This paper presents a model of the formation process of surface zones of external cylindrical grinding with traverse feed at a computer numerical control machine (CNC). This article, have investigated modelling features of the grinding process in reverse zones. On the basis of the model of grinding surface formation a detailed step by step calculations of the current values of the actual radial feed and radius dimension in different areas of a treated surface is presented. The model allows maintaining calculations with presence of the initial radial runout of the workpiece for estimated automatic cycle of radial and axial feeds changing and other technological parameters.