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OpenCNC Glossary

The following is an alphabetical listing of the terms used throughout OpenCNC documentation.

Absolution Position

The absolute position is the location of the axes with respect to machine zero.


Command that allows you to add a line of instructions to a part program after the current line.

Axes, Axis

Linear or rotary device driven by a servo motor. Turning machines usually have 2 or 4 axes, while milling machines can have up to 7 axes.


Counter-clockwise refers to the direction of rotation of the spindle or tool magazine.


Clockwise refers to the direction of rotation of the spindle or tool magazine.


A mechanism that holds the part in some machines, usually on a lathe.


A mechanism that holds the part in some machines, usually on a mill.


Controls that govern the individual parts of the machine tool including: spindle, coolant, conveyor belt, chuck or clamp, and tool.

Chip Conveyor

The belt that runs at the bottom of the machine tool to carry away the chips.


The liquid that is used to cool the part and provide lubrication to the cutting tools during the machining operation. Coolant flow can be operated manually or controlled by the part program.


The act of running a part program on a machine tool.

Cycle Start

The command to begin a cycle.


The incremental distance of a jog movement. The delta distance is determined using the SetDelta option, or one of the five standard selections, in the Jog menu.

Emergency Stop

This button instantaneously disables the axes and the spindle. Every machine tool is required, by law, to have at least one Emergency Stop button.

End of Block Stop

When this is turned on, the machine tool will enter a stop at the end of every block (line) of part program. Also known as Single Block.


See End of Block Stop.

External Chucking

A form of workholding where the part is clamped from the outside (pushing inwards).


Feedhold stops axes motion until the operator presses the Cycle Start button to resume program execution.

Feed Rate

The rate at which the tools move in relation to the part. It is programmed in inches per minute (ipm) or millimeters per minute (mmpm), or inches per revolution (ipr) or millimeters per revolution (mmpr).


Feet per Minute. Unit of measurement indicating the speed of the tool on the part.


See Feedhold.


A designated machine specific position where the axes are normally located when the machine tool is not in a cycle operation. It is the syncing location.


The part of the tool that comes in contact with the part being machined. When an insert wears or breaks, it can be easily replaced. Also, an insert can be a replaceable machining surface on some tools.

Internal Chucking

A form of workholding where the chuck pushes outwards. This is used when the part is being held from an inside diameter.


Inches per Minute. Unit of measurement indicating the speed of the tool along its cutting path. For example: feed rate.


Inches per Revolution. It is a unit of measurement indicating the speed of the tool along its cutting path.


A method of manually moving an axis without writing a part program.


This option allows you to type in the Absolute Position where you want an axis to move to. This command is found on the Jog menu.

Jog Home

Instructs the machine tool to move the axes to their Home position.

Jog Mode

The Control Mode where you can manually operate individual functions of the machine tool, including the jog movement, axis jogging, manually operating the spindle, and changing tools.

Jump Tapping

Jump will move the part program up or down three pages. The direction is determined by which direction the part program was last scrolled.

Machine Zero

The point where all machine coordinates are measured from. Machine zero is established when the operator completes a syncing operation on all axes.


There are two Modes in OpenCNC: Jog and Run. Jog mode is for manual operation of the machine tool. Run mode is for automatic operation of the machine tool.


An offset is the difference between the theoretical and actual length and position of a tool. An offset accounts for any variations in the tool.

Operator Control Window

The Main Window displays and controls some of the important features of the operation of the machine tool. It contains the Component, Override, and Running Controls.

Override Controls

These controls allow you to manually adjust the feed rate, spindle speed, rapid rate, and jog rate. The adjustments are defined as a percent of the programmed value.

OverTravel Limit Switch

A switch that trips before an axis moves outside its allowable limits. Once tripped, the machine tool automatically enters an Emergency Stop situation and needs to be resynchronized.

Rapid or Rapid Transverse

Movement that occurs at the machine's maximum velocity.

Run Mode

Mode that allows the operator to execute a part program.


The servos control the motors that power the axes, the tool changer, and the spindle.


This option allows you to reset the number of the tool that is in the transfer car. This is only available on some machines.


This option allows you to reset the number of the tool that is currently in the spindle. This is only available on some machines, usually a mill that has a tool changer.


This Jog menu option allows you to type in a specific incremental distance that you wish to jog a particular axis.

SetTurOffset (some lathes only)

The Turret Offset must be set before running a part. It is the difference between the z-axis' physical home position and the theoretical home position assigned to the z-axis in the part program.

Single Block

See End of Block Stop.


A touch screen control bar that allows you to continuously jog an axis while having full control of its speed and direction.

Slide Bar

A touch screen control bar that allows you to continuously change an input by an amount that it is determined by how far you drag your finger and how long you keep it in contact with the touch-screen monitor.


The part of the machine tool that rotates during operation. On a mill it holds the tool. On a lathe it holds the workpiece.

Spindle Speed

The rotational speed of the spindle programmed in revolutions per minute (rpm).


A command to tell OpenCNC to cycle a part program, or to make a jog move.


A group of commands within a menu from which you can select the appropriate option.


A procedure that coordinates the control with the actual position of the axes by moving each axis to its home position. It is necessary to do this when first starting the machine tool.


This is the recommended way of using the touch-screen monitor. Lightly touch a fingertip to the screen and quickly remove it. No pressure is needed, and you do not need to hold your finger there for any length of time.

Tool Changer

Most machines have a tool changer so that different machining functions can be performed automatically on one part. The tools are automatically changed, as specified in the part program.

Transfer Arm (only on some machines)

Part of a tool changer that moves the tool from the transfer car to the spindle.

Transfer Car (only on some machines)

Part of some tool changers that moves the tool between the transfer arm and the drum.


Part of the tool changer on a lathe. It holds the tools and rotates to ensure that the correct tool is lined up with the part.

User Interface

The user interface is how you interact with the control.


A window is an organizational unit of OpenCNC that contains information and buttons to run the control. Windows can be moved, opened, and closed.

Zero Reference Switch

Limit switch that helps the control locate the proper machine zero positions during a syncing operation.