Before I say anything about converting my gantry CNC milling machine to do 3D printing, I figured I'd cover the controller I designed and built for the extruder and heated bed. Unlike most purpose built 3D printers, like one built from user-sourced parts, a kit, or even a pre-built unit, a CNC milling machine doesn't provide for controlling the temperature of the extruder nozzle and the heated build bed. This project describe that part of the conversion process.