Installing the soundboard rib in the rib crowning jig.  The fixture pictured here is used in connection with the jointer to put a curvature on the ribs. This is to help us maintain the soundboard arch or crown. The center of the rib is drawn upward into the fixtures curve with a clamp, exposing the ends of the ribs to the jointer blade first.  When the bottom edge of the rib has been planed perfectly flat, we remove the clamp and the rib returns to its original (unbent) state.  The edge of the rib that was planed flat, now has the proper curvature on it.