How to Build Modular Boxes

Modular boxes, sometimes called shadow boxes, satisfy various needs, from a catchall in a child's room to a striking showcase for collectibles. Because they stack, you can easily move or rearrange them. Best of all, you can build seven 12x12x12-inch boxes from a single 4x8-foot sheet of plywood.

You'd think that a sheet of plywood labeled 3/4 inch thick would actually be 3/4 inch thick. However, that's not always the case. Because much of the plywood sold is of Asian origin (even if it's made with North American wood), it may be slightly smaller than its stated thickness. That inconsistency will throw off your measurements for the sides of these boxes, which are sawed to 10-1/2 inches wide to allow for joining to two thicknesses of 3/4-inch plywood at top and bottom. So before cutting, measure the plywood's thickness, then deduct twice that from 12 inches for the width of the box sides.

Painting the birch plywood box and adding the distinctive ash veneer tape to the edges creates a distinctive look. For a bright design option, completely paint the box. Or you can accent the birch plywood with walnut plugs and veneer.

You'll need roughly 4 hours to build seven boxes, plus finishing time. Before you begin, assemble materials and prepare your work area. 

Step 1: Cut Tops and Bottoms

To cut the tops and bottoms of the boxes, set the table saw fence to rip 12 inches wide (or use a portable circular saw and clamped straightedge for a guide).

Editor's Tip: When wood encounters a spinning saw blade, kickback can occur very suddenly. On a table saw, the wood can fly back at you. If you're using a portable circular saw, the saw jumps back at you. Wood pinching the blade is the usual cause of kickback. Avoid pinching by using a splitter in the saw kerf (the gap left by the blade) behind the blade and make sure the material you're cutting is fully supported. Also, stay out of harm's way. At the table saw, don't stand directly in front of the blade. Don't overreach when using a portable circular saw.

Step 2: Rip Wide Lengths

Rip two 12-inch-wide lengths from the 4x8 plywood sheet. Then rip two pieces 10-1/2 inches wide (or to your measurements) from the remaining stock.

Step 3: Support Plywood

To support plywood during crosscutting, attach an auxiliary fence of 3/4-inch stock to the miter gauge with screws. Keep it about 1/8 inch from the fence to avoid binding.

Editor's Tip: To make sure that all the box pieces are square (if they're not, they won't fit together properly), use a framing square to check the auxiliary fence before making a cut. Use some scrap plywood to make a test cut. With the framing square, check the test piece. Adjust the setup if necessary.

Step 4: Crosscut Lengths

Set the table saw blade and auxiliary fence to get a 12-inch-wide cut. Crosscut all the plywood lengths so you have 14 pieces 12x12 inches and 14 pieces 10-1/2x12 inches.

Step 5: Make a Clamping Jig

It's easy to go astray when assembling so many units, so build a clamping jig to help with assembly. Use it to hold the four sides square to each other while gluing and clamping. You can clamp the jig in just one corner, because if one corner is square, the opposite one is also square. To make a clamping jig, first clamp together (don't glue) a box top (B), bottom (B), and two sides (A). Be sure to assemble the pieces correctly. Measure the inside of the clamped box.

Step 6: Create Holes for Clamp Heads

Cut scrap of 3/4-inch plywood to the box's inside dimensions, minus about 1 inch on each side. Bore 1-1/2-inch holes with a spade bit in a drill about 1 inch in from two adjacent edges. These holes will accommodate the clamp heads.

Step 7: Clamp and Adjust

Assemble the top, bottom, and two sides with glue, then clamp the box, using the clamping jig to check for square. Make any needed adjustments before the glue dries.

Step 8: Remove Clamps and Nail in Place

After the glue has dried, remove all the clamps and drive 4d finishing nails into the corners to reinforce the assembly. Be sure the nails enter the wood squarely. A finishing option: Use screws and plugs.

Step 9: Fill Nail Holes

Drive the heads of all the finishing nails below the surface of the wood with a nail set. Fill the holes with wood putty or filler and later sand them flush.

Step 10: Fill Plywood Edges

Fill all plywood edges, except those at the front of the box, with wood putty or filler.

Step 11: Sand Boxes

Sand all filled edges smooth and lightly sand box surfaces. Remove sanding dust.

Editor's Tip: When finishing these modular boxes, remember that hardwood plywood such as the birch plywood shown has a thin face veneer. If you sand too heavily in one area, it's possible to sand right through the veneer, an error that will show through the final finish. Always maintain a light hand with abrasives, even those with fine grit. Most plywood is fairly smooth to begin with, especially on the face side, so it doesn't take much sanding to prepare a surface for finishing.

Step 12: Apply Primer

Apply a coat of primer to the box (except unfilled edges). Then sand lightly again.

Step 13: Paint Boxes

Touch up any blemishes, then paint on one or two finish coats of semigloss enamel.

Step 14: Add Finishing Touches

When the paint is dry, add ash veneer tape to the unfilled edges. Miter-cut the corners of the tape.

Editor's Tip: Accent boxes with walnut plugs, if desired. To install, join the pieces with screws in countersunk holes; plug the holes with walnut dowels for contrast. Then apply walnut instead of ash veneer tape and coat with a clear finish.