Portable dust filter for the shop made from 20" box fan and furnace filter.
View from the rear with door open and filter removed:
This is slightly more upscale than the classic design, which consists of a furnace filter duct-taped to the back of a fan. Highlights of the project:
- 20" box fan found at the local Goodwill store for $3
- Remove the fan assembly, wiring, and switch
- Cut the fan mounting brackets from the fan box
- Save the front grill and discard the rest
- Make a new body out of 1/2" MDF 21.5" x 21.5" x 7.0"
- Starting with a 20.5" square piece of 1/2" MDF, cut out a 19.5" dia. hole
- Mount the fan assembly in the box. I had to mount the switch inside the box and made an extension of the switch shaft to attach to a knob on the outside.
- Mount the piece with the big hole just in front of the fan blades. This significantly improves the performance of the fan.
- Make a frame to hold a 20" x 20" x 1" furnace filter and mount it behind the fan assembly.
- Cut pieces of 1/2" thick stick-on window sealing foam rubber to the frame surface that the filter will rest on.
- Place the filter in the frame and measure the distance from the back of the filter to the back side of the box. Add about 1/8". Make a 19.5" square frame from 1/2" wide material that height.
- Make the frame for the rear door frame from 2" wide 1/2" thick material. I used poplar.
- Glue the small frame to the inside of the door frame (centered). This clamps the filter in place when the door is closed.
- Mount the door using hinges and clasps.
- Mount the front grill.
- I added a handle on the top made from the finest wood (a chunk of 2 x 4) and it is ready for some paint.
I used a furnace filter that was washable. It cost $20, but I figured that was a lot cheaper in the long run than buying new filters every few weeks. It filters the air nicely and is still usable as a portable fan.