Shortcake N-stack Carbon / HEPA Filter for 3D Printers and Other Small Enclosures (Bento / Bentobox Alternative)

Props to thrutheframe for his Bentobox air filter, which inspired this work. Shortcake attempts to take the same ideas with optionally identical capacity, and realize them in a smaller space with fewer parts. Ideally, it is now so simple that people looking at it will ask, "What's so special about that?

The answer of course is that it works incredibly well with minimal cost, minimal effort and minimal parts.

Compared to Bentobox, this:

• Roughly 1/3rd the size by volume when configured for the same filter capacity.

• Roughly 1/3rd the part count

• Holds together using gravity in place of magnets.

• Supports a user chosen number of filter levels. One to at least several depending on fan choice and filter media.

I've included a directional fan duct for sending air under the print bed to help quickly warm the build chamber. A couple of these (or perhaps just the fans and duct) sitting in a backpack on an insulated Voron 2.4 will take it to 60C quickly.

Shortcake can simply sit inside some printers, including the enclosed Prusa Mk4S. Base mounts are included for Voron Trident and similar, Bambu P1S, X1C and similar, and Printsulation Sidehat/Sidepack/Backpacks of 55mm depth or greater for Voron 2 style printers. 

For those needing a much higher capacity filter, see Layercake… A filter of similar design in a larger footprint.

Shortcake is a stack of filter layers that slips over side-by-side mounted dual 40mm fans. If a base for your use case is not already available, creating one is a beginner to intermediate 3D modeling task. Part of the design intent is that anyone can fairly easily create their own custom fan mount. Anything that holds two 40mm fans tightly together and side-by-side should work.

NOTE: For this carbon filter use case, high static pressure is the most important quality to look for in your fan choice. See the BOM for recommendations.
 

SUPPORTING YOUR FAVORITE DESIGNERS:

If you like this, consider using one of the affiliate links below to buy your next roll of filament or other parts. Likes, follows and downloads are also appreciated.
 

BOM: 

• Polymaker ABS Filament: https://amzn.to/4pIhL6R 

• Voxelab ASA-CF filament: https://amzn.to/3KKZqXm 

• WINSINN 4020 24v 2-pin High Static Pressure Fan: https://amzn.to/48GPpCD 

• HEPA Filters: https://amzn.to/4rGchKW 

• Cheesecloth Option for Carbon Tray: https://amzn.to/3Z4jZ4k 

• Screws for mounting, such as: https://amzn.to/3zxFgtM
   

INSTRUCTIONS:

• Tolerances on this are tight. To work elegantly (fitting together smoothly and easily), your printer will need to be dialed in pretty well. Please give feedback on any printing issues, and I will try to adjust to make it better able to handle minor variances.
  

• The best (highest flow, easiest to accomplish) carbon filter layer is the cheesecloth version... Just print the tray and spring clip, push in grade 50 cheesecloth with that spring, cut off the excess cloth and fill with carbon. Stack a couple of these over the fans, maybe with a HEPA layer at the bottom (with fans blowing down) and you are done.
   

• For those who don't want to use cheesecloth to hold carbon, the “slicer trick” method is as follows:

  1. Set infill to 60%, using “Grid” pattern. 
     (Feel free to experiment with pattern and infill percent. You are just trying to get the largest holes that work well with your charcoal, with the least amount of plastic in the grid.)

  2. Set top and bottom layers (A.K.A. Shell Layers) both to zero.

  3. If your slicer has a setting for “Only one wall on top surfaces”, set this to off.

  4. Print the Carbon Filter Tray and/or Top Cap (not the other parts) using these settings. The infill will be exposed by the lack of top and bottom layers, leaving a screen to retain crushed carbon, while still letting air flow around it.
      

• There is only one filter holder part, which can hold either a HEPA filter or a carbon tray. The HEPA filters and the Carbon Tray are both the same size. So print as many of these as you want filter stages. Add HEPA filters or Carbon Trays as needed.
   

CHANGE LOG:
  20251207:
      - Revised description and instructions
      - Corrected completely messed up BOM.
  20250127:
      - Revised fan duct for directional base/fan mounts.
      - Revised “slicer trick” instructions.
  20250116:
      - Minor tweaks to layer height and fitment.
      - Added a duct for the directional flow fan mounts.
      - Made a mount adapter plate for Bambu Lab printers.
      - Improved tolerance of minor print quality issues.
  20250115:
      - Corrected gap between filter base and first filter layer.