This is my brand new interlocking puzzle design that should print perfectly on a well tuned printer. It consists of three pieces and makes a 3x3x3 cube. It isn't too difficult to solve but is the first design that is both interlocking and fully printable without support.

This will test how accurately your slicer/printer combination can print simple objects. I tried a range of offset distances and found that creating pieces with every face offset inwards by 0.1 mm gives the best fit. The model has a base cube size of 6 mm giving a finished puzzle of just under 1.8 cm whilst using very little filament. Feel free to scale the puzzle up for a larger version but be aware that this will tend to make the pieces fit more loosely. I used a 0.2 mm layer height and 0.3 mm extruded width from a 0.3 mm nozzle. Use medium infill to make sure that you get a nice smooth top layer. Finally, use a craft knife to remove any extraneous bobbles that might jam the pieces together.