I have built a CNC milling machine mostly from hardware store parts. My machine is more than just a proof of concept; It is compact, easy to work with and surprisingly precise, with a accuracy of 1/20mm. The machine is precise enough for milling PCBs and strong enough for milling wood, plastic and soft metals. A comprehensive youtube series about my machine finished as well, see links in the details below.
Source: Desktop size CNC milling machine from scratch | Hackaday.io