Device for machining an end of an elementary panel for its subsequent friction stir welding, the elementary panel comprising a metal body defining two opposite faces, the machining device comprising a chassis, at least two guiding members configured to guide a first face of the elementary panel, at least one machining tool mounted on the chassis, the machining tool being positioned between the two guiding members and at least one pressure member mounted on the chassis and configured to exert a pressure on a second face of the elementary panel so as to press the elementary panel against the guiding members along the horizontal reference direction.