It keeps the chamber free of deposits for over 1000 hours when printing ASA / ABS, and keeps my small room mostly odor-free for 4 to 6 months before needing to rejuvenate the 1kg (2.2lbs) of activated carbon.
The STL and 3MF files are on Github and MakerWorld
Now working on a P1 and a P2 version, with option for a beefy heater so we can finally heat up their chamber fast to 55-60°C for high temp filaments without warping.
Happy, clean and odorless printing to all !
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Overview
The hat just fits between the top glass and the top of the printer. It is held in place by the printer's rim, no screws, tape or magnets needed:
It doesn't interfere with the AMS, which can still be installed on top of the hat.
The toolhead, chute and bed plate remain visible when looking down into the printer. Even when an AMS sits on top of the glass. Something I find extremely useful when monitoring or debugging prints.
Any spot not used by the fan and the carbon filter is available as a storage nook, to keep nozzles, tools and bits handy. 2 removable storage bins can also be positioned in the front, though they'll obstruct vision:
The filtered air exhausts on the right side, away from the prints, to avoid any induced warping when printing ABS. That approach has been working wonders on my P1S for the last 3 years, so same design principle here.
View from inside:
The filter chamber holds ~1kg (2.2lbs) of activated carbon. Make sure to test that it is acid-free though !
Why ?
Not only does 3D printing emit toxic fumes (PLA included) but printing ABS and ASA also results in everything inside the printer being caked with a thin white translucent coating. Here is what my H2's glass panels looked like after 350 hours of printing ABS:
On the other hand my P1S after 1500 hours, 1/3 of the time printing with ABS, is squeaky clean. Never had to wipe the glass even once. The difference ? The home made recirculating air filter & heater hat holding 1.5kg (3lbs) of activated carbon on the P1.
Unlike many other onboard fumes-scrubbers out there, like the Nevermore, the intake is right above the toolhead, and the 120mm blower moves a lot of air. So I suppose this captures most of the fumes right away, thus preventing deposition inside the printer.
Worse, not only was the H2 fogging up fast but, the few times the window in the room was closed, I had to leave the room after ~15 minutes due to a too-strong PLA odor during prints with High-Flow nozzles. In 3 years that had never happened with the P1+Hat.
Yes, one should never stay in a room with an active 3D printer, I don't, but getting a headache in a matter of minutes is definitely wrong.
And yes the H2 has an integrated carbon filter but it is only 1-pass when printing PLA / PETG as, in this case, the H2 vents air out. And it only holds a few grams of activated carbon, which probably needs changing every couple of weeks to remain effective when printing 12/5.
Heck, look at what the Creality K1C's carbon filter looks like, what a joke:
Screw that. Hence my need for a recirculating filter holding tons of carbon like on my P1. But 3D printed this time, no more woodworking, and no more 120V fan / heater for safety reasons.
Printing
Settings for H2:
- 0.4 standard nozzle, 0.24 layer height
- default Bambu ABS settings: 0.95 flow, 100% Shrinkage, etc
- 2 walls, 3 top, 3 bottom
- 20% Support Cubic infill, Infill Combination on
- 0 Minimum Sparse Infill Threshold (reduces print time on grille / tall narrow features)
- Support enabled, Critical Regions only
It takes 3 plates, ~30 hours and ~1.1kg of filament to print. Or more when also printing 1 or 2 of the optional front storage bins.
This filter was designed to be printed in ABS so as to support 65°C chamber temps. Otherwise it would soon become a Dali masterpiece.
Once printed, there should be 1 to 2mm (~1/16") of clearance all around the printer's rim, and around the glass.
If one never prints with high temp filaments, then using PLA or PETG is fine. However, those are much less prone to shrinkage than ABS is, so the parts might print a couple of millimeters larger. Consequently, once dry assembled, carefully check the top-of-printer clearance and adjust the slicer's Shrinkage setting if need be so the hat sits inside the top rim.
Parts
Any 12V 120x32mm air blower will do. I chose one with a speed controler that directly plugs into 120V, and with a quick disconnect so a 12V switch can easily be inserted in series:
The fan is held in place with 3x 40mm M4 flat head screws and locknuts.
Foam tape is used to seal around the blower exhaust. Any tape ~1mm thick will do.
The activated carbon must be in the form of pellets, about 4mm in diameter
Anything smaller will dramatically reduce the airflow and possibly stall the blower. Do not use granulated carbon
To hold the carbon I used a 16x12" (40x30cm) muslin drawstring bag. But a bag is quite inconvenient as it makes it hard to fill the corners of the chamber, and the drawstring can't easily be tucked in flat when closing the lid. A cheese cloth would likely work better. In any case, it needs to be made of a very low density and aerated fabric, or airflow will be impeded.
The front switch is optional. But I wanted to control the blower from the front, and easily tell if the fan is on or off. So I used a pre-wired SPST 12V LED-illuminated rocker switch for 13x20mm openings. A 120mm blower draws less than 2A, so any 5A switch or up will do.
The blower's quick-disconnect uses standard 5.5x2.1mm barrel connectors, which made inserting the switch super easy, barely an inconvenience. It also facilitates swapping fan /switch / controler without having to cut and resolder wires. That helped a ton during prototyping.
To prevent carbon dust from being blown into the printer some MERV13 filter fabric is laid down on the exhaust side of the carbon chamber. This notably impedes the airflow, but letting carbon dust in would bring a fast end to anything lubricated in the printer, like the bearings riding on the X rail and Y&Z rods, and the ballscrews.
MERV13 fabric uses the same mechanical + electrostatic filtering principles as HEPA filters and N95 masks. And it's much cheaper over time: just cut a piece out of the large sheet each time the carbon gets refreshed, done.
I suspect that MERV11 wouldn't be enough to catch some of the dust, and that MERV16 would kill most of the flow. But these are just a backyard mechanic's guess...
Assembly
The glueing order is as follows, so I also chose to print in that order:
Once all 4 pieces are printed, dry assemble them, and check for clearance all around the printer's top rim, and around the glass. If there's not enough clearance, change the slicer's filament Shrinkage setting as needed.
After printing piece #1, break away the support wall of the blower exhaust:
CyanoAcrylate glue (Superglue) should be applied along all the ridges of the dovetails that connect the pieces together, as well as across all the faces on piece #1 to ensure that pressurized air doesn't escape through cracks before entering the filter:
Also, to ensure vertical alignment between the pieces, and catch glue run-off, the bottom of the dovetails is chamfered, with one side protruding, the other recessed. So piece #2 must be inserted top-down into #1:
Then #4 is glued to #3, making sure the assembly doesn't bow out or in. A ruler can help with that:
Finally, 3+4 is glued to 1+2.
Note that at each glueing step, clamps should be used to ensure parallelism between the faces to join, and to avoid gaps between the pieces while the glue cures:
Then the foam tape is placed around the blower exhaust opening:
And the blower can now be installed. A good trick to ensure it is tightly pressed against the tape is to wedge a tool between the blower and the wall opposite the opening, before tightening the screws:
The assembly is done at this point, if no front switch is needed. In that case, just glue the switch plug in the front:
(optional) Installation of the front switch:
- solder 1 male and 1 female barrel connector to the switch
- feed the barrels + cables through the opening in the front face of the box
- connect in series between the blower and the speed controler
- make a simple knot in the cable that exits the box, such that the knot rests against the slit in the back wall and provides strain relief
The speed controler can be left inside the box, or outside. However, since these are cheapo modules (most aren't UL / CE certified) and since a lot of my printing is done at 60°C (i.e. way past most consumer electronics' spec for ambient temp) it'll stay outside. I don't want the controler to fail or catch fire...
Before filling the chamber with carbon, install a 32x11cm (12x4.5") piece of MERV13 fabric against the exit openings on the right side of the filter chamber. Tape it down so it stays put when filling the chamber:
Filling the chamber takes about 1kg of carbon (tare weight was substracted in the pic):
Spread the pellets evenly and flush with the top of the chamber:
Finally, fold the fabric and close the lid. Do not force the closing or it'll make the lid bow up, letting air escape. Instead remove some pellets and try again.
Now the airflow can be tested. At full blower speed there should be a noticeable amount of air coming out all along the right side of the filter. If not, remove some pellets.
Das ist alles. Muy fácil. Ça casse pas trois pattes à un canard, non ?
Enjoy your now crisp fresh air ! (but always leave a window open, or exhaust air out of the room)
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