Lay the 20-inch plywood flat and horizontal. Find the 10-inch center along the top 20-inch edge and draw a dash at this measurement. Use your tape measure and square to draw a 7 ½-inch line down from the edge and ¼-inch to the right of the dash. Draw another 7 ½-inch line ¼-inch to the left of the dash. The lines should be perpendicular to the 20-inch edge and ½ inch apart. Repeat this process on the other 20-inch plywood.
Draw a line to the connect the ends of the 7 ½-inch lines on each 20-inch sheet of plywood. Drill a 1/2-inch hole at the 1/4-inch center of these lines. Cut along 7 ½-inch lines with your table saw until you reach the ½-inch holes. You should have a 1/2-inch wood slot extending towards the 7 ½-inch center of each 20-inch sheet of plywood.
Lay your 14-inch plywood flat and vertical. Draw two pairs of 7 ½-inch lines that are perpendicular to the top 14-inch edge of the plywood. There should be a pair of lines along each 15-inch edge with each pair 1 inch away from the each 15-inch edge. Draw a line at the end of each pair of lines to connect them and drill a ¼-inch hole just as you did in the previous steps. Cut along these lines with your table saw just as you did in the previous steps so you have two ½-inch-wide grooves on this sheet of plywood.
Position the 20-inch plywood pieces on their 15-inch edges so they are parallel and 13 inches apart. The 7 ½-inch grooves should be aligned. Match the grooves on the 14-inch plywood with the other two grooves and slide the three sheets of plywood together.
Place recycling bins in the two spaces provided.