Abstract : This paper introduces the application of Siemens PLC in the retrofitting of a C650 conventional lathe. The software and hardware design of the electrical control of the C650 lathe is presented. This system can be used for both the development of new lathes and the CNC retrofitting of lathes. Keywords : PLC; ladder diagram; lathe 1 Introduction Ordinary lathes are widely used metal cutting tools. Currently, ordinary lathes controlled by traditional relays are still widely used in small and medium-sized enterprises. Due to the complex wiring of relay systems, it is difficult to diagnose and troubleshoot faults, and there are inherent defects. Since it uses wiring to form various logics to achieve control, it requires a large number of mechanical contacts, so the reliability is not high. When the production process is changed, a large number of hardware wirings need to be changed, or even the system needs to be redesigned, which consumes a lot of manpower and resources and takes a lot of time [1]. As a result, these enterprises have low productivity and poor efficiency, and in turn, these enterprises do not have enough funds to purchase new CNC lathes. Therefore, the urgent task is to carry out technical transformation of these ordinary lathes in order to improve the equipment utilization rate of enterprises and improve the quality and output of products. Since programmable controllers (PLCs) have the following advantages: ① universality and strong adaptability; ② perfect fault self-diagnosis capability and convenient maintenance; ③ high reliability and strong flexibility, and the price of small PLCs is currently very cheap. Therefore, they play an extremely important role in the transformation of control circuits of ordinary lathes. This article takes C650 Taking a lathe control system as an example, this paper details the design process of upgrading a traditional control system using a PLC. (Lathe Electrical Control System Design Based on PLC.pdf)