In the world of CNC (Computer Numerical Control) machining, programming for multiple arcs can be quite complex. This article focuses on the use of G2 and G3 codes, which are used to create clockwise and counterclockwise arcs, respectively. These codes are pivotal in milling applications where smooth curves and circles are needed.
Usage Format
The G2 and G3 codes follow this general format:
 G2 for a clockwise arc
 G3 for a counterclockwise arc
 I for the distance from the starting point to the center point of the arc along the Xaxis
 J for the distance from the starting point to the center point of the arc along the Yaxis
Explanation
The G2 and G3 codes are modal and remain active until another motion command is given. The I and J parameters are incremental values that define the center of the arc relative to the starting point of the arc. It’s important to note that I and J values can be positive or negative, which will affect the arc’s direction and endpoint.
Example
Let’s consider a simple example with a text diagram to illustrate the use of these codes:
Starting Point

 I
<+>
  J
 V V
 *> End Point
 /
 / G3 Counterclockwise Arc
 /
 /
V
In this diagram, the asterisk (*) represents the center point of the arc. The starting point is at the top, and the end point is to the right. To move from the starting point to the end point using a counterclockwise arc, you would program:
G3 X100 Y50 I20 J25
This command tells the CNC machine to move in a counterclockwise arc to a point 100 units along the Xaxis and 50 units along the Yaxis, with the center of the arc being 20 units to the right and 25 units down from the starting point.