CAD/CAM/CNC Dictionary

Select the first letter of the word from the list above to jump to appropriate section of the glossary.
If the term you are looking for starts with a digit or symbol, choose the '#' link.

- A -

Axis - Joint, rotational, directional, or transversal movement of which the robot is capable.

A-Axis- The axis of circular motion of a machine tool member or slide about the X-axis. VAlues along the A-axis are degrees of rotation about the X-axis.

Absolute System- A numerical control system in which all positional dimensions, both input and feedback, are given with reference to a common datum  point.
APT Programming- Automatically Programmed Tools. A universal computer assisted programing system for multi-axis contouring programming. The regional   NC programming system, developed for AeroSpace, first used in building and manufacturing military equipment.
Algorithm- A computational method for solving problems. Much like a recipe in cooking, or a plan of attack in the military. Developing the algorithm in machining is the pre-planning process that creates the orderly procedure for  machining processes to occur.
Alphanumeric- A system of code that consists of the characters A-Z and numerals 0-9.
Analog- Pertaining to a system that that uses electrical voltage magnitudes or  ratios to represent physical axis positions.
Analyst- A person skilled in the development and definition of techniques to solve problems.
Arc Clockwise- G02- An arc generated by coordinated motion between two axes. Curvature of the arc is clockwise with respect to the part and the cartesian planes.
Arc Counterclockwise-G03-An arc generated by coordinated motion between two axes. Curvature of the arc is counter-clockwise with respect to the part and the cartesian planes.
ASCII-(American Standard Code for Information Exchange) A data transmission  code that has been established as an American Standard by the American Standards Association.

Auxiliary Function-M Codes-A programming function used in CNC machining that controls functions other than axis motion. Tool changing, coolant on and off, starting and stopping the spindle, etc.

Axis- A principal direction along which the relative movements of a tool or workpiece occur. Three linear axes, occurring at 90 degree angles from each other, named X,Y and Z.

Axis Inhibit- A feature of an NC unit that enables the operator to withhold command information from a machine tool slide.

Axis Inversion-The reversal of plus and minus values along an axis. Mirror  imaging is used to make a left-handed part from a right-handed toolpath. When a axis inversion is used circular interpolation is also reversed.

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- B -

Backlash-A relative movement between interacting mechanical parts as a result of looseness.

Batch Processing-Technique in which items to be processed must be coded and collected into groups prior to processing.

B-Axis-The axis of circular motion of a machine tool member or slide about the Y-Axis.

Binary Code-Code based on binary numbers expressed as either 1 or 0, true or  false, on or off.

BIT-Binary Digit-A binary digit has only two possible states. Eight BITS make up one BYTE.

BCL- Basic Control Language ...EIA/ANSI 494. A CNC controller language. For more information on BCL visit

Block-A single line of NC code is a block, a block represents sufficient information to a CNC machine to perform a single line or arc movement.

Block Delete-A function that permits selected blocks of code to be ignored by  the control system, at the operators discretion.

Buffer Storage-A place in which information in a control system or computer  is stored for use at a later time.

Bug-A programmed error or oversight, a glitch.

BYTE-A sequence of eight adjacent binary digits (BITS)

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- C -

CAD-(Computer Aided Design)The using of computers to assist and develop  phases of design.

CAM-(Computer Aided Manufacturing) The use of computers to assist in manufacturing.

Cancel-A command that will discontinue any canned cycles or sequence commands.

Canned Cycle-A preset sequence of events initiated by a single G coded command.

Cartesian Coordinates-A three dimensional system whereby the position of a point can be defined with reference to a set of axes at right angles to each other.

C-Axis-The axis of circular motion of a machine tool member or slide about the  Z-axis. C-axis values are degrees of rotation about the Z-axis.

Chip-A single piece of silicon cut from a slice by scribing or breaking. A chip can contain one or more circuits.

Circular Interpolation-The process of generating up to 360 degrees of arc using only one block of information as defined by EIA.

CL Data-Processor output that contains information regarding cutter location.

CNC-Computerized Numerical Control.

Command-A signal or series of signals that initiates one step or a series of steps  in the execution of a program.

Compile-To generate a machine language program from a computer program written in a high level source code.

Console-The part of a computer system used by the operator for communication  with the computer system.

CPU-Central Processing Unit of a computer. The memory and logic area of a computer that includes processing and execution of instructions.

CRT-Cathode Ray Tube-A device that displays alphanumeric data to the machine operator.

Cutter Diameter Compensation-CDC-A system in which the programmed toolpath may be altered to compensate for cutter diameter differences.

Cutter Offset-The distance from the part surface to the axial center of a cutter (the radius of the cutter).

Cutter Path The path defined by the center of the cutter.

Cycle-A sequence of operations that is repeated. The time the repetition requires  is cycle time.

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- D -

Data-The representation of information in the form of NC Words, symbols, numbers, letters, characters and/or digits.

Database-A comprehensive collection of information in a specific format applicable to a user's needs.

Debug-To troubleshoot, detect, locate and remove mistakes from a program.

Decimal Code-A code system in which each allowable position has ten possible states.

Digit-A single character in any numbering system.

Digital-Relating data in the form of digits.

Display-A visual representation of data.

Downtime-Time during which equipment is inoperable because of faults.

DNC-Direct Numerical Control-A system in which machine coded programs  are introduced into the CNC controller from a remote computer.

Dwell Time-A timed delay of programmed or established duration used in  specific machining operations.

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- E -

Edit-To modify the form of data.

EIA Standard Code-A standard code for positioning, linear motion, and contouring control systems proposed by the U.S. EIA Standard RS-244.

End-Of-Block Character-A character representing the end of a programmed block of information.

End of Program-A miscellaneous function (M02) that represents the completion of a programmed cycle.

End Points-The extremities of a span.

Executive Program-A set of programming instructions that allows a CNC lathe to have the capability to perform lathe functions or a CNC mill to perform milling functions. A set of instructions designed to output specific functions.

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- F -

Feed-A programmed or manually established rate of movement of the cutting  tool into the workpiece for the required machining operation.

Feed Rate-F Word-A multi-character code containing the letter F followed by digits that determine the machine slide rate of movement.

Feed Rate Override-A variable manual control function that allows the control  system to increase or reduce programmed feedrates.

File-An organized collection of relevant, orderly data.

Firmware-Programs or controlled instructions that are not changeable by the user and that are often held in ROM,Read Only Memory.

Fixed Block Format-A format where data blocks appear in sequentially arranged order.

Fixed Cycle- A preset sequence of events initiated by a single G coded command.

Floating Zero-A characteristic of a machine control unit that allows the zero reference point to be established at any point of travel along an axis.

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- G -

Gauge Height-A predetermined Z axis clear plane retraction point along the Z-axis to which the cuter retreats allowing safe XY axis travel.
GIGO-Anacronym for "Garbage In, Garbage Out", when a programmer is given garbled inaccurate information (geometry), the BEST that can be expected  is  an inaccurate toolpath. ALWAYS, proof every number given to you from any Engineer, if you don't you will be re-programming 75% of the work!
G Code-Active Preparatory Function-An NC word addressed by the letter G  and followed by a numeric value, G Codes are flags that when executed by the machine control unit, initiate axis motions, plane changes, feedrate changes, etc. G Codes have different uses and functions from one  Machine Tool Builder to another, use caution when changing to unfamiliar machines!
G00-Rapid Travel-Axis motion at maximum speed.-Milling-Turning-
G01-Linear Interpolation Straight linear axis motion at a controlled feedrate. -Milling-Turning-

G02-Clockwise circular motion using two axes in a single program block.- Milling-Turning-

G03-Counter-clockwise circular motion using two axes in a single program block.-Milling-Turning-

G04-A dwell, stoppage of axis motion, for a programmed length of time. -Milling-Turning-

G17-X,Y plane selection.-Milling-

G18-X,Z plane selection.-Milling-

G19-Y,Z plane selection.-Milling-

G20-G70-Inch units(G20 or G70 depends on the MTB)-Milling-Turning-

G21-G71-Metric units(G21or G71depends on the MTB)-Milling-Turning-

G28-Automatic return to a reference point.-Milling-Turning-

G29-Automatic return from a reference point.-Milling-Turning-

G40-Milling-Cancel Cutter Diameter Compensation

G40-Turning-Cancel Tool Nose Radius Compensation.

G41-Milling-Cutter Diameter Compensation on, cutter left.

G41-Turning-Tool Nose Radius Compensation Left

G42-Milling-Cutter Diameter Compensation on, cutter right.

G42-Turning-Tool Nose Radius Compensation Right

G70-Turning-Canned Finishing Cycle

G71-Turning-Canned Roughing Cycle

G72-Turning-Canned Facing Cycle

G74-Turning-Canned Peck Drilling Cycle

G75-Turning-Canned Grooving Cycle

G76-Turning-Canned Threading Cycle

G80-Cancel Canned Cycle.-Milling-

G81-Canned Drilling Cycle.-Milling-

G82-Canned Cobore Cycle.-Milling-

G83-Canned Deep Hole Drilling Cycle.-Milling-

G90-Absolute Positioning.-Milling-

G91-Incremental Positioning.-Milling-

G92-Repositioning or re-setting the origin point.-Milling-

G98-Milling-The initial machine reference positioning system. (Machine Reference Zero)

G98-Turning-Linear Feedrate Per Time.

G99-Milling-Cancel G92 position set.(PaArt Reference Zero)

G99-Turning-Feedrate Per Revolution

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H -

Hard Copy-A readable output of data on paper.
Hardware-The components that make up a computer or control system.
Hard-Wired-Having logic circuits interconnected on a backplane to give a fixed pattern of events.
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- I -

Incremental Dimensioning-A method of expressing a dimension with respect to the preceding point. NOT a good idea, incremental dimensioning allows users to fall into a trap. If a single error in data is entered incorrectly at the beginning of a project, ALL points determined afterwards will have that  amount of error built into them.
Inhibit-To prevent an action or event.
Input-Transfer of external data into the control system.
Interpolation-A function of a control whereby data points are generated between given coordinate positions.
ISO-International Organization of Standardization.
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- J -

Jig- A fixturing device used most often for drilling operations.
Jog-A control function that momentarily operates a drive into the machine.
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- K -

K - 1) An abbreviation for the prefix kilo i.e. 1000 in decimal notation. 2) Commonly used to describe the amount of addressable storage unit of computer systems. K in computer terminology equals 1024.

Keypunch - A keyboard-actuated device that punches holes in a card to represent data

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- L -

Leading Zeros-Redundant zeros to the left of a number.

Letter Address-Often called NC Words, such as X,Y,Z,F,G,M.

Linear Interpolation-A control function whereby data points are generated between given coordinate positions to allow simultaneous movement one, two or  more axes of motion in a linear path.

Loop-Repetitive operations can be programmed in a continuous mode until the  desired functions have been completed.

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- M -

Machine Code-Code obeyed by a computer that needs no further translation.

Machining Center-Machine tools, normally Numerically Controlled, capable of automatically repeating many operations such as drilling, reaming, tapping, milling, and boring multiple faces on a workpiece.

Machine Tool-A power driven machine used to form or shape metal and other  materials.

Macro-A group of instructions that can be stored and recalled to solve a recurring problem.

Magnetic Tape-A tape made of plastic or mylar that is covered with magnetic particles. It stores information by selective polarization of portions of the surface.

Manual Data Input-MDI-A mode of control that allows the operator to input data into the control system, the data input is identical to the data that can be input by other means such as tape or DNC.

Manual Part Programming-The preparation of a manuscript in machine control language and format to define a sequence of commands for processing by a NC machine.

Manuscript-A written or printed copy, in symbolic form, containing the same data as that punched on cards or retained in a memory unit.

Memory-An organized collection of storage elements into which a unit of information consisting of a binary digit can be stored and from which can later  be retrieved.

Mirror Image-The reversal of plus and minus values along an axis. Mirror  imaging is used to make a left-handed part from a right-handed toolpath. When axis inversion is used circular interpolation is also reversed. Use of (INV,X1Y0)  is a Type II language command.

Modal-Pertaining to information that is retained by the system until new information is obtained that replaces it.

Module-An interchangeable plug-in item containing components.

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- N -

N/C-Numerical Control-The technique of controlling a machine or process by  using command instructions in coded numerical format.

Null-Pertaining to a zero output from a device.

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- O -

Offset -A displacement in the axial direction of the tool equal to the difference  between the actual tool length and the programmed tool length.
Optional Stop-A miscellaneous function similar to Program Stop(M01) except  that the control ignores the command unless the operator has previously pushed a button to validate the command.

Output-Data transferred from an internal storage unit to storage or an output device.

Overshoot-The amount by which axis motion exceeds the target value.

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- P -

Parabola-A plane curve generated by a point moving so that it's distance  from a fixed second point is equal to it's distance from a fixed line.

Parabolic Interpolation-Control of a cutter path by interpolation between three fixed points, with the assumption that the intermediate points are on a parabola.

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- Q -

Quadrant - Any of the four parts into which a plane is divided by rectangular coordinate axes lying in the plane.

Quadrature - Displaced 90 degrees in phase angle.

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- R -

Reference block - A block within an N/C program identified by an "O" or "H" in place of the word address "N" and containing sufficient data to enable resumption of the program following an interruption. This block should be located at a convenient point in the program which enables the operator to reset and resume operation.
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- S -

Sampling period - The interval between observations in a periodic sampling control system.
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- T -

T word - The numeric code appearing in an N/C tape which is use to select a desired tool on a machine tool. It is preceded by the letter "T".

Tachometer - A speed measuring instrument generally used to determine revolutions per minute. in N/C it is used as a velocity feedback device

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- U -

Undershoot - 1) The tendency of an N/C machine to round off corner of a programmed path as a result of servo lag. 2) The mechanical system "lags" or follows behind, due to the inability of mechanical system to react at the same speed as the electrical system.
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- V -

Variable block format - A format which allows the number of words in successive blocks to vary.

Vector feedrate - A programed motion at a specified rate over a given distance in a given direction

Verifier - A device on which a copy or reproduction can be checked by comparing the copy with the original.

Verify - The process of comparing a copy with the original for accuracy

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- W -

Word - 1) The largest number of bits that may be manipulated as an entity. 2) an ordered set of characters which is the normal unit in which information may stored, transmitted, or operated upon. for example X03700
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- X -

X Axis - The x axis of motion is horizontal and parallel to the work holding surface. If z is horizontal, positive x is to the right looking from the spindle toward the workipiece. If the z axis is vertical, when looking from the spindle toward its supporting column(s) the positive x axis is to the right on single column machines or forward on dual column or gantry machines. On machines generating a surface of revolution, such as lathes, x motions shall be radial, and normally the positive direction of motion shall be away from the center of revolution. Where the linear motion can cross the centerline of rotation, positive motion shall be in the direction of maximum displacement from the center of rotation.
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- Y -

Y Axis - The y axis of motion is perpendicular to both x and z. Positive y is in the direction to make a right-handed set of coordinates, i.e., +x rotated into +y advances a right-handed screw in the + z direction
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- Z -

Z Axis - The z axis of motion is parallel to the principal spindle of the machine.

Zero offset - A characteristic of numerical machine tool control permitting the zero point on an axis to be shifted readily over a specified range. The control retains information on the location of the permanent zero.

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- # -

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