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How do I make this shape?

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  • How do I make this shape?

    How do I make the teardrop shape (pictured below) out of 24" of thin wall aluminum pipe/tube? The part is for an exhaust for a waterwitch outboard. I made the piece in the pic for a reference of pipe size for myself. The pipe was a 2" that I squashed in the vise and hammered and formed to fit the exhaust outlet on the motor. The tube or pipe I will order and actually be using for the project will be about half the wall thickness of the piece pictured. I will be using aluminum because I plan to polish the piece after it is formed.

    I have seen similar tube from race shops like chassis shop for aero dynamic suspension pieces and chassis pieces but they only list it in chromoly.

    I had the thought of using a sheet and forming it around a small tube and welding the small radius edge then grinding and sanding and lots of work to get it down to a polished state which will show a slight color difference where welded.

    I don't have mush as far as roll forming tools for tubes. I have one of those HF tubing rollers for long radius, a bead roller, and then just tube and pipe benders.

    Whats some ideas?

    Andy

  • #2
    Not sure if i understand the question, but would it be possible to turn the male part out of wood then form the aluminum around that??
    That's probably out to lunch, but it was just a thought by a 70 year old brain.

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    • #3
      Giggling to myself I thought: ice...

      Thought about that for a second, then googled this: Hydroforming

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      • #4
        How long is it? I would probably start with various sizes of round and square stock with one end sharpened and press them through a round piece of tube to stretch it into the shape needed, adding another piece every time...or at least close enough. might work

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        • #5
          Make 2 rolls, each 1/2 the final shape and size of the outside of the tube. Put these on the HF tube roller, one driven and one idler. Run the tube through them starting with round and going a little closer together each pass. When the edge of the rolls touch, you're done. With only 2 rolls it will be straight.
          Kansas City area

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          • #6
            Originally posted by lbhsbz View Post
            How long is it? I would probably start with various sizes of round and square stock with one end sharpened and press them through a round piece of tube to stretch it into the shape needed, adding another piece every time...or at least close enough. might work


            The exhaust piece would be 24" in length total. The exhaust pipe size is 2" round. That does sound like a good idea.

            I also like sasquatches idea of making up a wood form to pound threw the tube to get the shape. But I wonder how much force that would take and if the tube would come out decent looking or if it would start to twist or crimp.


            Cavebob, I knew ice was going to be brought up. haha Although making up a form for the hydroforming I think would be more work than I am looking to get into to make up this one pipe.

            I would think a slip roll would work with some tinkering if I had one.
            Andy

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            • #7
              VPT,
              I would think you could do hammer forming of the aluminum tubing with the wood idea or maybe, 2 round rods the correct size for each side and weld them together with spacers that give you the final shape and use it as a dolly to form around. Also get the aluminum tubing that is somewhat anealed .

              Just one more thought trying to think outside of the box.

              Keep us posted when you get going on it.

              Mr fixit for the family
              Chris

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              • #8
                Not Aluminum but might be of interest .....

                http://www.aircraftspruce.com/catalo...streamline.php
                If everything seems to be going well, you have obviously overlooked something........

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                • #9
                  Streamline aluminum tubing is available for aircraft struts and sailboat parts. http://www.carlsonaircraft.com/struts.html
                  Any products mentioned in my posts have been endorsed by their manufacturer.

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                  • #10
                    Originally posted by winchman View Post
                    Streamline aluminum tubing is available for aircraft struts and sailboat parts. http://www.carlsonaircraft.com/struts.html
                    Sent a request for an order form or "packet". Thanks for the link!
                    Andy

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                    • #11
                      One option would be to make a hydraulic press tool with that cross section. Doesn't have to be long, just something you can squash your pipe with in short segments. Does need some serious bevels or radiuses on the ends so that it doesn't do rough straight bends but more subtle transitions.
                      Amount of experience is in direct proportion to the value of broken equipment.

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                      • #12
                        Make the tube in two half-tubes -- the final tube sliced on the major-axis and then weld the two halves together?

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                        • #13
                          Maybe cut two rollers on the lathe each with half the profile? Then run the pipe back and forth through the rollers closing the distance between them with each
                          pass.
                          Location: Long Island, N.Y.

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                          • #14
                            Hand ground steel torpedo pulled through a round tube with threaded rod. Or check out the neighborhood kids bicycles. I've seen aluminum bike frames with a very similar profile.

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                            • #15
                              If you do it out of sheet and are worried about the weld seem not matching when polished, just get some small strips sheared out of the same sheet for filler. It will match perfectly when ground down and polished.

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