Step 2 of 3.
Place the cut 2 x 4′s on the back of the headboard birch pieces as follows. You can temporarily tack the boards in place with a few screws. Any holes through the backside of these 2 x 4s and through the front of the headboard pieces will eventually be covered.
As you can see I didn’t even bother to stain the entire back since it will not show.
Now flip this piece over and secure through the front side with the 1 1/2 inch long screws. Pre-drill holes in the birch plywood to prevent splitting. The screw heads need to be slightly recessed into the birch plywood. Don’t worry about the appearance of all these screws, they will be covered up.
The remaining 5 cut pieces of birch plywood are glued to the front side of the headboard covering up all the screws. Use wood glue and clamps to secure. Do not use clamps directly on pieces, use pieces of scrap wood on top of the glued pieces and then clamp. Let glue dry overnight.
I purchased a fullsize Sealy at Costco in the summer of ‘09. It was labeled as firm. It is actually very comfortable and used in my daughter’s room (who is 7) and also is the guest room bed.