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Thread: Under Floor Dust Collection

  1. #1
    Join Date
    Aug 2009
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    Colorado Springs
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    Under Floor Dust Collection

    My new shop will have a wood floor with probably joists over a small crawl space. Not something Iíd ever want to go down into to fix ducting. Iím thinking Iíll lay OSB with screws so they can be removed if I need to get to them from above.

    So, having read most of Bill Pentzí site and gone through the last 250 or so pages here at SMC, Iím at a crossroads. There are literally hundreds of dust collection posts, far outnumbering any other category, but there doesnít seem to be much consistency. Pentz pretty much says put your ducts overhead. Otherwise, expect clogs or bulky material damaging the impeller. Not to mention possible fire hazard from high amounts of residual material in ducts. That option isnít my best for several design reasons. Plus, in building a clear span structure w no internal posts, thereís no way Iím going to go anywhere but below to my central saw and jointer cluster.

    Whats the real world experience, assuming good duct layout with a powerful motor such as a 5hp ClearVu and 6Ē ducts as close as possible to each tool?

    One of my main concerns is the rise from the subfloor up to my DC intake.

    Have others seen these problems? If I have a clog I can probably get to it to fix it but not interested in anything more serious.

    Thanks much for any advice.

    Jon

  2. #2
    Join Date
    Mar 2003
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    SE PA - Central Bucks County
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    44,598
    Outside of unusual circumstances...excellent air flow and proper duct design cures all. Dust collection is about moving air. The air, in turn, moves the material. If you make that air move as efficiently as possible and with a volume (measured in Cubic Feet Per Minute - SFM) that exceeds the requirements of the tool collection expectation, etc., you should be fine regardless if your duct work is overhead or down below.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
    Join Date
    Jan 2010
    Location
    Yorkville,IL
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    220
    Never had clog in 7 years. I just finished building my new shop and I put duct in floor again.
    Jaromir

  4. #4
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    Quote Originally Posted by Jaromir Svoboda View Post
    Never had clog in 7 years. I just finished building my new shop and I put duct in floor again.
    Jaromir. 6” ducts?

  5. #5
    Join Date
    Oct 2005
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    Helensburgh, Australia
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    The short answer is it depends, if the dust extractor cannot transport the debris it will clog so don't buy a cheap DE and design the system so it can be got at if necessary.
    Chris

    Everything I like is either illegal, immoral or fattening

  6. #6
    Join Date
    Apr 2017
    Location
    Michigan
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    A couple of pointers;

    Install quick disconnects at places you may need to access.

    Sometimes vertical sections are designed smaller then the main run so stuff will be lifted by the velocity. As Jim says, "proper duct design"

  7. #7
    Join Date
    Apr 2006
    Location
    Phoenix AZ Area
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    2,186
    I have overhead ducts in my current shop. I do get small cut offs that get sucked up above the blade guard but the don't get all the way up to the horizontal so when the collector shuts off they fall down. I suppose you might get small pieces of scrap falling down into the ducts and then fail to go vertical back out of the floor, I never considered that. I am sure that disconnecting duct under the floor would be a major pain in the butt.

  8. #8
    Probably the biggest advantage of having overhead/above ground ducts is that they can be moved.

    I've had 3 different shops, and all 3 times I have installed dust collection, I have ended up not liking the initial result, despite weeks/months of planning. Same thing with the machines, I always seem to find a better layout after I get everything in there. I can't imagine being locked into a specific layout by underfloor ducts. I have 9' 8" ceilings with a 6" main and flex duct coming down from the ceiling. No problems with clogs or lack of pull with a 3HP Oneida.

    Granted a crawl space is a little more flexible than burying them in concrete. I'd say go for regular plywood rather than OSB. It will probably wear better. Also look for screws that can have the gunk cleaned out of the heads easily.

  9. #9
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    Oct 2005
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    I think my DE ducting is on the fifth iteration at least.
    Chris

    Everything I like is either illegal, immoral or fattening

  10. #10
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    Quote Originally Posted by Andrew Seemann View Post
    Probably the biggest advantage of having overhead/above ground ducts is that they can be moved.

    I've had 3 different shops, and all 3 times I have installed dust collection, I have ended up not liking the initial result, despite weeks/months of planning. Same thing with the machines, I always seem to find a better layout after I get everything in there. I can't imagine being locked into a specific layout by underfloor ducts. I have 9' 8" ceilings with a 6" main and flex duct coming down from the ceiling. No problems with clogs or lack of pull with a 3HP Oneida.

    Granted a crawl space is a little more flexible than burying them in concrete. I'd say go for regular plywood rather than OSB. It will probably wear better. Also look for screws that can have the gunk cleaned out of the heads easily.
    Thanks for your reply. Very helpful info!

  11. #11
    Join Date
    Sep 2009
    Location
    Fairbanks, Alaska
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    43
    6Ē pvc duct under concrete and steel. ClearVue 1800 sucking on it. No problems so far (3 years). Only issue is the permanence. So the entire run is not underfloor to each machine. Instead, I put them up along the far wall, and localized clusters of machines, and run along the walls for distribution. Not the best layout, but beats having it hang below the finished ceiling level above.
    This partial underfloor has accommodated me rearranging the shop a couple of times.
    So, yes if I were building again, I would run underfloor to key areas and above floor to the machine.
    Good luck, and enjoy
    Sean

  12. #12
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    Sep 2016
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    Modesto, CA, USA
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    Unless it is a deep trench the up turns will not be long smooth arcs so they will reduce flow.
    Bill D

  13. #13
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    There has been flow testing done in Australia that shows long curves flow worse than short curves contrary to what we all believed and to what seems logical.
    Chris

    Everything I like is either illegal, immoral or fattening

  14. #14
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    Aug 2009
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    Colorado Springs
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    Mine will be in a crawl space under joists so plenty of room for long radii.

  15. #15
    Join Date
    Jun 2017
    Location
    Saskatoon, Saskatchewan, Canada
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    Quote Originally Posted by Chris Parks View Post
    There has been flow testing done in Australia that shows long curves flow worse than short curves contrary to what we all believed and to what seems logical.
    Chris would you pm me the link if you can find it? I know two forty-five degree corners are worse than a large radius ninety but had seen nothing about a long sweep being worse than a short one. Thanks

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