This is a simple chain guard to keep you from losing a finger in the RecycleBot V2.2+ waste plastic extruder. Now that the RecycleBot is a little more safe - you will be interested to know that it is also much more environmentally friendly to print with recycled plastic at home than to buy commercial filament. See: Distributed Recycling
For more on the RecycleBot
Newer better designs are here: Aubrey L. Woern, et al RepRapable Recyclebot: Open Source 3-D Printable Extruder for Converting Plastic to 3-D Printing Filament. HardwareX 4C (2018) e00026 doi: https://doi.org/10.1016/j.ohx.2018.e00026 open access
Print out the two parts on your favorite open-source 3D printer and then cut out the wall from an appropriate sturdy board material (you can do this by hand - but if you are really cool use your laser cutter). There are screw holes in the prints to bolt everything together. Then, bolt directly to the gear end of main holder for the auger of the RecycleBot (see images for placement).
Thanks to Buck for designs and fitting and to an unnamed OSHA inspector for making the recommendation.
It would be a good idea to make a derivative for the Lyman extruder http://www.thingiverse.com/thing:34653 and all the other filament extruders out there if you are using one.