An end effector (30) adap ttachment to and accurate positioning by a robot is provided for positioning a channel-shaped workpiece (10) at a desired position and drilling an accurately located positioning hole in the work piece, even if the workpiece is curved or has a compound contour. The end effector (30) includes a conventional speeder assembly (68) with a taper that can be grasped by the robot and rotated for transfer of torque to the speeder assembly. A flange base (54) is attached to the speeder assembly (68) and has a central opening to accommodate a drill bit (67). A housing assembly (50) is slidably mounted around the flange base (54) through a linear bearing (109). An index shaft (32) is slidably mounted partially within the housing assembly (50) through a second linear bearing (110). A collet (36) is concentrically mounted slidably about the index shaft (32). The collet (36) is adapted to expand radially when it is forced over a wider portion (34) of the index shaft (32). The radial expansion of the collet (36) provides the necessary force to position the channel-shaped workpiece (10).