G Code for Milling Circle: Syntax and Example

To mill a circle in G code, use G02 for clockwise or G03 for counterclockwise arcs, specifying the circle's center with I and J offsets relative to the start point. The command moves the tool along a circular path defined by these parameters.

Syntax

The basic G code syntax for milling a circle arc is:

• G02 - Clockwise arc movement
• G03 - Counterclockwise arc movement
• X, Y - Coordinates of the arc end point
• I, J - Relative offsets from the start point to the arc center on X and Y axes
• F - Feed rate (speed of the tool)

This command moves the tool from its current position to the specified X,Y point along a circular path defined by the center offsets I,J.

gcode

G02 X10 Y0 I5 J0 F100

Example

This example mills a full clockwise circle with a radius of 5 units, starting at X5 Y0, moving around the center at the origin (0,0).

gcode

G90 ; Absolute positioning
G00 X5 Y0 ; Move to start point on circle edge
G01 Z-1 F50 ; Lower tool to cutting depth
G02 X5 Y0 I-5 J0 F100 ; Mill full clockwise circle
G00 Z5 ; Raise tool after cut

Output

Tool moves to X5 Y0, lowers to Z-1, mills a full clockwise circle around origin, then raises.

Common Pitfalls

Common mistakes when milling circles with G code include:

• Using I and J as absolute coordinates instead of relative offsets.
• Forgetting to set the correct starting point on the circle edge before the arc command.
• Mixing up G02 (clockwise) and G03 (counterclockwise) causing unexpected tool paths.
• Not specifying feed rate F, which can cause the machine to use a default speed that may be too fast or slow.

Wrong example:

G02 X10 Y0 I10 J0 F100 ; Incorrect I value (should be relative)

Corrected example:

G02 X10 Y0 I5 J0 F100

Quick Reference

Command	Description
G02	Clockwise arc movement
G03	Counterclockwise arc movement
X, Y	Arc end point coordinates
I, J	Relative center offsets from start point
F	Feed rate (speed)

Key Takeaways

Use G02 for clockwise and G03 for counterclockwise circular milling.

Specify arc center with I and J as relative offsets from the start point.

Always set the tool start position on the circle edge before milling the arc.

Include feed rate F to control cutting speed safely.

Double-check direction and offsets to avoid unexpected tool paths.