Adjust the miter saw to cut at a 45-degree angle by sliding the miter saw table and tightening the handle once it is aligned with the 45-degree mark.
Cut a 45-degree angle on each end of the 1-by-6-by-8-inch and 1-by-8-by-24-inch boards using the miter saw. Make the cuts on the same side of each board so that the long points on the ends are on the same side and the boards fit together to form a 6-by-24-inch rectangular box.
Fit the 1-by-6-by-8-inch and 1-by-8-by-24-inch boards together on a work surface to form a 6-by-24-inch rectangular box assembly. The mitered ends should fit together like a picture frame.
Drive two evenly spaced pan head wood screws through each corner joint of the rectangular box assembly with a screw gun.
Center the 1-by-6-by-24-inch board over the rectangular box assembly so that the edges are aligned with the edges of the assembly. Hammer finish nails through the board into the edges of the assembly every 2 inches.