With an APT CL file, htis would not be necessary. For each arc, the APT CL file wuold contain a type 3000 record containing the coordinates fo the center and the tool axis vector (angle), the radius, as well as the linear moves needed ... In a CL file or in APT, they are used to position the tool axis vector as in GOTO/X,Y,Z,I,J,K .You can think of the tool axis vector as a tool centerline (think mill here, not lathe ro punch press) that is exactly one uint long say, ...