A new kind of numerical control (NC) system for machining shafts with non-circular cross-section is proposed in this paper. It is composed of one X-Z platform, a special micro-feed mechanism driven by a simple cam, and one rotating tool. A new circumferential curve interpolation algorithm based on the cam mechanism is put forward to machine the shafts with any non-circular cross-section, and its efficiency is verified by the simulation. Especially, the larger cutting force can be obtained by use of individual rotating tool. The requirement on response speed is no longer strict. It shows more flexibility on manufacturing.