Idea taken from https://thingiverse.com/thing:2469830
Done with inkscape and https://github.com/fablabnbg/inkscape-paths2openscad/releases
The gap is set to 0.2mm, which is wide so that most printers will produce a loose fit. You can easily accomodate by adjusting the extruder flow to 110% or 120% -- 120% gives me a very strong fit requiring a sturdy workbench and applying my body weight to assemble.
Warning: Do not try to solve the puzzle from looking at the photos. To keep up the challenge, the pieces in the photos show a similar but confusingly different design. Sorry :-)