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How would you make this part?

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  • How would you make this part?

    It consists of 3 ½ turns of ¼” OD copper tubing with two stubby ends and a ¾” ID.

    Also the tubing must not be kinked or deformed from its round shape.

    I am getting ready to deliver my first batch of these coils. Here is the story behind them. About a month ago I got a phone call from a friend who was making these parts for a company that we both have done work for in the past. He tells me that he hasn’t been feeling well and would I take over the job and the next time he is in the shop we will give me a call to come over and he will show me his technique for making them.

    At the time I didn’t ask him any details. Having also worked with this company and knowing that they use lots of 1/8” tubing I just assumed that is what he was using. A couple weeks go by and I didn’t hear from my friend but I get a call from the purchasing agent of the company and wanting to know if I can make the part. Not having seen it yet I asked for a drawing.

    A few days latter I get the drawing and a sample, first thought is OMG how am I going to make this. So it’s time I call up by friend to find out his procedure. His wife answers the phone and tells me that he had just died the day before. This was a shock I have know him for over 20 years and the worst thing he ever complained about was having a cold. Turned out he had a fast growing form of pancreatic cancer.

    But now I have an order for 200 of these little gems and the company is becoming panicked because there stock is running low. Needless to say my first attempts were complete disasters. What would you have done?

  • #2
    Easy to coil but can you solder the 3/4 ends on?
    Feel free to put me on ignore....


    • #3
      For the part, I'd have gone for the cerrobend.......

      Keep eye on ball.
      Hashim Khan


      • #4
        3/4 ID ? or 3/16 ID?

        A mandrel on a lathe? Wind it like a spring.


        • #5
          Something on how it's made...freeze them with water inside then bend...


          • #6
            I second J's comment, Hornluv (a member here) makes brass instruments, and he uses the low temp allows & pitch? to make bends.
            -Dan S.


            • #7
              Go to your "friends" house and ask the widow to let you see his shop/tooling. Maybe you can find it.
              That is a "shocker". A good friend of mine picked me up at the airport
              one day a few years ago and two days later the wife called and told
              us he had died the day after he picked me up.
              Good luck on the fab.


              • #8
                I am totally making this up.

                Build a fixture that's a hole and a 3/4" rod. Cut the tube to length. Pack it with sand - tight. Stick one end in the hole. Bend it around the rod. I don't know what machine does that, maybe just the hands and some gloves? Or perhaps you rotate the fixture slow and use a block of wood to 'break' the tubing around the rod. Blow the sand out.

                I'd hate to do 200 like that unless the pay was good. I'd be unable to make one in under 10 minutes. Unless I had a device that could pack the tubes quick.


                • #9
                  IF you decide to attempt wrapping around a mandrel, I would suggest that you fill the tube with salt rather than sand. It is more of a cubic shape and packs tighter than sand, and if it sticks it willl dissolve out with water. Little tapered wooden plugs formed from dowel with a pencil sharpener will keep the salt in while coiling. Duffy
                  Duffy, Gatineau, Quebec


                  • #10
                    Okay, 200 and assuming they need consistency means fixturing and making some tooling.

                    First, turn a mandrel- a "screw", if you will, that fits the "thread" of the coil's "nut". If it were me, I'd use a ball-end type tool in something like a toolpost grinder to mill/machine the spiral groove, but you can do the same thing with a roundnose tool and conventional threading techniques, if your lathe can do 4TPI. Remember you'll need a clip or stop of some sort to hold the tube as it starts to bend. Polish the resulting mandrel.

                    Then make a matching roller for the lathe toolpost. Two ways: One, have a fixed roller and engage the thread dial so the carriage follows the mandrel's groove. Or two, have a stout rod sticking out parallel to the mandrel, and a loose roller that can slide sideways on the rod, so it can self-feed.

                    On the latter, with some practice and trial-and-error, you might be able to get it to self-feed a rod of a predetermined, fixed length, and the roller pops off the end of the rod at the right time to leave the stub end.

                    Not too positive on that one.

                    Either way, you'll probably have to hand-feed the lathe- turn the chuck by hand rather than under power. Similarly, you could use a rotary table as well.

                    But 200 is well worth making the tooling and fixturing for- packing sand or salt or Cerrosafe and then having to clean all that back out- especially from a spiral- would add a huge amount of needless run time.

                    But with a mandrel and roller to help support the tubing, like a tubing bender, and some annealed 1/4" tubing, using the above described setup on something like a hand-cranked rotary table eating precut lengths of tubing might get tedious, but it should be reasonably quick and fairly foolproof.

                    AND, it'll be worth every minute of time making the tooling, if it turns into a repeat job.

                    Doc's Machine. (Probably not what you expect.)


                    • #11
                      I made 55 similar coils (1/2" tubing instead of 1/4") and 4" diameter for my steam boiler...

                      You'll need to fill the tubes w/ something... I used sand; salt works well also. I don't know if ice would work.

                      I made a form to wind the coils w/ the appropriate radus; I wound them in my lathe (by hand). The straight tubing got fastened to the form (filled w/ sand and ends plugged w/ duct tape) and then I turned the lathe over in back gear.
                      The tubing came over an idler wheel fastened to the toolpost in the lathe; the carriage feed was set to the requisite pitch.

                      You can prob. wind these w/ power pretty easily; the 1/2" ones were too much for my 10" Atlas that I had at the time.

                      - Bart
                      Bart Smaalders


                      • #12
                        I agree with Doc for a change. All you need to do is make a helical groove the same half diameter as the tubing half diameter. At the point where the tubing winds on the die there is a roller that is grooved in the same manner. When the tubing passes between the roller and the helical die it is constrained to remain the same shape.

                        There is no need to fill the tubing. That is completely unnecessary with proper dies.
                        Free software for calculating bolt circles and similar: Click Here


                        • #13
                          I was thinking the same thing. This just cries out for a bending die similar to the JD2 type tubing benders. They have a ~40% enveloping die with a similarly configured sliding lead shoe. There is some slight distortion due to outer wall stretch/flattening, but this is generally not very visible and quite acceptable for most things...
                          Master Floor Sweeper


                          • #14
                            Packing may well not be necessary as Evan describes. However, if it is, I would suggest a pliable low melting point wax, (readily available cheesewax, is one). You would not pour but use a vacuum pump to suck the wax from the pot up the pipe. you could then prepare as many lengths as you need. Hot water would then remove it easily (dishwasher?).

                            possible vacuum technique for sucking the wax up the tube.
                            dip one end of the tube in the wax about 1" deep and remove and let cool so blocking the end
                            attach the length of copper tube to the vacuum pump with a valve. pump down as far a possible. Shut valve and iimmediately immerse the waxed end in the hot wax pot. The wax seal will melt and the pipe fill with wax. Then gently use a heat gun on the pipe to make sure the wax does not freeze in cold spots. take out of wax pot and then cool.
                            Last edited by derekm; 03-17-2009, 08:06 AM.


                            • #15
                              Threaded former and follower.
                              Don't have to be made of steel or metal.
                              I had a hand held bender that could take 3/8" tubing down to about 1" made out of mounded ABS for doing truck brake pipes.

                              I may still have it but may have thrown it as the 3/8" ABS wing was broken as they made that one the furthest out and unsupported.

                              I can remember it was easier to use than the steel / alloy benders we had as it stuck less.
                              the follower was just a curved strip that pushed the tube round, there was no profile on the follower but the groove was about 90% deep.

                              I'll look when I go into the shop but not hopefull, we broke about 3 of these on the 3/8" pipe [ common size on UK trucks ] we had them changed under warranty but gave up when the last one broke and just used it for the smaller sizes.

                              It wouldn't do the job in hand but the factors of using ABS or Nylon, 90% deep grooves and flat followers are factors worth thinking about.


                              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.