a fused filament fabrication printer has a fixed extrusion module having multiple printheads having print tips . the fixed arrangement of the printing heads allows the close spacing of multiple print tips in a printhead unit , and the simple routing of multiple plastic or metal filaments to the individual printing heads . the closely spaced print tips in the printhead unit share common components . an exemplary printhead unit has four printing heads which share a common heating block and heating block temperature sensor . the heating block incorporates a group of four print tips evenly spaced along a line . each printing head has a separate filament which is controlled and driven by its own stepper motor through the heating block to one of the print tips . printing of a part is by control of individual stepper motors which drive filaments through the heating block and through one of the printing tips .