Abstract: A transfer arm mechanism including a base assembly, a pivoting arm extending generally upwardly from the base assembly, a wafer support paddle, and mechanisms for pivoting the arm back and forth while maintaining the wafer support paddle in a horizontal plane. A base assembly includes a rotatable plate which can rotate the mechanism through 360.degree., and a support plate which can be moved up and down along guide posts attached to the rotatable plate. The mechanism for moving the wafer paddle along a horizontal plane includes a cam member attached to the support plate, and a cam follower which rolls along an upper surface of the cam member to compensate for the pivoting action of the arm assembly. A mechanism is also provided to prevent the wafer paddle from tipping which includes a drive chain extending between a gear which is rotationally fixed with respect to the support plate and a gear which is attached to a pivot pin supporting the wafer paddle.