Improving Box Fan Dust Filter

[@GGigabiteM]

Box fans don't make good filter fans, no matter what you do to them because they have virtually non-existent static pressure, which is needed to pull through restrictive filters. Anything more than the blue/green spun fiberglass is too much for them. Making a duct like you did will certainly improve the static pressure, but not by much since the blades are so far apart. There's just too much room for air to move backwards between the blades. The heavier filters also restrict the cooling airflow to the motor, causing it to run hot and significantly reduce its lifespan. Additionally, they have terrible open oil bearings. Any sawdust getting inside the motor will quickly wick away all of the lubricating oil and cause the bearings to run hot and eventually lock up. The types of plain bearings used in these motors are actually designed to have oil ports, because the bearings consume oil by design. But it's been 40-50 years since those have been removed from the motor design, these are just cheap throwaway junk motors. What I would recommend is finding an old bathroom exhaust extraction blower, as big as you can get. These things are designed to move enormous amounts of air, and have no problem pulling through heavy filters. I have one out in the garage with a couple of filters on it for my dogs to cut down on the pollen and dust. My GS has bad allergies and the filters help make her less miserable. Old HVAC blowers work too, but you need to be careful to not over-amp the motor. These blowers are designed to have a certain amount of drag on them so that the squirrel cage isn't ingesting too much air and causing the motor to pull excessive current. You can use an amp clamp and a baffle on the inlet to adjust the air drag and get the amp draw under what is printed on the motor. Then stick a filter over the remaining space.

[@bubbasdirtyhands5116]

Yeah i know there not great just trying to improve the fan for people who use them the shroud definitely helped but the small fan i got from the 40s moves more air than the walmart box fans I really appreciate the information tho