Most of us are familiar with the techniques for fitting dovetails during construction. You cut the pieces to size, mark your dovetails, and cut away. Even if you machine-cut, the process is basically the same. Everything is measured from the end of the board. However, there are times when this approach doesn’t work.
This blanket chest is a perfect example of this. Christopher Schwarz’s Anarchist’s Tool Chest is another. In both cases, a base or dust seal wraps around the basic structure of the chest, and is dovetailed into place. The problems start to arise when you realize that the pieces cannot be precut to length, but must be fitted to the existing structure to ensure a good fit. No, measuring with rule is not a substitute for a good direct measurement. Of course, your measurement doesn’t tell you how far past the end of the casework the board should extend for the overlap that will give a good, snug dovetail. This is how I do it:
Start by dovetailing one corner to act as a reference, leaving the board overlong. Then, with the assembled dovetail snugged into place, mark the corner of the casework on the other end. A marking knife will work, but I find that a pencil will angle into the corner more easily without wandering.
Next, stand the opposing board (or an offcut of the same) on edge on this board, with the inside edge flush with your pencil line, and mark the location of the outside face. This measurement isn’t really critical – you just don’t want to be too short. Next, crosscut the board to just outside this last line to establish the rough length.
Now comes the trick. Take your marking gauge, which you already set while cutting the first dovetail, and place it against the sawn end of the board. There will probably be, as shown above, a gap between the knife/pin and the pencil line. Simply plane away the excess with your shooting board (you do have a shooting board, don’t you?) until the marker touches the far edge of the pencil line. If your marking gauge was set correctly in the first place, you should now have the correct amount of overlap to yield a dovetail that wraps snugly around the casework.
With a little thought and modification, this technique will also work with dovetailing jigs. Simply set your marking gauge to the base of the first dovetails, and proceed as above. Since all you’re doing is effectively cutting a board to length, the dovetailing method is really irrelevant. Give it a try!