Decades ago, I remember reading a short by Philip K Dick called “Autofac” which was about replicating machines. It was a bit like his other short called “Second Variety, ” although not as sinister, which was also about replicating machines. Replicating machines, even machines capable of reproducing copies of themselves, has been a concept around for a very long time now. John von Neumann is most often cited but it might go all the way back to Samuel Butler or even “The Sorcerer’s Apprentice.”
Anyway, the technologies associated with 3D printing continue to improve, houses are being printed, clothes are being printed, scaffolds for tissue engineering are being printed and now steel bridges are being printed.
There doesn’t seem to be a limit once we figure out how to do it. For more than a decade, there has been steady work on building a 3D printing machine that print out a copy of itself from raw feed stocks.