Tapered Thread

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  • Tapered Thread

    I have a shaft with two ends measured (circles) and aligned with a 3d line through it. One on end is a tapered thread. I'm using an autocircle with a 0.25 pitch (4 TPI). I'm getting about 0.016" TP with a 0.015" call out. Any ideas? Should I be using a different calculation? Or is this really out?
    I used to be high on life but I built up a tolerance.

    Brown & Sharpe Global Advantage
    PCDMIS CAD++ v2011mr2


  • #2
    Well, other than the following, I don't have any suggestions.

    Is it an external thread? I have found on external threads that entering a positive value for the pitch results in the hits spiraling in the wrong direction. Double check to make sure that your hits are indeed following the thread pitch and not running the wrong way. Changing the pitch value to a negative is the fix.


    • #3
      Now that I have had time to think about it a little more...

      Your pitch is .25?

      If it is a standard pipe thread, the taper angle is .25 inch per foot on the diameter (.125 inch/foot per side).

      So, on 1 turn of your thread, the diameter decreases by .0625 inch.

      Now, lets say you measure your circle 0-360º and you fixed it so the first hit would be in the same place as the last hit if you didn't have pitch. Is this clear???

      So, lets say that your pipe is vertical on the table and that the first hit is at 1,0,0.
      Now your last hit with pitch and not taper would be at 1,0,-.25.

      But because of the taper, the last hit will actually be at .96875(one minus 0.3125),0,-.25.

      So, going once around (0-360º) will not give you a good location. Perhaps twice around (0-720º) would be better? Three times around (0-1080º)? I don't know if you will ever get to a true location but probably the more times around the better your results.

      Wes, I know you deal with oil drilling stuff. Do you have any experience with this.


      • #4
        What about using a CONE for that taper thread?
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.


        • #5
          Originally posted by Matthew D. Hoedeman View Post
          What about using a CONE for that taper thread?
          That is a possibility. Can you do pitch with a cone? I think the decreasing radius as you go around the part would still introduce some error though.


          • #6
            No you can't use pitch in an auto cone. I can try a manual cone and see how that works out. I'm using 720-0 as angles at the moment. I'll try with more revolutions.
            I used to be high on life but I built up a tolerance.

            Brown & Sharpe Global Advantage
            PCDMIS CAD++ v2011mr2



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