First one I did some time ago, a cyclone for my shopvac made out of five gallon buckets with less than 20 dollars worth of 2" PVC inside, a couple ferncos on the outside. I can say, doing about the same work in the shop, that I have to clean the filter in my shop vac about 1/3 as often with the cyclone. No cyclone, 3 filter cleanings. With cyclone, 1 filter cleaning, same about of chips and dust to the dump. If you decide to build one of these look super careful at the buckets in the youtube. I couldn't find a bucket with compatible upper rings local, so I cut all the top rings off a team blue bucket so it would fit down inside a team orange bucket.
https://www.youtube.com/watch?v=1WnitgYFnE0
Second, just this weekend I built a Corsi-Rosenthal air filter box and my wife loves it. I like it just fine, and I can see it working; but the wife thinks it is the cat's meow.
For the airfilter box I dropped $150 Fairbanks dollars on a new box fan, 4 20x20 furnace filters, a 2 foot square piece of 1/2 plywood and four caster of the two inch persuasion. I pulled four scraps of 4 inch long 2x4 out of the scrap bin and used close to a whole roll of duct tape.
https://www.youtube.com/watch?v=aEn2xzlvrdo
Compared to the PhD in Canada mine has a plywood floor and is on casters, otherwise about the same. I did not make a cardboard baffle for the top because I am good at taping stuff. I did use some wood glue and drywall screws to get the casters mounted to the plywood floor, the rest of the thing is held together with duct tape. When my wife first turned it on we could see particles moving through the air at eye level head directly to the filter. It has been running all weekend, I can see across the shop better and my wife is ecstatic. I have no numeric data on particles suspended in air. The fan motor is not detectably warm.
I did one lucky thing. I set the 2x4 blocks for the casters half inch back from both edges just because it seemed like a good idea. As I was taping up, the 2x4 blocks are far enough away from the edge that they didn't interfere with the duct tape wrapping around the edge of the plywood onto the bottom face of the plywood.
I did notice 20x25 furnace filters are cheaper (local to me) per square inch of filter area, compared to the 20x20 filters. And the box fan is slowed down a bit by having to suck intake air through the filter media. For the next one I will use 8 of the 20x25 filters so I have a thing nominal 20 inch square footprint but 50 inches high instead of 20. It will need some interior framework to hold up the fan. If I do it well I will only need duct tape around the edges of the filters to make it airtight. For that next build I will probably use 3/4 ply for the floor, 3 inch casters, and make a baffle for the fan at the top out of half inch ply so I can just run a bead of silicone caulk above the baffle to set the fan on.
I can see the 50" tall version at the end of my bench just past the trashcan, so as I am planing the whispy bits fall in the trash and the dust can fly across the trash can to the filter. If you build one 50 inches tall before I do please let us know if you had to upgrade the fan.
My next air quality project (don't hold your breath) will be to build a horizontal cyclone, like this fellow: https://www.youtube.com/watch?v=n2OStvRteRE , except you can skip to 33:00 in his 38 minute video. I am going to start with one sized for my shop vac, but will have an air quality meter and an anemometer (Thank you Larry Frank from I think 2016) and a water tube manometer so I can present it with actual data. If I can make a horizontal cyclone work I can use a less powerful dust collector to achieve similar air quality.
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