Carpenters in central California use this technique for cutting double bevels on hip or valley rafters fashioned from conventional 2x framing lumber. Set the tongue of the framing square on one end of the rafter as shown and draw two parallel pitch lines (they will be 1-1/2 in. apart). Then adjust the foot of the circular saw to cut a 45° bevel, and make the first cut in the direction indicated in the drawing. The second cut starts from the opposite side of the board. The resulting double bevel allows the carpenter to tuck the rafter between two perpendicular common rafters.
Andrew Kujawa, Santa Cruz, CA