Section 8: Computer Numerical Control Unit 1: CNC Basics

Turning center

A computerized numerical control (CNC) lathe equipped with an automatic tool changer.

Machining Center

A computerized numerical control (CNC) mill equipped with an automatic tool changer.

Polar coordinate system

A coordinate system used in CNC programming to identify locations by defining both an angle and a distance (like a vector in mathematics) from the origin to a specific location.

Automatic Tool Changer (ATC)

A device used in some CNC machines to automatically load, unload, and store tools.

Servo Motor

A hybrid electric motor that is half motor/half position sensor, which can both provide the power to move a machine axis and track how far the axis has moved.

Linear guide

A modernized version of ways that are sealed, have pressurized lubrication systems, and contain low friction ball bearings.

Absolute Positioning System

A referencing method used with coordinate systems in which the coordinates of all positions are referenced from the origin (X0, Y0, Z0)

Incremental positioning system

A referencing method used with coordinate systems which specifies a distance from the current position to the next position instead of a location related to the initial origin.

Ball Screw

A screw and nut assembly with steel balls in place of threads which can achieve high efficiency and zero backlash in computerized numerical control machines.

Conversational Programming

A special type of MCU function developed to simplify the machine programming process in which the operator selects the intended type of machining operation from an on-screen menu and the machine prompts the programmer with a series of questions.

Word address

A style of programming in which instructions are written in a code or format that can be understood and executed by a CNC machine tool.

Miscellaneous function

Activities controlled by M-codes in the CNC machining system. See also M-codes

G-codes

CNC programming codes that prepare a machine to engage in a particular mode for machining; for instance, a G! code tells the machine to feed in a straight line, or linear motion.

M-codes

CNC programming codes used to turn on and off miscellaneous functions

Circular Interpolation

Commanded by the G-codes G2 or G3, a type of motion that causes the cutter's path to travel in an arc so that CNC machines can cut full or partial circles.

Rapid Traverse

Designated by the G-code G0, a type of CNC machine motion used to quickly position tools near the workpiece before beginning a machining operation.

Linear interpolation

Designated by the G-code G1, CNC motion used to move the tool in a straight line along one or more machine axis.

Origin

In a Cartesian coordinate system, the point (X0, Y0, Z0) from which all other positions are based.

Quadrant

In the Cartesian Coordinate System, four regions that are created when the system is divided by the X- and Y-axes; they are numbered counterclockwise from I to IV, beginning in the upper right region.

Block

In the word address programming system, a group of program words that appear on the same line and are to be executed at the same time.

Rectangular Coordinate System

See Cartesian Coordinate system

Preparatory command

See G-Codes

Machine Control Unit (MCU)

Sometimes simply called a "contro," the system of a CNC machine that interprets the program and then uses the information to control machine functions and control axis motion.

End of block

The semicolon character at the end of a block of CNC code that instructs the MCU to move on to the next block.

Encoder

The sensor portion of a CNC machine's servo motor that works by recording the amount of rotation a motor makes (in degrees), which provides feedback to the machine control to ensure the desired amount of movement is obtained.