This is a classic puzzle that consists of two identical bent nails.
The gap where each nail crosses over itself is narrower than the thickness of the nails, yet the nails can be connected together and taken apart without any force.
The apparent simplicity of this puzzle is what makes it so great, and the solution is far more elusive than it seems.
In this Instructable I'll show you how to easily form the nails into the correct shape, as well as how to solve the puzzle.
This is a quick, fun puzzle you can make and share with others. Enjoy!!
Step 1: A Bending Jig!
The trick to making this puzzle is figuring out how to easily bend the nails into the correct shape.
The solution I found was to make myself a simple bending jig. It consists of two 3-inch metal rods (harvested from a pair of 5/16" bolts), and a block of scrap wood.
I clamped the bolts into a vise and used an angle grinder with a cutoff disc to remove the heads of the bolts as well as the threads. The resulting sharp edges were also carefully ground away.
Using a 5/16" bit I drilled two holes into the block of wood, 1 inch apart. One hole was drilled about an inch deeper than the other, which is important.
Step 2: Jig in a Vise
The metal rods were tapped into the holes and the block was mounted in a vise. That's the jig!
You could create this same basic jig using a variety of materials and tools - the main things you need are two strong posts mounted closely together into a solid base you can put in a vise or clamp to a table.
Step 3: Nails
I tried this with a few varieties of nails and concluded the best option is to use 16D 3 1/2" nails.
Nails come from the factory with a greasy film that will get all over your hands as you play with the completed puzzle, so I recommend wiping them down with a solvent or degreaser at this point.
Step 4: Bend
I recommend using vise-grip-style pliers to hold the nails while bending them in the jig.
To keep from marring the nail I wrapped the jaws of my pliers with several turns of electrical tape.
With a nail firmly gripped in the pliers, hold the nail in the jig as shown and bend the nail around the taller post.
This might take a few tries to get a feel for it, but after a couple of practice nails you should be able to pound these out.
Step 5: Almost Done
The nails should look like this.
Step 6: The Gap
The gap where the nail crosses over itself is crucial.
It must be slightly narrower than the thickness of the nail itself.
Use a hammer to gently tap the bent nail to close the gap if needed, just to the point where a same-sized nail cannot be passed through the gap.
Step 7: Make Another, and Another . .
Obviously for a single puzzle you need two bent nails.
But I recommend making a whole pile, as these make excellent gifts and spontaneous give-aways to people you socialize with.
Step 8: How to Solve It
First you've got to put them together.
The process is reversed to take them apart. The trick lies in the 2nd and 3rd frames - the movement required is more of a swivel than anything. The two nails must pivot around the middle point where they are touching.
Just fiddle with it and exert a tiny amount of pressure from different angles, and you'll get it.
Now, this is not nearly as easy as it seems, and for the joy of puzzling . . I strongly recommend only following these photos to get the nails together initially. Then try to solve it without looking back!
The bent nail puzzle is a simple classic, and I hope you'll make your own to enjoy and share with others.
Thanks for reading!