Abstract: A mechanism for precise translational positioning of a rotatable rod includes a reciprocating piston. A rotary motor is mounted on the piston for establishing rotation about a first axis, and a flexible coupling connects the rotary motor with a rod for precise rotation of the rod about an axis substantially parallel to the first axis. Further, the mechanism includes a pair of roller bearings. These roller bearings are distanced from each other, and each interconnect the rotatable rod with the reciprocating piston to permit rotation of the rod relative to the piston while preventing translation relative thereto. Additionally, a sleeve with a pair of O-rings is mounted to the rod between the pair of roller bearings to create a fluid chamber between the O-rings, the rod, and the piston. A fluid passageway in the rod then allows a vacuum pump to draw a vacuum from the chamber to the distal end of the rod.