alt Hacker NewsInteresting thought experiment, but I don't see why automating machines that build and repair other machines wouldn't be sufficient. At the limit, such a machine would be able to repair itself, or repair other long-running machines. I imagine it would come down to wear and efficiency loss.
Manufacturing requires micromanaging every aspect of the process, requiring special machinery, trained workforce (human or not), inventory management.
Reproduction, once we master its blueprint of course, is much less demanding: just provide the ingredients at approximate proportions and the chemistry will work its magic to provide a similar enough unit to achieve the required task.