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  • Building a pvc pipe reduction

    Hi, I am in the process of building a dust collection system for my home shop and have been searching for pipe fittings for a long time. I have finally given up finding them, so I want to build them myself.

    I first need a reduction from 150mm to 120mm. 150mm PVC pipe is already available, so that's taken care of. 120mm is not available (125mm is), so I bought 130mm round PVC stock and will turn a 120mm pipe on the lathe. I also bought 2mm thick PVC sheet stock. This will be used for the conical piece that joins the 150mm pipe to the 120mm pipe. I drew up the reduction as a sheet metal part on Alibre Design and have unbent the conical piece, so I know the dimensions that I have to cut out.

    But how do I bend that PVC sheet to be the conical middle part? Do I need a special tool? Do I need to heat it? If so, how can I uniformly heat it?

    Edit: There is a special glue available for PVC called Tangit, so joining the pieces will be no problem...

  • #2
    PVC forms well if heated appropiately. I would try it in some sort of
    "toaster" oven BUT be careful to not get it too hot or it'll sag all all
    over tjhe place. You will need to QUICKLY wrap it around a form and
    hold it till it cools.
    PVC cement is commonly available at all "big box" plumbing depts.
    That still sound like a hard way to make the adaptor though.
    ...lew...

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    • #3
      You might consider warming in a hot water bath on a plate to support it. This can achieve a uniform and controllable temperature.
      Byron Boucher
      Burnet, TX

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      • #4
        Some how I doubt they have a Home Depot in downtown Gebze.

        Slit the end of the 150 mm pipe by cutting out 4 pie slices at 90 degrees around the end. Wrap something elastic such as electrical tape around the very end. Heat the points where they must bend and the elastic will draw the ends together. Slobber some glue on the part and you have a cone. You could just wrap it with electrical tape instead of using glue. Save the 2mm piece for something else.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          A hair drier will work and should be available. It would be best to form the cone around a blank, possibly turned up from wood.
          Jim H.

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          • #6
            Originally posted by JCHannum
            A hair drier will work and should be available. It would be best to form the cone around a blank, possibly turned up from wood.
            If I understand correctly, this is the procedure you are talking about:

            Turn a rough cone using wood. I could also use the PVC stock left over from the 120mm pipe. Then screw one end of the stripe to the cone. Using a heat gun, continue heating one spot, press it against the cone and go on until the stripe is fully wrapped around the cone. Fix the stripe to the cone using tape and let it cool. Is this correct?

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            • #7
              Originally posted by Evan
              Some how I doubt they have a Home Depot in downtown Gebze.

              Slit the end of the 150 mm pipe by cutting out 4 pie slices at 90 degrees around the end. Wrap something elastic such as electrical tape around the very end. Heat the points where they must bend and the elastic will draw the ends together. Slobber some glue on the part and you have a cone. You could just wrap it with electrical tape instead of using glue. Save the 2mm piece for something else.
              After doing this, the 150mm will be touching the 120mm at 4 points. But how do I seal the 4 triangles that are left open? Do I use the cutoffs?

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              • #8
                Originally posted by Boucher
                You might consider warming in a hot water bath on a plate to support it. This can achieve a uniform and controllable temperature.
                Hmm, if the PVC will sufficiently soften up using water, I could also use the kitchen oven for this purpose. I am wondering how much time I will have after opening the oven lid

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                • #9
                  Actually, if I just use a 150mm OD, 120mm ID washer cut out of the 2mm PVC stock to join the two pipes, will I create too much of an air resistance? The saw requires about 550cfm and my dust collector is 1100cfm.

                  Would using such a washer be the difference between good dust collection and NO dust collection? The distance between the saw and the dust collector will be about 6m and there will be a flexible "accordeon" type of hose in between. Because of the structure of the hose, I am already creating a huge resistance...

                  Here is that hose:

                  Last edited by taydin; 12-13-2010, 12:02 PM.

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                  • #10
                    I soften pvc in the oven (it stinks and off gasses if too hot, don't use the wifes oven). After you remove the softened PVC from the oven, you will have about 30 seconds to form this. If you get it wrong, just pop it back in the oven and retry it. You get a few chances with this type of plastic. Typical PVC mets at 176F IIRC.

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                    • #11
                      Ok, I'm going to save you some cash here, google up PEP Plastics, they will fab up any kinda reducer you need. They do 12" to 4" and 6" for a product of mine, great people, super product.
                      James Kilroy

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                      • #12
                        Originally posted by jkilroy
                        Ok, I'm going to save you some cash here, google up PEP Plastics, they will fab up any kinda reducer you need. They do 12" to 4" and 6" for a product of mine, great people, super product.
                        Thanks for the link, but I am in Turkey and ordering those products internationally will be either very expensive, or impossible, because if they are held up at the Turkish customs, that'll be the end of it

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                        • #13
                          Originally posted by taydin
                          Actually, if I just use a 150mm OD, 120mm ID washer cut out of the 2mm PVC stock to join the two pipes, will I create too much of an air resistance? The saw requires about 550cfm and my dust collector is 1100cfm.

                          Would using such a washer be the difference between good dust collection and NO dust collection? The distance between the saw and the dust collector will be about 6m and there will be a flexible "accordeon" type of hose in between. Because of the structure of the hose, I am already creating a huge resistance...

                          Here is that hose:




                          Use the wire to ground that puppy unless you want a shock every time you touch your saw.

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                          • #14
                            You could also go the other way and start with the smaller piece and expand one end.

                            I believe there are directions on how to heat form PVC on somewhere on Bill Pentz' web site http://billpentz.com/woodworking/cyclone/index.cfm

                            IIRC you can expand PVC about 20% before it tears.

                            I wouldn't worry too much about pressure drop if you're going to use a lot of that hose.

                            Bill's site also has a pressure drop calculator in Excel which will calculate the drop of various pipe and fittings.

                            I tried forming a piece once and it was pretty time consuming.

                            I like the idea of cutting out triangles; I'd probably do at least eight, and make them at least 8" long to make for a more gradual transition.

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                            • #15
                              After doing this, the 150mm will be touching the 120mm at 4 points. But how do I seal the 4 triangles that are left open? Do I use the cutoffs?
                              Correctly calculated the openings will close completely. Made long enough the angle will be gentle and the end of the reducer may be turned enough to present a proper round section of pipe at the desired diameter. Make the reducer section longer than required so that you will have a section that is the right diameter to work with. Turn to fit and cut off the excess.

                              You can also do this by simply making a lot of radial saw cuts with a circular saw. That will leave small openings at the root of each but wrapping with tape will fix that. It's under suction so the tape will seal just fine. No heat required to bend the small sections.
                              Last edited by Evan; 12-13-2010, 02:07 PM.
                              Free software for calculating bolt circles and similar: Click Here

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