Copyright Goodheart-Willcox Co., Inc. Chapter 9 CNC Mill Programming 205 The G41 was defined with a D1, so the diameter of that tool must be entered in the Geometry column of the Diameter Offset page under tool #1, Figure 9-24. Again, D1 was used with tool #1 to match the diameter number to the tool number, but this is not required. The Wear column is where small adjustments can be made to the offset after the part is machined and measured. Once the part is set up and major adjustments are made, a small adjustment to the wear offset can bring the part dimensions to exacting specifications. These are meant for final, minor adjustments as the part is being manufactured. 9.10 Work Coordinate Offsets In the same way that the machine does not know how “long” the tools are, it also does not know where the part is on the table or fixture until it is defined by the work coordinate system (WCS). A program includes G54–G59 designations, and a specific point on the part is considered to be at X0. and Y0. The programmer must tell the machine where that zero point is, physically, in the work envelope of the machine, Figure 9-25. When a machine is initially started up and zero returned, it travels to its machine home position and stores an X, Y, and Z zero. Now, the pro- grammer must physically move the machine to find the same place on the material as the program zero. This zero point can be a corner, the center, or some existing geometry like a hole or boss. 9.10.1 Finding WCS on Material There are various ways to locate this point, such as an edge finder, an indicator, or a hard post, and each axis position can be found individually Goodheart-Willcox Publisher Figure 9-24. When using cutter compensation, the tool diameter is entered into the Diameter Offset column. PROBING TOOL 1 OFFSET 1 SPINDLE 2 3 4 5 6 7 8 9 10 0 0 0 0 0 0 0 0 4.5680 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. POSITION GEOMETRY WEAR GEOMETRY WEAR COOLANT H(LENGTH) D(DIA) TOOL OFFSET TOOL INFO Goodheart-Willcox Publisher Figure 9-25. The distance from machine home to programmed zero is the work coordinate value. Machine table Machine home Programmed part zero X axis distance Y axis distance