26 Replies Latest reply on Jun 21, 2018 8:13 AM by Arlene Garfield

    Tangency mysteriously reversing on fully defined sketches

    Eric Snyder

      This is a occasional issue that comes up and I don't know:

       

      1) What is causing it.

      2) What I can do to avoid it.

       

      I have fully defined sketches that "reverse" themselves occasionally. Below is an example. This is a quick sketch I did to illustrate the issue. The sketch on the left represents a box that has corners filleted. The arcs that create the fillets are tangent to all the lines and in a production sketch everything is fully defined. In this quick sketch not everything is fully defined but remember that in my actual models they usually are. The sketch on the right represents the issue that happens occasionally. I'll make some changes to something else in the model and my sketch somewhere else "reverses". In this case the arcs suddenly decide to go the opposite direction. Remember that the sketch below is not fully defined but in my actual model they usually are.

       

      tangency issue.jpg

       

      I also have a situation where a dimension suddenly reverses itself. I'll make a change somewhere else in the model and come back to the sketch and there will be a line offset to the right by 0.5" and it is now offset to the left 0.5". Sometimes these can be fixed by editing the offset dimension and changing it to be -0.5", sometimes not. It is like SolidWorks is losing it's sense of direction when rebuilding.

       

      Lastly I sometimes see a bug where my offsets suddenly become 10x the dimension visually but the dimension is still what I originally set it at. In other words I do an offset for 0.05" and the dimension stays at 0.05" but the display shows the offset at 0.5". The only cure for this issue is to quit SolidWorks, restart and reload the file and it usually fixes itself.

       

      I don't know if there three issues all have the root cause or not.

       

      Has anybody else run into these issues? Are there any fixes?

       

      Message was edited for spelling by: Eric Snyder

        • Re: Tangency mysteriously reversing on fully defined sketches
          Mike Agan

          Could it be the sketch is not fully constained/dimensioned?

          • Re: Tangency mysteriously reversing on fully defined sketches
            Paul Fey

            I've run into the first two issues before.  I've had the first issue occur when I make some change in the model that changes the angle of the plane the sketch is on.  I've had it pop up elsewhere, but I can't remember what I was doing.

             

            I can't remember what tended to produce the second issue for me because in all cases reversing the direction dimension fixed it.

            • Re: Tangency mysteriously reversing on fully defined sketches
              Kelvin Lamport

              Reversing a dimension would cause that to happen.

               

              Assume a 3" horiz dimension was applied to the LH sketch, changing that dimension to -3" would create the RH sketch.

              • Re: Tangency mysteriously reversing on fully defined sketches
                Jerry Steiger

                Eric,

                 

                I've seen the reversing tangents happen a few times with fillets. It happens a lot more often with splines. I've never tracked down the cause.

                 

                Jerry Steiger

                • Re: Tangency mysteriously reversing on fully defined sketches
                  Shan Lentine

                  BUMP!!!

                   

                  I am having this issue in a model I am trying to create and it is driving me NUTS!!.  I will have the sketch fully defined in all configurations and when I switch from one config to another, a tangent relation will flip and essentially blow up my model.  There are no external references.  The sketch in question is an arc at the end of a spline created by using an intersection curve.  I even tried Feature Freeze to lock it down, but it flipped anyway and I got rebuild errors on the frozen features all the way up the tree.  Let's just say that I am less than satisfied with the Feature Freeze function, but that would be another topic.

                  • Re: Tangency mysteriously reversing on fully defined sketches
                    Rick McWilliams

                    This flipping fillet problem bugs me. I have found that drawing the rectangular shape in a sketch. Then make another sketch on the same plane using convert entity for the lines, finally adding the sketch fillets. You can change the shape easily in the first sketch, especially if the shape is not fully constrained. The fillets will then follow as expected.

                      • Re: Tangency mysteriously reversing on fully defined sketches
                        Shan Lentine

                        Kevin, I wish I chould share the model so I could show exactly what I am dealing with.  Thanks for suggesting that.  I had actually tried that and it seemed somewhat more stable, but I still had to relation flip.  I can't say for sure it was more stable because it only flipped once then I resored the part back to what it was while fighting the urge to put my foot through the monitor. 

                         

                        Rick, The issue I am having is actually a sketch arc within a sketch.  It is an arc at the end of an intersection curve (spline).  If I understand what you are saying correctly, it is an interesting concept that I may be able to apply to my situation. 

                         

                        Right now I am keeping my fingers crossed because it seems stable and has not flipped lately (knocking on wood).  The sketch was originally a 3D sketch with relations to another 3D sketch.  I converted it to a standalone 2D sketch and that seems to have helped.

                         

                        The one thing that I still have a hard time understanding is how my tangent relation had flipped when that feature was frozen.  By the way there are no external relations in my model.

                      • Re: Tangency mysteriously reversing on fully defined sketches
                        Ditmars Veinbachs

                        Hi Eric

                         

                        The sketch solver tries to minimize the movement of points after any geometric change. Tangency is applied to the full circle and the infinite line. Even in a fully defined sketch, there are two possible solutions for arc tangency. In this case, one is biased to the left and the other is biased to the right. Small changes should always keep the same orientation. If the change in the sketch was large enough to make opposing offset less disturbing to the overall sketch, the sketch solver will pick that one instead. This can happen in models where a configuration or equation change causes a large movement in the sketch profile. To avoid that problem, you can create relations/dimensions which force the tangent arcs to remain convex rather than concave. The best solution will depend on the profile and the design intent of the model.

                         

                        This does not appear to be the case with the two figures in your image. I would view that as a bug that needs to be addressed in the solver. You should create a minimal case which demostrates the problem and pass it on to your VAR. Similarly, it would be helpful if you could document the case where a driving dimension is not being respected. This is also a solver issue.

                         

                        Best Regards,

                        Ditmars VEINBACHS

                        R&D Solidworks, Modeling, Development Senior Manager

                        • Re: Tangency mysteriously reversing on fully defined sketches
                          Craig Campbell

                          I am having the same trouble as your second problem. Where in one configuration i will have a offset of say 3 to a construction line and in another configuration will have a offset of 0 to the construction line, and the 1st configuration of an offset of 3 will have the offset reversed. I fix it by clicking reverse sense of direction on the offset but a lot of the time when i  switch configurations it will happen again.

                          • Re: Tangency mysteriously reversing on fully defined sketches
                            Chris Oxford

                            Have this problem all the time with splines. We like to set the ends tangent to a line to make nice sweeps in electrical wire and conduit runs, to approximate relaxed flexible conduit or wire. The spline can show as fully defined, but the handles can still be pulled in/out along the tangent line. This allows the end tangent constraints to flip.

                             

                            I've tried all kinds of ways to lock them down, but they all fail. Dimensioning to the handle over constrains, or does nothing.

                             

                            Before:

                             

                            first.JPG

                             

                            After:

                             

                            after.JPG

                             

                            Reversed tangent (detail):

                             

                            reversed tan.JPG

                            (the spline and highlighted construction line are tangent)

                             

                            style spline.JPG

                             

                            Converting to a style spline, reducing the control points to 3, seems to work. I don't like the control, can't seem to set or confirm tangency, but it looks ok for now. Leaving it under defined.

                            • Re: Tangency mysteriously reversing on fully defined sketches
                              Arlene Garfield

                              I get the offset flipping issue all the time.  It to the point that I avoid doing offset (because it can not be trusted) or if I do us it I tend to blow it away afterwards and just fully define the geo. it created after the fact.  I would make my like a ton easier if Solidworks would fix it.

                                • Re: Tangency mysteriously reversing on fully defined sketches
                                  Ditmars Veinbachs

                                  Hi Arlene

                                   

                                  The root cause has to do with the geometry underlying the sketch. The arc on a circle can have two different directional senses on the same circle. In older releases, we could not control that direction easily.

                                  I know you're not currently using SW2018, but we made a change to help this in SW2018.  The following blog post describes the change made in this release.

                                  Reverse Arc and Spline Tangency Options in SOLIDWORKS 2018

                                   

                                  Best Regards,

                                  Ditmars VEINBACHS

                                  R&D SOLIDWORKS, Modeling Applications Director

                                    • Re: Tangency mysteriously reversing on fully defined sketches
                                      Arlene Garfield

                                      I think maybe your missing the bigger issue.  I can create the sketch.  the sketch is correct.  Then on a rebuild the sketch will flip those tangents and sketch is no longer correct. I like that you gave us a button to fix it but a sketch should not be flipping after it created in the first place.  How do I know it flip? what warning is given? how many times will I or another user have to go back and fix the sketch?  those are actually the bigger issues.   This also happen with your offset geo. there are a couple of other post.  And again we could always fix it but the fact it had to be fixed and sometime more then once is scary.  I had one product that was released and the wall was in the wrong position because during a rebuild it flipped an offset.  This is not something I or anyone would visually see as the offset was small, like .100 but when your surface profile tolerance is .010 this is a big deal.  There were no broken feature as they could build just as well with the wall in that position as the correct offset side.  So only was to learn was when we check surface profile.  Even then we had to test the part and low see that the offset did like to auto flip on it's own to rule out user error. 

                                      • Re: Tangency mysteriously reversing on fully defined sketches
                                        Chris Oxford

                                        I read that blog post. So if you reverse the spline, is it now fixed in that position for ever, or can it still flip on rebuild?

                                          • Re: Tangency mysteriously reversing on fully defined sketches
                                            Arlene Garfield

                                            In 2016 you can enter a positive or negitive value for offset (It suffers from the same random flipping on rebuilds as well.) and this did not fix the issue.  In face I have set it and then right after rebuilding have it flip right back again.

                                             

                                            It does seem to happen more often when splines are involved (Which I use all the time).  IT will happen almost always if you flip a plan normal somewhere, even if that plane isn't directly associated to the offset (the plane can be deleted and the offset feature will remain.) Now I don't go flipping my plane normal all that often but I noticed this is one case where I can force a flip so it helps me spot trouble area before they become trouble.