Comment by anon6362

To build assembly lines, one has to first make custom tools, jigs, and parts and apply processes to them that cannot just be 3D printed in plastic or metal or FDM'ed.

The main show-stopper to them is the lack of working knowledge about precision tooling manufacturing.

For example, some of the best power machine tools in the world came from Germany and from Bridgeport, CT between 1910 and 1965. There are/were moderately large, 1 micron runout milling machines such as Moore No. 2 and No. 3. These things generally aren't made anymore and not many people know the tricks and processes to make similar or equivalent machines that make other tools and machines. Like that the unshielded body heat of an operator can swing the runout of a precision machine in an otherwise climate-controlled environment.