Nowadays, rotary friction welding (RFW) is increasingly used because of its outstanding advantages compared to traditional fusion welding methods such as plastic melting temperature below the melting temperature, good mechanical properties and durability of the joint material, high productivity, and being environmentally friendly. Operating parameters are set to suit each type of material, and the operating process is controlled flexibly and easily. Therefore, it is possible to weld a variety of sizes and materials, so rotary friction welding is widely used in the fields of aerospace, automobiles, machinery parts, and automation industry. The purpose of this paper is to study friction welding on lathes instead of specialized welding machines by improving the Yamazaki CT800 universal lathe into a rotary friction welding machine. The improved main mechanisms include the non-rotating chuck mounting mechanism, pressing pressure, rotation speed brake, parameter setting and welding process control. Results of testing rotation speed, vibration, shaft misalignment and weld durability for C45 steel show that the improved equipment meets the set requirements.