Lay two 34-inch boards on their 2-inch edge so they are parallel and the outside edges are 28 inches apart. Screw five 32-inch boards starting from one end of the two parallel boards so they are perpendicular to the two boards. Space them 2 inches apart, and use two screws for each board. There should be 6 inches of uncovered 2-by-4 boards at the opposite end you started from. This is the seat portion of the futon.
Lay the last two 46-inch boards on their 2-inch edge so they are parallel, and the outside edges are 25 inches apart. Attach seven boards in the same manner as you did in the previous step, leaving 6 inches of uncovered 2-by-4 boards at the opposite end you started from. This is the back portion of the futon.
Drill a 3/8-inch hole through the four uncovered 2-by-4 ends measuring 2 ½ inches from the end, and 1 3/4 inches from each side.
Lay the two frames next to each other so the 2-by-4s with the outside edges measuring 28 inches apart can fit over the 2-by-4s with the outside edges measuring 25 inches apart. Line up the holes you drilled and place the bolts through the holes. Be sure there is a washer on each side of the wood. These bolts will function as a hinges for your futon.
Lean the back portion up against a wall for support, and set your futon mattress over the frame, folding 1/3 of the mattress underneath itself for extra seat padding and seat height.