20 Inch Box Fan HEPA Fan Brackets.

thingiverse

--Note-- Had to re-up the recessed bracket as I discovered a flaw in it I missed. Since corrected and re-upped - bad version was only up for a few hours after posting. V1.2 - I took out some of the oblong cutouts as they proved to be points of weakness. I also extended the inward reach of the side mount version a bit. Also provided non-cutout versions. These are brackets to turn a standard 20 inch box fan into a HEPA filter using an off the shelf filter you can get at Homedespot / Lowes / Wallyworld etc.. Three variants - one where the screw holds are easily accessible, one for slightly recessed screws (My fan has this type on the bottom), and a third for fan guards with no screws where you can simply screw into the side of the box with self tapping screws or bolt in if feeling extra OCD assuming you can get the guard off to get inside. If using existing screws, may need to find longer ones. Cheap fans use as short a screw as they need so the beefed up screw area may be too thick for the stock screws. I use 4 of them, one on each side, two on the bottom, and leaving the top open for easy removal. They are not snug, there is enough for wiggle room depending on the filter, but when the fan is on it sucks the filter firmly against the back. This obviously does increase the load on the fan, so likely shortens it's life span in the long run. It does not cause overheating etc.. as it is pretty much self cooling. **Note:** There is a cutout specifically to fit a screwdriver through so you're not trying to screw something in at an angle. I'm printing in PLA at the moment, but I suspect ABS/PETG/Nylon would work better for these and require less infill, be more robust, and probably allow for a thinner base around the screws. PLA seems a bit too brittle and breakable around the screw hole. I've broken several of the thinner ones, and even the thicker one split when trying to use a screw just a shade too large.. a little super glue fixed that, but didn't take much to bust it. Update: PETG works WAY better for these. PLA is just to brittle to handle much mechanical stress for something so thin.