Abstract: A new kind of NC system for machining shafts with non-circular cross-section is proposed in this paper. On the basis of a special micro-feed mechanism, which is driven by a simple cam, a new polar coordinate interpolation algorithm, which is based on affine transformation, is presented. By this method, shafts with any non-circular cross-section can be machined. Comparing with other similar systems, it possesses such advantages as:larger cutting force, better flexibility and higher precision et al.