EDM terms explained

Abrasive Cutting Master (ACM) 
The tool used in the total form machining method of producing graphite electrodes.

Altered Metal Zone (AMZ) 
The mechanically and mechanically altered zones created by the EDM process on the workmetal surface.

Ammeter 
An instrument for measuring electric current in amperes.

Amperage (A)
In EDM, the amount of average current measured during the cut.

Ampere 
The unit of electric current. Equivalent to the steady current produced by 1m, volt across 1 ohm.

Angstrofine
An advanced grade of EDM graphite characterized by a particle size of less than 1 micron and having very high tensile strength, isotropy, and uniform structure.

Anisotropic
Exhibiting properties whose values change when measured along differing axes. Opposite of isotropic.

Anode
The positive terminal of an electrolytic cell or battery. Often incorrectly applied to the tool (electrode) in the EDM process.

Arc
A continuous flow of electrical current, visually recognizable as a yellow flash, between an electrode and workplace. An arc will damage both the electrode and workpiece.

Arc Dampener
Same as arc suppressor.

Arc Guard
Same as arc suppressor.

Arc Suppressor
A circuit in the EDM power supply that reduces that Guards or Suppresses an arc from occurring.

Automatic Depth Finder
(Refer first to Depth finder) An automatic depth finder is electrically connected to the servo and will stop the downward advance of the electrode at within 0.0001" of the workpiece surface and will hold it at this distance. Therefore, if the workpiece position is shifted by moving the table in any direction with its handwheels, the servo will constantly adjust the vertical relationship of the electrode to maintain its distance at 0.0001" away from even a previously EDMed cavity, even one with an irregular surface.

Automatic Tool (Electrode) Changer (ATC)
A device used with computer numerically controlled (CNC) EDM to provide automatic operation.

Average Current
The average value of all the minimum and maximum peaks of amperage in the spark gap, as read on the ammeter. For any given available current setting, the higher the average current, the greater the efficiency of the particular cut being made. See Machining rate.

Billet
A block of graphite, usually the uncut size as produced by the manufacturer.

Blind Hole
Any hole or cavity cut into a solid shape which does not connect with other holes.

Breakthrough
The exit point of a through-hole cavity.

Burning
A slang term for EDM.

Capacitor
An electrical component that stores current and discharges when they be come full. Traditionally used for EDM'ing tough to machine and exotic material. In some EDM power supplies, a bank of capacitors are connected across the machining gap.

Carbon
An abundant, naturally occurring element. Often used in place of the word graphite. Graphite is a form of the element carbon. There are four forms of carbon, the others being amorphous carbon (having no definite crystal structure), diamond, and the recently discovered fullerenes (also known as Buckyballs).

Catalyst
A material which causes an increase in the rate of a reaction due to its presence, but is unchanged at the end of the reaction. In EDM, catalyst refers to particulates of graphite and metal which aid in establishing a current path in the dielectric fluid.

Cathode
The negative terminal in an electrolytic cell or battery. In EDM, sometimes incorrectly applied to the workpiece.

Center Flow
The pumping of dielectric fluid through either the electrode or the workpiece for flushing.

Center Flushing
A method of flushing dielectric through a center hole in an electrode or workpiece.

Circuit
A continuous path allowing and directing the flow of electric current.

Coarse
A class of graphite characterized by a particle size of more than 100 µm large pores and voids, a non-uniform structure, and low strength. Not recommended as an EDM electrode material.

Collet
A device used to hold electrodes with round shanks.

Colloidal Suspension
Particles suspended in a liquid that are too fine to settle out. In EDM, the tiny particles produced in the sparking action form a colloidal suspension in the dielectric fluid.

Common Metals
The first group of metallic electrode materials. Includes copper, brass, and zinc.

Composite
Made up of more than one material. In EDM, copper tungsten is an example of a metallic composite. The copper and tungsten do not alloy, but are simply combined together. Copper graphite is a metallic/carbon composite.

Computer Numeric Control (CNC) 
Programmed control of EDM by means of microprocessors.

Condenser
An obsolete term for capacitor.

Conductor
Any material that will carry electrical current is a conductor.

Contamination
The accumulation of debris in the dielectric fluid, which can cause instability and a decrease in the fluid's dielectric strength.

Coolant
Sometimes used incorrectly to describe dielectric fluid.

Copper Graphite
Graphite electrode material that is infiltrated with copper. Use for very fine detail EDM'ing, but will also wear faster than standard graphite.

Copper Tungsten
A porous tungsten material infiltrated with cooper.

Core
The slug that remains after EDMing with an electrode that has a flush hole in it.

Coreless Machining
Refers to the Wire EDM'ing all the material from a shape by stepping from the center instead of producing a "slug". Similar to a pocketing routine in milling.

Corner Wear
In EDM, the corners of the electrode wear the most. Corner wear is the distance up the electrode corners that show signs of wear.

Crater
The small circular impressions that are formed by each individual spark as material is removed that creates the random EDM'd surface on the workpiece.

Cubic Inches Per Hour (in3/hr)
The units of measure used to describe the rate of metal removal from the workpiece. See Machining rate.

Cut, Take a Cut
To machine with EDM.

Cutting Rate
Same as Machining rate.

DC (Direct Current)
Constant polarity current, as opposed to Alternating Current (AC), which changes polarity from negative to positive in cycles.

DC Arcing
Same as Arc.

DDM
Is the process that produces HQSF (High Quality Surface Finishes).

Decalescent Point
The highest temperature at which a tool steel may be heat treated and still be hardened in a quenching medium.

Deionization
A return of the condition of the dielectric to a non-conductive state. Failure to accomplish deionization (through flushing) during off-time of the spark is responsible for DC arcing.

Depth Finder
An aid for machine set up. An electrical impulse is used to indicate when a downward moving electrode approaches to within 0.0001 inch of contact with the surface of the workpiece, either to start a cut or to reposition the electrode to resume cutting, as after dressing an electrode. Used when manually or power jogging an electrode downward. Usually used in conjunction with a dial indicator to set depth of cut at which EDMing will stop. NOTE: Do not confuse with Automatic depth finder.

Depth of Craters, Pits
The distance from the peaks to valleys on an EDMed surface.

Depth-to-Diameter Ratio
In small hole EDMing, the ratio of the depth of a blind hole compared to the diameter of the electrode used to make the hole.

Diameter (dia.) (Ø)
The length of a straight line through the center of a round object.

Diametral Sparking Distance
The difference between the electrode dimension and the dimension of the cavity produced.

Dielectric Fluid
In EDM, a nonconductive liquid. It fills the gap between the electrode and workpiece and acts as an insulator until a specific gap and voltage are achieved. It then ionizes and becomes an electrical conductor, allowing a current (spark) to flow through it to the workpiece. It also serves to cool the work and to flush away the particles generated by the spark.

Dielectric Strength
The voltage at which the insulating qualities of a material break down. In EDM, a specification applied to dielectric fluid.

Discharge
The EDM spark.

Discharge Channel
The conductive pathway formed by ionized dielectric and vapor between the electrode and workpiece.

Discharge Dressing
The process used to dress worn electrodes prior to finishing. The machine is programmed to move the worn electrode to a dressing block in the work tank. After dressing, the electrode is returned to the cavity for the finishing cut. Often used for forming micro diameter electrodes for small hole applications.

Disintegrator
An EDM technology used for removing taps and other broken tools for salvage purposes. The original EDM application.

Dither
A slight up and down vibratory motion of the machine tool ram and attached electrode used to improve cutting stability.

DN: Jump-Down Machining Time
This parameters specifies the duration of the jump-up motion to be used when removing chips from the gap by moving the axes during machining.

Downfeed
A control circuit to advance or retract the electrode.

Dressing
The re-machining of the face of an electrode to sharpen its detail after it has been used to produce a cavity. Electrodes used to make a through-hole are often dressed at the worn end.

Dual Power Supply
Two EDM power supplies in a single cabinet which can be used to operate two machines simultaneously, or can be connected to apply the full power available to only one machine.

Ductile
Capable of being drawn out or hammered thin.

Duty Cycle
The percentage of the on-time relative to the sum of the on-time and off-time setting for a particular cut.

Edge Finder
An electrically activated device on an EDM machine to aid in the accurate location of the workpiece with respect to the electrode. When any point along the side of the workplace is brought to within approximately 0.0001" of any point along the side of the electrode, a signal light or buzzer will be activated.

EDM
Electrical Discharge Machining.

Efficiency
A measure of EDM performance which varies with the on-time and off-time settings for an EDM cut. See Duty cycle (above).

Electrical Discharge Grinding (EDG)
An EDM machine resembling a surface grinder but Using a wheel made from electrode material. Can also be done with a horizontal spindle attachment (mounted on the quill of a conventional EDM machine) which has a built-in motor drive for the electrode wheel.

Electrical Discharge Machining (EDM)
A metal removal process using a series of electric sparks to erode material from a workpiece under carefully controlled conditions.

Electrical Resistance
The resistance of the flow of electricity through material. Measured in ohms.

Electrical Resistivity
The resistance of the flow of electricity through material. Measured in ohms.

Electrode
The tool in the EDM process. It must be made from an electrically conductive material. Its form, or shape, is a mirror image of the finished form or shape desired in the workpiece, with its dimensions adjusted to take into account the amount of overcut that occurs.

Electrode Growth
A plating action occurring at certain low wear settings which causes workpiece material to build up on the electrode, causing it to increase in size.

Electrode Management Technology (EMT)
Automatic methods of replenishment, redressing, and feeding of electrodes, especially in flexible machining applications.

Electrode Polarity (PL)
In EDM, the designation of positive or negative electrical polarity of the electrode. Positive polarity of the electrode (in CNC EDM) is considered to be Normal and produces the least amount of electrode wear. The positive or negative polarity depends on the machine.

Electroforming
An electroplating process used to make metal EDM electrodes.

Electrolyte
A normally conductive liquid or gas.

End Wear
A reduction in the length of an EDM electrode occurring during EDM'ing. Can be given as a dimension, or as a percentage of the original usable length of the electrode.

Entrance Opening
The point at which the electrode first enters the workpiece.

Eroding
Material removal by the EDM process.

Exit Point
The point at which the electrode pieces the workpiece in through hole EDM.

Exotics
The third group of metallic electrode material types used in EDM. Includes all rarely used metals such as tantalum, nickel, molybdenum, silver and even gold.

Exudate
Material that has flowed or diffused out of a porous body.

Farad
The unit of electrical capacitance. Used to rate the energy storing capacity of a capacitor. One farad = the capacitance of a capacitor between whose plates there appears a potential of one volt when charged by one coulomb (ampere = one coulomb/sec.).

Filler
In manufactured carbon and graphite product technology, carbonaceous particles comprising the base aggregate in an unbaked green-mix formulation.

Filtering
In EDM, removing the debris from the dielectric fluid before pumping it back into the worktank or through flushing holes in the electrode or workpiece.

Fine
A class of EDM graphite characterized by a grain size from 11µ to 20 µ.

Finish
The surface texture produced by EDM'ing. Usually given in µin Aa or Ra (U.S.).

Finish or Skim Cut
The final cut made with EDM on the workpiece. Therefore, roughing cuts, done with conventional equipment or with EDM, should be planned to leave only enough material to be removed by the finish cut to gain final size and surface finish desired.

Fire Extinguisher
Used in today's advanced EDM Sinking systems to allow for safer unattended operation.

Flashpoint
The temperature at which any flammable material will burst into flame an important factor in selecting a dielectric fluid.

Flexural Strength
A property of a solid material that indicates its ability to withstand a flexural or transverse load.

Float Switch
An adjustable float switch that monitors the depth of the dielectric fluid in the tank.

Fluid Level Switch
An adjustable float switch that monitors the depth of the dielectric fluid in the tank.

Flush Pot
A multipurpose box-like fixture which is clamped to the machine worktable. Primarily used when EDM'ing through-holes. The workpiece is clamped to its top, usually over an opening that will permit an electrode to pass through the workpiece without interference from the tank's top plate. It is connected to the dielectric system and can be used for either suction flushing or pressure flushing.

Flushing
Describes the dielectric movement through the spark gap that is necessary in EDM to cool the electrode/wire and workpiece and remove machining chips and debris caused by the ED machining process.

Flushing Hole
A hole through the workpiece or electrode used to introduce dielectric fluid to the gap for flushing purpose.

Flushing Pressure
The pressure supplied by pumps in the dielectric system supply fluid to the spark gap.

Frequency
The number of cycles (on/off) completed per unit of time. Usually expressed in Hertz.

Gap (Spark Gap)
The distance between the electrode and workpiece when the spark occurs.

Gap voltage
This can be measured as two different values during one complete cycle. The voltage, which can be read across the electrode/workpiece gap before the spark current begins to flow, is called the open gap voltage. The voltage that can be read across the gap during the spark current discharge is the working gap voltage.

Generator
An old term for EDM power supply.

Glazed Finish
A term that refers to a mirror or reflective EDM'd surface finish < 6 µinch Ra (1µmRmax) that is produced when charged particles in the gap are used with orbital motion to electro-mechanically polish the surface. Extreme accuracy and rigidity is required in order to maintain a precise spark gap.

Grain
In manufactured carbon and graphite product technology, a region in a carbon or graphite body that is identifiable as being derived from a particle or filler.

Graphite
One of the four forms of carbon. In EDM, a material used for electrodes which has high heat resistance and transfers electric current very efficiently. It is the most popular electrode material and probably the easiest to machine.

Head
That part of the EDM machine tool in which the quill or Ram (Z Axis) travels.

Heat-Affected Zone (HAZ)
The layer below the recast layer. This layer has been d subjected to elevated temperatures that have altered the properties of the material.

Hertz (Hz)
The international term for one complete electrical wave cycle. In EDM, the unit of frequency.

Hogging
Same as Roughing.

HQSF„˘
High Quality Surface Finish uses Diffused Discharge Machining (DDM) technology.

Hunting
Erratic movement of the EDM quill during a cut that can be caused by poor flushing conditions in the gap, servo response set for too much sensitivity, and build-up of carbon deposits on the bottom of the cavity being EDMed.

Inches Cube/Hour (in3/hr)
The units of measure used to describe the rate of metal removal from the workpiece.

Initiation voltage
Same as open gap voltage.

Injection
The introduction of dielectric fluid to the gap under pressure.

Injection Flushing
An external flushing method, also known as jet flushing. Fluid is directed into the gap by means of a flexible tube.

Insulator
A substance which blocks the flow of electric current.

Intelligent Expert System (IES)
Almost the same with "Fuzzy Logic". Intelligent Expert System is designed to automatically correct machining variables during machining.

Ion
An atom or group of atoms that carries a positive or negative charge as a result of having lost or gained one or more electrons. It is ionization of the dielectric fluid that provides the conductive path for the EDM spark.

Ionization
Generally accepted as a phenomenon by which the dielectric between two points on the electrode and workpiece become electrically conductive. See Dielectric.

Ionization Delay Time
The inconsistent delay between ionization start and completion times and is affected by changing Gap conditions.

Ionization Time
The time from the application of voltage until current begins to flow.

Ionization Voltage
The voltage at which current flow begins across the gap.

Ionized Path
The path of electrically conductive dielectric molecules between the two points on the electrode and workpiece through which the spark current will flow.

Isotropic
Exhibiting properties with the same values when measured along axes in all directions. Opposite of anisotropic.

JS: Jump Speed
The first and second digits of the parameter specify the axis travel speed for jump-up and jump-down motion. This parameter in (m/min).

Jump
Exhibiting properties with the same values when measured along axes in all directions. Opposite of anisotropic.

Lateral Flushing
Same as surface or splash flushing. Directing the flow of dielectric fluid through a hose pointed at the electrode in order to remove chips and swarf in a [shallow] blind cavity.

LL Generator
Is anti-electrolysis generator and stands for "Layer Less".

Low Wear
The result of certain settings for EDM machining which produces a very low degree of wear by plating the electrode with melted work material. In some cases less than 1%, which is also known as no-wear.

Machine Tool
It performs the purely mechanical functions and, along with the dielectric system and the power supply, makes up the complete EDM.

Machining Rate
Same as Metal Removal Rate. The rate at which material is removed from the workpiece by EDM.

Mean Overcut
The average of top and bottom Overcut.

Medium Grade
A class of EDM graphite materials characterized by a particle size from 21m to 100m, anisotropy, non-uniform performance, and high porosity.

Metal Removal Rate (MRR)
The rate at which material is removed from the workpiece by EDM. In the U.S., usually expressed in cubic inches/hour (in/hr).

Metallic Composite
A non-alloyed combination of metals, such as copper tungsten.

Micro ohm (mW)
One-millionth of an ohm (0.000001 ohm).

Micro second (µs)
One-millionth of a second (0.000001 sec.) used to control each EDM spark from the generator µs of On & Off-Times.

Micro-farad
One-millionth of a farad.

Microinch (min)
One-millionth of an inch (0.000001").

Micron Machining
A term for precision EDM machining.

Micron, Micrometer (µm)
A unit of length equal to one-millionth of a meter or 0.00003973".

Microprocessor
A computer-on-a-chip. Found in all advanced EDM systems, the microprocessors provide many control functions.

Mil
One thousandth of an inch (0.001").

Millisecond (ms)
One thousandth of a second (0.001 sec.).

Miss
A pulse that does not produce machining due to too great a gap.

Model Data
Provides the programmer the ability to pre-select from 1 to 15 burning conditions (roughing and finishing) based on electrode size and surface finish with ONLY two inputs.

Model Plan
Canned Cycles (Macros) that simplify EDM Programming through the use of commonly used Machining Positioning and Measuring Models (or Functions) that can be programmed easily using a graphic user interface.

Modular Construction
When used in EDM, a type of power supply where entire circuits are integrated on boards or modules. This type of construction provides a simple and rapid method of servicing and replacing electronic circuits in the field.

Monitor
In EDM, any mechanical or electrical device which is used to indicate various operating conditions, i.e., ammeters, indicators, lights, pressure gages.

Multiple Electrodes
The simultaneous use of electrodes to produce multiple cavities in one or more workpieces. A standard power supply usually has one wire lead connected to the electrode or workpiece and through which the total power available.

Multiple Lead (Multilead) Power Supply
A standard power supply usually has one wire lead which can be connected to the electrode or workpiece and through which the total power available can be channeled. With a multilead power supply, it is possible to divide the total power available into small units, each capable of being channeled through separate wire leads connected to multiple electrodes or workpieces for production work. Or, all power can be put through a single wire lead by connecting all the individual leads into one.

No-Load Voltage
Same as open gap voltage.

No-Wear
Defined by POCO® as a condition under which 1 unit or less of electrode is eroded to every 100 units of workpiece. (one percent or less)

Non-Directional Finish
A finish having no specific direction to its surface pattern. An EDM finish is non-directional.

Normal Polarity
Negative polarity to the electrode.

Off-Time
The time between sparks, measured in microseconds. Too short an off-time may result in unstable machining or worse, DC arcing.

Ohm
A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt.

Oil-Through-Chuck
A sealed holder for tubular electrodes through which dielectric fluid can be pumped or sucked for center hole flushing.

On-Time
The duration time of the EDM spark measured in microseconds.

Open Circuit
An electrical circuit which is not complete.

Open Gap Voltage
The voltage which can be read across the electrode/workpiece gap before the spark current begins to flow. See Gap voltage.

Operating Current
Same as average current.

Oscilloscope
An electronic imaging device which can be used to visually check the shape and voltages of pulses being generated by the EDM power supply.

Output
The voltage and current of an EDM power supply.

Overburn
Same as overcut.

Overcut
An EDM cavity is always larger than the electrode used to machine it. The difference between the size of the electrode and the size of the cavity is called the overcut. When discussing or calculating overcut, be sure to specify whether you are referring to total overcut (Diametral overcut) or overcut per side. Diametral overcut is most often used.

Overcut, per side
One-half of the Diametral overcut value. It is important to follow this procedure in designing electrodes: (1) Select surface finish settings to determine finishing cut overcut. (2) Design finishing electrode size with overcut allowance. (3) Design roughing electrode providing for overlap which will leave proper allowance for the finish machining cut to clean up the surface left by the rough cut.

Overlap
(1) The area by which the electrode for the next cut exceeds the workpiece cavity. (2) The difference between the rough machined hole or cavity size and the size of the electrode to be used for the next cut.

Particle Size
The average cross section of the solid graphite particles in a graphite system. The particle size is determined by the carbonaceous material from which the graphite is produced and the method of manufacturing. Also referred to as grain size.

Pause
The absence of electrical energy for a preset time following a discharge of electrical energy (pulse).

Pause Duration (off-time) in Time
The time between sparks, measured in microseconds. Too short an off-time may result in unstable machining or worse, DC arcing. Longer the off time will cause longer machining time. But this is an integral part of the EDM process must exist. The off time also governs the stability of the process. An insufficient off time can lead to erratic cycling and retraction of the advancing servo and result slowing down the operating cycle.

Peak Current (IP)
The maximum current available from each pulse from the power supply/generator. The peak current is the best defined as the high electrical current that can occur during the discharge. Generally the value of this peal current based on the code, the actual value in unit ampere for this current reading in manual book machine.

Percent Electrode Wear
The volume of electrode worn away as compared to the volume of workpiece worn away.

Pieced Electrode
(1) An EDM electrode made using a lower quality graphite as a base material with a higher quality material as the cutting surface. Such electrodes require careful mating to insure conductivity and correct positioning. (2) An electrode that has been repaired by replacing a broken part. All cutting surfaces must be of the same material for uniform performance. (3) An electrode made from several pieces of the same quality material to obtain a bigger electrode.

Plasma
A superheated, ionized gas that forms in the discharged channel due to the action of the thermoelectric force.

Platen
A large flat mounting surface affixed to the end of the quill or the ram of an EDM machine, and on which the electrodes or various electrode-holding devices can be mounted. It usually has tapped holes or machined T-slots for convenience in clamping electrodes or holders.

Pore
EDM graphite is made of individual particles bonded together. This leaves voids or spaces between them, called pores. Larger particles mean larger pores, or spaces, between them. No graphite may be machined to tolerances closer than its average pore size.

Potential
The difference in voltage between two points of an electrical circuit.

Power Pack
Same as Power supply (below).

Power Supply
The part of the EDM system that supplies the voltage and current that causes the sparks or discharges between the electrode and workpiece. It is usually housed in a cabinet separate from the machine tool and connected to it by a cable.

Premium Graphite
A material with a particle size of 5 microns or less.

Pressure Flush
The forcing of dielectric up through flush holes in the workpiece or down through flush holes in the electrode.

Pretensioned Axis Screws
The practice of stretching a ball lead screw by several tenths (0.0001"), between two supports in order to provide added rigidity, alignment and accuracy.

Pulsator
Not related to the generation of sparks. It is a unit added to, or built into, an EDM machine which periodically causes the electrode to retract for a short period of time to aid in flushing a deep or blind cavity. Also commonly called a RAM cycler.

Pulse
The discharge of a quantity of electrical energy having preset voltage and amperage and expended over a preset time.

Pulse Duration (on-time) in Time
The duration time of the EDM spark measured in microseconds. The longer spark is sustained more is the material removal rate. Except, during roughing all the sparks that leave the tool result in a microscopic removal of particles of the surface. More spark produce much more wear.

Pulse Duration (time)
Same as On-time.

Pulse Timer
This refers to the spark, not flushing. Used to set the length of on-time and off-time of the spark. On some machines, on-time and off-time can be set individually in microseconds.

Pulsed Flushing
Flushing that is synchronized with the pulsator of the EDM machine. When a machine is set for this mode (Systematic Coordinated Flushing), pressure flushing takes place only when the quill retracts the electrode from the cavity.

Quench
The rapid cooling of the EDM'd surface by the dielectric fluid. Partially responsible for the metallurgical changes forming the recast layer and the heat-affected zone.

Quill
The moving member of an EDM machine on which the electrode or electrode holder is mounted. A cylinder working in a bearing or bushing.

Ram
The moving member of an EDM machine on which the electrode or electrode holder is mounted. A dovetail guided arrangement.

Ram Cycler
Same as Pulsator.

RC (Relaxation) Circuit
An outmoded EDM power supply circuit which uses capacitors to store the charge that produces the spark at the gap. The capacitor is charged through a resistor and discharged across the gap when conditions are correct (gap distance, voltage, etc.). This is the original EDM circuit and is seldom used in advanced machines.

RC or Relaxation Circuit
An EDM powers supply (circa 1962) that used capacitors to produce a spark. This early EDM power system is seldom used in advanced machines.

Recast Layer
A layer created by molten metal solidifying on the workmetal surface.

Reciprocator
A hydraulic device attached to the ram of conventional EDM providing a longitudinal reciprocating action.

Rectifier
This converts alternating current to direct current.

Refeed
Automatic electrode replenishment.

Relaxation Circuit
Same as RC circuit (above).

Repetition Rate
Same as Frequency.

Resolidified Layer
Same as Recast layer (above).

Reverse Burning
The technique of mounting the electrode on the machine table or flush tank and the workpiece on the quill. Used in EDMing a blanking punch with female electrode.

Reverse Polarity
A term used to indicate positive polarity on some machines.

RMS (Root Mean Square)
An obsolete term used in surface finish measurement.

Rotating Spindle
Either an accessory mounted on the quill or ram, or a built-in machine spindle used to rotate the electrode to achieve more uniform wear and to improve flushing conditions. Its use is limited to round electrodes. Another use for the rotating spindle is in trimming the workpiece with an indicator, as you would on a jig borer, for setting locations.

Roughing (Hogging) Cut
The mode of EDM that removes the most material in the shortest time.

Safety Cut
The method of undersizing roughing electrodes to compensate for differences between them and the finishing electrodes.

Secondary Discharge
A discharge that occurs as conductive particles are carried up the side of the electrode by the dielectric e fluid.

Sensitivity
A control switch that adjusts the response time of the servo mechanism.

Servo Mechanism
The device that drives and controls the movement of the quill or Ram.

Servo Reaction Time
The time between a signal to the servo and its physical response to the signal.

Side Wear
In EDM, the wear along the side walls of the electrode.

Silicone
A dielectric fluid for special situations consisting mostly of the chemical polymer silicone.

Silver Tungsten
A porous tungsten material which is infiltrated with silver.

Slurry
A watery mixture of insoluble material and water. Used as an abrasive in ultrasonic machining.

Solid State Power Supply
Transistorized circuitry. See Transistor.

Sonotrode
The forming tool in ultrasonic machining.

Spark
An electrical discharge of very short duration between two conductors.

Spark Erosion
Another name for EDM. Used primarily outside the U.S.

Spark Gap
The distance between the electrode and the workpiece when discharges are occurring.

Spark Generator
Same as Power supply.

Spark Intensity
The amount of energy in the spark.

Spindle
An upper rotating member of an EDM machine to which the electrode or electrode holder is mounted.

Split Electrode
Multiple electrodes on a single machine electrically insulated from each other. Used with multiple lead power supplies.

Split Lead Power Supply
Same as Multiple lead power supply.

Square Wave
A term for an electrical wave shape generated by a solid state power supply.

Stability
Refers to the steadiness of EDM cut. The opposite of hunting.

Staged Electrode
A multiple electrode set designed to produce a single cavity. From rougher to finisher, each electrode must have dimensions that take into account leaving sufficient metal for the last electrode to produce the required dimensions.

Stepped Electrode
An electrode constructed in such a manner as to allow the roughing and finishing of a through-hole cavity in a single set up. The smaller front section is used to rough out the cavity and the larger rear portion is used for finishing.

Stroke
The distance the ram/quill travels under servo control.

Sublime
To pass directly from a solid state to a gaseous state. Graphite does not melt when heated at normal pressures, but passes directly into a gaseous state.

Suction Flushing
Using a vacuum to draw the contaminated dielectric away from the gap as opposed to forcing it out with pressure.

Superfine
A class of EDM electrode materials with a particle size from 6µm to 10µm characterized by moderately high strengths, usually isotropic.

Surface Finish
The surface roughness of a machined surface.  µinRa in the U.S. µmRmax or µmRy in Asia µmRa or VDI in Europe.

Surface Flushing
The use of nozzles or hoses to direct jets of dielectric at the cutting area to flush away the debris. Usually employed while pulsating the electrode.

Surface Integrity
The quality of the machined surface and subsurface and has little to do with surface finish.

Surface Roughness
Surface irregularities on a machined surface.

Swarf
The eroded particles or residue.

Synthetic Dielectric
Newer types of dielectric oils that are safer than mineral seal oils used.

Tap
A control on some early power supplies that changes spark frequency and on-time.

Tap Buster
Same as Disintegrator.

Taper
The dimensional difference between the entrance and exit opening of a cavity, or between the entrance and bottom of a blind hole.

Tapping Attachment
An accessory that holds and rotates an electrode as it EDMs a threaded hole into a workpiece. It advances the electrode to produce the pitch of the thread desired.

Tellurium Copper
An alloy of copper and tellurium.

Temperature Cut-Off 
The dielectric oil temperature at which the power is shut off.

Thermal Convectiona
Temperature Cut-Off A circuit that shuts down a system at a preset temperature. Used on EDM dielectric systems.

Thermoelectric
The combined action of heat and electricity.

Through-Hole Flushing
The use of a pre-drilled hole in the workplace to inject dielectric fluid up toward the gap by injection flushing or down from the gap by suction flushing.

Tilting Head
An attachment allowing the electrode to be tilted in two directions.

Time Controlled Machining
Through-Hole Flushing The use of a pre-drilled hole in the workplace to inject dielectric fluid up toward the gap by injection flushing or down from the gap by suction flushing.

Timed Retractor
Same as pulsator.

Timer, Timing Unit
A control unit that establishes the spark on- and off-times.

Total Form Machining (TFM)
An abrasive machining device capable of copying complete graphite electrodes.

Tramming Attachment
A mechanical accessory used in EDM to check the accuracy of the setup and to aid in the precise location of the workpiece in respect to the electrode.

Transducer
A device for changing electromagnetic force into mechanical force. A loudspeaker is a transducer. In EDM, a transducer is used in ultrasonic machining of graphite, though the sound produced is too high for most human hearing.

Transistor
An electronic component used as a switch to open and close with extreme speed. Replaced the vacuum tube due to its reliability, long life, and much higher switching speed.

Trepanning Electrode
A hollowed out or tubular electrode which is used in through-hole machining to remove a large amount of material from the solid so as to avoid pre-machining by conventional means.

Tubular Electrode
A round electrode with a center hole.

Tungsten
A metal used in pure or near pure state as an electrode material, Melting point is 3380şC.

Ultrafine
A class of EDM graphite characterized by a particle size from 1µ to 5µ isotropy, uniform structure, and high strength.

Unstable
Erratic or intermittent EDMing.

UP: Jump-Up Machining Time
These parameters specifies the duration of the jump-up motion to be used when removing chips from the gap by moving the axes during machining.

Vacuum Flushing
Same as suction flushing.

Vacuum Tube Power Supply
An EDM power supply which uses vacuum tubes to switch the electrical machining pulses (sparks) on and off.

Vibrator
An accessory used on an EDM machine to move the workpiece or electrode back and forth rapidly. Employed primarily for improving flushing in blind cavities.

Viscosity
The tendency of a fluid to resist flow. High viscosity liquids are thicker.

Voltmeter
An instrument that measures the Average voltage across the spark gap on an EDM machine during machining.

Volumetric Wear
The total wear of the electrode expressed in cubic inches.

Wave Form
A geometric shape that represents the output of a power supply as seen on an oscilloscope.

Wear Ratio
The ratio of electrode material volume worn away as compared to the volume of workpiece material removed by EDM.

Wear 
The erosion of the electrode during the EDM process.

Wire EDM
The electrode is a continuously spooling conducting wire that moves in preset patterns around the workpiece.

Working Gap Voltage
Same with Gap Voltage.

Workpiece 
Any part on which EDM is being used to cut holes or cavities.