A numerical control unit and associated method are provided for controlling a machine tool having linear and rotating axes. The control unit is adapted to machine the workpiece at an instructed feedrate, whereby it is first determined whether the machining mode is in a purely linear interpolation mode (G1). The control unit is also adapted to determine, if in the linear interpolation mode, whether a move command is for the rotating axis alone, this being the case, determining a new radial distance between the tool starting position and the center of the rotating axis. With these determinations, the instructed feedrate is corrected to become a feedrate equal to the actual relative speed of the tool with respect to the workpiece.