I was hired by the organization Open Source Ecology to reverse-engineer and build an Ironworker machine (a fabrication tool used to shear, punch, bend, and notch metals). The goal was to design it based on an industrial model, but to simplify it so that anybody could build it. Honestly, it is far too complicated for just anybody to be able to build it, but my plans are public, and a reasonably skilled fabricator could do it.
My model successfully cut up to 1"x10" flat steel, and ⅜"x4"x6" angle steel.
I did all if it myself- from doing structural calculations, to making a 3D design, to sourcing and ordering materials, and fabricating and machining all components. I taught myself the skills necessary to build it that I didn't already have, such as boring, freeze fitting bushings, and tolerancing.
It took me about 4 months from start to finish to build it. I got an education in all sorts of machining!