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Thread: DIY air filtration unit for <$200

  1. #1
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    DIY air filtration unit for <$200

    As payback to the lasering community, I'm sharing my "plans" (such as they are) for everyone to copy. Well, not so much "plans" as pictures of the completed unit, but it should be obvious how to recreate something similar.

    Due to poor planning on my part and a lack of any real sleep, I made one or two errors in the construction of this unit, but I'm happy to say it works like a dream. After a solid hour and a half of engraving a maple block at 100% power, there was only the faintest aroma of wood in the air, and not the tiniest touch of smoke haze. It all took a few weekends, each with a few hours here and there to allow for drying of the caulk, and the cost was under $200

    Materials:
    1) Trashcan ($25)
    2) 4" PVC piping, 2' ($6)
    3) 3.5" PVC cap ($4)
    4) 3/4" PVC piping, 2' ($2)
    5) HEPA filter ($23)
    6) Furnace filter ($10)
    7) Silicone caulk ($3)
    8) PVC cleaner/cement ($8)
    9) Activated charcoal, 50 lbs. ($115)

    Tools:
    1) Caulk gun
    2) Saw or Dremel

    The great thing about this project is there is no real measuring to be done, just align things by eye or what "feels" right. The first pic is of the outside of the unit. It's nothing more than a typical plastic kitchen trashcan. Two 4" PVC tubes allow air in/out, with a ring of the 4" pipe chopped into short segments glued both inside and outside of the trashhcan to help act as a barrier to air (with the caulk) as well as give the joint more strength.

    The second pic shows an inside shot so you can see a few 3/4" supports, roughly 6" in height, simply taped to the walls. These supports, along with friction from an over-size cut, hold up the furnace filter, just above the 4" inlet pipe.

    This furnace filter, shown in the third pic, is sold as a cut-to-size sheet of a basic blue filter and a charcoal filter. The final filter sandwich consists of a plastic support mesh, blue scrubber, black charcoal, and another support mesh, all tied together with the included plastic ties. I cut it about 1/2" too large all around to give me a friction fit.

    The final pic shows the whole shebang put together, minus the activated charcoal, with the HEPA filter installed. The HEPA filter was purchased at Sears as a replacement filter for one of their shop vacs, and the end was plugged using the PVC cap attached to the inside of a short length of the 4" piping.

    Air from the machine comes into the bottom of the machine, the blower connects to the top. Use about a 3" layer of activated charcoal on top of the furnace filter... the edge supports and the friction fit will hold up that small amount without issue. Dirty, smoke-filled air comes in at the bottom, the furnace filter traps large particle, like scrap paper, etc., the charcoal above it traps the smoke particles and/or noxious plastic fumes, and the HEPA filter traps anything missed.

    If possible, weigh the charcoal charge and the whole assembly as a separate item. Weigh the entire piece, charcoal and all, from time to time... when the weight of the charcoal roughly doubles, it's time to change it out.

    I hope I didn't miss anything, but if I did I'm sure someone will ask...
    Attached Images Attached Images
    Last edited by Dan Hintz; 07-05-2010 at 8:48 PM.
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  2. #2
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    Great job Dan, And without any LED's. This build is alot better than what I have built and simpler.
    Thank You

  3. #3
    Thanks for advice, Dan. Where you buy HEPA for $23? Here in Lithuania price start from $90
    GCC Dealer in Baltic countries

  4. #4
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    Nice one Dan, I love it when people think inside the box!
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  5. #5
    Dan

    Neat idea! Do you have any way to measure or judge the exhaust flow from the laser. There will be some flow restriction.
    Mike Null

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  6. #6
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    Viktor,

    Sears is a major retail store here in the States, selling everything from clothes to appliances to tools (under the Craftsman brand name). Their shop vacuums use a handful of interchangeable filters from standard filtering to HEPA levels. Here's a link so you can see what I'm talking about, but I'm willing to bet you can find a place closer that sells a similar item:
    http://www.sears.com/shc/s/p_10153_1...536S254315124P




    Mike,

    I have no way to judge actual flow (no in-line anemometer), but it's more than adequate. I'm using the red extractor from Harbor Freight with the variable speed controller unit for routers. At 100% speed, the blower is a complete noise racket... I turned it down to around 90% on the dial for a significant reduction in noise with no more than a very minor perceptible change in smoke removal. The smoke was heavy (I was burning 1/32" deep into maple at 100% power), but it practically hugged the substrate's surface as it was wicked out of the machine.

    I wasn't sure how well this would work when I built it, but I'm extremely happy with the results. When other pre-built machines cost $4k+ plus several hundred dollar filter replacements, I use a sub-$100 extractor, <$100 in materials, and $115 for 50 lbs of charcoal that will last me for 10+ refills. I can even send the charcoal back to be recharged, though I haven't tried it yet, so I don't know what kind of discount it would net me... shipping cost alone (about $25) may make it unfeasible.

    My main "mistake" was the direction of airflow. Initially, the design was to have the inlet up top, pass through the furnace filter, then charcoal, then a second furnace filter (used only to hold the charcoal up), and then the HEPA at the bottom before going out to the extractor. My thinking was the top-to-bottom airflow would compact the charcoal and ensure the best filtration of fumes, whereas a bottom-to-top airflow might float the lightweight charcoal and prevent any real filtration. After cutting the holes I realized it would be a PITA to get to the HEPA filter at the bottom, so I swapped direction, completely forgetting about my original line of thinking. I was nearly finished when I realized my goof, but I was so far along I couldn't change it back, so I decided to finish it up and at least give it a try. It doesn't appear to be an issue, but I would suggest looking for a convenient way to get a top-to-bottom airflow on the next iteration.
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  7. #7
    I doubt that bottom to top would be any sort of a problem with respect to the charcoal. Most of the range hoods in the kitchen which use charcoal work like that. They don't have an option but even so they do a respectable job given they don't have the advantage of a hepa filter.
    Mike Null

    St. Louis Laser, Inc.

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  8. #8
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    They also only have to get rid of some burnt chicken smell, not noxious acrylic vapor that would eventually eat away your lung cells I wanted this system to get rid of everything, not just reduce the smell a bit. Since I recirculate the air back into the room (and my health is always in question ), I wanted there to be no question.

    I was a bit nervous doing this last project because it was such a long burn and the filtration system hadn't been tested yet... I half expected the room to be filled with smoke in two minutes, but the only way I could tell wood was burning was when the top was opened.




    Oh, I should also add... the pictures don't show the trashcan's lid, but it's there, and the open edges are covered in tape to make sure all air comes through the laser.
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  9. #9
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    Great design Dan, and thanks for sharing. My design is a little different but the one thing I have learned that might help in any design is that I now use cheese cloth to surround the charcoal. It does not restrict air passage and makes removal/exchange of the charcoal much easier, at least with my design.

    The pics sure help - thanks for taking the time to show and tell.
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  10. #10
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    Quote Originally Posted by Randy Digby View Post
    I now use cheese cloth to surround the charcoal. It does not restrict air passage and makes removal/exchange of the charcoal much easier...
    I'll add it in during my next charcoal swap... I just need to lay down one layer and leave the edges long. Come time to swap, gather the edges and pull the whole package out.
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  11. #11
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    That's exactly what I do. Before the cheese cloth, I had to carry the scrubber down to the garage to change charcoal because of the dust. I leave the ends long, like you say, and simply gather the sides together and lift the charcoal charge out and replace in the same manner.
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  12. #12
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    Now to FIND some cheese cloth... <opening up Google.. tap tap tap...>
    Hi-Tec Designs, LLC -- Owner (and self-proclaimed LED guru )

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  13. #13
    Quote Originally Posted by Dan Hintz View Post
    Now to FIND some cheese cloth... <opening up Google.. tap tap tap...>
    Grocery store. Baking aisle.
    I read recipes the same way I read science fiction. I get to the end and I think, "Well, thatís not going to happen."

  14. Why not put the HEPA filter before the active coal? The main function of the active coal is to remove chemicals from the air and not particles, so it might be better to filter out as much particles as possible before the coal.

  15. #15
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    Where to get activated charcoal

    Great idea!! Where did you get the bulk activated charcoal? From an aquarium store?

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