There are different ways to join two pieces of flat wood together. But only the dovetails guarantee sturdiness. This is particularly the solution adopted for the realization of drawers.
The assembly called "tails" is based on the union of male protrusions (tails) and female parts (mortises or female tails).
We speak of straight tails when they are parallelepipedic, and of dovetails when they are trapezoidal, which confers to the assembly a much greater resistance.
They fit into notches of similar shape, ensuring perfect strength and resistance to traction in both directions.
Tails are "covered" when the notch and tails are not all the thickness of the piece, making them invisible on one side or both.
This type of assembly is mainly used for drawers, the face of the dovetails must be not visible on their facade (unless it is reported, which is often the case in industrial woodwork).
The tracing of the dovetails is more complex than that of the straight tails.
Here we use a false square or "grasshopper" that keeps the angle of the different cutting lines on the edge of one room and on the facing of the other. The precision of the line is of primary importance because it conditions that of the sawing and thus the adjustment of the pieces. Tooling side, it is essential to use a saw of very good quality, with fine teeth.
A backpack saw is suitable, but less than a frame (or frame) scoring saw, which ensures excellent blade tension and guarantees the range of motion. A Japanese saw is also suitable.
The saw cuts having been made with the greatest precision, the clearance of the mortises is done with scissors with wood perfectly sharpened (not to burst the wood), of width adapted to the difference between the tails.
It is essential to work with the chisel and not with a chisel whose cutting precision is insufficient.
In addition, do not try to clear the notch at once because there is a risk of breaking the male tails.
A cabinetmaker is able to make dovetails so accurate that their interlocking is enough to ensure the strength of the assembly.
This is not always the case for the amateur carpenter, who usually needs to guarantee this solidity with a little glue.
A tip in the tails of song can also contribute, even if it is hardly orthodox!
Note that DIYers who have a wood combination can make dovetails in series thanks to the tenoning and router functions.
The steps of making a dovetail assembly
- Using a false square, draw parallels from points dividing a straight line into equal segments.
- The angle of a dovetail, 78°, is the diagonal of a rectangle of 50 x 10 mm.
- Draw a triangle on the board at 78° to adjust the opening of the square.
- Postpone the angle obtained to finish drawing the dovetails.
- Hatch the falls.
- Block the piece in a vise.
- With a razor-sharp saw (fine toothing), saw the falls respecting the angle of the tail.
- Take care not to exceed the cut line.
- Hollow out the falls with a chisel.
- Hold the tool vertically, cut the edge of the chute and then hollow out it with the oblique part.
- Be careful not to damage the edge of the cut with the blade.
- Finish with a chopping saw.
- Saw inside the line and finish, if necessary, with the chisel.
- In case of imperfect sawing, finish with a fine grater.
- Postpone drawing of the dovetails on the end edge of the second piece.
- Then hatch the falls and cut the "tails" with the saw (thickness of the piece + 2mm)
- Hollow out with the chisel, as above.
- Do not force near edges, the wood could burst.
- Scissor work is tricky because you have to cut and remove trapezoidal drops without damaging the edges.
- Gently assemble the two parts by tapping with a mallet, after interposing a martyr hold.
- Cut the tails with a saw and finish with a plane.
- If necessary, sand with sandpaper on hold (grain # 180).
There are commercially available dovetail jigs for use with a router mounted router. We can use them as well "on the fly "only with a stationary milling table.
In case of difficulty to fit two pieces of wood, do not insist. There is a risk of breaking one or more tails. Mark the stumbling block and grind with a fine rasp.