Lay three 20-inch boards flat, parallel and spaced 12 inches apart. Lay the 48-inch board perpendicularly on top of them so one edge is flush with the ends of the 20-inch board and so the ends of the 48-inch board are flush with the edges of the two outside 20-inch boards. Screw through the 48-inch board so three screws enter each 20-inch board. Repeat this step with the last three 20-inch boards and 48-inch board.
Position the two 48-inch boards on end, parallel, so the 20-inch boards are between them and aligned. Position the 48-inch plywood against the edges of the 48-inch board and the ends of the 20-inch boards. The edges of the plywood should be flush to the sides of the 48-inch boards. Screw the plywood to the boards so five screws enter each board.
Set the 24-inch plywood sheets on top of the 20-inch boards so the edges are flush. Screw six screws through each sheet of plywood into the 20-inch boards. Three screws should be used on each board. These are the shelves for your two printers and other printing supplies.
Drill two 1-inch holes through the 48-inch plywood. There should be a hole 2 inches above the bottom and second shelf, with each hole 10-inches away from the 48-inch boards. These holes will provide outlets for your power and printer cords.