Here are my plans for a 3 stage filter, it has a rough filter, a fine filter, and a tray of activated carbon. It uses standard 14x20in home filters and bathroom ventilation fans for suction. The cost is about $50, not including filters.
It’s good for dust, smoke, and fumes at about 100 CFM. It’s great for my shop.
To start you’ll need:
- 2 – 24x48x0.5in plywood sheets
- 1 – 4ft 2x4 board
- 2 – 8ft 2x2 boards
- Screws or nails
- 2 Bathroom style ventilation fans
- 1 Tube of caulk
- 1 Roll of duct tape
- Vent tubes for input and output
Cut 1- 14x20in plywood piece, and attach a 14in 2x4 to the far edge, and 2- 17in 2x4 pieces to the side.
Once the base is complete, place the fans and mark where they will be cut though. I used a jig saw and drill to cutout the square slots. Mount the fans to the base as well as you can.
I used duct tape to seal the edges of the fan down to the base to eliminate leaks. Eventually the entire air path will be sealed except the input and output vents.
Use 2x2 boards to create a border around the base, the filters will rest against this frame.
Cut 2-14x14in board to attach 1 to the back of the base, that’s the side that the fans are blowing away from. Save the 2nd board for the front of the box later.
Cut 2-21x14in boards and attach to the sides of the filter, note the caulk on all edges.
Cut a 14in 2x2 board and attach it to the back top of the filter.
Cut 2- 18in 2x2 boards and attach it to the top sides of the filter, these three pieces will be the anchor for the top board. Note the caulk around all edges.
Cut a 15x21in board and attach it to the top of the filter, caulk around all edges.
That completes the main part of the filter, all your have to do to complete the box is make sure that the output air is directed correctly depending on your situation, in my case I used some scrap plywood to create sealed a channel that by output duct will attach to.
About the Carbon filter, I used a cheap air filter and just dumped a big pile of activated carbon granules on it. I used the activated carbon that you can buy at the pet store for cleaning your aquarium water, 3 pounds of carbon cost about $20 and filled the 14x20x1 tray perfectly. This isn't the most effective filter, but is is much cheaper then a “real” activated carbon air filter.
My laser, among other things does not have a air filter, and when I cut things the fumes get to be over-powering.
The filter works great, I estimate that for standard smoke it filters about 99% of it, and for the more acrid plastic fumes are reduced by 60%-70%, which is a big improvement.
Eventually I will buy a “real” activated carbon filter for this box, but they are kind of expensive, so I will make due with the DIY version for now.