An assembly cell for accurate placement of stringer clips in a channel of a stringer for a compound contour section of an airplane fuselage, and for holding the clips at a predetermined orientation while drilling holes for fastening the clips in the stringers includes a fixture having locating surfaces for holding the stringer in a configuration that is the same as the configuration it will have when installed at its designated position in the airplane. The fixture has headers adjustable to conform to the shape of the airplane in which the stringers will be installed, The headers have clamps for securing the stringers against accurately machined reference surfaces on the headers. An end effector is held by a machine tool in the assembly cell for gripping a stringer clip and inserting it into the stringer channel. The end effector has spreader bars for insertion in the stringer channel operable to spread sidewalls of the stringer and widen the channel to facilitate insertion of the stringer clip, and has clamp bars positionable on opposide sides of the stringer and operable to close on the stringer to squeeze the stringer sidewalls on the stringer clip after insertion in the channel. Opposed drills on the end effector have right angle drives holding drill bits for simultaneously match drilling holes through the sidewalls and through the stringer clip. The end effector machine tool operates as a positioning mechanism for accurately for positioning the drills at each stringer clip location along the stringer clip to positions corresponding to the contour of the fuselage at each of the locations under control of a CNC machine controller.