A hair cutting apparatus, including a chassis to support a motor to drive a cutting blade, the apparatus comprising a rotary ring, including an inner circumferential surface, rotatably mounted on said chassis, a threaded screw, constrained within said chassis against non-rotational movement, having a head including an outer circumferential surface to engage with the inner circumferential surface of the rotary ring and a shaft including threads, the threaded screw rotating in response to the rotation of the rotary ring, a longitudinal positioner, having a socket including threads to engage with said threads of the threaded screw, to move in a longitudinal direction relative to the cutting blade in accordance with the rotation of the threaded screw, and a hair engagement comb coupled with said longitudinal positioner to position hair to be cut by the cutting blade.