I built a downdraft table for <50% typical costs- Mtbr.com
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  1. #1
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    I built a downdraft table for <50% typical costs

    A good carbon acquaintance counseled me on what to do about how SLOW it is to sand and cut carbon using water. Sure, the water method is tidy, but oh-em-gee it takes so much time!! I made some changes from my acquaintance's design.

    (I should probably stop posting to that one other thread of mine repeatedly. This seemed like a good break point.)

    I needed to save some money, since my bratty little WRX is approaching 200,000 miles and needs a lot of money put into it before the aged interference engine rips itself some unwanted holes. But I also am badly overdue for dry carbon dust capture. My production pace needs to speed up now and this is a sorely needed solution. Some MERV 15 single micron filters from Wynn Environmental are the backbone of the assembly. Everything else, I cheaped on as much as possible. The fans (claim to) pull 2900 CFM each.

    I did an illuminated test of dry cutting a 22.2mm diameter tube and instead of a carbon mist spraying all over the room, I saw... nothing. Yes! Next test will be to do some serious work in an unused Tyvek suit, and examine the cuffs afterward.

    The electrical part of the setup is sketchy. Both the fans run on 120V, claimed 3.8 amps. A plugin Kill-a-Watt outlet measured 4.3 amps after an initial startup spike of 8 amps. Starting one-and-then-two of them makes for a spike of 14 amps, which falls just within the "don't fill the entire glass of water" margin on a 20 amp circuit breaker.

    One detail I did not anticipate: these filters were probably not ever designed in mind to be attached to a wooden box. The foam gaskets did not want to play kissy face with an uneven sheet of plywood. Hence the extra hold down levers.

    The positively ridiculous amount of tape is for scuff protection of nearly finished carbon parts.

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    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  2. #2
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    Are the fans housed within the filters?

  3. #3
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    Quote Originally Posted by mikesee View Post
    Are the fans housed within the filters?
    The fans are after, what I now realize are not pictured, in the back at the bottom so they just sit on the ground for easy mount and removal.

    I could have put them in front for more aggressive flow, but I was concerned about aging the fan prematurely.

    I am not an HVAC expert, so it will be interesting to see with time if I am satisfied with the setup or if I reconfigure it later.

    Here's the napkin style sketch that I did not exactly follow. I'll admit this was one of those things where I didn't quite know what I was doing and decided to "un-design" build it and just see what happened.

    The plan for cleaning the filters is to make a manifold that will hook up to my small-scale separator bin and shop vac, place that over the two inlets, remove the fans, start the shop vac, and blow compressed air at the outside of the filters. Due to the size of the fan holes, I can get a good part of my shoulder in there and almost reach around the filter.

    I built a downdraft table for &lt;50% typical costs-20191106_135305.jpg
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  4. #4
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    Interesting take. What are you going to do for a work surface?

    I've seen numerous wood-workers use filters from Wynn to make their dust collection systems and interface them with wood. There are many configurations of filters they offer. I've seen hold downs like you've used. Also 4-6 threaded rods evenly spaced around the perimeter that go all the way to another large body of wood on the other end of the filter and clamp it in between.

    For lack of better terms: 2900cfm of "blow" you can feel for a significant distance away. For "suck" you probably need to be right up on it to feel the air flow. The better you can reduce and channel the inlet side of the airflow at the work piece the better off you'll be.

  5. #5
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    Quote Originally Posted by bme107 View Post
    Interesting take. What are you going to do for a work surface?

    I've seen numerous wood-workers use filters from Wynn to make their dust collection systems and interface them with wood. There are many configurations of filters they offer. I've seen hold downs like you've used. Also 4-6 threaded rods evenly spaced around the perimeter that go all the way to another large body of wood on the other end of the filter and clamp it in between.

    For lack of better terms: 2900cfm of "blow" you can feel for a significant distance away. For "suck" you probably need to be right up on it to feel the air flow. The better you can reduce and channel the inlet side of the airflow at the work piece the better off you'll be.
    Regarding work surface - not sure yet. Dunno if my present one needs modifying, I'll know if dropping anything on the entry grate becomes a problem.

    Regarding blow vs suck - yeah you are exactly right, the inward air flow is felt most right at the inlet. I am thinking about doing a partial acrylic or polycarbonate window with the entire-protective-arms-through-the-window thing, whatever the F that is called. The basic deal there is (1) I need to channel further as you suggest, (2) I'm afraid of a little bit of eddy currents even with additional channeling, (3) I loathe taping up gloves to a Tyvek suit by myself, there's a reason surgeons work in teams. I'll be sure to post up once updates are in effect. Last few days were spent organizing cold side of my garage to properly house this behemoth.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  6. #6
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    Quote Originally Posted by Drew Diller View Post
    ..........I am thinking about doing a partial acrylic or polycarbonate window with the entire-protective-arms-through-the-window thing, whatever the F that is called. ......
    As a first pass you could try just the basic salad bar sneeze type guard. Have it slope down from the back wall and allow for just enough room for your arms and work piece to fit through the front underneath.

    Thinking about it more, you could make the guard flat and use height adjustable shelf type brackets. Then you could use some scrap wood to make moveable partitions (book ends?) that further confine the sides of the work area, as needed. This doesn't have to be fully airtight just slightly restrictive to channel the air flow.

  7. #7
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    This seems like something to build into an existing table and stow collapsed. Could you power it with a shop vac?

  8. #8
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    Quote Originally Posted by Darth Lefty View Post
    This seems like something to build into an existing table and stow collapsed. Could you power it with a shop vac?
    I think no, not so feasible. My shop vac is a Fein Turbo 1. Don't get me wrong, it's a nice vac for its purpose but it only really sucks at a range of a few inches. 151 CFM.

    @bme107 - I will consider that, and perhaps that notion can be extended to constricting the volume within the filter exit box as well. I'm wondering if the large volume is causing some kind of exit turbulence. At any rate after trying it out a few times, it's better than any solution I've had so far, and the idea that it can be better still is pretty cool
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

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