Knockdown Bookcase

Angled Mortising

A close look at the wedged through-tenons shows the recess behind the side that allows the wedge to pull the sides tight.

The next step is the through-mortises. For these to work correctly, they also need to be cut at a 5° angle, and they must fall directly in the dados you just cut on the saw. You could cut them by hand, but the 5° angle is tricky to maintain. You could also set up a mortiser to do the job, but I got a little smarter and came up with a router template.

By using a piece of 1/2″ Baltic birch with a strip added beneath one end, I made a router template that would make cuts at a 5° angle. It takes some rearranging of the guide for the different cuts, but the results work rather well.

Careful layout lines are critical here. To make the 5° ramp, I used a scrap piece of 1/2″ material for the back strip, nailed to the template 14″ from the end. Check this dimension carefully on your materials to get as close to 5° as possible.

The rest is fairly simple. Check the offset on your router template guide from the bit, and add this to the 3/4″ x 2″ dimension for the mortise. Mark that size on the template and use a drill and jigsaw to make a square hole.

Clamp the template in place over the mortise locations and cut your through-mortises using two or three depth settings. Depending on the router bit you’re using, you may want to use a backing board behind the side to reduce tear-out. I used a jigsaw and chisel to square up the corners.

Shaping up the Sides
The next step is to cut the sides to their “spade” shape. I used my band saw for most of this work, but used a jigsaw to cut the radii under the top shelf and the arch at the bottom. Cut a little wide of your layout lines, then clamp the sides together, aligning the sides by the shelf grooves on the inside surface. Plane and sand the sides to matching shapes.

Fitting the Through-Tenons
Now it’s time to fit things together. Start by checking the fit of your shelves in the dados in the sides. Mine were a hair thick, so I was able to run them down on the planer to make an almost-perfect fit. Check the width of the bottom shelf against the width of the sides at the shelf location, now that the sides are shaped. Rip the shelf to size. Next, fit the shelf into the dado and, from the outside, mark the tenon location through the mortise on the end of the shelf. Remove the shelf and mark off the 2″ length of each mortise, then head for the band saw again. The width of the tenons is the critical cut. The shoulder of the tenons should be neat, but that edge is buried in the side’s dados, so it doesn’t have to be perfect.

With the tenons cut for the bottom shelf, fit the shelf and sides together. You want a snug fit, but not too loose and not too tight. A chisel, file or rasp and some sanding should do the job. Take your time and get it right.

With the bottom shelf fit, check the dimensions on the top shelf, mark the tenons and repeat the fitting process. When that task is complete, fit the two center shelves and slide them into position. These shelves are designed to be left loose, but if they slide a little more than you like, a nail through the side into the center of the shelf will make a permanent solution, or you can drive a short wedge into the joint under the shelf for a temporary fix.

Tusks and the Home Stretch
To hold the top and bottom shelves in place – and the whole case together – disassemble the case and mark the 3/4″ x 3/4″ through-mortises on the shelf tenons as shown in the diagrams. I used my mortising machine to cut these holes. Another option is to use a drill press to cut the mortises and then square up the corners using a chisel.

Reassemble the case, then cut the eight tusks. Appropriately, the tusks should seat with their center at the shelf tenon. Fit the tusks as necessary, and tap them into place to make the whole case rigid. Now take it all apart one last time and sand everything to #150 grit.

For a finish, I used a simple dark-colored gel stain, wiping off the excess until I was happy with the depth of the color. I then top-coated the case with a couple of coats of lacquer.

The nicest thing about moving this bookcase is that after you knock out the eight tusks, everything fits in the trunk of a compact car. PW

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David Thiel is a senior editor at Popular Woodworking magazine.