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Making a Twisted Dovetail Box     

 © John Bullar 1998

This article by John Bullar was first published

by Furniture & Cabinetmaking magazine in 1999

This artist's pencil box in American black walnut (Juglans Nigra) and English sycamore (Acer Platenoides) was made with joints based on the twisted dovetail or nejiri arigata, displaying tail-type wedges both on the sides and ends. A drawer only gets pulled one way but the force on the joints of a box pull both sideways and lengthways - normal dovetails wedge the sides together in one direction and rely on glue to hold the box together in the other direction.

Dovetails only do half the job of holding the box together, and so I looked for a way to make a box with joints wedged both ways. The answer came when I was playing around with variations on the twisted dovetail - the Japanese nejiri arigata joint. Marking out starts by dividing up the width of the end between the total number of joints - but there the similarity with dovetails ends. For fine handcut dovetails you would probably try to make the pins very narrow and the tails much broader. But with this twisted dovetail joint, the pin on one face also forms a tail on the other face so they are all the same width. The cutting lines are made by marking the position of each cut, and then the angle of each cut. Unlike a dovetail, it is not easy to cut one piece first and then mark the mating piece off it.

 To maintain accuracy with the joints, mark both corresponding cuts on the side piece and the end piece together as two complementary pairs. To mark the positions of the cuts on each arris butt the two pieces tightly together end to end. Use one press of the knife tip to mark both end and side pieces simultaneously at each measured distance, so there are no possible differences. Next, line up the end and side pieces side by side ready for marking the angles of the cuts. Working first on the end piece, align the edge of a sliding bevel gauge between the position mark on the arris and the centre point of the opposite edge, then marked against it. The sliding bevel is locked in position and turned over to mark the same angle across the endgrain, so the lines meet at the arris in a chevron pattern. With the sliding bevel still locked, the same angle is then marked from the corresponding position on the arris, and across the endgrain, of the side piece. This process is repeated for every cut so that the lines focus on one point, making the flared joint pattern - you could use a more distant point to lessen the short grain if you wanted.

It's a good idea to number the cutaway socket pieces in order to lessen the confusion! Saw the joints with the piece clamped fairly low in the end-vice using a. fine-toothed dovetail saw with a very small set on the teeth. This cuts a kerf just 0.5mm wide. Because the set is so small it cuts a very straight clean edge, but it is unforgiving. The first couple of strokes are critical to the line it will follow - after that there is no way it can be pulled back into line if it starts to wander. It is possible to get it to run just down the inside edge of a knife line so that no paring is necessary to make a well fitted joint - at least that is the theory. After sawing down the sides of all the joints, cut the sockets across a couple of millimetres above the depth line with a fretsaw. Level up the bottoms of the sockets with downward chisel strokes, starting with a fairly coarse cut and finishing with a 0.5min slice up to the line. By clamping the piece under a stout guide block of right-angled hardwood you can guarantee a straight chisel cut. This guides the chisel in two ways - firstly, it accurately sets the position of the chisel cuts up to the line, and secondly, by holding the chisel back flat against the block, you know for certain it is slicing though at right angles.

Now the joints should fit together. But how? Of course they won't slide longways or sideways - that's the whole idea of this kind of joint! However, they can be persuaded to fit diagonally at 45º by moving both parts of each joint inwards together. It is probably best not to try fully engaging any of the joints before the final glue-up because if they are a snug fit there is the risk of damage while pulling them apart. If just the tips of the corners are engaged, it is quite easy to sight along the lines of the joint to check that it is going to engage smoothly. Glue the joints with PVA using an artist's brush. The four corners are engaged together, then the box is placed between a sash cramp and a couple of G cramps, not forgetting first to fit the bottom panel in its groove! Closing the joints is a matter of tightening the three cramp screws a fraction of a turn at a time to keep all the joints moving inwards together. Of course it is necessary to do this sensitively because any tightness would force the joints apart and is likely to split the wood. With all four joints closed up, remove all the cramps so as not to distort the wood whilst the glue sets. When the glue is dry, clean up the joints, using a low-angle block plane. A micro-chamfer, planed along the top and bottom arris helps to make them more durable - it stops the long fibres forming splinters and removes the temptation to sand over the sharp edges and make the shape look soggy - chamfers catch the light cleanly and help to visually define the edges.