A method for machining a helical bore of a stator comprises providing a stator body with a bore. In addition, the method comprises providing a first and a second machining device. The first machining device comprises a milling head coupled to the end of a shaft and a rotary cutter mounted to the milling head for rotation about an axis transverse to the longitudinal axis. The second machining device comprises a whirling head on the end of a shaft and a whirling cutter mounted to the whirling head for rotation about an axis parallel to the longitudinal axis but offset therefrom by a selectively variable degree. Further, the method comprises driving the first machining device through the bore multiple times with the rotary cutter following a helical path. Still further, the method comprises driving the second machining device through the bore with the whirling cutter following the same helical path.