In CNC milling, precise control over the toolpath is essential for creating complex geometries. One of the capabilities of CNC machines is the ability to cut arcs and circles using G-code commands. The G2 and G3 commands are specifically used for this purpose, allowing for the creation of multiple arc segments in a single program.

Usage Format

The G2 and G3 commands follow this general format:

• G2 for clockwise arc movement
• G3 for counterclockwise arc movement
• I and J are the incremental distance from the starting point to the center of the arc along the X and Y axes, respectively.

The syntax is as follows:

G2/G3 X_ Y_ I_ J_ (other optional parameters)

Explanation

• G2 moves the tool in a clockwise direction to create an arc segment.
• G3 moves the tool in a counterclockwise direction to create an arc segment.
• I specifies the distance along the X-axis from the starting point to the center of the arc.
• J specifies the distance along the Y-axis from the starting point to the center of the arc.

These commands are used in conjunction with coordinates that define the endpoint of the arc.

Example

Here’s a simple text diagram and explanation of a program that uses G2 and G3 commands to mill a circular pocket:

%
O1000
T1 M06 (Tool change to tool 1)
G17 G21 G40 G49 G80 G90 (Setup commands)
M03 S1200 (Spindle on at 1200 RPM)
G00 X0 Y0 (Rapid move to starting point)
G01 Z-5 F100 (Linear move to depth)
G02 X20 Y0 I10 J0 F200 (Clockwise arc to point X20, Y0)
G03 X0 Y20 I0 J10 (Counterclockwise arc to point X0, Y20)
G02 X-20 Y0 I-10 J0 (Clockwise arc to point X-20, Y0)
G03 X0 Y-20 I0 J-10 (Counterclockwise arc to point X0, Y-20)
G01 Z5 F100 (Linear move to retract tool)
M05 (Spindle stop)
G00 X0 Y0 (Rapid move to starting point)
M30 (Program end)
%

This program would create a circular pocket with a series of arc movements. The tool would start at the center, plunge to the desired depth, and then proceed to mill the pocket using a combination of G2 and G3 commands with the appropriate I and J values to define the arc’s radius and direction.