2008) Efficient rough-cut plan for machining an impeller with a 5-axis NC machine, International Journal of Computer Integrated Manufacturing, 21:8,[971][972][973][974][975][976][977][978][979][980][981][982][983] This study presents an efficient, rough-cut path plan for the 5-axis, numerically controlled (NC) machining of an impeller. The hub and blade surfaces of the impeller are customarily machined by a 5-axis NC machine. Much of the machining time of the impeller is, however, consumed in the rough cutting where unnecessary stock materials are removed. Simultaneous, 5-axis, rough machining requires a considerably longer time than 3-axis machining because all the five axes have to be controlled at the same time at almost all cutter location (CL) points. Based on the characteristic curves of a blank and a finished impeller, a rough machining area can be partitioned into several unit machining regions (UMRs) by using the characteristic curves of an impeller and their projection graphs. Then, an UMR is machined by means of the simultaneous, 3-axis control of a 5-axis machine instead of simultaneous, 5-axis control. In each UMR, the rotating and tilting axes of a machine bed are fixed in advance to perform 3-axis machining. Finally, rough-cut CL data is generated based on the 3-axis machining plan at each UMR while avoiding the collision between the tool and impeller blades. An illustrative example is shown for a prototype impeller, and the final tool paths generated by the proposed method are verified by using the cutting simulation function of Vericut 1 . Experimental results show that the proposed rough-cut plan has significantly reduced the machining time when compared to the conventional, 5-axis-control-based, rough machining.