There is a fantastic book called "Build Your Own Metal Working Shop From Scrap" that details how to make a working metal foundry and build a lathe and a drill press. I've worked through parts of it, I was able to build a metal foundry and cast some of the first lathe parts. It's totally doable on your own. 3d printing a lathe probably wouldn't be super feasible, but it's doable by a determined person with the know-how.