One Big Dovetail
Thursday 06 October 2011
John Bullar starts at the beginning
Dovetails don't have to be fiddly little things - a large single dovetail for example, could join the corner of the robust frame around a workbench where the stress would break a lesser joint.
A Tenon with flair
Think of the dovetail as a tenon with sloping sides. The tail is wide at the end, narrowing towards the shoulder line. It fits sideways into a socket sawn in the end of a second piece of timber held at right angles, and each side of this socket are the pins.
Tools for tails
You will need either a dovetail saw or a tenon saw for shaping the sides, and a coping saw for removing a chunk of waste to make a socket. Alternatively, with care, you could use a fretsaw or a scrollsaw. A decent chisel saves a lot of hassle in dovetail work - it needs to be one with bevelled sides and, most importantly, it must be very sharp. You need a fine pencil and a thin craft knife with a pointed blade for getting into tight corners. A try-square and a steel rule complete the kit for dovetailing
The dovetail is a right-angled joint, so before making it we must ensure the sides, faces and ends are precisely right angled. This means spending some time working with a sharp, carefully adjusted plane and a square
Use the square to mark a shoulder line with the knife. Position the square for the tail shoulder line by sliding it up against the socket wood, held endways to act as a gauge. Run the knife tip down the edge of the square
For the other three shoulder lines, position the square by placing the knife tip in the edge of the previous line. Slide the square up against the knife before running the knife across the wood
Woodworkers often say the angles for dovetail sides should be about 1:5 for softwood, or 1:8 for hardwoods - actually dovetails are immensely strong and so long as they look alright, the precise angle doesn't matter. You can use a special dovetail gauge to set the angles for the sides of the tails, or just a pencil and ruler
I marked the tail width 50mm wide at the end and 36mm wide on the shoulder. My shoulder line was 50mm from the end, so this made the angle of each side about 1:7 (50 divided by 7 is just over 7, so knock 7mm off each side to leave 36)
You need to extend the marking lines for the sides of the tail across the end grain. It is important these are precisely at right angles to make the joint a good fit
I shaded the pieces of waste to be removed. I normally do this as a teaching aid and it is not essential, but I suggest scribbling a cross on the waste areas as a good habit - it avoids the risk of removing the wrong piece, especially when you move on to more complicated joints and want to work quickly
Cutting tail sides
Clamp the timber as low as you can in a vice so it does not vibrate. For tail sides, the saw is held at an angle to the timber face, so you can watch the saw-teeth run down the outside of two knife marks at once
Start the cut with the tip of your saw, holding most of the weight off the teeth so it does not jump. Use your thumb as a guide against the side of the saw to keep it aligned with the pencil mark
When the saw cut (or kerf) is well established, the saw can be levelled so the teeth run horizontally, allowing you to cut level down to the shoulder line. Throughout these cuts, the sawblade stays tilted to follow the angle on each side of the tail
Accurately cut shoulders are one of the trickiest aspects of producing tidy dovetails. Clamp the timber edgeways in the vice to remove the wedges of waste from each side of the tail. Saw against the shoulder line, just inside the waste
Making the socket
Although the exact angle and position of the tail sides are not important, these details are critical when it comes to transferring them on the end of the second piece of timber, ready to cut a matching socket. Large pieces like this are best laid flat on the bench and pressed firmly together, while you use the tail as a template to mark around its matching socket
Use the square to mark a socket shoulder line with the knife. Position the square for the shoulder line by sliding it up against the tail held endways to act as a gauge. Run the knife tip down the edge of the square
You need to extend the marking lines for the sides of the tail down the long grain as far as the shoulder line. It is important these are precisely at right angles to make the joint a good fit
I shaded the socket waste to be removed with a pencil. Again, not essential, but it's a good idea to mark this with a large cross
Cutting the socket
With the timber clamped low and vertical in the vice, saw down inside the knife-lines to make the sides of the socket. This time the saw is running at a slight slant to the faces of the timber, so extra care is needed to start the rip cut on course
Remove the large wedge from the socket with a coping saw, cutting some distance above the knife line. Cutting with a fine blade is bound to make the kerf a bit wiggly, so give yourself a
margin inside the line
Remove the timber from the vice and lay it flat on a piece of scrap board so you can chop down against it with a chisel to flatten the socket base. Stand edge-on to the chisel so you can ensure its underside is truly vertical. Firstly, chop to within a millimetre of the shoulder line...
... finally, chop down the last millimetre against the shoulder line. Check the base of the socket with the square - it should be completely flat, or if anything, slightly undercut. Any protrusions in it would prevent the tail fitting. The tail should slide into the socket with firm pressure and lock itself there securely - but don't force it. If the socket is too narrow for the tail, it may be necessary to pare down the sides with a chisel
There is very little difference between a joint so tight it splits the socket, and a sloppy one that doesn't stay together. Smack in the middle of that small difference is the magical thing - the well-fitted dovetail.