CNC (Computer Numerical Control or computer controlled machines) are on the rise. Mainly (self-built) 3D printers are extremely popular. This group contains various mechanics, controllers and accessories to build your own CNC system.
RuubLJ12A3-4-Z / BX Proximity sensor N / O NPN 4mmDoes it work well, can sink enough current to ground (certainly more than 100 mA), must come really close to the metal for good detection, indeed according to specs best at 2 mm.