PRUSA Enclosure 120mm fan adapter and filter box

I know “just buy the addon then”, but I like designing in Fusion and am a DIYer so I came up with my own solution for an air extractor / filter box for my Original Prusa Enclosure (OPE). What I already had on hand was a 120mm 12VDC fan and some nuts and screws. In the pictures, the black square with the hole resembles the fan whereas the red parts is the sandwich of parts you're going to print. 

Content:

1. What to buy
2. Why to print 
   (Cost and specs comparison to OPE add on “Advanced Filtration System”)
3. What to print
4. How to assemble
5. How to mount
6. How to power the fan

What to buy:

• 120mm fan
  (make sure the fan only has openings on front and back - this is standard but essential since my design isn't a closed system around the fan. makes for easier prints w/o supports)
• 4 pieces of M3x45mm screws
• 4 pieces of M3 nuts
• 4 or 8 pieces of M3 washers (optional)
• 120x120mm hepa cloth (amazon: these are 260x150mm but you can cut them into 2 pc.)
• 120x120mm activated carbon “sheets” (amazon: 120x120mm)
  (HEPA and AC can be bought in 8, 10, 16 pieces if you want to replace them regularly)

Why to print / comparison of this assembly to the Prusa OPE addon, the "Advanced Filtration System".

• specs:
  • OPE AFS:
    • “over 600 hours of run time”
    • averages at ~95% filtration for 7nm-5µm particles
  • my design:
    • can be replaced at least 8 times (if you took the link above)
    • filtration quality and lifetime depends on your choice of material
• Costs:
  • OPE AFS: 
    • € 80 if bought seperately
    • € 120 (if bought as an option with the enclosure!)
    • € 40 “It requires the Basic Board and PSU (sold separately) to work.”
    • ~€ 10 shipping
    • total: €90-170 depending on how you buy it and if you have the basic board and PSU
  • my design:
    • €5-20 Fan
    • €5 fan power supply
    • €5 screws and nuts
    • €9 hepa / 0,84€ per piece
    • €9 ac / 1,13€ per piece
    • total: 48€ 
      less if you already have anything from the list
      less if you plan to power the fan from the printers PSU (see “How to power the fan”)
      and you can replace the filter stack for at least 8 times
  • conclusion:
    • €90-170 AFS vs ~50€ my design

What to print:

• 10mm OPE hex to round adapter
• box cover
• hepa / activated carbon box,
  depending on those sizes, take measurements and trim the STL to your needs (see attached picture with detailed instructions to do it using prusaslicer)
• If you want you can print a thin screen to protect your fan from the filter materials:
  • Survival88's grid-for-120mm-fan-gitter-fur-120mm-lufter
  • Anatoly SL's 120-mm-fan-filter

How to assemble:

1. print parts (see “What to print”)
2. mount adapter and empty filter box to enclosure (see “How to mount”)
3. fill the filter box with your air filtration stack (HEPA and activated carbon)
4. put the Cover on the whole assembly and fix it in place with 4x 14mm of 1.75mm filament
5. route your fan power line using zip ties to an adequate source of power (see “How to power the fan”)

How to mount:

1. cut open the hexagon in the plexiglass sheet on the back of your OPE using a lighter and a carpenters knife (the little studs will easily melt away around the knife)
2. Put in 1 screw and washer (if you prefer to use washers) from the inside into one of the upper holes that are predrilled around the hexagonal cutout. You will put the other 3 screws in later, otherwise it'll get sketchy.
3. From the back put on the hex-round adapter with the hex face to the OPE.
4. Do the same with your 120mm fan. Watch out for the air flow indicators. They need to point outwards, otherwise you will push filtered air into the OPE.
5. Now put the (empty!) filter box on the screw as well and fix everything loosely in place using a nut (and washer if you like). 
6. Go ahead and put in the other 3 screws and nuts.

How to power the fan:

• use your printers Power Supply Unit (PSU) if you can safely use it together.
  (I am not a registered electrician and I didn't ask Prusa if this works, so do this at your own risk of injury, damage and such) 
• use a dedicated power supply that you can put directly in a power outlet

Wow! You read all this. I really appreciate it. If you like my design, please let me know and leave a like.

Changelog:

• (DD.MM.YYYY: adding models for M4 hardware)
• (DD.MM.YYYY: adding some space between fan and filter for better air flow)
• (DD.MM.YYYY: adding model for enclosed fan housing to compensate for air leakages around an uneven fan)
• 12.01.2024: adding filter box model with pockets for M3 screws, resizing filament holes
• 07.01.2024: initial upload with assembly and STL splicing instructions