Enclosure Air Filter using Ikea Förnuftig

Description

As part of my Ender 5 enclosure to be used for printing ASA, I designed and printed this air filter that takes an off-the-shelf Ikea Förnuftig active charcoal filter and runs with 2 140 mm fans. The overall filter is 76 mm high, 391 mm wide and approx. 460 mm deep, meaning it will fit on the underside of an Ikea LACK table. 

The filter is recirculating, i.e. it will blow air back into the enclosure, to keep the enclosure air temperature from dropping too much. There is no HEPA filter, as that would likely require stronger fans/a thicker filter, so it won't filter out potential microparticles, but the active charcoal will filter outgassing from ABS/ASA. 

The bottom of the rails (20 mm wide) work well as LED strip mounts, so on top of air filtration it doubles as an enclosure lighting mount. 

I've not measured airflow, but with a very scientific experiment I could show that the pressure differential across the filter is strong enough to hold a small piece of plastic against gravity. 

Printing

The filter is split into 4 parts to allow printing on my 220x220 mm build surface and the parts are designed to be printed in the orientation of the STLs. 

I printed it in PLA and a 0.6 mm nozzle. The two main parts were at 1 perimeter at 0.6 mm line width, 5 % infill and the two fan adapters with maxed out parameters, i.e. 100% infill. (With a 0.4 mm nozzle one would likely want to do 2 perimeters for a 0.8 mm hull width. ) Even with these thin walls and infill, this print took 400 g of filament overall, so be sure you're ready for large and accurate prints. 

Assembly

Required parts

• IKEA Förnuftig gas cleaning filter
• 2x 140 mm fans (e.g. Arctic P14 PWM)
• Heat inserts
• Wood screws
• M3 Screws
• washers
• PSU or buck converter to power fans (and LEDs) at correct voltage
• (optional) 12V/24V LED strip
• (optional) wiring to PWM-control the fans
• (optional) fan/heater port (or MOSFET) to enable dimming of LEDs

Instructions

To allow aligning the two main parts I've added slots, however the tolerances on some of these may be a bit too narrow for some printers; if so, you may want to cut off/shorten these pins and take a bit more care with aligning, it should still work without them. 

Step 1

First, we add the 8 M3 5 mm OD 6 mm length heat inserts to the back of the main part. Make sure they're sitting flush. Then we mount the fan adapters to the main plates (the cutout on the fan adapter is on the inside, see picture). The adapters are then mounted to the main part with M3x10 screws (the inner screws can be a bit of a hassle; take your time). 

Step 2

The next step will be mounting the 140 mm fans. Make sure they're blowing in the right direction, i.e. they should pull air through the filter and blow it out at the back. To mount them, use M3 or M4 screws and corresponding nuts. Note that the top screws need not protrude more than 1 or 2 mm after tightening, as that would interfere with mounting. If you don't have M4 screws that are just right in length, you can use a short M3 screw (e.g. 10 mm) that goes only through one hole and that you screw on with an imbus (see picture). 

Step 3

After the fan adapters and fans are mounted, the next step is mounting the assembly to the top of the enclosure. If possible, removing a shelf, turning it by 180° and mounting things on a table is by far the easiest option. In any case, before screwing the assembly down, slide in the Förnuftig filter to ensure alignment of all parts. Then use wood screws with washers to fix the assembly to the shelf/bottom of LACK table at the 4 outer screw holes (be careful to not overtighten it with the LACK table, you may strip the cardboard, reducing holding strength). As the last step before wiring, remove the Förnuftig filter once to add the two wood screws inside the assembly (they keep the assembly from sagging in the middle, shown in the picture, I accidentally overtightened them a bit). 

Congratulations, you've got the mechanics part done (I hope)! 

Wiring

Note: If you have specific questions regarding software, I can only help you with klipper. 

To wire up the fans, you can connect their voltage (e.g. 12 V) and ground connectors together, as well as the PWM pin (if you want to control them). The mentioned Arctic fans do have a cable that allows you to do this without modification, for others, you may need to splice them yourself. 

(Note that these fans have an internal pull-up to 5 V, so make sure the GPIO pins on your MCU are 5 V tolerant.)

[optional] LED strip

If you want to have nice lighting, you can take an LED strip with self-adhesive and glue it to the bottom parts of the rail. Soldering is possible after gluing, but keep the time short. I recommend adding some flux to the pads to solder to, then add some solder onto the pads, let it solidify, and only then add the wires you are soldering on. As the adhesive and pads are a bit sensitive to force, I also added some duct tape as strain relief. 

Feedback

And you're done (I hope)! Please leave positive and negative feedback and questions (as long as they don't involve software configuration for smth other than klipper) below, hopefully helping others in the process. Remixes that fix things or add functionality are also highly appreciated!