Circular interpolation – G2 and G3

Circular interpolation with G2 and G3 explained: clockwise and counterclockwise arcs, programming the center with I/J or the radius with R – with example.

After G0 and G1 for straight movements come G2 and G3: the commands for circular interpolation. With them, the machine cuts or engraves circular paths – arcs and full circles.

G2 – clockwise

The G2 command stands for clockwise circular interpolation (CW). The tool moves from the start point along a defined arc in a clockwise direction to the end point.

G3 – counterclockwise

G3 is the counterpart: counterclockwise circular interpolation (CCW). The arc is programmed with the same parameters, just in the opposite direction of rotation.

Specifying the center or the radius

Besides the end point, the control needs information about the arc geometry for G2 and G3. There are two ways to provide it:

As with G1, the feed rate (F) applies here as well and determines how fast the tool moves along the circular path.

Example

G1 X0 Y20 F200      ; move to the start point of the arc
G2 X20 Y0 I0 J-20   ; 90-degree clockwise arc, center given via I/J
G2 X0 Y-20 R20      ; another 90-degree arc, programmed via radius R

Both arcs run around the same center (0, 0) with a radius of 20 – once programmed via the center coordinates I/J, once via the radius R.

In summary, G2 and G3 extend the capabilities of G0 and G1 to round and curved contours. They are indispensable for machining parts with radii, fillets and bolt-hole circles.