Dovetail Lap JointComments (0)
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.
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 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 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.
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.
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.
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