Saturday, May 12, 2012
Dust control: Shop air filter
The whole thing cost about $70-$75 and took an afternoon to build.
1 --- 1/2" AC fir plywood -- $29
1 ---2x4 kiln dried fir -- $3
2 ---20x20 furnace filters -- $20 ea. (you can get much cheaper ones, but I wanted as close to HEPA as I could find.)
Misc -- Switch, electrical box, wire, wire nuts, glue, screws, duct tape, aluminum flashing (to extend exhaust port)
Please note: this design is only as good as the filters you choose. Most furnace filters only filter out large particles. I used 3M's Filtrite filters with their highest proprietary MPR rating of 1900. They claim to filter out 90% of particles down to .3 micron. From what I can tell, they achieve this by relying on the physical filter to trap particles in the 10+ micron range, and an electrostatic charge to get the smaller ones. I'm skeptical of the longevity of the electrostatic charge, so I'm only going to assume this filter will trap the larger dust particles and also use dust collection at the router and ventilation to control dust.
*years ago, I taped a furnace filter to a box fan for a dust filter. It worked, but not well. A radial fan doesn't do well with restricted air flow. The the airflow over the blades stalls and pressure drops off significantly. A centrifugal (squirrel-cage) blower operates much better under conditions with resistance to air flow.