Master the mortise-and-tenon joint
Mastering mortise-and-tenon joinery has always ranked at the top of woodworkers’ skill priority lists. That’s because its great strength makes it the premier joinery technique for furnituremaking.
Machining mortise-and-tenon joint members takes only a moderate amount of time and fuss, provided you have a few basic tools. To help you succeed at the king of joints, we’ll walk you through making the blind mortise-and-tenon joint (the most common, where the tenon is completely enclosed in the mortise), letting you choose the options that best suit your tools and preferences. But before we begin, take a minute to review the basic terms and design proportions in the drawing, below.
Start with the mortise
Always cut the mortise first and then size the tenon to fit snugly. It’s quicker and easier to adjust the dimensions of a tenon (as we’ll show later) than to change a mortise.
Establish the mortise width at 1⁄3 the workpiece thickness. This ratio results in a joint with plenty of strength in both the tenon and the sidewalls. Most woodworking projects call for 4/4 stock, which measures approximately 3⁄4 " thick after surfacing and sanding, so a 1⁄4 "-wide mortise works well for most of your projects.
Also, avoid mortising less than 3⁄8 " from the end of a workpiece. This prevents splitting as you shape the mortise and assemble the joint. For strength, make the mortise depth approximately 1⁄2 to 2⁄3 the width of the workpiece.
Mortise method 1: Rely on your drill press
Pro: This method requires no expensive or specialized equipment.
Con: Cleaning up the mortise with a chisel takes time.
If you have a drill press and chisels, you’re ready to mortise. Equip your drill press with a brad-point bit that matches the mortise width; a brad-point bit wanders less than a standard twist bit as you drill overlapping holes to form a mortise.
Now use a sharp pencil or marking knife and a combination square to lay out the mortise opening. Then set the drill-press fence to center the bit between the mortise sides and adjust the depth stop. Finally, follow the two-step process shown in the photos below.
Mortise method 2: Add a mortising attachment
Pros: A no-chisel way to drill and square the mortise in one step. Moderate price.
Cons: Installing and removing the mortising attachment takes time, and the drill press can’t be used for other tasks with the attachment in place.
To speed up your work, avoid hand-chisel work by equipping your drill press with a mortising attachment. Its hollow-chisel design—a drill bit surrounded by a sharp, square sleeve—lets you form a mortise by drilling a series of square holes. We bought a kit that includes hollow chisels in four sizes from Tool Crib at 800/635- 5140. Before you buy any mortising attachment, check with the dealer or manufacturer to make sure that it fits your drill press. The photos below describe the simple procedure for using this handy accessory.
Mortise method 3: Step up to a benchtop mortiser
Pro: Yields quick, clean mortises with minimal setup.
Con: A benchtop mortiser serves only one purpose in your shop.
Woodworkers who make a lot of mortises find it handy to own a dedicated machine. A benchtop mortiser works like the drill-press attachment, but it’s always ready to use. Refer to the photos below for details.
Now it’s tenoning time
After you finish the mortises, use your scrap test pieces to set up for forming tenons. The ideal tenon slides into its mating mortise with firm hand pressure. Center the tenon on the edge of the workpiece (between faces) and make it 1⁄16 " shorter than the mortise depth; this hidden gap provides a place for excess glue and guarantees that the tenon won’t bottom out in the mortise, spoiling the fit of the joint.
What’s the best way to cut the tenons? Match your equipment to one of the operations discussed below. If you have it all— dado set, tablesaw, and bandsaw—experiment to discover which method you prefer.
Tenon method 1: Keep it simple with your tablesaw and a dado set
Pros: No jigs are needed, and you make all cuts with the workpiece completely supported by the table.
Cons: Some lesser-quality dado sets produce a rough surface and can splinter wood when crosscutting; such surfaces must be sanded. Also, you might find it awkward to handle workpieces over about 4' in length.
In the WOOD® magazine shop, we usually choose this method for cutting tenons because it’s quick, simple, and reliable. Align your tablesaw rip fence parallel with the dado set and make sure that your miter-gauge fence sits at right angles to the dado set. These steps are critical for making a square, tight-fitting tenon.
You’ll also need to install a miter-gauge auxiliary fence that extends to the rip fence. Make this fence by attaching a 2"-wide strip of straight material to the gauge with screws or double-faced tape. Now follow the step-by-step photos below.
Tenon method 2: Stay with the tablesaw, but add a shop-made jig
Pro: Smooth results at little cost.
Cons: Saw blade’s working height limits tenon length; jig takes up storage space in your workshop.
If you’re not prepared to pay $100 or more for a high-quality dado set, cut tenons with the workpiece held vertically on the tablesaw. You need a dependable jig for this operation; the drawing below shows you how to build one at minimal expense. We designed it to clamp the workpiece in place and ride flush against the rip fence.
Now, mount a combination blade in your tablesaw and add an auxiliary fence to your miter gauge. Also install a zero-clearance throat plate to keep the thin waste pieces from being caught and kicked back. Now proceed as shown below.
Alternative tenon method 2: Buy a commercial jig
Pro: A fine-tuning knob makes this jig easier to adjust than our shop-made version shown above.
Con: Not designed to cut edge cheeks.
Would you rather buy a jig than make your own? We tested three similarly priced models and liked them all. A tenoning jig, such as the Delta version shown below, offers great convenience and accuracy and should last a lifetime.
Tenon method 3: Try the bandsaw for smooth cuts and versatility
Pro: It’s easier to handle pieces over 4’ long on a bandsaw than on a tablesaw.
Con: A dull or poorly tensioned blade results in an uneven face cheek.
None of the tenoning methods discussed so far solve the handling problem you face when cutting oversize workpieces. Rather than hold big pieces vertically on your tablesaw, cut their tenons on your bandsaw, supporting the weight of the rail with a table-height support. Set up for this technique by installing a blade designed for resawing; a 1⁄2 "-wide blade with three teeth per inch (tpi) is a good choice. Make test cuts in scrap to determine whether you need to compensate for blade drift by setting your fence at an angle. A bandsaw works just fine for short workpieces, too, and surpasses many dado sets in producing smooth tenon cheeks.
Fine-tune tenons for a good fit
Despite your most careful efforts, sometimes you’ll need to make a tenon thinner or thicker to achieve a good fit. Don’t count on glue alone to fill gaps—that approach will only weaken the joint.
For a tenon that’s slightly oversize, use a sanding block to remove a modest amount of material as shown in the “Sanding” photo, below. Sandpaper wrapped around a block is likely to ruin the straight line of the shoulder, so use self-adhesive sandpaper on the bottom only. Or, if you prefer, use a rabbeting plane and a light touch, as shown in the “Planing” photo, following.
Fix a tenon that’s too thin by gluing on oversize filler piece, as shown in the “Shimming” photo, below. Saw, plane, or sand the tenon to final thickness after the glue dries. Finally, use a sanding block to form a chamfer around the end of each completed tenon, as shown in the “Chamfering” photo, following. This simple step helps you get the tenon started into its mortise with no fuss at assembly time even if the glue has begun to swell the wood fibers.