Quadruple clamp jig
This jig performs the function of joining a set of 4 lengths together to make either a face assembly or a wall assembly. The jig consists of a single piece of plywood, whose exterior dimensions match the desired frame size, with four screw clamps at the corners to hold the pieces together to form butt joints. I place a small piece of wax paper underneath each joint to prevent the glue squeeze-out from bonding the pieces to the jig. Despite the effectiveness of the jig, it is not fully automatic. Care need be taken to ensure alignment of the joints with the perimeter of the rectangular base, and to ensure the assembly is planar by making sure each side of each joint is pressed down snugly against the plywood surface.