On a through dovetail, each part projects through the mating piece. This means the end grain on one piece shows through the face grain on the opposite piece. This style of dovetail can be done by cutting dovetails on the band saw.
A dovetail slope of either 1:6 or 1:8 is commonly used to produce the correct tail angles on dovetails. 1:6 is used for softwoods and 1:8 for hardwoods. You’ll need this information to make a dovetail ramp for your band saw. The ramp allows you to cut angles, both left and right of the band saw blade, without changing measurements on the band saw table. Make the ramp by cutting two wedges at an angle that match the dovetail slope you want to use. Sandwich the wedges between the upper and lower boards on the ramp and add a cleat at the edge for your project material to rest against.
Before laying out the dovetail joint, you’ll need to mark out the thickness of each project piece onto its mating piece. The easiest way to do this is with a marking or cutting gauge. Set the gauge slightly greater than the thickness of the material and scribe a line on to the face of the material.
Lay out the pins of the joint. Part of the beauty of this technique is that you can be creative and use any lay out you like for the dovetail. Just be sure that the lines you make are perpendicular to the end of the board. Mark the waste area of the joint so it’s easy to keep track of which side of the line to cut on.
I cut this joint with a 3/16-in. 10 tpi blade. The narrowness of the blade allows me to easily make turns when I need to. The fine tooth count provides a nice surface finish.
Use the ramp angled in one direction to cut one side of the dovetail socket. Then angle it in the opposite direction to cut the other side of the socket. I keep it straight by cutting the left side of the sockets when the board is angled down to the left, and the right side of the socket, when the board is angled down to the right. Even it you miss your line a little it’s OK, but be sure your cuts are perpendicular to the end of the board.
In order to get the waste out of the sockets, cut into the waste area, then turn and follow along the base line you made with the marking gauge. Be very careful to cut this line straight, since the face of the tails will be up against this surface. In order to finish the cut to the inside corner, you’ll need to lift one edge of the board slightly. You’ll need to make two series of cuts; one with the board to the left of the blade, the other with the board to the right.
Make tails a perfect fit for the pins and sockets by tracing the pins on to the tail board. Be sure your pencil is very sharp so you have a crisp line. Position the face of the tail board on the line you made with the marking gauge. Mark the waste.
When cutting dovetails, very carefully follow the pencil lines, and try to cut right up to the pencil line. You’ll need to experiment with your own technique to determine where to cut on your lay out. Softer woods are more forgiving the tails can be slightly oversized, because the fibers will compress as you assemble the joint. Hard woods have to be cut more precisely. You’ll need to “turn the corner” and trim to the baseline to cut the waste out between tails.
The joint should go together with just a little pushing or tapping. If you have to drive the parts together, they’re too tight. If you put the parts together and there is not enough friction to hold them in place, they’re too loose. Once the joint is assembled, you can trim the end grain back so that it’s flush to the face grain using a plane or sander. With practice, the band saw is an excellent way to make through dovetails, allowing you lots of creativity on lay out.