This is an inexpensive unit to build and does a good job picking up dust especially sanding dust.
I used 3/4 plywood to build the box and 3/4 oak for the door
I used a felt weather stripping on the door provides an airtight seal
The unit has two filters. The primary filter is a 14×20 furnace filter.
The secondary filter is a “K&N Performance Filter” #33-2035, made for a Corvette,
and can be bought at most auto parts stores.
This one I wash out a few times a year.
I just spray it with any household cleaner like Fantastic and rinse with water
The three-foot long duct on the discharge moves the clean air away from the unit
so as not to pull the same air into it repeatedly, like the store bought cleaners