Copyright Goodheart-Willcox Co., Inc. Chapter 9 CNC Mill Programming 195 the X direction from the start. The “J” would be used if the center was in the Y-axis direction from the start. 9.6.3 Programming Angles Typically, cutting angles requires moving along two axes simultaneously. This is typically X and Y, but can be performed in X and Z or Y and Z directions. An example of this method was presented earlier in the sam- ple program that created a 1/2″ by 90° angle for the part in Figure 9-7. This is all completed with a G1 movement, and no special code is required. X5.5 X6.0 Y2.5 X and Y on same line create angle Y0. Many prints will require knowledge of trigonometry to calculate the start and endpoints needed to create a program. Consider the following example: There appears to be no coordinate for Point 2 in the X axis, Figure 9-17A. This omission requires the right triangle calculations, as explained in Chapter 4. There is a triangle highlighted in Figure 9-17B with enough measurements for the programmer to calculate Point 2. 9.7 Pocketing Pocket milling is a fairly common machining operation on CNC machines. A pocket is a term for machining inside a closed area or boundary. The inside of a pocket can include islands or internal components that are not meant to be machined, and the walls or bottom of the pocket can be flat or tapered. A typical example of a pocketed part appears in Figure 9-18. 9.7.1 Cutter Entry In the contouring example, the cutter entered and exited the part from out- side its boundaries. Obviously, the same strategy will not work for a pocket, so cutter entry is a concern that must be considered in the program. There are three strategies that can be deployed for entering the cutter safely. A Goodheart-Willcox Publisher Figure 9-17. A—A print might require some additional calculations to plot toolpath. B—Part shows the resultant right triangle and point coordinates. B Goodheart-Willcox Publisher Figure 9-18. A typical part requiring a pocket-cutting cycle.