Dust Collection Port Sizes

This week’s question comes from Rich. He writes:

Firstly, thank you for all the time and effort you put into producing such a wonderful Website. My question is this: In one of your video segments you mentioned that increasing the dust collection port diameter of the table saw to 6 inches probably decreased dust collection efficiency. I would like to know more about your experience in that area. I am in the process of redesigning my own dust collection system and, after reading about the hazards of wood dust, really want to do it right this time. What would you do differently if you had to design your dust collection system over again? What specifically is unsatisfactory about the 6 inch port on the table saw and do you also use an overhead saw guard with integral dust collection? Once again, many thanks for your time and contributions to the woodworking community. Keep up the good work. Live long and prosper!

And here was my reply:
Hey Rich. Thanks for checking out the podcast. The dust collection port on my tablesaw was originally 5″. In an attempt to increase airflow, I modified the port to make it 6″, so that it would match the size of the main trunk of my dust collection system. Afterward, I added the overhead guard with dust collection, which has a 3″ port. So between the overhead port and the cabinet port, its actually way too much surface area. In general, when you split off the main line, its a good rule of thumb to keep the sum of the two new lines no greater than the main line itself (within reason, of course). So I would have been better off leaving the saw alone at 5″. I still would have exceeded the total of 6″ when I added the dust collection from above the blade, but I wouldn’t have had to modify my saw’s port and the dust collection most likely would have been better. Lesson learned, I suppose.

I have some new equipment in the shop now and I am having a hard time deciding how to modify and lay out the new lines. As it exists, I feel like I have a big collection of branches as opposed to one main line. And I think my dust collection is suffering as a result. So I might do a little modification soon, but I’m not sure what the plan is just yet. The best advice I can give you is to put it all on paper first. Make sure it makes sense and let a few friends look at it. Peer review is a good thing! Then once you are comfortable with the layout, go for it. Good luck with your woodworking Rich. And a heartfelt “live long and prosper” to you too!

***Special Correction*** From Tom Cissell- “The area of a circle is PI times the radius squared with PI being = to approximately 3.14. So, you would have been fine with a 5 inch main port on your TS and a supplemental guard port of 3 inch because the sum of both those areas would be less then the 6 inch main.”
See Tom’s full post in the comments section. And get your calculators out if you want to get the exact figures!

Category: Tools


  1. Marc,

    Remember those hot spring days in geometry class and how your mind wanderded to micro-biology, girls, woodworking, or anything but geometry? Miss Magilicuty taught us that the area of a circle is PI times the radius squared with PI being = to approximately 3.14. So, you would have been fine with a 5 inch main port on your TS and a supplemental guard port of 3 inch because the sum of both those areas would be less then the 6 inch main.

    Two three inch ports equal a total area of about 57 square inches while one six inch port equals about 113. I agree on simple rules of thumb so I will ignore the length of the run, the number of bends, type of material, etc. But it is simple and quick to calculate the areas of the ports and compare it to the main’s area. Or better yet, we can solicit our kids or neices and nephews to do it as an “exercise”.


    I skipped geometry and went right to calculus. ;)

  3. Brian November 6, 2007


    The math is a little off.

    pi*(5/2)^2 + pi*(3/2)^ = 26.7 sq. in

    pi*(6/2)^2 = 28.27 sq in

    You squared the diameter of the six inch port to get 113, but I’m still not sure how you got 57 for the total are of the two combined…5 in radius plus two 1.5 in radius pipes would get right around there.

  4. Brian November 6, 2007

    Well, ignore my last line, i got confused with the math as well. What I meant was an 8.5in radius pipe would get you to ~ 57 sq in.


    lol. now you see why I like the grossly over-approximated method? :)

  6. Mattias in Durham, NC November 6, 2007

    The other thing to keep in mind is the friction next to the tube’s wall. This causes turbulent air, moving much slower than the air in the center of the tube. It depends on the material used. Smooth tubing = less friction. I would venture an estimate that for flexible tubing, a half inch next to the tube wall is lost, meaning a 6″ tube is effectively 5″. A 3″ tube is effectively 2″ which is a huge difference in surface area.

  7. Mattias in Durham, NC November 6, 2007

    Oh – and if you close up your table saw completely, thinking you will get awesome suction through the 1″ hole that remains, think again. Most of what you’re doing is to decrease the air flow. The intake holes (in your equipment) must be as big as the tubing area to keep that air moving.

  8. Morton November 6, 2007

    Awesome tips, as I’ve been looking for my first “portable” dust collection (one of those small units I’ll wheel to each tool). A few come with 6″ ports and a Y into 2 4″ ports. Makes sense that 1×6″ = 2×4″ then in terms of surface area (and thus I guess airflow).

  9. Mike November 6, 2007

    Good to know (math aside) I am finishing up my cyclone ductwork install and have 5 to the saw and 3 to the eventual guard.

  10. muddler mike November 6, 2007

    you guys think too much. My brain hurts now…

  11. Tim aka Mopardude November 7, 2007

    Yea I dunno about all you guys and your fancy math but I agree with Mattias, keep the tubing smooth and try to maintain the same size tubing. Anytime you either reduce the size or increase it you are changing how how the air flows through.

  12. Brad Nailor (http://) November 7, 2007

    Geez, did a busload of rocket scientists just log on to your site Marc?

  13. Yep. I used the diameter instead of the radius. Miss Magilicuty is rolling over in her grave. My excuse . . . I took geometry in 1966. The brain cells have begun to break down.

  14. Claude Stewart November 7, 2007

    Hey my brain hurts too. I know that math is a part of woodworking but I just stick with + n -. I seem to think that all the other stuff is for engineers. Claude Stewart

  15. Frank November 7, 2007

    Next year I’m planning on upgrading to a cyclone dust collector. Most of the brands that IĆ¢

    • jHop March 7, 2010

      While I loved Bill’s site for the theory, not being an engineer certainly did not help in reading his site.

      (BTW, many may have noticed my absence for a few months… it has been due to this very issue. At the very minimum, I need some sort of “pseudo-cyclone” for the shop vac, with a dedicated DC system in the future.)

      As an aside, it seems we all want to get that uber-cool collector system before we really try out all the options. My suggestion (and it is only a suggestion) is you look at the tools you want to hook up to the DC, and determine what you need it for. (really need it for, I mean. pushing sawdust around on the workbench to see if the benchtop dust hood works is not the same.) My original plan called for a DC with about 20 feet of main trunk. Now, I think I need only 6 feet. Smaller shop, you see.

      I was perusing another website (Instructables.com) where they mentioned vacuum tubing instead of PVC. I know most of us use S&D (Sewer and drain) due to cost. Anybody know where vacuum tubing (solid wall) fits into the pecking order of plastic pipe? (I’m in an alliteratory mood, as well as the mood to completely butcher the printed english language.)

  16. David Turgeon (http://) November 7, 2007

    I know that you don’t have an Oneida dust collector, but I do. They designed the duct sizes based on my location and equipment info. Perhaps it’s money well spent to get the most out your system, to ask them for a price to re-design your layout. I know mine works awesome. info@oneida-air.com


  17. Jim Jones November 7, 2007

    Not to beat a dead horse, but just for the record, the correct areas are as follows:

    pi = 3.142
    Area = pi/4 * D*D
    pi/4 D Area (sq in)
    0.785 6 28.3
    0.785 5 19.6
    0.785 4 12.6
    0.785 3 7.1

  18. Jim Jones November 7, 2007

    This may be easier to read than my previous post.

    pi = 3.142
    Area = pi/4 * D*D
    pi/4 D Area (sq in)
    0.785 6 28.3
    0.785 5 19.6
    0.785 4 12.6
    0.785 3 7.1

  19. Chris D. November 7, 2007

    Good Gravy….

  20. Ron November 13, 2007

    Would someone please tell me where Marc described his modifications and the addition of the overarm dust collector. I’ve wandered around the web site but can’t seem to locate it.

    Thanks in advance.

      thewoodwhisperer March 7, 2010

      Hey Ron. I think I went over that in a live session that didn’t get posted. Well to be honest, the footage was all jacked up. So I wouldn’t spend too much time looking. :)

  21. Tim Dibble November 19, 2007

    In a previous life I designed and installed Industrial dust collection systems (90,000+ cfm size units serving many machines over an entire plant). While I can go through the calculations, the basic rule is that for a small area, the trunk is your biggest line (which will actually decrease over long runs to maintain laminar flow), all branches should reduce somewhat to the point of use. Your objective is velocity at the point of collection. I agree that closing a saw completely does impede the airflow, but at least with a contractor’s saw there are a few too many openings and closing some of them is beneficial.

    Branches should be angled into the trunk, not perpendicular. Flex hose is fine for runs up to 5 or 6 feet, but solid pipe is preferred for longer runs.

    A 4″ diameter is fine for most saws, and the over-head line can be accomplished with a 2″ or less because you can take advantage of the blade’s imparted velocity to get it into the airstream.

  22. Paul Andrus March 19, 2009

    I love pie…Apple,pumpkin,blueberry etc. lol :)
    Seriously, I just purchased an Oneida V3000, and they are going to design the layout for me.Is there a reason all the ports on most standard power tools are 4″? So, that being said,I have to increase the port to 5 or 6″? I guess Oneida
    will make all the calculations.
    Oneida sent me the dust collector layout form as a pdf,and one of the things on it asks for the list of power tools, and the percentage (approx.) of use. Would that not be a constant in most woodshops? Table saw,router table,planer, jointer band saw??…and the sanders somewhere inbetween?
    I also have all my power tools on mobile bases,so I can move them anywere that Oneida suggests.



      Hey Paul. Not really sure what the reason for most tools being 4″. I would imagine its the best compromise. I am thankful for it and wish the portable power tools would do the same……..

      If it were me, I would not change all the port sizes. I did that on my last tablesaw and I regretted it. It was a lot of work and really didn’t improve the dust collection.

      If you are already in touch with the Oneida folks, I would simply ask them their opinion. They would certainly know if increasing the port sizes would help or hinder dust collection.

      As for the percentage of use, I imagine it would be constant for MOST woodworkers, but certainly not all. If you do a lot of home sawn veneering, you are going to be much heavier on your bandsaw and drum sander than most other woodworkers.

      Let me know how things work out.

      • Paul Andrus May 28, 2009

        Hello again!I am not happy with Oneida.They sent me a plan and wanted to sell me almost a thousand dollars’ worth of snap lock pipe,fittings & odds & ends.I wrote back and asked
        them to take a look at my diagonal layout,and give me the costs associated with that layout.They never replied.I guess
        the efficiency and compact layout would not yield them enough of a sale,but I’m just guessing here.
        I would like to send you a jpg or pdf file,but have no way of attaching it.Please send me another email address so I can send this for you to check out.I believe it is a very good solution to a efficient dust collection system.
        In a nut shell, it’s a diagonal layout;1 6″ dia. PVC S&D pipe;green in color, and a 10′ length is just 14.65 as of
        May 28, 2009.The wye’s are a bit pricier; 3458 ea. The cost for 6 6″ wyes & 6 10′ 6″ dia. pipe comes to a total of
        $272.08, (not counting the cost of either additional 45 deg.
        elbows. I am going to use as little flex hose as possible, as it decreases air flow, and dust collection.

          thewoodwhisperer May 28, 2009

          I am no expert, but I will certainly offer an opinion. You might also post this in the forum so you can get some more opinions.

  23. Chester March 4, 2010

    is it right that the volume of 2-4″ hoses isn’t as much as 1-6″ hose?

    4″ = 12.57 square inches
    6″ = 28.28 square inches

  24. David in Seymour March 8, 2010

    I’m not a fan of Onieda either. Design sevice very pricey and not worth it at all. I did all the work. My order was not filled correctly at all and it took forever to get right. I’m not a fan.

  25. Ed Lewis March 27, 2010

    I spoke with a central vac tech who gave me enough info to build my own DC sys using a central vac motor. He had experience with CNC people who use the same sys for vac tables to hold thier work. My sys works good but there is a threshold of CFM where too big of a diameter might increase air flow, but not DC. All the math in the universe cannot tell the difference between heavy and light dust.

  26. Kenji Horvath December 7, 2012

    This year i’m working on saving my lungs. For christmas I’m getting about $1200 of dust collection equipment including a 1200 CFM delta dust collector with a 4″ port. Something that I read from multiple places was that port reducers really kill the performance of a dust collector. I can understand that the dust collector may work most efficiently with a 4″ host all the way through to the tool it is connected to but if I were to say connect up the 4″ hose to tool that only has a 2.5″ reducer am I really losing that much? So talking real numbers. A 4″ port has an cross section area of about 12.56 square inches. A 2.5″ port has 4.9 square inches. Am I really losing 61% efficiency? Am I really knocking down my dust collector from 1200 CFM down to 368 CFM? I would think the motor would have enough power to pull the air through the 2.5″ port at a higher speed so my CFM wouldn’t be hurt too much. If someone could explain this to me I would really appreciate it. Thanks!!

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