Place the 3/4-by-13 1/2-by-11 1/2-inch plywood panel with one 13 1/2-by-11 1/2-inch side flat on a work surface. This is the back panel. The 13 1/2-inch edges are the top and bottom edges.
Position one 13 1/2-by-13 1/2-inch panel with the 3/4-by-13 1/2-inch edge flush on the work surface against the top and bottom edges of the back panel. These are the top and bottom panels.
Insert the four 11 1/2-by-12 3/4-inch panels between the top and bottom panels so that they are perpendicular to them and evenly spaced. Place one on the outside edges of the top and bottom panels. These are the sides. Place two evenly spaced in the inside of the sides. These are the dividers. The 3/4-by-12 3/4-inch edges should be flush against the inside faces of the top and bottom panels. The 3/4-by-11 1/2-inch edges should be flush against the inside face of the top panel.
Drive flush trim wood screws through each joint where the parts come together from the outside of the panels. Space the screws evenly approximately every 2 inches using a screw gun.
Fill the screw holes with wood filler using the tip of a putty knife. Allow the filler to dry for 24 hours.
Sand the filler flush with the surface of the wood using fine-grit sandpaper. Be sure to sand with the wood grain.
Wipe the surface of the cube down with a tack cloth to remove any dust and debris. Apply a wood finish to the exposed surfaces of the wine rack. Allow the finish to dry for at least 72 hours before use.