A challenge to make and even harder to solve
A friend recently showed me a dovetail joint that not only demonstrated great craftmanship but also provided a puzzling challenge and an opportunity for some fun.
I expect many amateur woodworkers have made one of these over the years. The dovetail joint, we all know what they look like; one piece of wood with what might be called a tenon cut in the end of it, except that it widens out towards the end (like the tail of a dove) and needs a similarly shaped slot to fit into. If the tail widens out sufficiently, it is virtually impossible to pull the two pieces apart.
However, if you look at the drawing of the ‘Impossible Dovetail’, you will see there is something wrong with it. The joint fulfils its usual function of being difficult to pull apart — but how do you get it together in the first place? And how do you get it apart if you want to? You cannot simply lift the dovetail out of its recess as there is another one stopping it.
There is a way of getting the two pieces apart which if challenged, the hapless victim is expected to do within a specified length of time, or they will be asked to pay a forfeit of some sort. If the puzzle is well made, it is hard to spot the solution. I wonder how many readers who have not come across this teaser before can see how it is made.
To solve this puzzle probably requires a bit of lateral (or possibly diagonal) thinking, as things are not quite what you expect them to be. You naturally tend to assume that the dovetail will have been cut at right-angles to its surface, so any of the four dovetails in the puzzle will go straight through to its partner on the opposite side of the block of wood. This is not what happens, so where are the cuts made? The answer is that when the dovetails are cut and each one joined, not to its partner on the opposite side but to a dovetail on one of the surfaces at right-angles to it. This makes it possible to slide the joint apart quite easily by pushing the two halves diagonally in opposite directions. If the joint is not made accurately enough, it is possible to see that the cuts do not go straight through. It is, therefore, quite a challenge to make the puzzle so that it is a close fit and yet will come apart without difficulty when necessary.
For more information including project plans on how to make ‘Impossible Dovetail Joints’ see: