Exhaust/Recirculate Selectable HEPA Filter Fan for enXLosure

Suitable for everyone:

1. You are about to print/build your enXLosure and want to include a HEPA filter.
2. You might incorporate a HEPA filter in the future and want to be prepared.
3. You want to retrofit your enXLosure with a HEPA filter.

There are two purposes for an enclosure; one is to prevent drafts and keep the part warm while printing, the other is to exhaust the fumes released by some plastics.  The standard Prusa enclosures for the MKx and Mini offer a HEPA filter that recirculates the air.  The XL Enclosure’s HEPA filter exhausts the air. Not knowing which is best, I designed a solution with a movable control flap that lets you choose where the warm filtered air should go.

You’ll need:

• High Pressure Blower £44.99 and a HEPA filter £24.29 from Prusa.

OR 

• A combined package of blower and filter from Blurolls (China) for $35.90. According to @Voxel3D: “Note; these parts are not original Prusa, but they function the same and have the same specifications and compatibility.”

https://blurolls3d.com/products/blurolls-air-hepa-filter-for-enclosure-prusa-mk4-mk3s-xl-3d-printer-air-cleaning-12032-fan-24v-3d-printed-box-petg-filament?VariantsId=10782

• 18x         Brass Inserts
• 26x        Bolts M3 x 8mm
• 3x           Bolts M3 x 12mm
• 4x           Magnets (optional) 2mm diameter x 1mm thick 

If you haven’t built your enXLosure yet, print Split_Top_Structure.stl. It is a copy of @PeterM’s (another Peter M - not me) Lid_Remix_Top_Cutout.stl (I’ve include it here just to save you figuring out how to split it out in his STEP file). Replace @Voxel3D’s original enXLosure’s enXLosure-top.stl with the Split_Top_Structure.

If you’ve already assembled your enXLosure, you can either print Split_Top_Structure.stl, disassemble your enXLosure’s top, and replace it (might be a bit tricky) or print Top_Cutout_Template.stl and use it as a guide to cutting and drilling the original top (also a bit tricky but still easier than cutting an acrylic panel).  Note: the square cutouts don’t need to be exact but the five drill holes do – they’ll be taking brass inserts.

If you want to include this HEPA filter now, print HEPA_Top_Panel.stl.  If you simply want to prepare for a filter in the future, print Split_Top_Full_Panel and come back and print the fan box when you’re ready.  Use four perimeters as these will be taking brass inserts

Print the rest of the parts (HEPA box, HEPA Door, Fan Box, Fan Box Lid and Control Flap).  Use variable layer height as there are some printed screw threads.  Use 1mm top and bottom horizontal shells so you don’t have just one internal infill layer.

Assembly:

• Carefully install in the brass inserts: twelve into the Split_Top_Structure, five into HEPA_Panel (the sixth hole is in just case the hinge bolt is too long), and one into HEPA_Box (on the side for the door latch).
• (Re)assemble your enXLosure.
• Just to ensure the threads are well made, screw and remove an M3 bolt into each of the printed threads; six on the HEPA box, four on the Fan Box, one on the Control Panel.
• Optionally, glue magnets; one on the HEPA box, two on the Fan Box, one on the Control Flap (reversed polarity). The magnets help hold the flap in place and also allow you to set ½ Exhaust/½ Recirculate. 
• Snap the Control Flap into the HEPA Box and fit one M3x8mm bolt (not too tight).
• Attach the Fan Box to the HEPA Box (five M8 x 8mm bolts).
• Attach the HEPA Door to the Fan Box and HEPA Box (two M3 x 8 bolts).
• Insert the blower fan and attach Fan Box Lid (three M8 x 12). **
• Attach the whole unit to the HEPA Top Panel (five M3 x 8).
• Attach the whole thing to the Split Top Structure (twelve M3 x 8).
• Insert a HEPA filter (black side up) and close the door.
• *Connect the fan wire to FAN1 on the XL sandwich board. See Steps 30+ of the Prusa XL Enclosure Assembly Guide https://help.prusa3d.com/guide/3-printer-upgrade_668674 (but without the XL enclosure splitter assembly - see note below).

• Enable the fan in Settings by selecting Enclosure on your printer.  The printer will test the fan by running it for a few seconds. You can now access the Enclosure menu.

Important for any enclosure:

XLs shipped before June 2024 have some high stress components printed with PETG that Prusa reckons should be replaced with parts printed in polycarbonate carbon fibre (PCCF) when using an enclosure. I've included them with this model or they can be found here:  https://www.printables.com/model/449554-xl-printable-parts

You'll need to print an Idler-lever-a, Idler-lever-b, Idler-nut, two Idler-swivels and a Fan Shroud for each printhead. Recommended print settings: 0.20mm STRUCTURAL, 4 perimeters, 30% Grid infill. Follow instructions for the Nextruder Upgrade https://help.prusa3d.com/guide/4-nextruder-upgrade-multi-tool_690321

Also, the two Belt Clamps need to be replaced. Prusa XL Enclosure Assembly Guide https://help.prusa3d.com/guide/3-printer-upgrade_668674 Steps 50-58.  You can find instructions for getting the belt tension correct here: https://belt.connect.prusa3d.com/

Note: The exhaust pipe is 40mm at the base and 38mm (1½") at the end.

*Prusa's XL Enclosure comes with an “FDM XL Enclosure splitter” that the fan plugs into and then a wire runs from the splitter to FAN1 on the sandwich board.  This allows you to disconnect the fan to remove the enclosure.  This is not available for sale from Prusa so you may want to insert some sort of quick disconnect into the fan cable.

** Some makers have noted that the Fan Box was too tight for their fan (read Makes & Comments).  I don't know if the manufacturer has changed the size of the fan a bit or there's a material shinkage or a printer calibration issue.  Regardless, I've uploaded another version called “Fan_Box 1.5mm larger.stl” that you can print if you have the same problem.  I've just made the walls a bit thinner to make the interior space a bit bigger.