CNC machining method selection principle is to ensure the machining accuracy of the machined surface and surface roughness requirements. Since obtained with an accuracy and surface roughness of the processing methods are generally many, thus the actual selection, in conjunction with the part of the shape, size and heat requirements for full consideration. For example, the use of IT7 level precision hole boring, reaming, grinding and other processing methods can achieve accuracy requirements, but on the general use of the box hole boring or reaming, grinding and should not be used.Generally small size of the box to select reaming holes, when the aperture is larger bore should be selected. Also, consider the actual situation of productivity and economic requirements, as well as factory production equipment. Economic machining accuracy and surface roughness of common processing methods can be found about the process manual.