Electro Arc.  This self-contained unit is great for high production plants and tool shops.

3-S – The model 3-S originally offered with no built-in coolant tank offers great portability for use in confined spaces.

Not shown on this flyer, the Carbide Impregnator was another flagship product Electro Arc was known for between the 1940s and 1970s.  Electro Arc is the original and best manufacturer of metal disintegrators in the world.  Our machines are known for their durability and long-lasting design.  Now among over 40 configurations available, we are confident you will find an Electro Arc metal disintegrator is still the best value for your application!

The location and contact information is NOT correct in this vintage promotion

Over 75 Years of Michigan Manufacturing

As you can see, the original disintegrating head is different than our current Arc-er, IQ, and Servo disintegrating heads.  The features of Electro Arc metal disintegrators are the same great features allowing anyone to use our machines.  Electro Arc Metal Disintegrators have castors, the choice of AC or DC, and portable or tabletop, including the option to order a custom table top size.  Most models allow you to choose your KVA power rating.  Additional features include support options, head options, remote start/stop, and more!

In 2004, Electro Arc purchased Uni-Tek and integrated DC metal disintegrators into our product line.  Our most powerful machine, the Bolt Eater represents the heavy-duty application of metal disintegration with both portability and the power to remove large bolts!

Stillion Industries is proud to carry on the Electro Arc Metal Disintegrator legacy in Dexter Michigan! We continue to improve the metal disintegrator design and offer repair and refurbishing services for old machines. Learn more about Electro Arc’s history.

Electro Arc Portable AC Metal Disintegrators

Setting the Record Straight With Metal Disintegration Machining | Terminology

In the industry of metal disintegration machining, oftentimes there is misinformation about the terminology that is used to describe the machines, parts, and processes. We at Electro Arc Manufacturing are here to show you what is what when it comes to metal disintegration. Below are terms and proper definitions for processes and machinery-related items in the world of metal disintegration.  People in different areas use different terms to refer to our machine process. Some are misleading.  For our process, a real arc is essential. We don’t burn the material; we vaporize it to turn it into particles.

EDM is the correct term for a very different process. Electric Discharge Machining is much more precise than arc disintegration but also very slow. EDM machines are also MUCH more expensive. On the other hand, “MDM” stands for Metal Disintegration Machine, which is what we build. Terms like “spark eroder, spark erosion, spark burner, or spark disintegrator” are misleading and incorrect. Aside from superficial campfire embers, sparks are relatively low-power, momentary electrical effects like those in automotive spark plugs to ignite fuel. By contrast, our arc is a powerful current path operating at very high temperatures like in carbon-arc searchlights. Our arc process literally vaporizes the metal to be removed in a controlled way.
Metal Disintegration Machining (MDM)

Metal Disintegrators or MDM machines are manufactured for the specific purpose of removing broken tools from workpieces. The metal disintegration process removes a tap, bolt, or drill leaving the hole intact and allowing a part to be reclaimed.  MDM removes material very fast. MDM uses a spark erosion process commonly used for destructive cutting. Typical application includes broken tool extraction (taps, drills, reamers, drill bits) metallurgical sample excavation, and bolt removal. There is no faster or efficient or cost-effective method to remove broken tools, studs, or fasteners than MDM.


Electrical discharge machining (EDM), also known as spark machiningspark erodingdie sinkingwire burning or wire erosion, is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the “tool” or “electrode,” while the other is called the workpiece-electrode, or “workpiece.” The process depends upon the tool and workpiece not making actual contact.  When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some places), which breaks down, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser) (see also breakdown voltage). As a result, the material is removed from the electrodes. Once the current stops (or is stopped, depending on the type of generator), the new liquid dielectric is usually conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as “flushing.” Also, after a current flow, the difference of potential between the electrodes is restored to what it was before the breakdown so that a new liquid dielectric breakdown can occur.

Spark Erosion

Spark erosion is sometimes miscommunicated as being metal disintegrating but it is not. Spark erosion is a form of EDM or electric discharge machining that is a machining technique principally used for hard metals and metals that are difficult to machine using traditional methods. EDM normally operates with materials that are electrically conductive and is designed to erode (remove) intricate depressions or contours from pre-hardened steel negating the requirement for heat treatment to soften and re-harden the steel. We use this method on many different types of metals and alloys, such as Monel, Titanium, Tool Steel, Tungsten Carbide, Tantalum, Super Duplex, and Inconel.

Learn more about the spark erosion process.

Spark Eroder, Spark Burner, or  Spark Disintegrator (You may have heard these referred to as Metal Disintegrators)

Our metal disintegrators are sometimes referred to as Spark Eroders. This is a common term used throughout the UK. However, spark eroders produce sparks in the application, and metal disintegrators do not. So spark eroders are the machines that are used in the electric discharge machining field.

Metal Disintegrator

Metal disintegrators are primarily used for bolt removal, tap removal, stud removal, drill removal, and seized or broken bolts. The process can also be used for roll marking or branding for rebar identification, tool and die work, and metallurgical core sampling. The cutting action of a metal disintegrator is accomplished by creating a series of intermittent electric arcs that break down the hardest metals into minute particles. An electrode, held in the head of the disintegrator, vibrates as it cuts while coolant is pumped through the electrode to wash away the powdered metal.

Metal disintegrators or Metal Disintegration Machining (May be abbreviated as MDM in the machining industry) are primarily used for bolt removal, tap removal, stud removal, drill removal, and seized or broken bolts. Other terms used to describe these machines include bolt eater, tap zapper, and stud buster.
Electro Arc