Lay the shelf on two sawhorses, with the finished side facing down. Clamp the board into position using hand clamps.
Measure the shelf to the desired length and mark it with a pencil. Use a straightedge, such as a ruler, to get a plumb line across the board.
Cut the board with a circular saw and a plywood blade. Always cut away from the body and wear gloves, a dust mask and goggles.
Brush the sawdust off the edge using a tack cloth.
Unroll self-adhesive veneer edging along the cut edge so it completely covers the wood inside.
Iron the edging using a clothes iron on low heat. Do not use a steam setting. The adhesive will adhere to the shelf.
Trim the edging using a file with a sharp edge. Cut all the edges so they are smooth and have an invisible 90-degree corner as they would if you hadn't touched the shelf.
Sand the edges smooth using 120-grit sandpaper. Wipe with a tack cloth.