The dimensions and part sizes in this class may differ from the project you're working on.
Locking Rabbet joinery is an easy-to-do joint that's as strong as it is simple. The drawing below shows how a locking rabbet fits together and why it’s such an effective joint. In a nutshell, a rabbeted tongue is cut into each end of the drawer front and back. Then a dado, sized to fit the tongue, is cut into the drawer side. The result is a solid mechanical lock as well as good gluing strength. And to top it off, as you can see in the photo above, the appearance of the joint is unique.
A locking rabbet joint works best if the front and back are thicker than the sides. A thicker front gives you more material in which to cut the rabbeted tongue while still leaving plenty of thickness on the front lip. It also lets you create more separation between the end of the sides and the dado. This all comes together to make the joint stronger. For large drawers, 3⁄4"-thick fronts and backs and 1⁄2"-thick sides are pretty standard. (For small drawers 1⁄2"-thick fronts and backs and 3⁄8"-thick sides work well.) But, I confess, I've done drawers that have all the parts are the same thickness and they've worked just fine.
When you cut the pieces to length, keep a couple of things in mind. The fronts and backs are cut to the width of the drawer opening, allowing for clearance. The sides are cut to the full depth of the drawer, minus the thickness of the front and back lip.
Once all the drawer pieces are cut to size, you can start setting up the table saw. Since most of the work goes into accurately cutting the rabbeted tongues on the front and back, this is where I like to begin.
The First Cut. There are two steps involved in making the rabbeted tongue. The first is to cut a groove or slot along the end. The table saw setup for this task is shown below. In 3⁄4"-thick stock, I generally cut a 3⁄8"-wide groove that’s positioned to leave a 1⁄4"-thick lip and a 1⁄8"-thick tongue (a saw kerf’s width), as shown in the detail below. And the depth of the slot needs to match the thickness of the drawer sides.
To make the cut, you’ll need to stand the workpiece on end and pass it over the dado blade. A tall auxiliary fence and a featherboard help you with control while a backer board minimizes chipout.
Cuts. As you can see, the setup for this cut (and the ones that follow) is pretty basic. But, the real key here is the accuracy of the setup. So before making any cuts on the actual workpieces, I always tweak things with the help of a few cuts on test pieces the same thickness as the actual parts.
The Real Thing. Once your test cuts tell you the blade height and fence setting are dead on, you can cut the slots one after the other. The featherboard keeps the workpiece snug against the fence, so you just need to make sure it doesn’t ride up on the dado blade.
The Rabbeted Tongue. Cutting the groove leaves you with a narrow lip on the inside face of the workpiece. The next step is to cut back the lip to create the tongue, as shown below.
This task is pretty straightforward. You can use the same dado blade to make the cuts but now you’ll need to bury it in the auxiliary fence. And an auxiliary fence attached to the miter gauge is used to feed and back up the workpiece. Your only real concern is cutting the tongue to the right length. Here again, a test cut or two is all it takes.
A good rule of thumb is to cut the length of the tongue to half the thickness of the sides.
The Dadoes. After this second step is completed, you can set the fronts and backs aside and turn you attention to the sides. This final step is cutting the dado in the side that will capture the tongue and create the “lock.” The setup I use here is shown below.
The main difference is that you’ll need to switch to a standard, 1⁄8"-kerf blade on the saw.
This final cut determines how well the joint fits, and there are a few things to consider. First, the depth and width of the dado needs to match the size of the tongue. Finally, the dado needs to be positioned properly so that the end of the side fits snugly, but not too tightly, into the rabbeted front and back. This may sound like a lot to ask, but again a few test cuts are all it takes to get it done.
Once you’ve adjusted the setup, the cuts go pretty quickly. Just be certain to keep the workpiece tight against the rip fence and flat against the table.
Assemble the Pieces. That’s it for the joinery. Once you’ve cut the grooves to hold the bottom, you can assemble the drawer. The mechanical lock of the joint makes this easy. You just need to apply enough side-to-side clamping pressure to pull things tight. In my shop, the locking rabbet cut on the table saw is a mainstay.
