Wednesday, September 28, 2011

Triangular Dovetail Joint

Woodworkers have made trick dovetails for years, probably centuries.  I designed this trick joint because I hadn't seen any triangular dovetail joints.  Not surprisingly, it has been done before.

All three exterior sides show identical dovetail-like joints, which makes it look impossible to open.

But the pieces don't slide like a conventional dovetail.

The two pieces rotate until they gently let go of each other.

There's a hollow cavity inside, so it can be used as a puzzle box.  Not that anyone would be terribly puzzled--it looks odd, but it's easy for anyone to open once they pick it up.

This is a simple, traditional puzzle box so I've posted the STL files at Thingiverse for anyone who wants to play with it.


  1. That looks very nice! If you wanted it to be more difficult as a puzzle you could always give it a simple gravity pin lock. Then if the fit was tight enough it could be much more puzzling.

  2. Ordinarily I don't like to add locks or other complications unless it's consistent with the premise of the puzzle. But while watching colleagues open this joint I noticed a subtle psychology which suggested a feature that would be counter-intuitive yet elegantly simple. It's worth building a successor to test that idea.

    In the meantime I've found other designers who've worked with similar three-sided dovetails.

    Buried in Rob's Puzzle Page is a picture of R.D. Rose's "Triple Dovetail Triangle" in which Rose took the same basic dovetail mechanism and added locking cylinders to it.

  3. Gravity pins and the like should be banned from puzzles, IMHO. Those things drive me nuts.

  4. Adding a slot half way round the dovetail, requiring the halves to be lifted apart, then rotated back on themselves to open would make for a nice puzzle with no pins. Almost a maze, but not quite.

    Given your familiarity with threads, putting a left handed thread onto the centre hollow would also make things interesting.

    Neither would be difficult puzzles, but they would slow people down. (especially a left handed thread)

  5. I just found this post. I have been struggling with an old design that i want to renew. It involves puzzles, made of plastic, that can be made to change the final shape, but fit together as a cohesive, solid unit.
    Are you still working on such puzzle matters (?) since this post is a # of yrs old...