Abstract: A method of friction stir welding is provided. The method includes providing a stir tool configured to rotate about and move along a stir tool axis and includes a pin with a pin axial end surface and a pin tapered surface that extends radially outwardly from the pin axial end surface. The method further includes providing the first member with a first member faying surface and defining a normal line that is normal to the first member top surface, is perpendicular to a longitudinal axis, and extends through a reference point. The method further includes providing the second member with a second member faying surface and forming a joint interface between the first and second members. The method further comprises contacting the rotating pin with the second member faying surface, the stir tool axis being disposed at a side tilt angle upon contact.