LEGO parts are plastic. 3D printers make parts out of plastic. So the transitive property tells us that a LEGO 3D printer should be able to recreate itself. This one’s not quite there yet, mostly because it doesn’t use plastic filament as a printing medium. Look close and you’ll probably recognize that extruder as the tip of a hot glue gun. If all else fails you can use the machine as a precision hot glue applicator.
The instructions to make your own version include the design reference and a few ideas for getting the most out of the glue dispenser. For the design phase [Matstermind] used LEGO Digital Designer. It’s basically CAD with the entire library of LEGO parts available as building blocks. from there he assembled the machine which is controlled by an NXT brick. He goes on to link to a few different printing mediums. There’s instructions for using crayons to make colored glue sticks, as well as a method of printing in sugar using the hot glue extruder.
We remember seeing one other LEGO 3D printer. That one didn’t use an extruder either. It placed blocks based on the design to be printed.