AW Extra – Torsion-Box Workbench and Expandable Assembly Table

Torsion-Box Workbench and Expandable Assembly Table

Double your work space without doubling your shop space.

By Randy Johnson and Luke Hartle

In our shop, we used to pile tools, parts and hardware on top of a wobbly workbench made from 2x4s. When we had to glue a project together, we shoved everything aside. Finally, we got tired of searching for tools and space and set out to make a new style of workbench.

Our new workstation is two benches in one. The best part is a rolling storage unit that opens into a huge assembly table. Closed, it tucks right under the bench. We built the bench’s top as a torsion box, so it can span the distance over the assembly table without sagging. Both parts are made from home-center materials using simple joinery. Two work surfaces, lots of drawers and shelves—what a great excuse to buy more tools.

Click on any image to see a larger version.

THE WORKBENCH

Build the Torsion Box

1. Cut out the parts according to the Workbench
Cutting List, and the plywood cutting diagrams
(Fig. E). Cut the top and bottom
skins (A) to width on your tablesaw. Because this
skins are so long, we found it easier to rough-cut
them to length with a circular saw and then trim
them to final length with a router and straightedge,
rather than wrestling with them on our tablesaw.

2. In the skins, drill the screw holes that will be
used to attach them to frame boards (Fig. A).

3. Lay the bottom skin on a pair of plywood
I-beams (Photo 1) and glue and clamp on the outer
torsion-frame parts (B, C). The I-beams guarantee
that the parts clamp up flat (see “Working with
I-beams”). It’s OK to glue and clamp one
outer frame part to the skin at a time; just keep at
least one clamp at each corner of the skin to keep it
flat on the I-beams.

4. Cut the inner torsion-frame parts (D, E) to size
and use a dado blade to cut the bridle joints on your
tablesaw (Photo 2). Make sure to cut test joints first.
You want these joints to interlock perfectly, so the
parts line up flush on the top and bottom. You also
want them to go together smoothly. It’s better to have
joints that are a little loose rather than tight.

5. Screw the short inner torsion-frame parts (E)
to the long center one (D) with a screw at each bridle
joint.

6. Test-fit this grid assembly in the outer frame that’s
glued to the bottom skin (Photo 3). When you are satisfied
with the fit, predrill holes through the outer torsion
frame, glue the inner torsion-frame assembly to
the bottom skin and drive screws through the outer
frames into the ends of the inner frame parts.

7. Flip the assembly and add screws through the
bottom skin into the inner grid frame parts (Photo 4).

8. Now flip the torsion-box assembly back and glue
the vise screw blocks (F) in the front left corner of
the top (Fig. A).

9. Next, add the top skin with glue and screws.

10. Drill the access holes through the torsion box
(Fig A). Should you ever need to remove the top, you
can push a stick through these holes to lift it.

11. Cut the side trim boards (G, H) to final size.
Double-check the size of your torsion box and then
cut the trim boards to fit. Attach them with glue and
clamps (Photo 5). Use a biscuit at each corner to
help them line up. Note that the trim’s top edge stands 3/4 in. above the torsion box. This space provides
a recess for the work top (J).

12. Screw the work top into place (Photo 6). For a nice
finished look, counterbore the screw holes and add wood
plugs. Trim the plugs flush using a router, chisel or belt
sander. When the top gets worn and you want to flip it or
replace it, simply drill out the plugs and remove the
screws.

13. Now is good time to glue together the three parts
(L) for the vise jaw. When the glue has dried, drill the
holes through which the vise will fit (Fig. B).

Build the Base Cabinets

14. Cut out the sides, top and bottom, and back (M,
N, P) for the base cabinets. Add iron-on edge banding to
the front edge of Parts M and N (see the Workbench
Cutting List and “Iron-on Edge Banding,” AW
#113, March 2005).

15. Cut slots for biscuits in the cabinet parts (Fig. A).

16. Because these cabinets are only 10-1/2 in. inside
when complete, it’s easier to install the drawer slides
(see Sources) before the cabinets are assembled.
Spacers (DD, EE, FF) simplify the job of positioning
the slides (Photo 7).

17. Assemble the cabinets with biscuits, glue the cabinets
and install levelers (Photo 8).

Assemble, Install the Drawers

18. Cut out the drawer boxes’ parts (V through CC)
and assemble them with biscuits and glue. Screw on the
remaining drawer-slide components and slide the drawer
boxes into the cabinets.

19. Cut out the filler front (Q, Fig. C, right), which fits
around the vise mechanism. Cut out the drawer fronts
and toe kicks (R, S, T, U). Apply iron-on edge banding to
these parts.

20. Install the toe kicks first. Then add the drawer
fronts, starting at the bottom. Place a 1/8-in. spacer on
top of the toe kick. Set the bottom drawer front (T) on
top of the spacer. Attach the drawer front with a couple
drops of hot-melt glue and then add screws from inside
the drawer. You can scrape off the hot-melt glue when you
remove the drawer front for finishing. Reuse the spacer
and repeat this step for the rest of the drawer fronts.

Assemble the Bench, Add the Vise

21. Place the torsion box on top of the base cabinets.
The cabinets should be flush with the back of the torsion
box and set in 3/4 in. from the ends.

22. Remove the drawers and screw the cabinets to the
torsion box.

23. Install the vise mounting board (K) to the torsion
box’s bottom with screws and glue (Fig. D).

24. Mount the jaw to the vise mechanism and screw the
vise to the vise mounting board.

25. With the building complete, you can disassemble
the workbench, do a final sanding and then stain and varnish
it.

26. When the finish has dried, reassemble the entire
workbench, level it and attach it to your shop wall by a
couple of L-brackets screwed to wall studs.

Sources

(Note: This information may have changed since this story's original publication date.)

Woodworkers Hardware, woodworkershardware.com, 800-383-0130,  Workbench Hardware Kit, #KIT0601,
$75.72 (includes seven 9-7/8" stainless steel drawer pulls, seven
sets of drawer slides, eight cabinet levelers, two L-brackets and all
mounting screws;  Nickel Plated Continuous Hinge, 2" x 72", #C112723, $13.26 each (3 required).

Woodcraft, woodcraft.com, 800-225-1153, Quick-Release Front Vise, #17A11, $215;
7/64" Self-Centering Hinge-Drilling Bit, #830810, $11.50; Large Wooden Vise Handle, #17E52, $7, 5-3/4" Stainless Steel Drawer Pull, #836227, $6.79 each (6 required); 4" Double Locking Swivel Caster, #141050, $20.50 each (6 required).

Home centers and hardware stores,    Sash Lock, about $4 each (2 required).

Workbench Cutting List

Fig. A: Exploded View

Fig. B: Vise Jaw

Fig. C: Vise Filler Drawer Front

Fig. D: Vise Mounting Board

Fig. E: Plywood Diagrams

Rigid Top. This bench’s top is amazingly
strong, although it’s only plywood. The
secret is easy-to-build torsion-box construction.

Sturdy Vise. The front vise has a large
4-in.-tall by 15-in.-wide by 10-1/2-in.-deep
clamping capacity. The hardware comes
as a kit and you make the jaw to fit.

Replaceable Top. The bench’s top is
removable and reversible. If you ever
wear it out, drill out the screw plugs,
remove the screws and lift off the top by
pushing a stick through access holes in
the torsion box.

1. A torsion box is composed of two sheets of plywood, or
skins, separated by a frame. The first step is to glue the outer
frames to the bottom skin. Clamping the parts to a flat surface,
such as these wooden I-beams, guarantees that the top will turn
out flat.

Working with I-Beams

2. Cut the bridle joints on the inner torsion-frame parts with a
dado blade. You can cut them as a group by clamping them
against an auxiliary fence on your miter gauge.


3. Test-fit the inner torsion-frame assembly. It should slip into
place using hand pressure only. Then remove it, add glue
and reinstall it. Hold it in place by adding screws through the
outer frame parts.


4. Flip the assembly and screw the bottom skin to the
inner torsion frame. Then flip it back and add the top
skin. Keep the torsion box clamped to the I-beams during
each step to ensure that it stays flat.


5. Glue the trim boards to the torsion box. Install them
flush with the torsion box’s bottom. This will create a
recess on the top side for the removable work top to fit into.
Make long clamps by joining short clamps with couplers.


6. Install the work top. Screw it to the torsion box and use
wooden plugs to hide the screws. The top should fit
loosely into the recess, so it’s easy to remove if you wish to
replace it.


7. Use spacers to position the drawer slides for mounting to
the sides of the base cabinets. It’s best to mount the
slides before the cabinets are assembled, because it’s hard to
fit a cordless drill inside cabinets after they are put together.


8. Add levelers to the base cabinets if your shop floor is
uneven. These heavy-duty levelers are easily adjusted
from inside the cabinet through an access hole in the bottom.

THE EXPANDABLE ASSEMBLY TABLE

Build the Base Cabinets

1. Cut out the parts for the base cabinets according to the
Assembly Table Cutting List, and the plywood diagrams
(Fig. C)

2. The cabinet subtops and subbottoms, ends, partitions,
and backs (A through D) are assembled using dado and biscuit
joinery (Photo 1; Fig. A).

3. Apply iron-on edge banding to the front edges of the
end panels (B) and the partitions (C).

4. Assemble the partitions, subtop, subbottom and back
first. Then add the end panel (Photo 1). Make sure the cabinets
are clamped squarely.

5. Attach the bottom (F) and top (G) with screws and glue.

6. Add the top and bottom door guides (H, J, Fig. B; Photo 2).

Add the Hinged Panels

7. Make three sets of hinged panels by attaching the
center hinge to pairs of panels (E). It’s important that the
hinges be perfectly centered on the joint between the two
panels. Any variation will cause the hinges to bind and prevent
the two cabinets from closing evenly when folded
together. The best way to accurately install the hinges is to
draw a line 1 in. inside the edge of each panel. Clamp the
hinge to the panels, aligning it with the line. Use a self-centering
bit (see Sources) to drill pilot holes for the screws.
Don’t remove the clamps until you’ve installed the screws.

8. Add hinges to the outer edges of the panels. They go on
the opposite side from the center hinges (Fig. A). Install
these outer hinges the same way as you did the center hinges.

9. Mark the locations for the hinged panels on the back of the cabinets (Fig. A). Center the middle panel and then
space the two end panels 28-1/2 in. away from the center
panel (Fig. A). When the end panels are installed, you
should have a small gap between them and the cabinet end
(B). This small gap helps accommodate any slight out-ofsquareness
that exists in the cabinets. It’s very important that
the hinged panels be installed at a 90-degree angle to the
bottom (or top) of the cabinet. Use a framing square to draw
these lines, using only the top or bottom for reference, but
not both. If you do and they are not perfectly square to each
other, it will throw off the accuracy of your hinge installation.
Getting the hinges to operate smoothly is not difficult, but
you do have to pay careful attention to the installation.

10. Attach the pairs of panels to one cabinet first
(Photo 3). Use a 1/16-in. spacer to center the hinged panels
between the subtop and subbottom (A).

11. Next, attach the panels to the back of the other cabinet
(Photo 4).

12. With the hinged panels installed, fold the cabinets
together and add the sash lock to the ends.

13. With the cabinets locked together, roll them over
onto their tops and add the wheels (Photo 5). Install the
corner wheels so the foot lock is easily accessible from the
ends and sides.

Add the Removable Top

14. Roll the cabinets back upright and unfold them.

15. Carefully measure the opening width for the removable
top (K, Photo 6). Measurements for this part are in
the Cutting List, but variations in materials and assembly
may require you to adjust the size of this part.

16. Glue the edge strips (L) to the removable top panel.

17. After the glue has dried, test the fit. It should fit
snugly in the opening, requiring only medium hand pressure
to slip into place.

18. Check the fit of the removable top with the cabinets
folded together. Again, the fit should be snug but
not too tight. If it’s tight, see “Oops!” at left for an easy
fix. If the fit is loose, add a strip of wood to the back of
the edge strip.

19. When the removable top fits correctly, round the
top and two bottom edges of the side trim using a
1/4-in. round-over router bit. Rounding these edges
makes the top slide into place more easily. Also, ease all
other sharp corners with a sanding block or 1/8-in.
round-over router bit.

20. Drill holes for shelf supports and add the adjustable
shelves (M).

21. Finally, add the sliding doors (N, P, Photo 7) and
install the door pulls.

22. We finished our cabinet with a golden oak stain and
varnish topcoat. If you remove the hinges for finishing,
make sure to clearly mark their original locations so everything
goes back together correctly aligned.

 

Assembly Table Cutting List

Fig. A: Exploded View

Fig. B: Door Guide

Fig. C: Plywood Cutting Diagrams

This story appears in American Woodworker January 2006, Issue #119.

January 2006, Issue #119.

Purchase this back issue.

Expandable! This assembly table opens
like an accordion. The top comes off the
two cabinets and doubles as a table leaf,
giving you a huge mobile work surface.

Lots of Storage. The base cabinets
provide loads of storage space. Sliding
doors won’t get in your way when they
are opened.

Perfect Height. The large work surface
is at a comfortable height, perfect for
assembling furniture and cabinetry
projects.

1. The assembly table is composed of two identical cabinets. Joinery
is simple; it’s all held together with dadoes and biscuits.

2. Glue and clamp the door guides to the doubled-up top
and bottom. Doubling the top makes the work surface
extra solid. Doubling the bottom provides a strong place to
attach the wheels.

3. Install the hinged panels to the back of one cabinet,
using spacers to center the panel between the top and
bottom. The hinged panels must be installed perpendicular
to the bottom so they open and close square to the cabinets.

4. Attach the hinged panels to the back of the second cabinet.
Make sure the spacing between the hinged panels
on the second cabinet is identical to the spacing on the
first cabinet or binding will occur when you fold the cabinets
together. When the panels are folded together, the
panels fold into the recess at the back of the cabinets.

5. Install the wheels. The center wheels provide support for
the back of the cabinets and are offset from the middle of
the cabinet so they don’t hit each other as they swivel. Sash
locks hold the cabinets together when the table is folded up.

6. Measure for the removable top. You want the top to fit
snugly, yet be just loose enough to be pressed into place
using hand pressure.

7. Slip the sliding doors into the slotted guides. The doors
go into the deeper upper slot first and then drop down
into the shallow bottom slot. If the doors don’t slide freely,
reduce their thickness by sanding the back of the top and
bottom edges.