[Stiglr]

You absolutely could create things to an engineering specification; although, the tools you already use in an AutoCAD, for example, probably have built-in features that automate some of the processes you'd have to figure out more mechanically in AC3D. That's the "tolerance" part of an architectural or CAD software that AC3D doesn't specialize in. Or, for machined parts, your tools would also have some kind of data plugins that would enable you to get plastic mockups created for prototypes.

But, you can "get down to the fraction of a mm" you need and have it reflected in your models, for sure. It just might not be the exact best tool for that.