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36 American Woodworker NOVEMBER 2004

Copyright 2004. All rights reserved.

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Torsion-box

construction creates

sag-proof shelves

that “defy” gravity.

Some time ago, an Ace Hardware ad in

American Woodworker sparked a surpris-

ing number of inquiries from readers.They

all wanted to know how to build the cool-

looking shelves that appeared in the back-

ground. We liked the shelves, too. Their

contemporary design and invisible mount-

ing created a dramatic effect.

The secret was torsion-box construction.

A torsion box is a simple grid of slender

ribs glued between thin plywood skins. It

makes these shelves stiff and flat, yet

incredibly light. This rigid architecture

means torsion-box shelves won’t sag or

twist, and they can be mounted without

any external support.

We’ve made these shelves easy to build

and install by using simple shop-made jigs

and dividing the process into four steps.

We’ll make the torsion boxes, attach the

face moldings, then glue the C-shaped

units together and, finally, hang them on

the wall.To create the wall of shelves shown

here, you make four identical C-units and

hang every other one upside down.

We wanted our shelves to be a uniform

light color, so we chose hard maple instead

of birch. The cost is the same, but maple

lumber and plywood colors are easier to

match.The Multiply brand of underlayment

(available at home centers) makes great rib

stock, because it’s inexpensive, stable and

exactly 1/4 in. thick. We spent $220 to make

our four C-unit shelves.

Copyright 2004. All rights reserved.

American Woodworker NOVEMBER 2004 37

by Tim Johnson

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P ROJECT R EQUIREMENTS AT A G LANCE

Materials for four C-units:

12 bd. ft. of 6/4 hard maple

15 bd. ft. of 5/4 poplar

Two sheets of 1/4-in. x 4-ft. x 8-ft. hard maple plywood

Two sheets of 1/4-in. x 4-ft. x 4-ft. underlayment

One sheet of 3/4-in. x 4-ft. x 8-ft. MDF

One sheet of 3/4-in. x 2-ft. x 4-ft. fir plywood

Cost: $220 for four units

Hardware:

One box No. 9 x 1-in. brass screws

A handful of No. 6 x 3-in. drywall screws

Tools:

Tablesaw, 1/4-in. dado set, chop saw, jointer, planer, router, 1/2-in.

flush-trim bit, drill, plate jointer, wood glue, roller, clamps, level,

compass

F IGURE A E XPLODED V IEW

D ETAIL 1 Template

G5

7-1/4"

G1

7/8"

G2

D

3"

1/4" x 7/16" NOTCH

D

C

G4

C

G3

D ETAIL 2 Molding Profile

C

Each C-unit requires three torsion

boxes. They’re all made the same

way, just in different lengths.

• Torsion box for upper shelf

1-1/4" x 9-3/8" x 34"

• Torsion box for upright

1-1/4" x 9-3/8" x 18-1/4"

• Torsion box for lower shelf

1-1/4" x 9-3/8" x 51"

45 ° BEVEL

1-1/4"

F3

F1

F1

5/16"

F2

1-1/4"

D

16"

#20 BISCUITS

45 ° MITER (TYP.)

1-3/8" W CAVITY (TYP.)

E2

E5

B

E1

C

A

E3

E1

D

E4

F IGURE B N OTCH -C UTTING J IG

POLYCARBONATE

GUARD 1/4" x 3" x 7-1/2"

F IG . C Box Beams

F IGURE C B OX B EAM

MDF

7/16"

SLED

3/4" x 6" x 24"

18-GA. x 1-5/8" PIN NAIL

3"

FENCE

3/4" x 2-3/4" x 24"

1/4"

SLOT

MDF

INDEXING PIECE

1/4" x 7/8" x 8"

18-GA. x 1-5/8" PIN NAIL

38 American Woodworker NOVEMBER 2004

Copyright 2004. All rights reserved.

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B UILD THE T ORSION B OXES

LEDGER BOARD

CAVITY

LONG

RIB

1. Cut the torsion-box skins (Fig. A, E1, F1 and G1,

page 38) from 1/4-in. maple plywood (see Cutting

List, page 45). To get skins for all four C-units from

two sheets of plywood, rip each sheet into five 9-1/2-in.

x 8-ft. blanks. Cut eight of these blanks into 51-in. and

34-in. skins for the shelves. Cut the eight 18-1/4-in. skins

for the uprights from the remaining two blanks.

2. Cut the sheets of 1/4-in. Muliply plywood underlayment

into 7/8-in. x 48-in. ribs (A).

3. Plane poplar edging stock to the same 7/8-in. thickness as the

ribs’ width. Cut the front and end edging pieces (C and D) to width

and length.

4. Build the notch-cutting jig (Fig. B, page 38).

5. Cut notches in the ribs (Photo 1). Butt the ribs against the index-

ing piece to cut the first notches. Use these notches to index the ribs so

BOTTOM

SKIN

TOP

SKIN

SHORT

RIB

SIDE

EDGING

FRONT

EDGING

HOLD-

DOWN

INDEXING

PIECE

TEMPLATE

LONG

RIBS

1 Cut notches in the ribs, using a shop-made indexing jig

2 Cut short ribs from some of the

BOX

BEAM

TORSION

BOX SHELF

TOP SKIN

3 Glue the torsion boxes together by sandwiching the

4 Clamp the torsion boxes between box beams. Box

Copyright 2004. All rights reserved.

American Woodworker NOVEMBER 2004 39

and a 1/4-in. dado set. The notches allow you to assemble

the ribs into the grid sections that comprise the core of

the torsion boxes.

long ribs. Use a template

(Fig. A, Detail 1) and an

indexing piece to make sure

you cut them consistently.

beams distribute clamping pressure evenly and guaran-

tee your glued-up shelves will be flat.They’re well worth

the effort to make.

edging and the grid section between the plywood skins.

This is a complex glue-up, so use glue that won’t dry

too fast and a roller to spread it quickly and evenly.

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M AKE THE B EVELED M OLDING

RIDGE

5 Glue on molding blanks that are slightly thicker than the

6 Rout the edges flush. Use a second shelf to support the

router and a piece of scrap plywood as a spacer.

SUPPORT

FENCE

45 o BEVEL

fence and make a second light pass to clean the edge. 8 Bevel the end molding with your miter gauge and a long

support fence. Rough-cut the bevel and then make a

light final pass.

Caution: If your shelf and miter gauge are unstable in the starting

position because they hang off the front of the saw, use a sled to

make this cut (see “The Ultimate Shop-Built Crosscut Sled,” AW

#75, October 1999, page 38).

40 American Woodworker NOVEMBER 2004

Copyright 2004. All rights reserved.

shelves. Make sure you feel ridges on both sides of the

blanks as you tighten each clamp, and again after all the

clamps are tight.

7 Bevel the molding. It’s difficult to get good results when

you cut thick, hard wood at an angle, so make two pass-

es. First, make a slightly oversize rough cut. Adjust the

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