Nowadays, CNC machining plays a leading role in the manufacturing industry, thus affecting social development. However, when the CNC lathe fails, the operator should stop the operation of the machine tool, keep the scene, and should not cut off the power supply of the machine tool unless there is a serious electrical failure of the system. The maintenance personnel will go to the scene to analyze the running state of the machine tool at that time and confirm the fault. In the process of fault detection, the self-diagnosis function of the CNC system should be fully utilized, such as system startup diagnosis, operation diagnosis, and PLC monitoring function. At the same time, the following principles should also be mastered in the process of detecting faults:   

(1) External first and then internal. The maintenance of CNC machine tools requires maintenance personnel to master the principle of first external and then internal, that is, when the CNC machine tool fails, the maintenance personnel should first use the methods of looking, listening, and smelling to check one by one from the outside to the inside.

(2) Mechanical first and then electrical. In the maintenance of CNC lathes, firstly check whether the mechanical part is normal, whether the travel switch is flexible, whether the pneumatic and hydraulic parts are normal, etc. Before troubleshooting, first pay attention to eliminating mechanical faults.

(3) First static and then moving. The maintenance personnel themselves should be quiet first and then move, not blindly. They should first ask the machine tool operator about the process and status of the failure, read the machine manual, drawing data, and analyze it before they can find and deal with the failure.

(4) Public use first and then dedicated. Only by resolving the main contradiction affecting a large area first, can the partial and secondary contradictions be solved easily.

(5) Simple and then complex. Solve easy problems first, and then solve more difficult problems. Often in the process of solving simple faults, difficult problems can also become easy, or be inspired when troubleshooting simple faults, and have a better understanding of complex faults. Clarity, and thus a solution.

(6) General first and then special. When troubleshooting a fault, first consider the common possible causes, and then analyze the special causes that rarely occur.