Sound-dampened Active Filtration Unit CoreOne - SAFUCO

Motivation and Background

This is a slightly overengineered filtration unit for the Prusa CoreOne printer.

Initially, I printed the HEPA and Charcoal filter from CNC Kitchen (https://www.printables.com/model/1187562-core-one-hepa-charcoal-filter). This, however, required me to run the chamber fans with quite high rpm, which created a lot of noise. Even with that higher rpm, the chamber still did not stay cool for longer PLA prints. As the printer is right next to my desk, I wanted something quieter.

In contrast, the original Advanced Filtration Unit sold by Prusa required the use of these specific filter cartridges. I prefer the modular style of using those vacuum filters and charcoal pellets over this approach. Further, I did not like that the exhaust of the blower fan is not muffled in any way.

The actual Build

Design Criteria

So I decided to create my own design with the following goals:

1. Be as quiet as possible

   1. Try to Isolate the moving fan from the housing

   2. Allow for sound dampening the exhaust of the fan

2. Increase surface area for hepa and charcoal for less flow restriction

3. Use off the shelf activated carbon pellets

4. Use cheap hepa filter

5. Use original Prusa blower fan for Advanced Filtration Unit for easy integration into printer

   1. This should also make it compatible with any other 120x32mm style blower fan

6. Look somewhat decent

7. Print without supports

8. It should be easy to use and maintain

9. Use existing mounting holes

10. Each part needs to fit the CoreOne's print bed

Ok, so where is the downside? It's bigger than the Filtration Unit provided by Prusa and with filament and all the required hardware it's probably not even a lot cheaper than the original. At least not without a few changes of the filter. I guess with a few changes of the filter material it will be cheaper than the original filter cartridge.

Print Settings

All parts are printed without support. There are some parts with larger bridges and 45° overhangs.

Other than that, there are no special requirements. Even PLA seems to hold up fine, even with Chamber temps of 55° C. 

The part called DampeningVolume should use about 30% Gyroid infill and no outer walls and no top layers. I used about 3 bottom layers. Make sure that these are on the correct face of the part. (I will improve the instructions to give more info on that.) This part will slip into the sound dampening chamber.

Additional Hardware required

The first three items are the same as required for the CNC Kitchen filter.

1. 4x M3 x 40mm Socket head screws

2. HEPA Filter (https://www.amazon.de/gp/product/B09HHM1YRR)

3. Proper Filter Charcoal: e.g. Nevermore https://github.com/nevermore3d/Reseller

4. 3x3mm foam stripes as seals (I had some left over Armaflex 3mm tape, but any 3mm foamed rubber cut to 3mm strips will do)

5. Some thicker foam or packaging material to stuff behind the blower fan

6. 12x 8x4mm neodymium magnets (the ones I bought were marketed with about 1.5 kg of "force", which seems to be just the right amount)

7. Schmutzradierer / Melamin foam for sound dampening

Remarks

I intended to print it in black PETG but wanted to print a prototype with cheap PLA first.... Well the prototype worked to about 95%, and now it's still in use...

Some improvements that are necessary or might make it better:

1. Right now the magnets are glued in. I prefer press fitted magnets. Therefore, I will decrease the hole size for those.

2. Maybe create a version that uses screws instead of magnets

3. I simply stuffed in one of those Melamin foam cleaning pads. This worked surprisingly well. But I'd like to create a jig to cut this foam to a correctly fitting shape. 

   1. I also wanted to create some 3D-printable geometry that serves as a muffler and compare it to the foam

   2. A dummy volume that fits into the cavity, so that anyone else interested in this add-on can experiment with their own design.

4. The biggest TODO is a detailed description of how to build and assemble this

But for now I want to get it out there so that it maybe is useful to others as well. I hope I will get around to improving these instructions.