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Thread: Time to add ductwork for my dust collector...I have questions

  1. #1
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    Time to add ductwork for my dust collector...I have questions

    In my shop I have a 14" bandsaw, lathe, drill press and several small benchtop machines. I just bought the 2HP Harbor Freight dust collector. It's time to get things piped in. I have to determing PVC or metal. I have read that it is best to use 6" ducting. WOW this seems huge! I suppose it is all about air flow but has anyone actually used just 4" ducting? That seems plenty to me. My bandsaw dust is pretty fine. I cant imaging it clogging up a 4" duct. Now my lathe would produce some large curlies but I would think 4" would still be big enough???? My smaller benchtop machines will also be very fine "dust" and easy to pick up. So for MY use would 4" be ok to use?
    I'm also going to need a few blast gates. I think I will probably make them my self. I will have to look around and find a good plan for them. I think I remember Stu making some. I do understand to use (2) 45 degree curves instead of a 90.
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  2. #2
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    the idea is that you need air flow tom,, its not the plugging of a space that the 6" is preferred its all in air flow..the least amount of 4" lines you run the better.. are you planning on moving your collector to each machine? its not the difficult to do in a smaller shop space. and it would save you time and money in the long run if you were closer i have some metal duct work you can have..
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  3. #3
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    There is more to it than meets the eye. Duct size needs to matched with the amount of air you are pulling. You want the air speed inside the duct to be fast enough to keep the dust floating (so to speak). If you went to a 10" duct for example, it would be like a gentle breeze inside the duct and the dust would fall out of the air stream. Drop to 4" and you will have higher air speed, but depending on the blower, you could restrict the volume/amount of air. Volume is what you need to pull all the dust from the machine. So you need to match the duct to the blower your using.

    Confused yet?

    Don't worry, there is a lot more to it than than this if you really want to get into it! I asked for cash for Christmas so I am about to dig into this myself.
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  4. #4
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    Quote Originally Posted by Jeff Horton View Post
    I am about to dig into this myself.
    Makes two of us Jeff. I am wanting to do a hard pipe to the tablesaw and flex to everything else.
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  5. #5
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    Tom,

    Larry said it. You are not concerned about plugging the 4 inch duct. You are concerned that the air will flow freely so it can carry your stuff---Especially the very fine dust. My system has 6 inch every place except the drops from the 6 inch to the machines. I even have 6 inch drops a couple places.

    I have posted to several people who have asked the same question you are asking. Several years ago I thought having a DC and 4 inch flex was hot stuff. Well, I purchased some books on dust collecting, I read about DC on several sites. I got buried in math that I am not sure my 87 year old brain would understand today.

    Basically what I learned is that you can compute and use some smaller ducts in certain locations. The smaller ducts then feed into larger ducts, etc. The consensus of what I read was to go 6 inch all of the way. Use 4 inch only for drops and keep them as short as possible.

    Your enemies are:
    Flex ducting (it is murder on air flow).

    Turns really take a tally on the air flow. Avoid 90* (degree) turns. Avoid "Tees." For turns use two 45* Els with a very short coupler between them. With 6 inch PVC the Els, Wyes, etc.take 3 inches of pipe. So a short coupler would be 6 inches (three inches into each El). Some companies manufacture gentle 90* turns. Basically they were not available when I did my system.

    Wherever you bring a branch into the main duct, use a Wye that has 6 inches straight through with the branch coming in at 45* (whether it is another 6 inch or a 4 inch). If the branch is coming to the main at 90* you will need a 45* on the end to mate to the 45* of the Wye to give you a gentle curve.

    There is nothing that says your ducts need to run parallel to your shop walls. If going at 45* is shorter, go ahead and do it. However, don't try to run the duct through garage door openers, etc. If the only thing in the way is a light fixture; consider moving the light.

    I have more and nastier power tools than you have. After 5 or 6 years the insides of my ducts are so clean I would not be afraid to eat off of them.

    I absolutely promise you that whatever you do, you WILL change the set-up. That is one of the huge disadvantages to using ducts of different sizes. When I get a new machine, or rearrange my shop, I have ducting that is the correct size to work with. (A piece I took out to make the change will fit. Or a piece I had left over from the original will fit.) If you start with small pipe and work up to large pipe and you move a machine, you will need a piece of five inch duct and all you have is 6 inch. If everything is 6, you won't have that problem.

    Don't hesitate to PM me if I can help. Myrna called dinner. I will look and see if I have some pics that will help you and put them in later this evening..

    Enjoy,

    JimB

    Pic 1) Inside of 4 inch flex duct after several years.

    2) Inside 6 in duct after several years.

    3)At the back, left, note the 6 in duct approaching the 6 in main at a 45* angle. There is no 45* El here. The 6 in main goes straight through. Since the duct approaches the main at 45* there is no need for an El here.

    At the back, from the right, see the 6 in duct go through a 45* El to join the 45* part of the Wye.

    Note that each 6 in drop has two 45 degree turns to go from horizontal to vertical. Notice where the the 4 inch flex meets the 6 inch. The turn is in the 6 in, not the 4 in. This disturbs the air flow much less than if the turn was in the 4 in.

    4) Note where the 4 meets the 6. There is a 6 to 4 "reducer." In the case of our air flow, however, it is really a 4 to 6 expander. Again note the two 45* Els making a 90* turn.

    5) This is my lathe drop. Note that one 45* was used up at the main. Then a longer piece brought the duct down (at 45*) towards the lathe. Then another 45* El was used to make the rest of the drop at 90*. You can see, below the blast gate, that the 4 inch duct goes through a wye with two 2.5 inch "stand alone" ducts to get close to the turning.

    6) This is a good view of two 45* Els making a 90* turn.

    7) This is an overall view from South to North through the shop. It gives you an idea of my set-up. It is a bit different now. (Remember, I told you that you would make modifications.)

    I hope this helped.

    Oh yes. Very important as far as I am concerned; all joints are dry fit. The pipe joins very nicely (If you don't believe me, wait until you try to take it apart. PM me if you have problems.); it is air tight. Even if there were a small leak I would not care---remember we want to move air. We must get as much air into the system as we are trying to get to go out the other end into the bag or cyclone. Besides that, a small patch of duct tape will close it if you wish.

    Shut Up Bradley. Goodnight and good luck doing your dusting.
    Last edited by Jim C Bradley; 12-24-2011 at 03:22 AM. Reason: Add Pics and text for pics
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  6. #6
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    Tom, if you not familiar with Tom Pentz, Google his name and search through his web site. It's quite large and a bit overwhelming but just scan around and you will pick up a lot of good info.

    I was reading on his site again last night and found the answer to your question about duct size. In a nut shell he said to keep the duct work at same size as the inlet on the blower. I think the HF models have 4" inlet, double check me on that. (That is in not the size of the hose adapters on there, but the size of the inlet on the blower.) He says that will keep air flow close to what the manufacturer designed it for, assuming smart duct layout. Jim covered that very well. Blowers are designed to have some restriction in the lines and if you go to large with the duct work and don't have enough restriction, the motor can actually overload and burn itself up.

    Seems backwards but it does make sense after a minute. The more air it is pulling the larger the load on the motor. No air flow and there is no load on the motor. It's not doing anything, It just sitting there spinning.
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  7. #7
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    Bill Pentz . . . the coffee hasn't kicked in yet eh, Jeff? Mine just dud . . er, did.

    When I got my first 1HP bag unit, the difference in comparison to a shop vac was so significant that I thought it was overkill. In practice this did not prove to be the case. This same unit is still in service with modifications; oversized AFF top filter and a solid lower bag make this unit very usable with a short, smooth walled 4" hose connected to my jointer. It was woefully inadequate for the tablesaw and a joke on the planer. It would probably do OK for one feed to a bandsaw but, you would possibly want at least one other.

    The good thing about a bag unit is that it will generally move more air per HP than a cyclone. The downside is that you don't want a bagger venting back into your shop air without some serious filter upgrades which generally knocks down the airflow advantage. The filters (if used) will also clog quickly and require more routine maintenance to keep your airflow up but, I am wandering pretty far away from the question . . .

    IMHO go with at least 6" solid ducting as close to your machines as you can; all the way if possible. I currently drop to a 4" just before the blastgate and run a short piece of hose to the machine. On some machine's secondary ports I even drop more to gain access to tucked away areas. Once I finish a current project, modifying for 6" all the way to any machine that I can is under consideration. Plumbing with 4" is a waste of time and money but, that is also JMHO.
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  8. #8
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    I almost hate to chime in on a discussion like this anymore, but here goes. You can find someone to advise you to go whatever direction you want - that's the biggest problem I see. I went with the basic design from the manufacturer from which I decided to buy a DC. They know how their machine works and based the duct layout on their machine and my shop. The DC inlet is 8" and the first connection is a 7-7-8 wye. Seven inch duct goes as far as the first drop on either run, then to 6", then to 5". None of the main runs is any smaller than 5" and that reduces to 4" at all machines. I have two blast gates with 4" flex because several of my machines are mobile. Flex isn't the best thing to use in many cases, but it works just fine on my jointer, planer and 16-32 drum sander. I used metal duct (except for the flex, of course) because I had received enough shocks from plastic pipe to convince me to go that way.
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  9. #9
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    Jeff is correct - Dust Collection is MORE than just CFMs. The air VELOCITY may be more important. As I recall the air must be moving at or better than 4000feet per minute and as Jeff clearly points out - a larger pipe actually slows the air speed so it is a critical balance.

  10. #10
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    Quote Originally Posted by Tom Baugues View Post
    In my shop I have a 14" bandsaw, lathe, drill press and several small benchtop machines. I just bought the 2HP Harbor Freight dust collector. It's time to get things piped in. I have to determing PVC or metal. I have read that it is best to use 6" ducting. WOW this seems huge! I suppose it is all about air flow but has anyone actually used just 4" ducting? That seems plenty to me. My bandsaw dust is pretty fine. I cant imaging it clogging up a 4" duct. Now my lathe would produce some large curlies but I would think 4" would still be big enough???? My smaller benchtop machines will also be very fine "dust" and easy to pick up. So for MY use would 4" be ok to use?
    I'm also going to need a few blast gates. I think I will probably make them my self. I will have to look around and find a good plan for them. I think I remember Stu making some. I do understand to use (2) 45 degree curves instead of a 90.
    Tom,
    The intake port on my HF 2 hp DC is only 4".... if you use a 6" duct, you'll have to step down to the intake port... I don't know how that will affect air flow in the rest of the pipes.... I only use the 4" pipes through out my system... I have the same DC and ran a pipe through the outside wall of my shop so I could set the DC in an add on closet outside.. (noise abatement)... then I ran the 4" hoses all around my shop... I have a band saw, two lathes, and a table saw on mine... the drill press, belt sander, Rockler saw and chop saw doesn't get suction, or I use my 16 gal shop vac.... one thing I have noticed, since I don't have a gate on my band saw, it's pulling anytime the DC is running, it does seem to reduce the pull at the lathe.... I may have to add a gate at the BS to try in increase the draw from the lathe.... a lot of my hoses are overhead and I think I'm losing some pull by having to go up and over to the DC... I would think the shorter your run, the more draw you'll get, not scientific, just a thought.
    Last edited by Chuck Ellis; 11-25-2012 at 03:42 PM.
    Chuck
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