An improved scan and tilt apparatus for an ion implanter wherein a wafer-receiving platen assembly is received on the end member of a multiple axis arm system which is operable to effect scanning motion of the wafer along a straight line which intercepts the wafer tilt axis in any tilt position of the platen assembly. The arm system includes a rail and linear bearing system which interconnects an input member with the end member of the arm system to restrict the scanning motion to a straight line.