[Fred Hargis]

My first filter is a 2 dollar filter....the second filter Is a 5 dollar filter...and the final filter is a 20 dollar high end furnace filter. I change the first stage every month or so...the second stage is still original....but probably getting close to needing replacement. The final stage is as white as the day I put it in....



http://www.woodworkingtalk.com/f32/home-made-air-filter-45667/

And very cheap maintenance on the first filter.

This was the way I built mine as well, I think I did finally have to replace the 3rd filter, but it was only after several years. The first one got replaced about every 3 months or less, if i was doing a lot of work in the shop.