Abstract: A positioner for moving an article along three mutually perpendicular axes includes a first slide coupled to a second slide by a first sliding joint, a third slide coupled to the second slide by a second sliding joint, and a base plate coupled to the third slide by a third sliding joint. The three sliding joints are mutually perpendicular. A first rack and pinion mechanism moves the first slide relative the second slide, a second rack and pinion mechanism moves the third slide relative to the base plate, and a carriage engaging a threaded shaft moves the second slide relative to the third slide. The pinion gears are mounted on shafts parallel to the threaded shaft and the three shafts extend from opposite sides of the positioner. A knob is attached to each end of the shafts for rotating the shafts to operate the positioner. The sliding joints are preferably dovetail joints, each of which includes a shim for adjusting the friction of the joint.