The beveled working surface of the beveled part cannot be expanded into a flat surface, but in the process, the moment when the working surface is in contact with the circumference of the milling cutter is a straight line. 

It is best to use the 4-axis and 5-axis CNC milling machine to perform the angle processing. In the absence of the above machine tool, the 2.5 coordinate approximation can also be performed on the 3-axis CNC milling machine. Surface Classes (Stereo Classes) Parts whose working faces are spatial surfaces are called surface-like parts. The feature of the part is that the machined surface cannot be unfolded into a plane; the second is that the machined surface and the milling cutter are always in point contact. Such parts generally use a 3-axis CNC milling machine.