Lessons/Guides – Mystery Dovetails

PRESS A DOVETAILED BOARD into another board with matching sockets, and you’ve created woodworking’s most iconic joint.

The dovetails and sockets wedge the boards together, so the joint can’t pull apart; the only way to disassemble it is it is to lift the dove-tailed board back out of the sockets.
So, what if you can’t lift out the dovetailed board? How do you disassemble the joint? And how would you assemble this joint in the first place? Those are the questions to ask when you show a friend the dovetail joints shown here. These puzzling joints appear to wedge together on more than one surface-an impossible feat for traditional dovetails!

Test your hand tool skills

The secret behind these joints, of course, is that they don’t assemble the traditional way. The first two are elaborate sliding dovetails and the last is a comp l ex pivoting joint. There’s no simple method to machine these joints; they must be cut primarily by hand. And creating them will test your hand-dovetailing skills, because of their compound angles and large joint surfaces.

Unlike most wooden puzzles, these joints shouldn’t be constantly assembled and disassembled. The pieces include fragile short grain that can easily break and delicate edges that will quickly show wear. It’s best to glue the joints together as soon as they’ve been satisfactorily fitted.

You’re bound to make some mistakes, so always start by making a practice joint. Make sure to use stock that is straight-grained on all four sides – it’s difficult to pare against the grain’s slope. Also, it’s a good idea to use hardwood for one piece and soft-wood for the other. This method is more forgiving, because the softwood piece will conform to the hardwood piece when you assemble the joint. Using hardwood for both pieces requires absolute precision, because there’s no forgiveness: If the pieces don’t fit perfectly, short grain parts will simply break off.

Use the same steps you would follow to cut dovetails by hand to create all three joints. Start with pieces that are cut perfectly square. Layout the dovetails and sockets on each piece. It’s best to scribe or knife the layout lines, so you can precisely bed your chisel for paring; if you pencil the lines , make sure they ‘ re crisp and narrow. Clearly mark the waste areas.

Make sure your tools are razor sharp. Cut the cheeks first (Photo 1). The safest method is to cut outside the lines. Next, remove the waste (Photo 2). Finish by paring to the lines (Photos 3 and 4).

Secret to easy assembly

When all of the cheeks and shoulders of these joints are pared absolutely flat, it’s difficult to slide the pieces together, due to friction resulting from the joints’ large surface area. Fortunately, there’s a work-around. The only places where the joints have to fit perfectly are the faces that show. So, to make the pieces slide together more easily, slightly hollow the joint surfaces that don’t show.

Devious End Joint

Through dovetails appear to cross inside this joint, which of course, is impossible. Instead, two dovetails run diagonally across the top of Piece A and two diagonal sockets are cut into the bottom of Piece B (Fig. A). On each piece, the layout is identical on all four sides.

Make the pieces

1. Layout the dovetails and sockets. Mark the waste. Assemble this joint by sliding the pieces together from corner
2. Saw the dovetail cheeks in Piece A and the socket cheeks in Piece B (Photo 1). Sawing these compound angles accurately is tricky, so don’t be a hero: Cut in the waste area, outside the lines.
3. Remove the waste to establish the joint shoulders (Photo 2). Insert the coping saw into one of the cheek cuts, turn the blade and saw to the other cheek cut.
4. Pare to the lines (Photo 3). Use a wide chisel to pare the cheeks and a narrow chisel to pare the shoulders. Beveling the sides of the chisels makes it easier to get into the acutely angled corners (Photo 4).

Ease the fit

On this joint, all four faces of both pieces show. To ease the fit, hollow each dovetail cheek on Piece A and the shoulder of each socket on Piece B. Always start paring 1/16″ inside the outside edge, to create a lip. Then pare to the center. When the pieces slide together, the 1 /16″ lips at the outside faces will be the only parts of the joint that fit flush.

Devilish Lap Joint

On a typical lap joint, Piece A would simply press into Piece B. Well, that can’t happen here. Neither can the two pieces pull apart. So what gives? A clever version of a tapered sliding dovetail, that’s what (Fig. B). The dovetailed tenon on Piece A tapers on the bottom, from the shoulder to the end. On the top, its edges slope in the opposite direction, at com-pound angles. The mortise in Piece B mirrors the tenon on Piece B, sloping up on the bottom, and down and out on the top.

1. Layout the dovetail and mark the waste. Cut the 1/8″ bottom shoul­der on the tablesaw.
2. Tilt the blade and use a tenoning jig to cut the tenon’s angled bottom face.
3. Use a handsaw to crosscut the dovetail’s canted square shoulders.
4. Saw the dovetail’s compound-angled cheeks. Cut in the waste area, outside the layout lines.
5. Precisely pare the cheeks and shoulders to the layout lines.
1. Layout the mortise and waste.
2. Saw the mortise’s compound-angled cheeks; cut outside the lines.
3. Make a lengthwise cut in the center of the mortise, to divide the waste in half. Cut deep at the butt end and shallow at the open end, following the slope of the mortise.
4. Saw out the waste. Insert the coping saw in the lengthwise cut, turn the blade and saw to one corner. Remove the waste and then saw to the other corner.
5. Pare to the lines. When you pare in from the butt end, the acute angles inside the mortise will trap the waste, so be prepared to progress slowly.

Ease the fit

Fortunately, only the top face and out-side end of this joint show; the other hidden joint surfaces can be “adjusted.” The sloped bottom f ace of Piece A and its beveled dovetail cheeks are the easiest surfaces to access. When you hollow these surfaces, however, do not disturb the narrow wedge-shaped end of the tenon, or the edges of its dovetail-shaped top surface.

Diabolical Corner Joint

The flared ends of the dovetail pins mean this corner joint can’t disassemble the traditional way. And no evidence of a sliding joint appears on the back side, so it can’t go together like the double-dovetailed tenon in the previous joint. The secrets are dovetails that slope at three different angles and sockets with coved shoulders (Figs. C and D). They allow the boards to slide together in line and then rotate 90 to form the corner. For the record, the dovetails on the outside face of Piece A match the sockets on the end of Piece B, the dovetail ends on the end of A match the sockets on the outside face of B, and the dovetails on the inside face of A match the sockets on the inside face of B. The coved sockets in A provide clearance for the outside corner of B as the boards pivot.

Make the pieces

1. Layout the dovetails and waste.
2. Saw the dovetail cheeks, following – but staying outside – the layout lines on the end and the outside face. This cut won’t follow the lines you’ve laid out on the inside face, because they slope more steeply.
3. Saw out the waste.
4. Pare to the lines. On the cheeks, work from each face to the center-on the inside face, you’ll have to remove more material. Because the outside and inside slopes differ, the faces of the cheeks will be faceted, rather than flat. Notice that the dovetails on both faces are the same width at the neck.
Follow the same procedure used to cut Piece B, with this exception: Hollow out the socket shoulders, leaving tiny (1/16″ wide, or less) flat lips at the outside face, to seat the joint.

Ease the fit

The cuts on the ends and outside faces of both pieces are the ones that show, so theyrl1ust remain precise. To ease the fit, slightly widen the socket cheeks and shoulders on the inside face of A-but do not disturb any dimensions at the end of the board. Gently ease the facet lines. Make sure each socket shoulder in A is hollowed into a fair curve, so the ends of B can rotate through.

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