Cut your 2x4’s in the shape and dimensions indicated below. To begin, draw out the cut lines as you see them here, go slow, and be accurate. You will have the most success cutting this, with either a circular saw or jig saw. A jig saw can cut right along the lines you draw, whereas with a circular saw, you will need to stop at each change of direction and angle, and carve out the triangular piece you began with, before moving on in another direction. You want to be sure both legs match and that the bottom of the legs, and the 3” vertical center (where the seat will connect), line up as perfectly as possible. To ensure matching dimensions and angles, clamp the legs together after you cut them out, and sand the matching faces of both at the same time for all 4 sides. Once they are matching and sanded, connect them with the rail as indicated below. It will sit at the bottom of the 3” vertical space on the legs.. You can sand and finish this section or wait until you attach it to the chair front, but be sure to finish it prior to attaching the seat with it’s upholstery.