The selection principle of CNC processing method is to ensure the accuracy and roughness of the machined surface. There are many processing methods for obtaining the same degree of accuracy and surface roughness, so in the actual selection, the shape, size and heat treatment requirements of the parts should be taken into consideration. For example, boring, hinges, grinding and other machining methods for IT7 precision holes can meet the requirements of precision, but boring or reaming are generally adopted in the holes on the box, and it is not suitable for grinding. Generally, small size box holes should be reamed, and when the diameter is large, boring should be chosen. Besides, we should also consider the requirements of productivity and economy, as well as the actual production facilities of factories. The economic processing accuracy and surface roughness of commonly used machining methods can be consulted with the relevant process manuals.