Stapling the Short Core Strips
1. Position each core crosspiece with the help of other core pieces acting as spacer blocks.	2. Keep using spacer blocks to position the parts on the opposite side to get a correct alignment.
Positioning the skins
1. Place the first skin upside down, align the overhang by feel and put two clamps on one edge. Align the other three edges and add a clamp.	2. Put a small pool of hot-melt glue on a 1/2" x 1-1/4" x 1-1/4" MDF locator block and fix it tightly into one corner with finger pressure.
3. Repeat locator block process in the corners and other locations to hold the core assembly square.	4. Mark the skins so they can be returned to the same position.
Gluing Up
1. Squeeze a healthy line of glue on each edge. You will not put glue on the skins.	2. Pressure will be required to spread the glue. You should see even squeeze-out.
Clamping the skins
1. Position the torsion box between a pair of purpose-built cauls.	2. Put a piece of cardstock under the center of the battens to apply more pressure to the centers.

Once the short core strips have been stapled in place (see photos at right), the torsion box can be assembled.

Aligning the Skin and Core

Positioning the parts: The three parts — top skin, bottom skin and core — must be glued and clamped in a single operation, which raises the question: How do you keep the parts from sliding out of place on the glue during the clamp-up?

The answer starts with making a dozen 1-1/4" x 1-1/4" location blocks out of core material. Lay the top skin upside down on the corner of the bench and use it as a template to align the core. Align one edge of the core and skin and clamp using two clamps. Align the adjacent edges and clamp. The overhang should be equal all around: about 1/64" because the skin is cut 1/32" oversize.

Dab a drop of hot-melt glue onto one of the location blocks, then press it into position in one corner of the open torsion box. Position a block into each of the remaining three corners and anywhere else you feel necessary to keep the core aligned to the skin. If the long front and back core pieces have a slight bend, for example, use the block to hold them aligned.

Finally, lay the bottom skin upside down on the bench, align and clamp the core, and repeat the location block procedure.

Gluing up: Glue is applied only to the core. It’s transferred to the skin by pressure during the clampup. Squeeze a line of glue onto all the core edges. Position the skin, turn the box and repeat.

Once the core has been glued on both edges and the skins positioned, the box must be clamped. To distribute the pressure, put a piece of 3/4" or thicker material top and bottom. If the torsion box is more than 10" wide, use a couple of battens to apply pressure to the center. Place some folded cardstock under the middle of the battens as a quick way of making them cambered.

Finishing the Edges

Refining: Even if the skins, the core and the glue-up were made and done perfectly, the edges still would need refining after the box comes out of the press to deal with beads of glue squeeze-out and misalignment here and there. A sharp plane and the removal of two or three shavings will put it to rights. Confirm that all edges are square to faces and that ends are square to sides.

Lipping: Regardless of how you intend to finish the box, you must lip the edges to hide the plywood edges of the skins, unless you used MDF for the frame material and the skins.

Lippings are generally made as thin as possible to avoid another set of visual or technical problems such as shrinkage. One-quarter inch thick MDF on poplar works well for a painted job since you are likely to radius the edges, because paint crawls off a sharp edge, leaving a thin layer where it is the most vulnerable. Similarly, if you want to cover the box with leather, a 3/16" radius softens the edge nicely.

If you use a “show” wood skin, then you would probably want to lip the box with the same species as the veneer. The finish you want on your completed torsion box determines the kind of material used to make it. Now that you know how to make one, you realize that lipping and other decisions must be made before construction begins.