For my senior design project, my partners and I tried to research the creation of an ultrasonic 3D printer, that can make things out of metal (or maybe even things made of plastic, metal, etc fused together). The technologies already exist for must of it, it's more a matter of combining them.
With the interest in finding ways to make guns at home, I figure this might be helpful. Problem is that we don't have the financial resources to continue working on this, because the appropriate components needed are more expensive than what we have in our pockets. If you're interested in this idea or know of a way that could help with getting this to the market, please let me know.