Set the fence on the table saw 2 7/16 inches away from the blade. Position the blade 1/8-inch above the table. Run both 9-inch boards across the blade so you end up with a 1/8-by-1/8-inch groove down the center of the board.
Position the 9-inch boards on edge, parallel and 15 ¼ inches apart with the grooves facing each other. Set the 17 ¼-inch board perpendicularly against the ends of the 9-inch boards so the corners are flush. Screw through the 17 ¼-inch board and into the ends of the 9-inch boards. Use four screws for this task.
Lay your 10-by-17 ¼-inch plywood on top of the three boards so the edges are flush. Screw through the plywood and into the 9-inch boards. Use four screws for this task.
Turn the plywood and three boards over so the boards are on top of the plywood. Set your 7-by-17 ¼-inch plywood on top of the boards so its sides are flush with the 9-inch boards and so it's 17 ¼-inch edge is flush with the 17 ¼-inch board. Screw the plywood to the 9-inch boards using four screws.
Slide the last sheet of plywood into the grooves cut into the 9-inch board. This piece of plywood will act as a divider in your paper rack.