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Thread: PVC forming

  1. #1
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    Default PVC forming

    I have a machine dust port that's a rectangle. An easy way to make the transition to my 150 diameter round duct may be to get some PVC pipe to make the transition by re forming it over the rectangle.
    I've done that a few times on smaller things and scorching the PVC is to easy.
    This being a larger job I was wondering about using boiling water to heat the PVC . Holding it in a drum of boiling water for some time . Like 5 minutes. Has anyone tried heating the PVC in a boiling water and did it work?

    I googled PVC temps and it says 170deg F is the temp used for long radius bending. Water boils at 212F so its sounds like it should work.

    Rob

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  3. #2
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    first time I've seen someone write water boils at 212F.

    I would have thought a heat gun, or blow torch and just continually move the PVC (or the heat source) would be a much simpler setup.

  4. #3
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    +1 heat gun, slowly slowly catchy monkey. Keep nozzle 30-50mm away from pipe and move back and forth at same time turn the 150mm pipe. You could make a smaller timber block to help square off the pipe to start.
    cheers

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    I've tried boiling water.
    a) It's not really hot enough for tubular pieces to get hot enough, to stay soft enough for long enough to form. As soon as it's removed from the boiling water the PVC cools down too fast.
    b) I've tried forming the workpiece inside a bath of boiling water and it's as dangerous as all get out. I scalded my self a few times and then gave up.
    Hot oil works - you can get it up around 110C, but its even more dangerous nd 10X messier.

    The 170F quoted softening temp is for ordinary PVC but
    - Softening just means you can poke it with something and it dents a little but it will not expand/stretch at that temp, it needs to be well over 100C and the thicker/larger the piece the hotter it needs to be.
    - DWV is not the same as regular PVC as it has additives and UV stabilisers added and needs a higher temp.

    When I form the SWV PVC BMHs I use a hot air gun, former, and a lathe.
    The former mounted on the headstock (over which the workpiece is pushed and formed into the BMH) is pre-heated to 110C
    The piece is then turned at about 60 rpm while heated, even heating is essential otherwise the piece skews over and may even split..
    While heating I monitor the temperature of the former and workpiece with an infra red thermometer and when they are both at 110C - that's when I crank the tailstock handle to push the workpiece over the former. The hot air gun is kept running while it moves.

    process2.jpg

    At the mens shed we did a squarish to round on a PVC 90 bend on a thicknesser port - 3 blokes and 2 hot air guns - not pretty but it worked.
    see.
    Improving machine cabinet dust ports

    These days I make square to round adapters using the SS sheet metal from clothes dryer drums.
    Here's one example
    The generic 2HP 10" planer/thicknesser dust control issues

    Here is another
    PlanerThicky1.JPG

  6. #5
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    Thanks Bob . That saves me the trouble of setting up and trying a drum of boiling water over a fire tomorrow. Perhaps Ill try the heat gun again but for such a large size I imagine it'll be hard to get an even heat or I'll end up scorching it to much. Ill give it a go.

    That's what I'm trying to make work. The steel sleeve was made in two parts around that wood block and welded together. The PVC would be a quick way of joining them if it works. The two parts are a similar cross section area .

    IMG_1668a.jpg IMG_1670a.jpg IMG_1671a.jpg

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    Just use the fire you where going to make anyway, at least if it all goes pear shapped you can still sit around the fire and enjoy a beer.

    Can you cut a thin slit into the pvc and just form the two halfs and then just shove some epoxy into it at the end if there is a gap?


    Does the metal ducting (or pvc) actually fit over the machine port?

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    Quote Originally Posted by auscab View Post
    Thanks Bob . That saves me the trouble of setting up and trying a drum of boiling water over a fire tomorrow. Perhaps Ill try the heat gun again but for such a large size I imagine it'll be hard to get an even heat or I'll end up scorching it to much. Ill give it a go.

    That's what I'm trying to make work. The steel sleeve was made in two parts around that wood block and welded together. The PVC would be a quick way of joining them if it works. The two parts are a similar cross section area .

    IMG_1668a.jpg IMG_1670a.jpg IMG_1671a.jpg
    That looks pretty straight fwd to make in sheet metal.

    O'd also check out this thread
    Square to round adapters

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    Quote Originally Posted by havabeer69 View Post
    Just use the fire you where going to make anyway, at least if it all goes pear shapped you can still sit around the fire and enjoy a beer.

    Can you cut a thin slit into the pvc and just form the two halfs and then just shove some epoxy into it at the end if there is a gap?


    Does the metal ducting (or pvc) actually fit over the machine port?
    I was thinking last night of maybe heating the pvc over afire in an open ended 20 lt drum with some metho in the bottom. I used to heat the old smaller cold workshop with that method in winter mornings. Its slow burning. Could be good.
    I gave up beer, for most of the time anyway. Once or twice a year is Ok when I see old friends.
    Not sure about epoxy sticking to pvc ?
    The steel sleeve I made fits over the port . Haven't decided whats next . PVC in or Over that or do a steel transition which was what I was thinking before playing with the idea of pvc.

  10. #9
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    Quote Originally Posted by auscab View Post
    I was thinking last night of maybe heating the pvc over afire in an open ended 20 lt drum with some metho in the bottom. I used to heat the old smaller cold workshop with that method in winter mornings. Its slow burning. Could be good.
    I gave up beer, for most of the time anyway. Once or twice a year is Ok when I see old friends.
    Not sure about epoxy sticking to pvc ?
    The steel sleeve I made fits over the port . Haven't decided whats next . PVC in or Over that or do a steel transition which was what I was thinking before playing with the idea of pvc.
    If you decide to try the fire make sure you do it outside. If the PVC catches fire it will release chlorine and water which combines to make hydrochloric acid and will corrode every exposed metal surface in a shed.

    A meat rotisserie above a fire will get it evenly soft but then you have to handle a 100C+ lump of floppy stuff.
    Wrapping one end in cloth and continually spraying water on it will keep that end more rigid but it will still be hot to handle, use gloves? . . . . .
    Suddenly the boiling oil is starting to look attractive,.

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    Quote Originally Posted by BobL View Post
    That looks pretty straight fwd to make in sheet metal.
    I was thinking sheet metal at first but the metal forming YT clips Ive watched are forming reducers from a large square or rectangle down to a smaller round and don't have these rounded corners. They look reasonably simple.
    My round is the same height as the rectangle but wider by 25 mm each side. And then the rounded corners ?? Its a bit hard to visualize what needs to happen to make it work even when I'm holding the two in front of me.
    I could add a wood round end to my wood block form I made for the rectangle and shape the transition between the two following the easiest line with band saw and spoke shave. If that works out then hammer form the sheet around that in two parts . Join then weld.
    Think Ill have another look at that and if it looks good try that first before pvc.

  12. #11
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    Quote Originally Posted by BobL View Post
    If you decide to try the fire make sure you do it outside. If the PVC catches fire it will release chlorine and water which combines to make hydrochloric acid and will corrode every exposed metal surface in a shed.

    A meat rotisserie above a fire will get it evenly soft but then you have to handle a 100C+ lump of floppy stuff.
    Wrapping one end in cloth and continually spraying water on it will keep that end more rigid but it will still be hot to handle, use gloves? . . . . .
    Suddenly the boiling oil is starting to look attractive,.

    Heat and smoke are one thing . Boiling Oil though , that is setting off fire sirens in my head. Bugger that

  13. #12
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    Quote Originally Posted by auscab View Post
    Heat and smoke are one thing . Boiling Oil though , that is setting off fire sirens in my head. Bugger that
    Very hot oil is indeed awful stuff.
    I heat about 4L of motor or canola oil to around 150 - 170C for various steel hardness treatments.
    Also ~2L of motor oil to about 120C for the final stage of acid fume bluing.
    These activities fill the shed up with an oily stench that can take days to disperse but I usually do this on my my welding bench above which I have a fume extractor which minimises this.
    Skin burns from boiling oil are also very nasty.
    Then there's a fire risk

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    Quote Originally Posted by auscab View Post
    I was thinking sheet metal at first but the metal forming YT clips Ive watched are forming reducers from a large square or rectangle down to a smaller round and don't have these rounded corners. They look reasonably simple.
    It doesn't matter which was around the large/small is - if you roll the squarish end along one edge of the piece sheet metal, and the round one along the other and and make sure the mid point is perpendicular to both then they will always line up.

    Rounded corners have a start and finish point of the round, once clearly marked partially wrapped these around a piece of pipe preferably slightly smaller in radius than the required corner ss they will easily open up and be tight on the radius of the piece you want to connect to.

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    I have seen videos on YT of guys wrapping the PVC in foil and then putting it in an enclosed BBQ.. Seems to work well(?)

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    I walked out to the shed this morning and started playing with the wooden form. Thinking about extending it, then shape and shift sheet metal to be welded and thought " This is going to take ages . Go have a look at the PVC".

    So I turned around and went and found this small off cut of PVC I had . Heated it with the heat gun and took it slow, and it ended up going well with hardly any scorching . I must have been rushing through it the last time I tried this.
    It was a bit like putting a rubber band around the steel sleeve I made to fit to the saw.

    IMG_1680a.jpg
    I remembered this morning that I had a big torch that I was using last week. "How do I forget stuff like that ?" I found this in a garage sale for something like $15 years ago. Its got its own funny looking spark plug up front for ignition. It sends out a big wide flame.

    IMG_1681a.jpg

    So I heated the PVC with that and slid it over my steel sleeve and inserted the 150mm duct the other end. I used a couple of clamps and some flat wooden pieces on the flat sides as well. Let it cool. Then glued both ends in with poly glue that dries in 15 minutes.

    IMG_1686a.jpg

    Quite neat .

    IMG_1706a.jpg

    I need to fit some screws through it to the saw and tweak it a bit with sealer and duct tape . My PK is now fully working with dust extraction which is great!


    Ill be doing more of that if needed . Glad I asked about the boiling water .

    Thanks for the suggestions.

    Rob

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