This puzzle is not my idea it's just my version of it.

The design side of things was pretty straight forward really in the free design software I use, have a look at the attached photos which shows you the basics of it, sketch a 60 x 60 square, extrude it to 30 mm and then sketch in 15 mm 45 degree in each corner, then join the corners and the corner to corner as in the photo, extrude the segments down to 15 mm and draft this to 15 mm creating the dovetail shape, turn this body into a component, create another 60 x 60 sketch using the extruded bottom face on the first component then turn this component off and extrude the sketch to 30 mm, create new body and convert into a component, using the combine tool as a cut, use the 2nd component as the target body and cut it with the first body, and tick keep the tool, we now have the impossible dovetail cube, the next job is to add the holes for the magnets etc.

For this project you will need 1 x 6.3 mm steel ball and 1no 5mm diameter 2 mm thick neodymium the magnet is placed in the recess in the Part 1 half of the cube.

You now have the Impossible Dovetail, the puzzle is to place the steel ball into part 2, slide part 1 into part 2 and turn upside down, you will here the steel ball click onto the magnet, now it's impossible to open, to open you want part 1 on the top and tap it hard on a surface to release the ball from the magnet, the ball falls into the part 2 and this allows you to slide open the puzzle to reveal a note or whatever within the puzzle.

The first prototypes I made were that sharp on the points of the dovetails that I ended up cutting myself a couple of times, so I filleted the whole cube to take the sharp corners away, the cube still performs perfectly as it should without injury now.

I hope I've tried to explain it as well as I can, A very clever idea unfortunately not mine.

One thing to note is that I printed the 2 components separately and not as in the 3mf model, this model needs to be in 2 colours to avoid confusion.

Great learning curve project.

Thanks for looking.