Working with plywood

Cutting dados

Most case goods have some combination of permanent shelves, adjustable shelves and cross-rails, sometimes with vertical dividers as well. From there, you can add drawers, doors, mouldings, and so on to really dress them up. One of the most difficult tasks is making dados to hold the permanent shelves.

If you use a dial caliper to measure the thickness of a sheet of plywood at different points, you might be shocked at the results. It isn’t unusual for a sheet to vary by 12- to 20-thousandths of an inch from one end to the other. This distance is about the thickness of one or two standard business cards. Imagine a dado that is two business cards too small-there’s no way the shelf will fit. Two business cards too loose isn’t much better, unless you use screws or other mechanical fasteners to secure the shelf.

By using a shop-made jig, I can customize the fit of each dado to get a snug fit every time. I use a router instead of a tablesaw for a couple of reasons. First, the jig is easier to adjust to customize the width of each dado, compared with a dado set. Second, I prefer dados that are stopped at the front of the gables. The stops preserve the vertical lines when you look at the front edges of the gables, uninterrupted by the shelf dados. After stopping the dados about 1/2″ from the front of the shelves, I notch the corners of the shelves to fit flush to the front edges of the gables. You can do this with the shelves sitting vertically on a cross-cut sled, or pull out that trusty Japanese dozuki saw and practise some hand skills for a change.

The ingenious part of this jig is that I can rout matching dados in both gables at the same time. By placing two gables on the workbench, rear edge to rear edge, the dados are stopped at both ends of a single cut. I use a 1/2″-diameter straight bit to cut the dado, first pressing against the back fence of the jig while travelling from left to right and then pressing against the front fence while continuing from right to left. Two 1/8″-deep passes gives the 1/4″- deep dado I’m after. Before beginning the cut, I can sandwich the actual shelf that goes into that dado between the jig’s opening, which sets it to the proper width for a good fit. In this method, I can customize the dados to each and every shelf as I go along.

If you’ve been working with solid wood for many years and haven’t yet tried veneered materials, there is a whole new set of skills to be learned. It is satisfying work to build larger case pieces without having to spend all those hours milling, edge-gluing and levelling massive solid-wood panels.

Before you get too judgmental about using sheet stock, remember that some very fine antiques were made using veneers glued to block-board cores. Had other core materials existed back then, they surely would have been used. Also, veneered materials offer many new options to use parts of wood that can be quite unstable in solid form, such as burls and crotch figures. Open your eyes to all the new possibilities that await you.