Automatic 120mm Fan Damper for Prusa Original Enclosure

Installing an exhaust fan to keep your Original Prusa Enclosure cool for PLA or PETG?  But don't want air escaping when you print ABS or ASA?  Then you need a fan damper!

This damper is designed to fit the 120mm cutout on the back of the Original Prusa Enclosure. The flaps (louvers) will be blown open automatically by the fan exhaust when the fan is on, and automatically close from their own weight when the fan is off.  

Important:  While the Prusa enclosure is not entirely airtight, the exhaust fan used must have sufficient static pressure to create some vacuum, thus causing air intake through the various extra holes and gaps. A standard 120mm, 1200rpm PC case fan will NOT suffice.  You will want a fan labelled as “high static pressure”, max rpm of 1700rpm or higher – such as the 120mm fans made for PC watercooling radiators.  

Print the Damper frame, and one each of the Louver-R and Louver-L flaps, in the material of your choice (I used Prusament PETG).  A layer height of 0.2mm or less for the frame will provide a smoother face, and a layer height of 0.15mm is recommended for the flaps (louvers). Use care removing the flaps from the print bed, as the pivot pins (axles) are delicate!

Assemble the frame and louvers per the diagram and photo provided.  Be sure to put the longer pivot pin (axle) towards the bottom of the frame and use care not to break the pivot pin during assembly.  

Place your fan on the inside of the enclosure, facing outward (exhaust), and aligned with the enclosure's precut bolt holes.  Place the Damper frame on the outside of the enclosure, with the thicker part at the bottom, and aligned with the enclosure's bolt holes.  Insert 3mm screws through the (4) holes in the frame, then through the precut holes in the enclosure plastic, and into your fan's mounting holes.  The screw length needed will depend on the thickness of your fan's frame, but generally 12-14mm should be sufficient.

Note that the mounting holes for 120mm fans are larger than 3mm diameter.  A simple 3mm hex nut will usually still work, with or without a washer.  But if you have some TPU handy, I recommend these mount adapters:  Fan mount for 3mm bolt by ScottW | Download free STL model | Printables.com

Powering and controlling your fan:  You will, of course, need a power supply appropriate for the fan you select.  With a simple, inexpensive pwm fan controller, you can manually monitor the enclosure's thermometer and adjust the fan speed as needed.  For a more automated approach, the choices are infinite (for example, I added a temperature sensor to a Raspberry pi running Octoprint, and let it automatically control the fan based on enclosure temperature).

Happy Printing and Keep Cool!  :-)