Mirror-surface machining is a very important technology in the manufacturing of precision parts, especially optical parts. At the present time these are parts produced by multi-processes, i.e. grinding and polishing, which are inefficient. In this study, ultrasonic vibration cutting as a substitute for such processes in the precision machining of optical plastics (CR-39) which have been used for optical lenses is suggested and experimented upon. To analyze the characteristics of surfaces machined by ultrasonic vibration cutting in the ductile mode, wavelength spectrum analysis is carried out and the micro-structure is compared with that of conventional cutting. As a result, in micro cutting by ultrasonic vibration, it was confirmed that surfaces of ductile cutting are obtained, for depths of cut of less than 2.7 mu m. (C) 1997 Elsevier Science S.A.