[vonmoltke]

If you have the plans, it's manufacturing, not engineering.

The engineering in the design is in developing the prototypes and proving that theoretical concepts can be implemented practically. There is nothing straightforward about that, unless it is an incremental improvement to an existing implementation.

The engineering in manufacturing is about deriving ways to manufacture parts with greater yields and greater efficiency. In some cases, it is about developing manufacturing techniques that were hitherto impossible. Again, not much straightforward about this.

All of the above is rigorous, but that is not the same thing. This rigor can be applied to software development just as easily as any other product development, and when it is it becomes software engineering.