Full instructions in the HardwareX paper https://doi.org/10.1016/j.ohx.2018.e00026
More information : http://www.appropedia.org/RepRapable_Recyclebot:_Open_source_3-D_printable_extruder_for_converting_plastic_to_3-D_printing_filament
FreeCAD users: The entire assembly is available in the STP file. Open it in FreeCAD and pick what part you would like to modify, export it as .stp, and you will be left with just the part you need. Once you have that, you can save it as just about anything.