For less cost than some exotic high end plastic printer
setups, makers can move to designing cloning and learning
anything using surplus metal tooling equipment, scrap metal, ...

https://www.youtube.com/results?search_query=fabricating+homemade+engine
https://www.youtube.com/results?search_query=50+bmg
https://www.youtube.com/watch?v=zp67DpYJsBE
https://www.youtube.com/results?search_query=railgun
https://www.youtube.com/results?search_query=homebuilt+turbine