| Torsion Box -- Support Grid |
From "Wood Works"
episode WWK-409 |
|
|
|
advertisement
|
With the, flat and level work-surface created using sawhorses, shims, 2x4's and MDF sheets (figure A), work can now begin on the MDF grid that forms the internal core of the torsion box. Materials: Table saw; crosscut sled
Pneumatic nail-gun (brad nailer)
1-1/4" finishing nails
Yellow woodworker's glue
Carpenter's square
Straight-edge
Carpenter's pencil
Carpenter's tape
Safety glasses or goggles
Note: Cut sizes may vary. For exact measurements, please contact David Marks through his Web site -- information below under Resources. Safety Alert: Always wear safety goggles or safety glasses when working with wood, power-tools, saws, drills, routers, etc. Building the Internal Grid - The size of your torsion box will depend on the types of projects for which you plan to use it. The size of the grid squares may vary also. In general, smaller grid-squares result in greater strength and stability. The assembly table built in this episode has a work surface that is 4 feet by 5 feet. We used 1/2-inch MDF for the grid, and 3/4-inch MDF for the frame. The squares are evenly spaced, and stand 3 inches tall (figure B).
- To ensure that all of the stock pieces for the grid are cut precisely the same, plan ahead to know how much 3/4-inch MDF and 1/2-inch MDF you'll need. To maintain consistency, batch cut the stock, making all the rip cuts for the grid stock without changing the fence setting.
- At the table saw, rip all of the MDF stock to consistent width -- 3 inches (figure C). Batch cut the stock all at once to ensure that all the 1/2-inch grid stock is even and uniform. It's a good idea to use anti-kickback rollers to hold the stock firmly against the fence.
- Next, rip four strips of 3/4-inch MDF for the frame, using the same setup on the table saw.
- Add the cross-cut sled to the table-saw to cut the frame pieces to proper length. Measure 46-1/2 inches for the short frame-stock (figure D), set the stop-block and cut the MDF to length(figure E).
- Measure 60 inches for the long frame-stock, set the stop-block and cut the MDF to length. Use a long strip of plywood attached to the fence of the cross-cut sled to help support the stock (figure F).
- With the frame stock cut, assembly can begin. To start, only the two corners of the frame are glued and tacked. A carpenter's square is used ton ensure squared corners, and the sides are clamped to the work surface.
- Join the frame corners by adding yellow glue to the ends of the frame, then secure the corners with 1-1/4" finishing nails (figure G).
- Add clamps to the center and corners of the frame pieces to add stability and prevent the MDF from flexing. Take a measurement for the exact length of the long dividers that will be needed to make the grid (figure H).
- At the table saw, trim the long dividers to length. In our case, the stop-block was set at 58-1/2 inches to get the length we needed (figure I). Again, we used a long strip of plywood attached to the fence of the cross-cut sled for support.
- A diagram is made to plan the grid, dividing the frame into equally sized boxes (figure J). The size of our squares was determined to be 6-7/8 inches by 7-3/8 inches.
- At the table saw, batch-cut 42 short grid-pieces out of 1/2-inch MDF (figure K).
- To ensure that the placement of the short grid pieces is consistent, make a spacer (6-7/8 in length) from MDF. As you begin assembly of the grid, start on one end of the work surface and proceed in one direction across the surface to keep the spacing uniform.
- Tip: Before glue-up begins, wax the surface of the MDF. The wax will help prevent the glue from sticking to the work surface. This will assist in making cleanup of excess glue easier.
- As you assemble, apply yellow glue to one end of each grid pieces (figure L), and position each piece using the spacer to ensure proper placement of each crosspiece.
- Secure each piece using the air gun (figure M). Repeat this process all the way across the frame.
- Once the first row of crosspieces has been attached, secure the first MDF divider. Add glue to the ends of all the crosspieces, and to the ends of the long divider. Position the divider, check the alignment using the spacers, and secure the divider to the ends of the cross-pieces with finishing nails (figure N).
- Next, begin building the second row of the grid, using the spacer to confirm proper distances between crosspieces. From this point, you'll need to secure the crosspieces by toeing in the nails (figure O). In the design for our grid, we made sure that the grid squares were large enough to accommodate the pneumatic nail-gun within each box.
- Continue in this manner, building the grid one row at a time until you reach the last row (figure P).
- Before finishing the grid, there may need to be a slight adjustment to correct for cumulative error that may have developed during the making of the grid. Set a long straight-edge where the frame will be installed, and scribe a line along the inside edge onto the work surface (figure Q).
- Line each cross-piece up one-by-one, and mark each to indicate the proper length (figure R).
- Trim each piece to the precise length according to the marks.
- Fasten the trimmed cross-pieces with yellow glue and nails to complete the grid, and install the final 3/4" MDF frame-piece (figure S).
- Allow the glue to dry for several hours. Clamps are not necessary since the structure was nailed securely during construction.
In the segment that follows, the top and bottom skin are added to the torsion box. Sponsored Resource
> Click here to order your tools and materials for this project from Woodcraft!
RESOURCES :
Fine Woodworking
A magazine devoted to high-quality craftsmanship in woodworking.
The Taunton Press Inc.
Website: www.taunton.com
The Small Wood Shop (The Best of Fine Woodworking)
Author: Helen Albert (Editor)
Publisher: Taunton Press
ISBN: 1561580619
Woodworking Techniques: Best Methods for Building Furniture from Fine Woodworking
Author: Editors of Fine Woodworking magazine
Publisher: Taunton Press
ISBN: 1561583456
David Marks Website
David Marks, DIY's Wood Works host, is a master woodworker. For more information on cut sizes and project details, please contact him via his Website at www.djmarks.com
|
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
