Ev-technologyHow-ToBeginner · 3 min read

G Code for Turning Radius: Syntax, Example, and Tips

In CNC turning, the radius of a curve is controlled using G02 or G03 commands for clockwise or counterclockwise arcs, respectively. The radius is specified with the R parameter, which defines the arc's radius directly in the program.

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Syntax

The basic syntax to program a turning radius in G code uses G02 or G03 for circular interpolation. The R parameter sets the radius of the arc.

G02: Clockwise arc movement
G03: Counterclockwise arc movement
X, Z: Target coordinates for the arc end point
R: Radius of the arc

Example syntax: G02 X... Z... R...

gcode

G02 X20 Z-10 R5

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Example

This example shows a clockwise arc with a radius of 5 units from the current tool position to the point X20 Z-10.

gcode

N10 G00 X10 Z0      ; Rapid move to start point
N20 G01 Z-5 F0.1    ; Linear move to start arc
N30 G02 X20 Z-10 R5 ; Clockwise arc with radius 5
N40 G00 X50 Z0      ; Rapid move away

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Common Pitfalls

Common mistakes when programming turning radius include:

Using R with the wrong sign or value, causing the arc to move in an unexpected direction.
Confusing G02 and G03, which changes the arc direction.
Not setting the correct start point before the arc command, leading to incorrect tool paths.
Forcing arcs with a radius too small for the machine or tool, causing errors.

Always verify the arc direction and radius with a dry run or simulation.

gcode

N30 G03 X20 Z-10 R5  ; Wrong: counterclockwise instead of clockwise
N30 G02 X20 Z-10 R-5 ; Wrong: negative radius may cause error
N30 G02 X20 Z-10 R5  ; Correct: clockwise arc with positive radius

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Quick Reference

Command	Description	Parameter
G02	Clockwise arc movement	X, Z, R
G03	Counterclockwise arc movement	X, Z, R
R	Radius of the arc	Positive number
X	End point X coordinate	Coordinate value
Z	End point Z coordinate	Coordinate value

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Key Takeaways

Use G02 for clockwise and G03 for counterclockwise arcs to control turning radius.

Specify the radius directly with the R parameter in the arc command.

Ensure the start point is correctly set before programming the arc.

Avoid negative or zero radius values to prevent errors.

Simulate or dry run your program to verify arc direction and radius.