A New Twist on Dovetails:
The secret to clean, crisp joinery is maintaining accuracy at every stage of the process. David Barron’s latest alignment board is designed to keep your layout lines exactly where they need to be; on the straight and narrow.
For this project I’m using twisted dovetails and making a very useful dovetail alignment board. This board allows you to line up the bottom edges of your work against the fence of your router table so that the grooves for the box or drawer base will also line up. In addition it keeps things square so that the finished drawer or box sits level. Of course, in order for the alignment board to work well it needs to be made extremely accurately.
Preparing the stock
It is best to use quartersawn timber for long term stability and using a single board will allow both pieces to move in harmony. In this case I’m using some nice quartersawn elm (Ulmus procera). It’s very important the cut is exactly at 90°. I use the tablesaw and, by flipping one board against a straightedge, any error is doubled and clearly visible. Shim as necessary until you have a perfect 90° on both pieces.
Marking and cutting the dovetails
With the stock prepared and marked with dots it’s time to look at the dovetails. I’m lucky enough to own the joint that Alan Peters used in his article for Fine Woodworking back in November/December 1986 and I chose to copy his spacing and layout. The spacing between the tails on the baseline of both boards is even and this makes the joint look balanced. Having said that, the possibilities and layouts for this joint are endless.
Cutting the tails requires concentration as it needs to be at two angles at the same time. I find it best to do this with the saw at 45° to the corner, nibbling gently to get things just right with both lines. Once on track the cut goes smoothly. The bulk of the waste was removed with a fretsaw as close to the line as you dare, with the remainder being chiselled out. I found the elm very soft with a tendency to collapse, so I made sure my chisels were razor sharp.
With the tails cut and cleaned out it’s time to look at marking the pins. In Alan Peters’ article he marks out both parts of the joint in advance and just cuts to the pencil lines. I prefer David Charlesworth’s method in his excellent book Furniture-making Techniques where the pins are marked from the tails after they have been cut out. With this method you can use a knife rather than a pencil, which I find much more accurate. The actual marking needs to be done with one board directly on top of the other. These also need to be flush on their edges as well as faces and I found it best to clamp them up and make adjustments with a brass hammer. With a final tighten on the clamps and a check with a straightedge, I secured the whole thing in a vice which made the actual marking easy.
Assembling the joint
I finished knifing the pins on the face side with a 1:6 marker and then cut the pins using the same technique as the tails. After checking the fit it was time to assemble the joint which needs to be done simultaneously at a 45° angle. Both Alan Peters and David Charlesworth used a combination of cauls and clamps on both sides to gradually pull the joint together, a slow-setting glue is definitely helpful here. Instead I used a more low-tech method, a dead blow mallet and a block of wood! This is equally effective for disassembly if needed. I alternated from one side to the other making sure to keep things square and it went together without much trouble.
It’s most important to make sure the joint closes without gaps on both baselines, otherwise all the hard work getting the pieces to an exact 90° is wasted. Undercutting the end grain when cleaning out the tails and pins is very helpful for this. With a final check to make sure the two pieces are at 90° to each other, the board is left overnight to set.
After planing up the surfaces and edges, being careful to keep them flat, it’s time to choose which side the fences are going to be mounted. With the board on its edge on a dead flat surface, take a square and check to see if the corner is square with the surface. Do this from both sides and on both edges to see which is the best. If any adjustment is needed on the better of the two sides this can be done by carefully shimming the fence with veneer.
Before attaching the fence the inside edges have a strong chamfer which acts as a dust groove preventing any debris from giving a false reading when the board is in use. The fence is made to protrude about 4mm above the surface of the board and screwed in place, rather than glued, so that it can be shimmed as mentioned above. It’s quite possible to make an accurate dovetail board with plywood and butt joints, but it just wouldn’t look as nice!