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Thread: DC duct sizing

  1. #1

    DC duct sizing

    I am using the duct sizing guide at https://airhand.com/designing/ to size our ducts appropriately. I have identified our 'main' machines and have increased the ducts appropriately as these main machines enter the main trunk.

    My issue/question is that we have a corner of our shop that contains only one 'main' machine but contains 4 other non-main machines. Each of these machines has a 4" port. The way I currently have the system designed, the one main machine in this corner connects to the trunk and the trunk size increases at that point. But the 4 other machines in this corner tie into this main machine's branch and the duct DOES NOT increase in diameter. If I'm reading that sizing guide correctly, this is what we're supposed to do. The duct only increases in size when a main machine enters the trunk. If I am reading that guide correctly, and I have 5, 4" machines all feeding into one little 4" duct, that seems like a lot for that duct to handle. Granted, we will only be using at most 3 of them at once, but even so, it seems like a lot for it to deal with.

    So should we increase this duct to 5 or more inches to accommodate the multiple machines that feed into it? But then I worry that we won't have a high enough CFM due to the increased duct size.

    I'm probably making this more complicated than it needs to be, but we're dropping $5k+ on our little dust collection system and I want to make sure we do it right.

  2. #2
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    Very generally speaking, going to a larger duct is usually better. Most machines will do better with a 6" line over a 5" line and even better than a 4" line.

    If I follow you correctly, it sounds like you have 5 machines each with 4" ducts and that feed into a 4" duct that then feeds into the trunk. And you plan to run at least 3 of these at a time. The 5 4" into 1 4" that then feeds into the trunk sounds like a bad design to my ears.

    First, separating each of the 5 4" into their own ducts that feed into the trunk would be better.

    Second, increasing each of the 5 4" to something larger will usually be better.

    Personally, I like to take at least 6" duct to each machine and do the following:
    (1) I will modify the dust port on the machine to accept 6" OR
    (2) I will take the 6" as far as possible before tapering down to something smaller OR
    (3) I will split the 6" duct into 2 4" ducts (for example, the cross-sectional area of a 6" pipe is just a bit more than 2 4" pipe cross-sectional areas) and connect those to the machine (this is good for a table saw with a blade shroud in the cabinet and one above the blade)

    Now all this depend on your DC and its impeller size and the trunk size, etc. I think if you have a decent cyclone and 14"+ impeller, that using at least 6" is pretty darn good if you don't want to think too hard. A larger impeller like in the 16"+ size likely benefit from a larger trunk (8", for example) with 6" drops.

    If you can provide more details on the overall system, we can provide more succinct answers.
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  3. #3
    I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine. And that a branch should only be upsized if it's part of the trunk, where a "main" machine enters the trunk, and a "main" machine is your worst case scenario of which machines are operating at one time.

    I'm having my much more artistically talented wife draw up a rough floorplan which will hopefully clear things up a bit.

  4. #4
    Here is a bird's eye view of our floorplan as it currently stands. Due to ceiling height restrictions (Only 12') I would like to keep things in the wall-ceiling corners as much as possible. We also have to contend with an overhead door that we need to go around, as well. The miter stations have no DC right now, so that is open ended. We will probably build a plywood hood and shove a 6" duct into it but I'm sure someone here will have a better idea if that one is stupid.

    If someone could help me by providing the pipe layout, I can do the work of piecing it together. I just want to make sure that we don't have to tear anything apart to clear a clog down the line.

    Our worst case scenario is probably both table saws, the planer, and the jointer/a shaper running at any given moment, though it's certainly possible that we might have the edge sander, the big shaper, the jointer, and then planer going at once, as well.

    The DC isn't mounted anywhere yet, and can move freely along that front wall, so long as it's not over the garage door really. We have a roll off on that side of the shop that we had intended on dumping into, however.

    Any and all help is very much appreciated!
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  5. #5
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    Quote Originally Posted by Kevin Cackler View Post
    I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine. And that a branch should only be upsized if it's part of the trunk, where a "main" machine enters the trunk, and a "main" machine is your worst case scenario of which machines are operating at one time.

    I'm having my much more artistically talented wife draw up a rough floorplan which will hopefully clear things up a bit.
    A machine manufacturer has determined what is best..........I can hear the laughter form here. No machine manufacturer to my knowledge has even the vaguest idea of what good dust control is.
    Chris

    Everything I like is either illegal, immoral or fattening

  6. #6
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    Quote Originally Posted by Kevin Cackler View Post

    I'm probably making this more complicated than it needs to be, but we're dropping $5k+ on our little dust collection system and I want to make sure we do it right.
    What dust extractor is going to drive this system?
    Chris

    Everything I like is either illegal, immoral or fattening

  7. #7
    It's a 5HP grizzly motor from this guy http://www.grizzly.com/products/5-HP...ollector/G0672

  8. Wow, if you want to run a couple of table saws, shaper, and a planer or sander running concurrently I would suggest you'd want approximately 3000cfm - approx 800cfm to each machine. For that you would want something like a 10-12" main trunk with 6" drops to each machine. You would want to plan the ducting and position of the machines to get the relative flow required to each machine (some require more, some less) and you would need to keep at least 3 ports open all the time to ensure you maintain enough cfm and velocity in the main trunk to prevent buildup. It's not a quick thing to work out if you want to do it right and if you are running a production shop I'd suggest taking the time to get it right. You are going to want a 10hp + system i'd expect.

    Sorry out and on a phone right now so a detailed response is not easy.

    Cheers, Dom

  9. #9
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    At that price I would be buying a cyclone, either Oneida or Clearvue and you will not have to deal with bags which don't filter worth a damn, leak and have to be cleaned and emptied. As a guess a CV Max would have the largest flow capacity or their new metal version which may flow more.
    Chris

    Everything I like is either illegal, immoral or fattening

  10. #10
    Chris, We are dumping directly into a container outside. The output of the motor will go straight into the container.

    Dominik, this blower is what we have for now. We will be moving to a new shop within the year, and that one will be custom built from the ground up to suit our needs, including professional duct and blower design services.

  11. #11
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    Fair enough if you are going to remove the bags and exhaust externally to atmosphere. I don't know your climate but to do that you are going to have to have a door or windows open all the time if the blower is operating.
    Chris

    Everything I like is either illegal, immoral or fattening

  12. #12
    Quote Originally Posted by Kevin Cackler View Post
    Chris, We are dumping directly into a container outside. The output of the motor will go straight into the container.

    Dominik, this blower is what we have for now. We will be moving to a new shop within the year, and that one will be custom built from the ground up to suit our needs, including professional duct and blower design services.
    If you have a five horse power motor you probably have about a 16 inch impeller. You can get away with usually only 7 inch trunk. 8 inch would be pushing it. You really need to check your amp draw. I have an oversized impeller and an undersized 5 hp motor. I tuned my system to keep my amp draw down by using a 6 inch main duct. I could’ve used 7 inch but I would over amp my motor if I had more than two blast gates open. Most manufacturers do exactly what I’ve done to prevent you from burning out there motor under warranty by choking air supply.

  13. #13
    The motor that we have has a 15" impeller.Having 4 ports open at once is an absolute worst case scenario. We spend a LOT of time not at the tools hand sanding, assembling, etc... so the most likely scenario is that 2 ports are open at one time, occasionally 3 possibly. If this motor can only support 2 at a time, then fine, we'll just open two at a time. Right now my primary concern is getting the duct sizing right. We can always upgrade the motor if it's just too small / it burns out.

  14. #14
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    DC threads have a way of going off the rails depending on your enthusiasm. I'm a bit of a DC-Nazi since I now enjoy health issues from not doing enough soon enough. Sounds like you are well on your way to missing that road.

    In DC you want to do the best you can. Some folks make it their obsession but, not everyone has that interest. Your 5HP blower exhausting directly outside will move a lot of air. If the four machines you are worried about include the 3 shapers, I doubt you will be generating spoil at all three simultaneously whether they are running or not. this is an important point; it is not how many machine you are running, it is how much spoil you are generating.

    Unless you are going with NorFab or something like that modifying your system after the fact is pretty painless. If the 4 x 4" collection point doesn't cut it in actual operation, change to some other form of transition. I have multiple 4" leaving a 6" trunk via 6x6x4 wyes with gates at each 4" end of the wye and this is working well even for an overly-concerned citizen like me ;-)
    "A hen is only an egg's way of making another egg".


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  15. #15
    Thanks, Glenn. I appreciate that this isn't the best way to achieve it, but we've got to work with what we have in this instance.

    I am taking the 4x4" off of the DC, which exposes a 10" inlet. It will be mounted high up on the wall, exhausting into a container outside. My main concern right now is making absolutely certain, without a doubt, that I'm not going to be cleaning clogs every day. As my plans are drawn right now, the stuff on the right side of the wall all goes into a 6" branch duct and heads toward the planer. As it joints the 5" planer duct, it transitions into 7" and continues toward the table saws. As it passes the table saws, it increases to 9". And then bumps up to 10" right at the end so that it can connect to the DC input.

    As far as which machines will be running, it's usually just going to be a combination of a table saw or miter saw or two and the planer. Sometimes the shapers. But it's important to note in this particular case, that the planer is used in long-running spurts, as are the shapers. If we need to work around the restrictions of the DC, that's fine. I just want to make sure that I've sized things appropriately to avoid clogs.

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