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  • -Project Pipe Problem?

    6 inch clear PVC PIPE, I am machining the inside bore . NOW the thing isnt even round, I got the length machined and used my internal spinning 3 jaw chuck gizmoe to hold it. BUT it was sure wobbly, NOW when I got to machine the inside I will have uneven wall thicknesses,How do tyou correct this problem ?? Any ideas Guys Thanx Mike

  • #2
    My solution to these types of problems is custom soft jaws. If you can make them so they cover most of the outer or inner diameter and then take it easy on the clamping it will come out much better. I have experienced the same problem you are having. The only other way I have gotten around it is to chuck an extra long length and then support the other end on a bullnose center, course this won't work for the inside. works better but not as well the soft jaws that are bored to fit the job. Oh and on all of these, take it easy on the cuts. One other dodge that just came to mind is to fit a plug to help stop the lobing, I have done this but still got a little lobing on plastic pipe.

    I have always wanted to try a self centering six jaw but haven't every been able to get past the entry fee for one of these.

    -brian
    -brian

    Hello, my name is brian and I'm a toolaholic.

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    • #3
      If you can, turn down a piece of "something" to match the inside diameter. That way you can grip with the chuck without distorting the part.

      I turn alot of slippery PEX, and because of the design of the part in question I have to take an aggressive cut otherwise I'll be there all day. Problem arose when the material started slipping in the chucks. I came up with this solution, haven't lost a part do to slippage since then.

      Might have some marks on the part from the jaws when you are done. Couple seconds with a file or a really light finishing pass or two takes care of them.
      This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
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      • #4
        I think the old rule of thumb that allows for 1.5Xdiameter protrusion from the chuck (without supporting the work with either a steady rest or tailstock center) goes out the window with plastic since it can flex in the jaws...moreso with tubing.

        If you are boring down the center, I would suspect that a shop made plug for use with a live center won't work. The bummer is that likely even a roller steady rest is going to "leave a mark" although if precision is not critical, a layer or two of clear packing tape on the outside (cut so that its no more than x layers thick at any given point) might make a good running surface.

        In any case, its got to not flex while you work on it. I think I would even turn a plug to size for the chuck end so that it won't flex when you clamp down on it.

        Paul
        Paul Carpenter
        Mapleton, IL

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        • #5
          Seems like you could figure out a way to hold the tubing in a fixture, fill it with water, and freeze it. That would keep the pipe from flexing while you machine it.

          For machining the outside, you could just cap one (or both) end, fill it with water, and freeze it.

          For machining the inside, the fixture could be a piece of larger pipe with water, filling the void between the two.

          Roger
          Last edited by winchman; 01-28-2009, 06:09 PM.
          Any products mentioned in my posts have been endorsed by their manufacturer.

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          • #6
            The frozen water thing is clever, but I wonder (given that we know the propensity of this stuff to flex) if the ice would very quickly pop out of its mold in which case you would have an arbor mounted spinning accident waiting to happen.

            Frozen water is very unlikely to flex with the tubing. Plus, PVC at cold temperatures ends up about as brittle as the frozen water

            Paul
            Paul Carpenter
            Mapleton, IL

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            • #7
              You didn't say how long the pvc was but here's what I did.

              I turned some aluminum about 1 1/2" long for a tight fit into the end of the pvc. I left it proud on the end nearst the chuck so the chuck grabbed the plug and the pvc. You could then slip a turned ring over the other end to hold it round if you aren't working on really long stock.

              Next time pick your PVC off the top of the pile !!
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              • #8
                Originally posted by winchman
                Seems like you could figure out a way to hold the tubing in a fixture, fill it with water, and freeze it. That would keep the pipe from flexing while you machine it.

                Roger
                When water freezes it expands, so it's going to distort the pipe. There
                are several low melting temp. materials that dont but are very
                expensive for that much (to fill a 6" pipe).
                ...lew...

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