I had been meaning to make an air filter for the workshop to clean up the suspended dust from sanding for a while, but just never got around to it. I knew I didn’t have a fan lying around, and I just didn’t fee like running out and buying a box fan just to tear it apart to make a filter. The other day I happened to be in a seldom used part of the basement and I found an old window fan that was forgotten about. A quick test showed it was in perfect working order and it moved a lot of air. Now I had the fan.
First I removed the fan assembly from the plastic shell that’s meant to mount it into the window. With it being mounted close to the ceiling means I needed to extend the wiring for the controls so that they could be mounted onto the side of the box. That took about 20 minutes to cut and splice the wires and then wrapped them in split loom tubing.
I found a piece of used 3/4″ MDF board that was part of the old table where my Radial Arm Saw now lives. Cut it to 20″ square and then marked the where the hole for the fan would be. It took awhile for my little scroll saw to cut through that heavy MDF but it eventually made it the whole way around. The box frame is pine from a box that was laying around for the past few years. I rabbited the top so the fan would inset into the box, and dado’ed a groove along the bottom for the filter to fit into. I designed this around a 20″ filter, which happens to actually be 19.6″ square.
Before gluing up the box I cut one of the sides to act as a door for installing the filters. There’s an old 12″ piano hinge for the door. Everything glued up, and a few staples just to hold it together and it was almost done. The fan board is held in place with some 1 1/2″ wood screws and I added some eyelets to the top so it could be hung from the ceiling.
With that done, I cut and drilled a piece of 16gauge sheet metal as a place to hold the fan switch in place. The starter cap for the motor is mounted near the switch on the inside and then I used a vintage lever type knob for the switch. I actually didn’t have one of these filters when I started building it, but once I got one and installed it, I was surprised at how well it did fit. The fan moves a lot of air, and I have it mounted right above my sander. Over all, the only money I spent on this was the filters, $9.51, everything else was just laying around the workshop.