What factors are involved in machining accuracy? The production of manufacturers and mechanical equipment, with the help of machinery, our workload, effect, speed is much faster. Although there are mechanical equipment to help, but the face of the customer on the quality of the product requirements are so high. Nature in the process of high accuracy requirements, such as precision machinery parts processing. When machining parts for precision machines, digital programmed contour systems are widely used on milling machines, including phase systems with a wide range of technological capabilities, which are simple, reliable and inexpensive, in particular, used to control the large-scale three-dimensional surface of precision machinery parts processing. One of the main conditions to ensure the machining quality of precision machine parts is to compile control program correctly. For the Digital Program Control Phase System, the preparation of the control program is carried out by the automatic program preparation system, the quality level of which largely depends on the price of the preparation control program. The other is the processing error caused by the manual control equipment, which includes the accidental error and the systematic error of the process system. The system error plays a major role in the total machining error, and it will cause a series of NC process system error for the whole machining of precision machine parts. For example, the clearance, which is the same as the insensitive belt in the transmission chain of the machine tool, but does not include the clearance of the reverse transmission chain; the amplification factor of the unstable transmission; the phase error in the control tape;. The periodic step instability of sensor feedback is mainly in the form of phase instability.