Copyright Goodheart-Willcox Co., Inc. 188 CNC Manufacturing Technology In the print, the origin is shown as the bottom-left corner, indicating that this print is in quadrant 1, or the X+, Y+ quadrant. With that origin as a start- ing point, examine each line of the following program to contour this part: O3283 Program number G20 G17 G40 G80 Default line G91 G28 Z0. Send machine to Z0. home T1 M6 (1/2” End mill) Tool change to tool #1 G0 G90 G54 X−.5 Y0. M3 S5000 Rapid, G54 WCS, go to XY position, spindle on to 5000 rpm G43 H1 Z2. M8 Height offset 1, move to Z2. coolant on G01 Z−.5 F30. Feed to Z−.5 at 30 inches per minute X0. Move to X and Y positions Y3. X5.5 X6.0 Y2.5 X and Y on same line create angle Y0. X0. X−.5 G0 Z1. Rapid to Z1. M9 Coolant off G91 G28 Z0. M5 Incremental mode, home in Z, spindle off G28 Y0. Home in Y M30 Program rewind 9.5.1 Tool Start Position In the preceding program, notice that the starting point of this tool is G90 G54 X−.5 Y0. In the diagram in Figure 9-8, that position is shown relative to the WCS zero, or origin. In a contour toolpath, it is important to start the end mill off the part, take the tool down to the initial Z depth, and then move into the part whenever possible. Driving the tool straight down the edge of a contour will create a mark or defect in the finished contour. Goodheart-Willcox Publisher Figure 9-8. The same sample print showing a possible start position for the end mill.