It's a popular internet joke: the danger of 3d printing is that once you have a 3d printer, you can just print out more 3d printers. This would be a concern to 3d printer manufacturers. But if you've spent some time with 3d printers, you know that this is nowhere close to becoming a reality.
But you can print parts for a 3d printer and many people have (I've printed out a spool holder for a 3d printer using the same 3d printer). Instructables member redhatman and his roommate were curious about how much of a functional 3d printer could be created using only printed parts. He did this because he and his roommate bought a 3d printer together and had to decide what to do with it when they parted ways. King Solomon was not available to provide a solution, so they resolved to duplicate their printer.
It was successful! Redhatman and his roommate were able to build a 3d printer that successfully prints objects, including this dragon figurine. He suggests eventually developing self-replicating printers, which isn't necessarily just a crazy concept from Star Trek.