The seat backs attach to the seat bottoms with sections of P3 hinge material. There are three pieces of hinge attached to the seat bottom, and one piece attached to the seat back. That along with the adjustment mechanism at the top gives you a number of choices for the seat position. First up, I cut eight pieces of hinge material 15.5″ long.
The six hinge pieces that attach to the seat bottom need the center two eyelets removed so that the hinge pins can be inserted from the middle.
The holes were laid out and drilled on one of the pieces according to the plans. This was then used as a template to drill the other five pieces of hinge.
The hinges were then clamped to the seat bottoms at the position specified by the plans.
The seat bottoms were then match drilled to the hinges.
The aft hinge overlaps several holes that are used to attach the seat bottoms to the seat ribs. The hinge is back drilled to these holes so that all three pieces can be blind riveted together.
The hinge pieces are then riveted to the seat bottom with AN470AD4-4 rivets (skipping the holes that will also rivet in conjunction with the seat ribs). I’ve seen a few builders use LP4-3 here, but the plans only specify those for attaching the seat bottoms to the seat ribs.
