The flag box has always been a way for people to remember family members who served in the military or those who died on the battlefield. The box always holds the flag that drapes a casket and is then presented to a family by members of the military, American Legion or Veterans of Foreign Wars at the deceased's funeral already folded as a triangle. You can always buy a triangular box for the flag, but you can also build your own.
Cut the 4 1/4-by-3/4 inch, 6-foot-long board into three pieces: two 20-inch-long pieces and one 26-inch-long piece. Cut each end of the boards at 45-degree angles so each piece will butt up together during assembly. Use a miter saw to make your cuts.
Measure the thickness of the piece of Plexiglas and the hardboard. Cut a groove 1/4 inch from the edge of the 4 1/4-inch board that is thick enough for the Plexiglas to slide into. Make the groove 1/8 inch deep.
Use a router along the edge of each of the three boards, and shape it as desired. This step is optional.
Line up the two 45-degree-angle ends of the sides, and glue them together. Let the wood glue dry.
Cut the Plexiglas to a dimension of 19 5/8 inches on two sides and 25 5/8 inches along the bottom. These dimensions will help compensate for the 3/4 inch that needs to be subtracted for the thickness of the board, but the 1/8 inch that needs to be added for the grooves.
Slide the Plexiglas into place, and attach the bottom piece with wood glue, butting up the 45-degree angles.
Cut the hardboard backing to 20 inches on two sides and 26 inches along the bottom.
Place the folded flag into the box with the stars facing out. Add any military service medals into the box in front of the flag.
Squeeze wood glue along the edges of the box. Press down the hardboard backing.