The RepRap project hopes to build a universal constructor; a machine that can replicate itself and make a number of useful products. The machine is open source and uses fused deposition modeling (FDM) to layer melted material into parts. One of the key technologies in self-replication is the ability to lay conductive circuit paths. The RepRap machine is able to lay down conductive material and an insulator. For a conductor they are using Wood’s metal, a fusible alloy that has a melting point of 158degF. To demonstrate this conductor laying ability they built the FDM head pictured in a commercial FDM machine. The project makes some reasonable compromises; it doesn’t attempt to make common items like brass bushings, microcontrollers, stepper motors, self-tapping screws, and power supplies.