Torsion Box Panels

Yesterday I outlined how modular design for this closet system. One of the core components is the 2" thick vertical panel. Free-standing vertical panels create several interesting problems for cabinetry. Thick panels create a few more problems, but that also server to solve others. In general I think they work out much better than the standard 3/4" thick panels used by large closet shelving providers.

The norm is to use 3/4" sheets of plywood or manufactured boards for vertical dividers in closet systems. This is cheap from both a material and labor stand point. But long pieces of plywood are flexible, and subject to warping. It also creates a problem when attaching it to the wall or floor.

The normal procedure is to attach an anchor board to the wall and floor, which can be secured with nails or screws, then nail or screw the panel to the anchor board. When combined with fixed shelves and cabinets, this can be effective, but not exactly high-end as it leaves the method of attachment obviously exposed. But it is cost effective.

For high-end design I prefer to hide, as much as reasonably possible, any obvious clues as to how things were installed. In this case I designed the vertical panels to be 2" thick. This was not just for appearances, but thick panels do make the entire project look more substantial, and 2" was not just a random dimension.

I chose 2" because I knew I would build torsion boxes using 1/2" plywood. 1/4" plywood is too thin (being highly prone to lack-of-flatness and leaving a panel with very drum like sound qualities), while 3/4" is unnecessarily thick and heavy. 1/2" plywood is not much cheaper than 3/4" (often less than 1% price difference!) but the reduction in weight is one major benefit (Just try manhandling 30 or 40 sheets in a day and tell me which you like better!)

If the two sides of the panel are each 1/2" thick, then they must be spaced 1" apart. Using thick strips of plywood glued in place to provide the spacing makes a nice box. Adding a few extra ribs to the box makes a torsion box ("t-box" for short). T-Boxes are rigid, much more rigid than single panels or multiple panels just glued together, plus they are light and easy to handle. (For more T-boxes, check out my mantle project from November 2007)

There is another key advantage of using a t-box: hollow spaces. In this case, I arranged to leave space between the face panels open on the back and bottom edges of the panels. Later, during installation, I can attach cleats to the wall and floor which will fit into these slots. If the fit is snug, all I need to do is glue the panels to the cleats and they will be fixed in position without visible screws or nails. But the cleats can be very securely fastened to the wall with all the screws and anchors I want! It's a nice system.

So here are some pics of these panels being assembled:


Besides the slot in the bottom of the panel, you will also notice that I left the front and back spacers protruding from the bottom. This was intentional. These will hold the panel 1/2" off the subfloor, leaving space for the edges of carpeting to be tucked under the panel (the same thing is done with base boards installed before flooring). At the top the spacers extend 6" beyond the panels, which will fit between the cabinets and help prevent tilting the the assembly as it is installed.

Each completed panel uses one whole sheet of plywood for both sides, but because it is hollow and made with 1/2" plywood instead of 3/4" it weighs less than 50 pounds. Since the design calls for 16 such panels, the 25 pounds weight savings per panel will be greatly appreciated during the rest of the staining, delivery and installation process.