Floating Serpentine Shelf #3: Building the Torsion Box Skeletons

(I actually cut and beveled the edges of the thin plywood skins first, then sized the skeleton parts to match, but I’ll describe the work in reverse order because it seems more natural.)

Aside from wrestling with half sheets of 3/4” birch plywood (I had Lowe’s cut the sheet in half lengthwise so I could fit it into my Honda Element), cutting the torsion box skeleton parts was straightforward. All of them (aside from the ones in the back panel) are the same width, so I started by ripping a set of thin strips. Then I crosscut the long shelf spines and shorter side spines. Then it was just a matter of setting the stop block on my crosscut sled to cut all of the (75!) ribs. That left me with a small mountain of parts.

Before assembling the skeletons, I used my drill press to drill dowel holes through the outside ribs of each shelf and through the top and bottom ribs of the sides.

Assembling the skeletons was easy. I used two pocket screws in each outside rib (to make certain nothing rotated) and one screw in each end of every other rib. The ribs are spaced 8” apart on-center, so I cut a pair of 7 1/4” long spacers so I didn’t have to measure. I clamped each rib in place, and made sure the rib was pressed down onto my bench’s top, before driving each screw. That kept each torsion box nice and flat.

I didn’t use any glue on the skeletons. That turned out to be helpful, because I later had to move one of the ribs. (It was right where the 3/4” dowel from the back panel needed to be.)

Cutting and attaching the plywood skins was much more involved, and I’ll cover that next.

-- Ron Stewart