How to Build Shelf Bracing

Measure and note the depth of the shelf. Multiply that dimension by .75 to calculate the length of the legs of the brace.

Set the chop saw to make 90-degree cuts. Measure and mark the 1-by-4-inch plank to the calculated length of the legs. Lay the marked plank on the saw table with its four-inch surface horizontal. Hold the plank firmly against the guide fence. Trim the plank on the cutting line. Measure, mark and cut another leg to the same length.

Set the chop saw to make 45-degree cuts. Place a 1-by-4-inch plank on the saw table with its four-inch surfaces vertical. Hold the plank firmly against the guide fence. Trim one end of the plank to 45 degrees. Measure and mark the long side of the plank to the length of the legs of the shelf bracket, minus one inch. Trim the plank on the mark so the cuts are divergent, not parallel.

Lay one leg of the bracket on a flat surface with its four-inch surfaces horizontal. Apply a bead of wood glue to the cut end that is closest to work surface. Position the other leg against the glued end of the leg resting on the work surface to make a 90-degree butt joint. Place a brick or other heavy object on each end of the horizontal plank to hold the joined planks together as the wood glue dries.

Apply wood glue to each end of the diagonal brace. Position the brace between the legs of the shelf bracket to form mitered 45-degree joints between the legs and the diagonal brace. Wrap one or two rubber bands around the bracket, holding the vertical leg and the diagonal brace together. Allow the glue to dry without disturbing the bracket for at least four hours.

Drill two evenly spaced pilot holes through the butt joint that holds the legs together at 90 degrees. Screw the legs together using drywall screws. Drill pilot holes through the backs of the legs into the ends of the diagonal brace. Attach the diagonal brace to the legs by screwing them together from the horizontal and vertical legs of the shelf bracket into the diagonal brace.