Futon sofa beds are supplied in their components. To assemble them, you have to join the back to the seat to form a single, hinged frame. This frame is responsible for turning the futon sofa bed into a futon couch or chair. The frame is also mounted on another frame of support rails held between the arms of the futon. While the design of each futon may differ, the basic assembly requires building the two configurations of support rails and hinged frame and putting these two together.
Lay the component pieces of the futon sofa bed on the ground. Check to see that you have all the components listed on the futon box. Move the two stretchers and the two arms to the same side and the back deck and seat deck to another side.
Slide the ends of the stretchers into the receiving ends on the arms so that bolt holes align. Screw the bolts in loosely with an Allen key. Turn the bolts just far enough to hold together the arms and stretchers.
Slip the ends of the back deck into the mouth of the seat deck. Lock the two pieces in place with pins so that they both formed a hinged frame.
Mount the hinged frame on the support rails formed by the arms and stretchers. Connect the hinged frame to the support rails with bolts and pin. Tighten the bolts on the support rails with the Allen key.
Set the futon mattress on the futon. Flip the back deck flat to form a futon sofa bed.