Lay your 18-inch board flat. Draw an 18-inch line down the center of the board so it is 2 ½ inches from each 18-inch edge. Draw a line that is perpendicular to the first so it is 9 inches from each end.
Drill a 2-inch hole where the lines intersect, and cut the board in half using your miter saw. Cut on the 5-inch line.
Sand the three pieces of wood with your medium-grade and fine-grade sand paper.
Position the the two 9-inch pieces of wood on their ends with the half-circles facing up. They should be parallel and 15 inches apart. Place the 15-inch board between them so it is flat and flush with the sides of the two 9-inch boards. Screw through the 9-inch boards and into the 15-inch board.
Apply wood stain to the sword display stand and let it dry according to the instructions.
Set your sword on the stand when it is inside its sheath. The sword should rest inside the half-circles that were cut.