Dovetail Lap JointComments (0)
This article is from Issue 67 of Woodcraft Magazine.
Connecting stretchers to rails in tables, chairs and other furniture.
The half-lap dovetail is a remarkably strong and versatile joint. Its most common application is joining top rails to the sides of a carcase (see page 36-37) or to the legs of a table. Due to its wedge shape, the dovetail is extremely effective at locking parts together. In fact, because of its great mechanical integrity, a well-fitted, unglued half-lap dovetail can be an ideal joint for knockdown furniture, as shown in the desk on page 50. (It’s this application that’s shown in these photos.)
As for the dovetail angle, it depends on the wood: for hardwoods, I typically use a 7° slope, while softwoods get a 9-14° slope. Keep the tail fairly wide for strength, and remove no more than 2/3 the thickness of the stock under the tail.
In spite of its angles, the joint is not hard to make. You could use machines to do some of the work, such as cutting the initial half-lap at the tablesaw, but I prefer to make the joint entirely by hand. Doing so is quick, and I get a lot of satisfaction from the direct contact of my hand tools with the material, especially when I end up with a nicely fitted joint.
Precise layout matters
Begin with a hand-cut half lap
Use a sharp, high quality backsaw with a short blade to cut the initial half-lap. Guide starting cuts with your thumb, taking a few light initial strokes, and then carefully staying to the waste side of the scribe line throughout the process. If your cuts aren’t perfect when the sawing is done, you can pare excess material to the scribe lines using a wide chisel.
Make a 3-stage cut. Angle the workpiece away from you, keeping the saw horizontal as you cut, and stopping just short of the shoulder mark. Then pivot the piece toward you and repeat the maneuver, working slowly and precisely. Finish with the piece vertical, laying the saw in the previously cut kerfs as you work down to the shoulder line.
A guiding notch. Begin the shoulder cut by making a guide notch for your saw. Using a sharp, wide chisel held at an angle, gently pare in about 1⁄32", stopping at the line you scribed with a knife in the first step.
Saw the shoulder. Now saw the shoulder down to the cheek, again staying to the waste side of the line.
Keys to Success
- Cut the tail first, then use it to lay out the socket.
- Use a good quality dovetail saw.
- Create razor-thin layout lines with a marking gauge and marking knife.
Make the tail
Mark out the dovetail on what will be the outside face of your finished joint. You can do this using a commercial or shop-made dovetail gauge, a bevel gauge, or even a straightedge. Work carefully, but don’t worry if the slope of the tail isn’t “perfect.” Whatever it is, you’ll be laying out the socket to match it so that the parts mate precisely for a tight fit.
Lay out the tail. I usually mark out dovetails with a simple gauge I made when I was 20. After marking the face, use a small square to extend the lines across the end of the workpiece to guide your saw cuts.
Saw the shape. As you saw each tail edge in turn, clamp the workpiece in your vise with the cutline perpendicular to the bench, which aids cutting precision. Pay special care to sawing squarely from front to back. Afterwards, use a small square to check that each edge is square to the face of the tail, which is especially important to a well-fitted joint. If necessary, pare with a chisel to make corrections.
Lay out the socket
Start by marking the full width of the dovetailed rail across the outer face of the mating piece (here, the KD Desk leg on page 53) at the location of the socket. Then extend these lines squarely across the adjacent inner face.
Gauge the tail length. Set a second marking gauge to register the exact length of the dovetail.
Transfer the length. Use the set gauge to scribe the length of the socket onto the mating piece.
Trace the tail slope. Snug the dovetailed rail up against the mating piece, and trace the tail angles with a knife or very sharp pencil. Then extend the lines at the neck of the tail squarely across the adjacent face, and mark the socket depth on that face using the marking gauge you set when scribing the lap thickness. (See page 66.)
Saw and chop the socket
The first step in cutting out the socket is to excavate most of the waste by first sawing the sides, and then chopping out the rest of the material with a chisel and mallet. Throughout this “roughing” step, make sure to stay a bit inside your layout lines.
Saw the sides. Cut just inside your tail’s side layout lines, holding your saw at 45°, and stopping at your socket length and depth scribe lines.
Chopping spree. Begin by chopping out the waste in layers, working toward the bottom of the socket. Angle your chisel blade slightly upward to ease cutting as you tap with your mallet. Stop just short of your socket depth line, and then begin work on the socket sides. For that, tap downward, carefully holding your chisel vertically, and continue until you have removed all of the waste in the socket to just a bit inside your layout lines.
Pare to fit
Set your mallet aside and pare with your chisel to arrive at the perfect fit. Alternate between the socket bottom and sides, removing a tiny bit at a time as you work your way toward your scribed layout lines. Test the fit as you go, taking care not to damage the edges of the parts as you assemble and disassemble the joint.
Leaning in. It’s OK to undercut the socket sides a tiny bit for a good fit. Just don’t remove too much at the top edges or things can get ugly.
A perfect pare. When paring, hold the chisel so that your dominant hand powers the cut while your secondary hand firmly guides the tool.
Friction fit. The ideal fit should be snug enough to require a few light hammer or mallet taps. Be sure to use a piece of scrap to prevent damage to your workpiece.
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