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Tube coping setup for lathe

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  • Tube coping setup for lathe

    A while back I think someone was asking about how to cope tubing. Now that I can post photos...

    The tool post fixture I use to hold the tubing:

    The kind of miters possible in .028" wall heat treated 4130:

    For bicycle frame building. I use Simmonds bi-metal hole saws. They're available in 1/16" diameter increments.


  • #2
    Nice jig...never thought of doing it in the lathe. Thanks for the pics, looks like excellent craftmanship!


    • #3
      Nifty fixture, Excellent workmanship.
      To invent, you need a good imagination - and a pile of junk. Thomas A. Edison


      • #4
        Now that I have a mill almost up and running I'll probably end up making more neat tooling, jigs, tube benders and fixtures than I do bicycle frames...but that's half the fun.


        • #5
          I have two questions.
          1) What is the purpose of the C clamp?
          2) Are there any provisions to ensure a set of coped ends are on the same plane?

          The fit is really nice and the device would work on both the lathe and the mill.


          • #6
            The "C" clamp is used to keep the block and tubing from moving in and out as the cutter turns. The staggered teeth of the hole saw engaging the tube was causing it to move. I found that if everything was as rigid as possible then the cuts were much better.

            It's rather blurry but if you look at the upper edge of the photo you can see another tube block. I put one on each end at the same time on a surface plate and use them to make the cuts in plane or 90deg from each other. I use layout ink on the ends and mark the cuts then line up the largest radius tooth of the hole saw on the line then turn on the lathe and engage the feed. I use about 200rpm and the slowest feed rate my lathe will do.



            • #7
              I do it on a bpt with simple vee blocks.

              you do have a tough time going past 60 deg or so as the head gets in the way.

              that'a a very nice fixture.

              very important to have that wonderfull fit if you are brazing. but if youre welding you might chop the "sharp" ends of the tube that wrap arouns back until they have full wall thickness exposed.

              like a tubing notcher leaves.

              that may give you a better joint to lay your tig bead in, and it won't burn back the thin edge.


              • #8
                I found v-blocks don't offer enough support. Some of these tubes have 0.015" thick walls in the center section so they can dent and deform easily. For some of the newer non-round profile tubing I was thinking of casting "liners" in my blocks using CerroBend low temp alloy.

                I do tend to clean up the cut edges with a disc sander and take at least part of the thin edge off for better TIG penetration.

                [This message has been edited by glenj (edited 03-02-2004).]


                • #9
                  what sort of welding jig do you use.

                  I've never tried anything as precise and complex as a bike frame. I imagine that will be a real chore to weld up.

                  and will a jig be used to support it during heat treat?

                  also, how do you orient each end to each other? With a jig block clamped to each end of the tube (while set on a flat) you could then just flip the tube around and do the other end. maybe that's what youre doing?

                  that is a really nice job you have done so far.

                  [This message has been edited by dsergison (edited 03-02-2004).]


                  • #10
                    I made a jig out of 1"x2" aluminum that I fly cut the wide faces down on both sides to make them flat and parallel. I hold the important parts (head tube, bottom bracket shell, top of seat tube and rear axle mounts) very accurately then let the miters of the other tubes locate themselves. I can post a photo of the jig later. The head tube is shown in the one photo supported on two stainless cones. I modelled the whole thing in SolidWorks and use a drawing of the jig/frame assembly to set everything up.

                    I have a pulser for my TIG welder so the welding isn't too bad. I've been pretty lucky so far and not had any frames that were so far out of plane that I couldn't cold set them. Generally the head tube is not more than 0.03" in 12" out of plane with the bottom bracket shell faces.

                    I do clamp blocks to both ends and leave them on until all cuts and drill holes are completed to maintain alignment.


                    • #11
                      is this a cottage industry for you? sounds like you have it all down.

                      what sort of tig? I have a thermal arc 185.

                      (and I use Pro/e)

                      I would like to try to make a trials motorcycle frame some day.


                      • #12
                        It would be more of a cottage industry if I could get cheap liability insurance.

                        I use a Miller SyncoWave 250 with the pulser. I'm thinking a nice new Dynasty 200DX would be good and take up a lot less room and not weigh 450lbs (I just moved it).

                        A trails frame would be about as complicated as a full suspension mountain bike. The tubing you'd use would be a lot thicker and easier to weld but you'd have lots of engine mounting brackets and stuff to worry about getting straight. Sounds like a fun project!


                        • #13
                          Do you get much distortion of the head tube with both welds on the same side? Do you have to do any machining after the welding to get the bearing seats parallel again?

                          Any products mentioned in my posts have been endorsed by their manufacturer.


                          • #14
                            There is a bit of distortion after welding but tight tube joints help. I have a special hand reaming tool that cuts the ID and faces the ends parallel post welding. I'm going to make some expandable bronze plugs to act as heat sinks inside the head tube. I've been told that works great at keeping the distortion down.