5 Replies Latest reply on Nov 17, 2017 12:29 PM by Kevin Chandler

    Avoiding Cross-Threading

    John Wayman

      Not strictly to do with Modelling & Assemblies, or even Solidworks at all, but there are lots of clever people on this forum, so I thought it was worth asking:

      I have seen videos of manufacturing plants, such as car plants, where multiple spindles are used to drive a number of nuts simultaneously. For example, I have seen a 5-spindle nut-runner fit all 5 wheel nuts at once.

      How do these systems prevent cross-threading of the nuts?

      I can see how getting all the nuts on the end of the studs aligned in X and Y could work, but I struggle to see how to avoid a small angular misalignment between the axes of the nut and the stud, particularly when there are several such pairs being aligned at the same time.

      I know there are thread forms that are impossible to cross-thread, but wheel nuts are just common-or-garden M10 threads, I think.

      Any tips from the experts on how to automatically fit nuts to studs without cross-threading?



        • Re: Avoiding Cross-Threading
          Eric Allen

          Here is how Nascar and other race cars do wheel studs. The smooth shank is real close to the same as the minor diameter of the nut.


          • Re: Avoiding Cross-Threading
            John Stoltzfus

            Not sure if you're asking about the design end of it or the physical assembly- my reply is based on the design end - Each helix has a start angle and I would recommend always staying with the same start angle every time and only changing "If" it's required.  Here I always have my helix start angle at 90 degrees which puts the cut or extrude profile in the Right or Front Plane..  Then I would suggest adding a 3D sketch and selecting the helix and converting the entities, this will create a spline which you can use to mate the nut.  Before you close the 3D sketch drag the spline line ends just a little bit and add a distant dimension from another point in the part or sketch or plane.  Then open the Nut File add a helix the same size as the Stud Helix and add a point somewhere in the Helix, this sketch point is then used to mate the Nut to the Stud, by mating the point in the Nut and the Spline Helix Line in the Stud and then adding a concentric mate between the nut and the stud, now you can move the nut up and down the stud and the nut will follow the helix, now if you add one more mate from the face of the nut and the face of the part it will angle the nut at the proper angle....

            • Re: Avoiding Cross-Threading
              David Matula

              Most of the time the chamfer at the end of the bolt stud or thread really helps preventing the cross thread.  I run across some straight cuts that are screws and other types of threaded fasteners that are easier to cross thread because there is no lead in with the chamfer.   Pipe threads are another crazy one. 

              • Re: Avoiding Cross-Threading
                Josh Brady

                I come from an assembly automation background, and I've specified a number of single and multi-headed spindle driver assemblies.  Typical methodology is similar to what a (competent) technician will do by hand... align as carefully as possible by design of tooling, fixturing, etc, then do a turn and a half or so of reverse rotation.  Then turn forward carefully for a few turns, monitoring feedback torque and displacement, then drive home at high speed.  The automated spindle can do these steps very fast.

                • Re: Avoiding Cross-Threading
                  Kevin Chandler



                  Maintaining an exact coaxial alignment (angular mostly and centers less so) that machine assembly can provide, cross threading is minimal since it's two aligned helixes rotated at different starts.


                  Manually, rotating the nut backwards until its start drops over the bolt's start (then rotate to engage) works well, which could also be replicated by machine.




                  Kevin C.