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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.


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