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Thread: Connecting spiral duct work

  1. #1
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    Default Connecting spiral duct work

    A few weeks ago, I made a 5-h round trip to Welbeck Sawmill, to see Gary, their dust collection expert. I am so glad I did - he spent hours with me laying out a plan and then picking out all the pieces I would need. He was a wonderful help and I highly recommend anyone thinking about this to pay him a visit.

    Anyways as I understand it, lengths of pipe are female at the ends and thus need to be connected with male connectors (MCs). My problem is that the MCs I have don't really fit inside my pipes. Well, *some* do after a long time of jimmying around, but some just refuse to go in - they seem just slightly too big, even after deburring the inside and outside of the pipes/connectors.. The pipes fit in no problem into my various fittings, and the MCs I have fit easily into various female connectors I have, so there must be something just slightly off with sizing of either pipe or connector.

    I called Welbeck and Gary offered to exchange any pieces I was having trouble with, but I can't afford spending another 5-h driving out there.

    I've been thinking about making a few very small relief cuts, in the direction the pipe runs, in either the male or female side of the connection, and then using these cuts to make one end either a bit smaller or a bit bigger. Once I can get all of the MC inside the pipe, I think I ought to be able to force the rest of it together.

    Does this sound like a sensible plan ? I'm wondering whether it makes more sense to make those relief cuts on the male or female end. If I did it on the male end, it could possibly create a small obstruction to airflow and/or trap particles ?

    Also, what do you guys use to cut the stuff ?
    - I tried a jigsaw, but the motion of the blade has a tendency to bend the outside of the metal.
    - I also tried a cutoff disc on an angle grinder, but it wasn't really that accurate and I don't like the shower of sparks in my shop.

    Neither option led to very nice looking cuts.

    Things I haven't tried but have thought about:
    - how would a wood/metal blade in an oscillating tool (e.g. http://www.homedepot.ca/product/jobm...t-blade/997458) work ? Would the blade stay sharp enough to cut more than a few lengths of pipe ?
    - I've heard of people using Rotozip spiral saws but the guy at Home Depot thought it wouldn't work any better than a jigsaw.
    - how about using the mini-circular-saw Dremel attachments :?

    I don't have a chopsaw that I can use right now.

    Thanks for looking.
    terry
    "I am on a drug. It's called Charlie Sheen"

  2. #2
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    Default Re: Connecting spiral duct work

    You'd want the direction of your male to female connections be the same direction as air flow (otherwise chips, shavings, etc will get stuck).
    I've tried this relief cuts in one or two situations to fit things and has worked fine.
    As for cutting spiral pipes, I used very thing/small grinding wheels in my dremel. Went through many of them to make all the cuts but the results were acceptable.
    For thinner fittings used snips. Make sure you wear some thick leather gloves.

  3. #3
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    Default Re: Connecting spiral duct work

    Cant you just crimp it? $24 tool at home depot.

    http://www.youtube.com/watch?v=6Rd-C...e_gdata_player

  4. #4

    Default Re: Connecting spiral duct work

    I will second the HD tool. I should have got one at the start of the re assemble of the DC pipes when I bought the used Gorilla and all the pipes.

    hobby woodworking since 1972

  5. #5

    Default Re: Connecting spiral duct work

    Wrap a piece of paper around the duct to give a straight guide line. Cut with hacksaw. Deburr with file.

  6. #6
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    Mreza... thanks...when joining two lengths of pipe, if i have to make relief cuts on all my connections it seems like there would always be one facing the wrong direction, no? It is reassuring to know that I am not the only person who has had to this.

    Kevin, thanks for the pointer to that crimper. The Guy in the video was using it to connect female to female, so it should certainly do what I want ( get supposed male into female). It probably would have saved me money over buying the connecting fittings, too :-(

    Ed, I will have a try with a hacksaw. I made starter cuts for my jigsaw attempts with one, but it felt like it would be tiring to cut a bunch of pipe all the way through... but probably faster than figuring out an"optimal" solution. When figuring out this dust thing I have been a victim of paralysis by analysis.


    Thanks guys.

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  7. #7
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    Default Re: Connecting spiral duct work

    Quote Originally Posted by NuggyBuggy View Post
    Kevin, thanks for the pointer to that crimper. The Guy in the video was using it to connect female to female, so it should certainly do what I want ( get supposed male into female). It probably would have saved me money over buying the connecting fittings, too :-(

    Good, I was afraid you were going to have a logical reason not to use the crimper. I have ducts and a crimper on the floor of my shop. It's the next task after I spray my cabinets tomorrow. I learned not to have the ridges pointing upwind in this thread.

    K.

  8. #8
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    Default Re: Connecting spiral duct work

    I too just bought some pipe from Welbeck. Dealing with Gary as well. They have a good bunch of people working there. I purchased a KIng 5" dual counter rotating saw with carbide tipped blades when I was there. I plan on using this to cut the pipe. If I am correct there is no difference in either end of the pipe. I have not started my install as of yet. I looked at some of the fittings and did not like the seal, so I started to silicone seal all of the joints. I plan on doing this to all of the fittings before assembling the system. I will post more info on my install later.

    Andy

  9. #9
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    I'm not really sure what happened but last week some
    Of my pieces started fitting together properly. The only thing that has changed is the temperature has dropped quite a bit, although I really doubt that could explain anything.

    Anyways, Gary suggested I connect the pieces with self tapping screws and and duct tape, as I did not want to use silicon sealant.

    The screws I bought were 1/2" which means that some of the screws are exposed and project inside the ductwork. Do you guys think this poses a problem? Should I try to file down the tips of the screws inside the ducting ?

    Obviously, I will only be able to reach half of the screw tips....

    Thanks, terry

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    Last edited by NuggyBuggy; 08-19-2012 at 01:14 PM.
    "I am on a drug. It's called Charlie Sheen"

  10. #10
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    Default Re: Connecting spiral duct work

    The 1/2 in screws projecting will not really pose much problem. Wyes and turns in the duct work will easily lead to more resistance than the screws projecting into the air stream. The only issue might be long strands and shavings being caught on the screws. I have used the same fasteners and have not had any problems with the screws leading to plugging the duct. If the air is moving quick enough you won't have a problem. Metal duct tape on the joints provides a nice tight seal.

  11. #11

    Default Re: Connecting spiral duct work

    I just use 2 screws, at 2-2:30 and 9:30-10 (on the clock).

  12. #12
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    Default Re: Connecting spiral duct work

    The pros cut that duct with an angle grinder, yes, lots of sparks but it is the easiest way and, if you draw a cut line you can get it pretty even. In any event the joint will be covered with tape. Definitely tape all your joints. I would strongly suggest you use the metal tape that is designed for this purpose. Ironically, duct joints is the one thing that duct tape is not very good at as it gets brittle and comes off with age! Also use this tape to seal all the joints in the system, for example the three or four sliding joints in a typical elbow. Each one lets a little air in and, while each one is not significant they can add up to a lot of air leakage.

  13. #13
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    Default Re: Connecting spiral duct work

    I'd use a riveter. You can fine-tune your rivets to protrude no more than 1/32", perhaps 1/16" on the inside. In some cases, depending on the part's length and diameter, you may be able to drive the rivet from inside out. Since there will will some friction and knocking inside the tubes, I'd go for steel rivets rather than aluminum.
    In order to understand recursion, one must first understand recursion

  14. #14
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    Default

    Thanks again for the replies everyone. I discovered that the angle the jigsaw is at made a huge difference in how smoothly I could cut with it. It worked pretty well but I did have to spend a lot of time taking down the burrs after. The latter would have been easier if I used the grinder but I've got tons of dust everywhere from when my cyclone backed up and I just didn't want to worry about the sparks.

    Doug... after taking a closer look at the fittings I will definitely be putting duct tape everywhere. The gaps in some of them - especially the wyes - were big enough to see through. That surprised me. At the prices I paid for this stuff I would expect it to be leak free.

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  15. #15
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    Default Re: Connecting spiral duct work

    Quote Originally Posted by darius View Post
    I'd use a riveter. You can fine-tune your rivets to protrude no more than 1/32", perhaps 1/16" on the inside. In some cases, depending on the part's length and diameter, you may be able to drive the rivet from inside out. Since there will will some friction and knocking inside the tubes, I'd go for steel rivets rather than aluminum.
    After putting a few pieces together, I've decided I really don't like how far the 1/2" tapping screws project into the ductwork. I tried cutting down the ends that I could reach (obviously, only half of them), with a mini-hacksaw, but that was a lot of work for not too much gain.

    Darius, what sort of riveter would you recommend ? Can I get by with a hand-powered unit like this one, or should I go for a pneumatic one ? Recommendations welcome.

    Thanks !
    terry
    "I am on a drug. It's called Charlie Sheen"

  16. #16
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    Default Re: Connecting spiral duct work

    I have a shop full of spiral ducting and the pipes the same size at both ends and the elbows slip inside the pipe and no cutting was necessary. If you go to a HVAC shop they will sell you a product called Duct Seal. It is a liquid that you brush on the joints to give you a permanent seal. When installing screws or rivets make sure you avoid having them located on the bottom of the run. This will avoid alot of your problems with plugged ducting. I used 1/2 in. sheet metal screws and no problems
    " It is nice to be important but more important to be nice"

  17. #17
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    Brian... Thanks. I never thought about the location of the screws, but that makes a LOT of sense!! I've sunk a few screws in what i am sure will turn out to be the wrong orientation, but not so many I can't undo what I did, and better now than later. I dont think I want to apply any sealant as I have a feeling my layout will be a constant work in progress.

    However, I will say this : some of my pieces just will not fit together without modifying them somehow... Some are definitely not slipping together. For instance, I had a 90 that would mate on one end with a pipe but not with the other end, unless I crimped. I had another 90 which looked the same as the first but would not go on the pipe that the first 90 would partially mate with. After a lot of struggling I put a heat gun on the pipe and was able to whack them together. Without the heat there was no way to get them together without a crimp. I am a little surprised that the gun worked, but as I mentioned I suspected that the pieces were fitting together better once the outside temperatures dropped, and that shocked me,

    I guess I could try filing down the seams but I was afraid of compromising the seal.
    Last edited by NuggyBuggy; 09-04-2012 at 08:52 PM.
    "I am on a drug. It's called Charlie Sheen"

  18. #18

    Default Re: Connecting spiral duct work

    Quote Originally Posted by NuggyBuggy View Post
    Brian... Thanks. I never thought about the location of the screws, but that makes a LOT of sense!!
    Quote Originally Posted by Ed in Leaside View Post
    I just use 2 screws, at 2-2:30 and 9:30-10 (on the clock).
    I guess I should have said keep your screws well above the centerline.
    Last edited by Ed in Leaside; 09-04-2012 at 10:13 PM.

  19. #19
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    Default Re: Connecting spiral duct work

    Quote Originally Posted by Ed in Leaside View Post
    I guess I should have said keep your screws well above the centerline.
    You should have ! ... I just thought you were saying that two screws were enough and that you choose opposing but otherwise arbitrary locations for convention's sake. LOL. Although as I look at it carefully now I realize they *weren't* (exactly) opposing, which might have been a clue.

    Thanks Ed.
    "I am on a drug. It's called Charlie Sheen"

  20. #20
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    Default Re: Connecting spiral duct work

    Quote Originally Posted by NuggyBuggy View Post
    Darius, what sort of riveter would you recommend ? Can I get by with a hand-powered unit like this one, or should I go for a pneumatic one ? Recommendations welcome.

    Thanks !
    terry
    Terry, I use a manual one. Given the right size rivets they will hold the pieces together for a very long time.
    For this application, due to internal material friction, I would use steel ones, not aluminum. For shorter connections, such as parts of elbows, you may be able to insert the rivet from inside out to further minimize the amount protrusions within the piping.

    In general though, I think good ole aluminum tape alone will hold straight sections very well too.
    In order to understand recursion, one must first understand recursion

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