Shop Cart Air Cleaner

When doing woodworking, air purification becomes a big deal. Go on YouTube and look at any of the woodworking vlogs and you will see that even hobbyist woodworkers go to great lengths to control the dust in their shops. Here are some examples.
April Wilkerson
Jay Bates
DIY Tyler
Matthias Wandel

I have barely done any woodworking as of yet and already the dust levels in my dad's workshop are becoming intolerable. Unfortunately, most dust collection and air purification solutions are rather costly, so you see a lot of people going the DIY rout.

I tried using the 20x20x1 furnace air filter taped to the back of a box fan scenario, and while it did capture some dust, it was just too inefficient. I have seen several variations on this theme that claim to improve efficiency by creating more filter surface area, and thus more air flow. So I thought I would give that a try. But I didn't want to make a large box that would take up valuable floor space. I thought about hanging it from the ceiling, but that seemed like a lot of effort. So I decided to build a box out of the wheeled parts cart that we already have in the shop. We never use the lower level anyway, so I could just box in the lower level with air filters and a box fan and create a movable air cleaner cart that doesn't take up any more room than was already being used.

First I had to measure the cart to see what sized air filters I would need. I concluded that things would fit just about perfectly if I used a 25x25x2 inch filter on the front, a 16x25x2 inch filter with a 16x25x1 in pre-filter on the one side and a16x25x1 inch filter with a 16x16x1 inch pre-filter on the other side. I would have liked to use two inch thick main filters with one inch thick pre-filters all the way around, but the math didn't work out that way.

 When I say pre-filter, I mean those really cheap blue fiberglass air filters that are not pleated. They don't catch much (something like 50%) but they don't impede air flow much either. I am hoping that they will catch the big particles before they get to the good filters, hopefully making the good filters last longer. And by good filters, I mean the $3 economy brand pleated filters. I'm not paying $10+ for a HEPA filter. I'm far too cheap for that.

 The filters fit like a glove. I just needed a small wooden spacer at the bottom to hold them up, because they were just about an inch short, but I'm working with standard sized filters, so I had to take the closest thing I could get. I sealed the edges with some masking tape, which will cut down on air leakage, and help to keep everything in place.

 The filters went in very quick and easy. The fan was going to be a little tougher. I'm using a super old box fan. It's probably from around the late 1960's. I took off the covers and gave it a rudimentary cleaning as it was already covered with filth. I also took this opportunity to re-rout the cord to come out the front grill instead of the back.

 I attached two strips of scrap wood to the bottom of the fan, with a gap that would fit over the lip of the bottom shelf of the parts cart. This would help keep the fan stationary. I attached these with some 2P-10 CA glue. It doesn't need to be terribly secure. Who knows if this thing will even work. Until I assess its effectiveness, I'm not too concerned about making this thing a permanent fixture.

 I used the same CA glue to add a strip of wood along the top of the fan. This would fill the gap and jam the fan under the top tray fairly snugly. I added two tabs to keep it from pushing in too far.

 This left me with just a small gap on one side of the fan that I filled with a piece of cardboard and some masking tape.

 I couldn't find a 25x25x1 inch pre-filter for the front, so I bought a roll of the fiberglass filter material and cut off a piece. I attached it to the front of the cart with masking tape around the edges.

All the parts were already in the shop except the air filters, which cost me about $20 total. The whole project took about an hour and a half to build. I turned it on and it seems to work. It will take me a little while to assess its effectiveness at cleaning the air, especially since I don't have an air quality meter. I will just have to use it a while and see how I feel about it. At least it doesn't take up any additional space in the shop!

UPDATE:
After about a week of use, I'd say it seems to be working pretty well. I've vacuumed off a good amount of dust from the outside of the pre-filters, maybe three times so far. I haven't taken the pre-filters off to look at the main filters yet, but I suspect they are still pretty clean. I've been doing a lot of turning and sanding this past week, and I leave the cart running while I am in the shop. There is still quite a lot of dust that settles over everything in the shop, but I do feel that the air in the shop seems a little cleaner.