How to Build Modular Boxes

This story is the introduction and overview for a modular boxes project.

Modular Boxes

These 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.

Measure before cutting
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 (see the exploded view drawing). 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 (bottom left) creates a distinctive look. For a bright design option, completely paint the box (bottom right). Or you can accent the birch plywood with walnut plugs and veneer (top).


About 4 hours to build seven boxes, plus finishing time

Tape measure, clamps, electric drill/driver, 1-1/2-inch spade bit, 1/16-inch drill bit, table saw or portable circular saw, 40- to 60-tooth blade, handsaw, try square, framing square, hammer, nail set

Sawing, gluing, clamping

Assemble materials; prepare work area.

Cutting Parts: Step 1

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).

Cutting Parts: Step 2

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.

Cutting Parts: Step 3

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.

Cutting Parts: Step 4

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.

Assembling the Parts

It's easy to go astray when assembling so many units, so build a clamping jig like the one shown in the following Steps 1-3 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, as shown in Step 3. If one corner is square, the opposite one is also square.

Sand with caution
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.

Assembling the Parts: Step 1

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.

Assembling the Parts: Step 2

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.

Assembling the Parts: Step 3

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.

Assembling the Parts: Step 4

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.

Assembling the Parts: Step 5

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.

Applying the Finishing Touches: Step 1

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

Applying the Finishing Touches: Step 2

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

Applying the Finishing Touches: Step 3

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

Applying the Finishing Touches: Step 4

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

Applying the Finishing Touches: Step 5

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

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