Copyright Goodheart-Willcox Co., Inc. 194 CNC Manufacturing Technology distance (−.125), and the second G03 move will go to Z−.25. This creates the following toolpath: G1 X0. Y0. F20. Feed to XY 0 at 20 ipm Z0. G41 D1 X1.5 Cutter comp left to X1.5, still in G1 at Point 1 G03 X-1.5 Z-.125 R3. CCW arc to Point 2, helical to Z-.125 X1.5 Z-.25 R3. Still G03, CCW arc to Point 1, helical to Z-.25 G1 G40 X0. Y0. G1 cancel cutter comp, move to XY 0 9.6.2 I, J, and K Method An alternative process to creating arcs is the I, J, and K method. This works with older machine controllers and is sometimes seen in the creation of circles or in output from CAM systems. I, J, and K are referred to as alter- nate axis addresses, and they are simply another way to designate X, Y, and Z. In this method, position the tool, program a G02 or G03, and move the tool to the arc endpoints. Instead of using an R for arc, use the incremental position from arc start to arc center. See Figure 9-16. Again, if the machine starts at the center and moves to Point 1, and then G03 is used to move to Point 2, the code will look like this: G1 X0. Y0. F20. Feed to XY 0 at 20 ipm Z−.25 Feed down to Z−.25 G41 D1 X1.5 Cutter comp left to X1.5, still in G1 at Point 1 G03 X−1.5 I−1.5 CCW arc to Point 2, I−1.5 is distance from start to arc center, incrementally X1.5 I1.5 CCW arc to Point 1, I1.5 is distance from start to arc center, incrementally G1 G40 X0. Y0. G1 cancel cutter comp, move to XY 0. This method can be useful in creating circles, but it is not necessary on most controls. The “I” was used in this case because the arc center was in Goodheart-Willcox Publisher Figure 9-16. Using the I, J, and K method of arc movement requires the incremental position from arc end to arc center.