YOKOTA AIR BASE, Japan — Tech. Sgt. Tylar Cravens believes he has an idea that could change the way the Air Force trains aircraft maintainers, and he’ll soon pitch it to top leaders at the Pentagon.

The moment you finish setting up your first 3D printer, it may feel as though the entire world is at your fingertips. After all, you can craft all sorts of things, from handy tools to beautiful ...