G2 & G3 - Arc Movement Commands
Description
G2 and G3 commands create circular arc movements in the selected work plane. G2 creates clockwise arcs, while G3 creates counter-clockwise arcs. These commands are essential for creating smooth curved paths in CNC machining and other motion control applications.
Arc movements interpolate between the current position and a specified endpoint along a circular path. The arc is defined either by its center point (using I, J, K offsets) or by its radius (using the R parameter).
Syntax
Parameters
Parameter | Description | Example |
---|---|---|
X, Y, Z | Target endpoint coordinates for the arc | X10 Y20 Z5 |
I, J, K | Center point offset from current position (I=X offset, J=Y offset, K=Z offset). Always specified relative to the start point. | I5 J0 |
R | Arc radius (alternative to I, J, K). Positive for arcs ≤180°, negative for arcs >180° | R10.5 |
F | Feedrate for the arc movement (modal feedrate shared with other commands) | F1000 |
Feedrate Behavior
Important: Shared Feedrate
The feedrate (F parameter) is shared between G1, G2, and G3 commands. Setting the F parameter in any of these commands will affect the feedrate of all future G1, G2, and G3 movements until a new feedrate is specified. This allows for efficient programming where the feedrate only needs to be set once for a series of movements.
Examples
Basic Clockwise Arc (G2)
Counter-Clockwise Arc with Radius (G3)
Shared Feedrate Example
Complete Circle
Working Planes
Arc movements operate in the currently selected working plane:
- G17 (XY Plane): I and J offsets define the arc center, Z moves linearly
- G18 (XZ Plane): I and K offsets define the arc center, Y moves linearly
- G19 (YZ Plane): J and K offsets define the arc center, X moves linearly
Note: The default working plane is XY (G17). Use plane selection commands before arc movements to change the working plane.