The cutter compensation commands allow for small adjustments to the tool paths to be made without making any changes to the part program. These adjustments are often made in response to a decrease in end mill diameter caused by wear. Cutter compensation also simplifies the task of programming by allowing the programmer to program the centerline of the tool on the edge of the part. The tool can then be offset the radius of the tool to create a tool path that will produce a part with the desired dimension. The offset distance is stored in a table in the CNC machines controller's memory. Small adjustments to the offset value compensate for wear of the end mill and other conditions. To take advantage of the cutter compensation commands the program must be set up correctly. The G codes associated with cutter compensation are listed below.
Let's examine the example shown below. The tool begins at the "Start" position and moves sequentially to the numbered positions shown in order to mill a rectangular part. The part programmer will offset the tool to the left of the tool path by the radius of the endmill. This swill be accomplished with a G41 D31 call out. G41 sets the cutter compensation to the left and D31 is the memory location in the controller that contains the offset value. The offset value is usually the diameter of the endmill. Note that the start position must be more than 2 diameters of the tool away from the offset path. This distance allows the machine tool time to make the calculations to properly offset the tool. Failure to leave this distance will result in a fatal program error.