Copyright Goodheart-Willcox Co., Inc. 192 CNC Manufacturing Technology 9.6.1 G02 and G03 Radial Movements The G02 and G03 codes are the simplest methods to program arcs. The term arc refers to a circular shape less than 360°. At 360°, the arc becomes a circle by definition, not an arc. G0, G1, G02, and G03 are all modal commands, meaning once they are turned on, they stay on until they are turned off. Just like a light switch, if you turn on a G0, you will continue in rapid movements until an alternate movement is commanded, or until the modal command is turned off. The difference between G02 and G03 is simply which direction the cutter is headed. G02 will take the tool in a clockwise direction, while G03 takes the tool in a counterclockwise direction. This is true in both lathe and mill programming. Visualize the desired tool direction as it enters and exits the arc to select the appropriate code. See Figure 9-12 for a modified version of the part from the previous example, Figure 9-8, with an arc added. To program this arc, look at the following code from the origin or WCS, to Point 1, the arc command, and then out to Point 3: G1 X0. Y0. Origin Y2. Point 1 G02 X1. Y1. R1. Arc to Point 2 G01 X5.5 Move to Point 3. G1 turns off arc for a straight line. This method can be used for all arcs less than 180°. For an arc that is more than 180° but less than 360°, things become more complicated. As shown in Figure 9-13, there are two mathematical possibilities for this arc. The 90° arc has the same start and endpoint as the 270° arc, so the control cannot differentiate between the two arcs. By default, the control will do a less than 180° arc. So how can the programmer create a path for a 270° arc? Simply make the R value in the program a negative (−) number. G02 X1. Y1. R−1. Arc to Point 2 with a 270° arc As already stated, the G02 and G03 codes can only be used with an arc less than 360°. So, is there a simple way to program a full circle using this technique? Yes—break the circle in half and create two 180° arcs on two separate lines of code, as shown in Figure 9-14. Goodheart-Willcox Publisher Figure 9-12. A part toolpath that will require an arc command of G02. 2 1 3 Goodheart-Willcox Publisher Figure 9-13. There are two possible arcs with the same radius and endpoints. 1 2