I remember there was a lot of discussion on the old Savage///Circuits website regarding metal fabrication, routing, milling, welding, etc with regards to robotics and other projects. These topics would often get lost in the forums, but this area will hopefully make any discussion easier to find.
I was originally going to include 3D printing and Laser cutting / engraving here, but wanted to separate them due to possible discussion of them as tools / options and not really about fabrication, necessarily.