JKINNARD created the topic: Impossible Dovetail Box
There are a number of projects for making impossible dovetail joints but I think this is the easiest way if you have a router table. This makes a storage box that many people will not be able to open.
You can scale this as desired. I made a 3"x3" box starting from two 5 1/2" squares of wood 1 1/2" thick.
The fist step is to lay out the final box size as a diamond centred on one of the squares. Find the centre of each side and extend lines to the ends of the square as shown here:
Extend the lines down each end of the square and mark the positions for the dovetail grooves:
Clamp the second square onto the first and mark the dovetail positions:
Use a router table with a dovetail bit to cut the dovetail grooves. Cut one from each edge using the same setup. I used a 9/16" dovetail bit.
On the second square, saw away most of the unneeded wood leaving some for cleanup with the router and dovetail bit. Use the router table to finish the dovetails. Make small cuts checking against the other block to get the dovetails in the right positions.
When the dovetails are finished, fit the two squares together and saw out the square box:
These are the remains of the squares after the box is cut:
These are the completed box with a fist pass at rounding the edges:
You can make a cavity in the groove side square to make a storage box. I used a Forstner bit to make this cavity: