Write an article based on this "Measure the item that you plan to place in the frame. Buy a piece of 1⁄4 inch (6.4 mm) thick plywood for the backing. Cut the plywood to size, if necessary. Get an 8 ft (2.4 m) board measuring 1 by 4 inches (2.5 by 10.2 cm). Cut the top and bottom pieces from the 1 by 4 in (2.5 by 10.2 cm) board. Subtract 1.5 inches (38 mm) from the length and cut the side pieces. Sand all of the pieces of wood with 180-grit sandpaper."
The artwork or objects that you plan to place inside of the shadow box frame needs to fit inside of it. Use a ruler or a tape measure to find the length and width of the item so you can make a shadow box frame that fits it.  Write down your measurements so you can easily remember them. For example, you could have a painting that measures 18 by 24 inches (46 by 61 cm) that you want to install inside of a shadow box frame. If you’re giving the shadow box as a gift, or you don’t know the dimensions of the artwork, choose a common shadow box measurement such as 10 by 10 inches (25 by 25 cm), 11 by 14 inches (28 by 36 cm), or 12 by 12 inches (30 by 30 cm). Purchase a sheet of plywood in good condition that is as close to your measurements as you can. Look for pre-cut sheets of plywood that fit the dimensions, or purchase a larger sheet that you can cut to size. You can find 1⁄4 inch (6.4 mm) thick plywood at your local hardware store or online. Use a ruler and trace the dimensions of the shadow box frame onto the thinner sheet of plywood that will serve as the backing. Then, use a circular saw to cut along the lines and cut out the plywood so it matches the measurements.  Use a pencil or marker to mark the dimensions on the board. Use the ruler to draw a straight line so you can cut along it with the saw. Buy a length of thicker plywood that you can measure and cut to size to build your shadow box frame. The thicker board will form the top, sides, and bottom of your frame, so cutting them from the same piece of plywood will ensure that they’re uniform and consistent. You can purchase plywood boards at hardware stores, at home improvement stores, and online. Measure the top or bottom of the plywood backing that you cut and then mark the measurements onto the 1 by 4 in (2.5 by 10.2 cm) plywood board. Use the circular saw to cut 2 segments from the board to form the top and bottom pieces of the frame.  You can also use a table saw or a hand saw to cut the board. You will end up with 1 sheet of thinner plywood and 2 lengths of the thicker plywood. Subtract the thickness of the top and bottom boards from the total length of the backing to find the length of your side boards. Then, cut them out of the 1 by 4 in (2.5 by 10.2 cm) plywood. The 2 top pieces will be the same length as the width of the plywood backing of the frame. The 2 sides will be slightly shorter than the length of the backing because of the top and bottom pieces. Use gentle, circular motions to lightly sand all of the pieces of wood to remove splinters and rough patches. Pay extra attention to the edges and the sides that were cut so the boards are even and consistent.  Wipe or blow off any sawdust from the surface of the wood when you’re done sanding. You can use an electric sander as well. Look for sandpaper at hardware stores and online.