6 Replies Latest reply on Dec 20, 2009 4:23 PM by Samuel Schweighart

    Controlling Edges in 'Boundary Surface'

    Samuel Schweighart

      Hi all,

       

      Yet another edge post...

       

      This post is about boundary surfaces.  When making a boundary surfaces with sketches that do not have a smooth corner (such as two lines coming together at a corner) SW places an edge on the resulting surface at that corner. That's fine.

       

      The problem is when you have two sketch entities that are curvature continuous, (such as two splines, or a spline and a line).  Some of the time, SW will not put an edge where these two sketch entites meet. (Which is what I want).   But occasionally, it DOES place an edge.

       

      This isn't really that big of a problem except when you have several curvature continuous splines.  SW will place an edge at one or more arbitrary places.

       

      The real problem lies, that if this is early on in your tree, and you modify the sketch, SW will randomly place the edge at a DIFFERENT  location.   Now every split line, or anything that references that surface will fail.

       

      I've attached a file where SW has placed an edge on one of the spline-line interfaces (top), and not on the other.  If you make some changes to the sketch, SW will randomly place that edge on the bottom.

       

      1) Is there any way to force SW to not place that edge in the first place.

       

      2) If SW needs that edge, is there any way to make SW keep it at the same point?

       

      This is also another example of where it would be nice to be able to remove split lines.  If after making this part, I removed the split line, and then built the rest of my tree, I wouldn't worry if SW places the edge in a random place.

       

      Thoughts?

        • Re: Controlling Edges in 'Boundary Surface'

          Hi Samuel,

           

          In this case, you have "Merge Tangent faces" option checked, and what Boundary is doing is merging your spline surface to override the bottom planar face and absorb it. So I would not check this option.

           

          You can also use Connectors to control this situtation but if you desire no edges at all, you would be best to create a Fit Spline over your first and second sketches to make them single continuous entities.

           

          Regards

           

          Mark

            • Re: Controlling Edges in 'Boundary Surface'
              Samuel Schweighart

              Hi Mark,

               

              Thank you for your continued help!

               

              I see how unchecking "Merge Tangent Faces" will give me more definitive control as all the edge will be present. (Definitive control is what I want.)  How come the 'Merge Tangent Faces' didn't merge the top one as well?

               

              In the demo part, I added a connector, and the edge did move to the connector.  If I add a second connector, it appears to be arbitrary which connector the edge appears on.

               

              I guess the answer is the insight on how "Merge Tangent Faces" works.  It appears that SW has to put a second edge in for some reason. (Is it even  possible to create a surface with just one edge?)

               

              I was going to try with a spline that loops back on itself, but then I remembered that splines now seem to enforce tangency when you loop them back on itself. (Why is that?)

               

              My work around (since I want as few edges as possible) is to create two surfaces and knit them together.   This way I have definitive edge control.

               

              Sam

                • Re: Controlling Edges in 'Boundary Surface'

                  How come the 'Merge Tangent Faces' didn't merge the top one as well?

                   

                  Sam - the bottom face was a closer match tolerance-wise (flatter curvature) than the upper one.

                   

                  In the demo part, I added a connector, and the edge did move to the connector.  If I add a second connector, it appears to be arbitrary which connector the edge appears on.

                   

                  When adding the connectors they are place where you pick on the curve - you can then drag them to the appropriate location, in your case the one end goes on the vertices between the line and the spline and the other is place as you see fit.

                   

                  I guess the answer is the insight on how "Merge Tangent Faces" works.  It appears that SW has to put a second edge in for some reason. (Is it even  possible to create a surface with just one edge?)

                   

                  I don't have an adequate answer for this - only that we don't give you the controls for this, but we could. As with my answer above, In your case, it is not working as intended but rather the planar face is being completely eliminated. As I've mentioned in other posts, we are considering implementing the 2010 knit algorithm into many other feature where merging takes place like this feature and mutual Trim.

                   

                  I was going to try with a spline that loops back on itself, but then I remembered that splines now seem to enforce tangency when you loop them back on itself. (Why is that?)

                   

                  Because that is what most users want and need over not (enforcing tangency on closed loop) but I agree that there are definitely cases where you'd want this like on the airfoil. Can you please submit an enhancement request to be able to break the tangency.

                   

                  Mark

                    • Re: Controlling Edges in 'Boundary Surface'
                      Samuel Schweighart

                      Sam: How come the 'Merge Tangent Faces' didn't merge the top one as well?

                      Mark: the bottom face was a closer match tolerance-wise (flatter curvature) than the upper one.

                      Sam: My question was, why doesn't it merge all three faces into one? (Although it is interesting to learn how it chose between the two.)   It seems to me that there is an inherent problem with having a surface with one edge connected to another, (imagine rolling a piece of paper into a tube with one edge touching the other). SW doesn't seem to be able to do that. Is that's why the boundary surface always put in a second edge? If so, I could use that knowledge when building.

                       

                      -----------------

                       

                      Sam: In the demo part, I added a connector, and the edge did move to the connector.  If I add a second connector, it appears to be arbitrary which connector the edge appears on.

                       

                      Mark: When adding the connectors they are place where you pick on the curve - you can then drag them to the appropriate location, in your case the one end goes on the vertices between the line and the spline and the other is place as you see fit.

                       

                      Sam: I was trying to say that there always is at least one extra edge created, and if you put one connector in, then the edge is aligned with that connector, but if you need 3 or 4 connectors to create the shape,  the edge will arbitrarily pick which connector/GC to align to.   I have an airfoil shape that I'm lofting to another shape, and I need multiple connectors/guide curves.   One extra edge always appears, but small changes will make that edge appear in completely different spots (It randomly picks which GC/connector to use as the edge.) 

                       

                      I'm just saying that if there has to be an extra edge creation (which I still don't understand why there has to be) then I'd like control over where it appears. My workaround is to make the surface using two separate surfaces.  When I do that, there is no unwanted edge that pops up in the middle of my surface.  It's not that bad of a workaround, I admit.

                      ---------------


                       

                      Sam: I was going to try with a spline that loops back on itself, but then I remembered that splines now seem to enforce tangency when you loop them back on itself. (Why is that?)

                       

                      Mark: Because that is what most users want and need over not (enforcing tangency on closed loop) but I agree that there are definitely cases where you'd want this like on the airfoil. Can you please submit an enhancement request to be able to break the tangency.

                       

                      Sam: Yep, I'll submit the enhancement request.  This was added in 2009 right?  The solution is to use two splines with a continuity between the two, which works ok.

                       

                      -----------------------

                       

                      Sam: I guess the answer is the insight on how "Merge Tangent Faces" works.  It appears that SW has to put a second edge in for some reason. (Is it even  possible to create a surface with just one edge?)

                       

                      Mark: I don't have an adequate answer for this - only that we don't give you the controls for this, but we could. As with my answer above, In your case, it is not working as intended but rather the planar face is being completely eliminated. As I've mentioned in other posts, we are considering implementing the 2010 knit algorithm into many other feature where merging takes place like this feature and mutual Trim.


                      Sam:  Yeah, all of these posts come down to control on how SW handles edges, and the sometimes inconsistent handling of how surfaces are created and merged.  Having edges appear in surfaces (at what appears to the end user) at random locations that vary with small changes to the initial conditions (sketches) does cause a lot of headaches.  Mainly because the appearance, change in position or disappearance of these edges will cause most features (such as future boundary surfaces, lofts, split lines) to fail, and it can take 30 minutes to rebuild an entire model by hand, simply reselecting new edges.

                       

                      This same theme also applies to the arbitrary removal of split lines with some functions and not others.

                       

                      The fact that the 2010 knit algorithm no longer removes split lines is nice, and I look forward to more consistancy in future releases in SolidWorks.  I would also be interested in having control of merging tangent faces as a surface tool.

                       

                      I feel like all of this should be placed in an enhancement request, but I envision it will be difficult to convey what I'm looking for.

                       

                      Thanks for your help in all this. I do feel like I'm gaining some insight on how to build my models better. (For example, never try to make a single surface that folds back on itself.)  I hope we aren't beating the proverbial dead horse too much...

                       

                      Sam

                        • Re: Controlling Edges in 'Boundary Surface'

                          Sam,

                           

                          You insight that the Boundary surface has this default arbitrary connect is actually fundamental to a lot of our surface features and NURBS in general. When you have a "closed" surface like loft or boundary feature, this this default connector serves as an internal seam that allows for you to do closed loops in the first place. It appears in other surface features but we just don't expose it like we do in Boundary. The bottom line is - don't fight it but let it place itself whil you concentrate on the other user-defined connectors. My experience is that the default will be reposition dependent on where you place your other user-defined connectors. I'm obviously a big fan of connectors because once you learn how to use them, they are very powerful.

                           

                          Regards

                           

                          Mark

                            • Re: Controlling Edges in 'Boundary Surface'
                              Samuel Schweighart
                              Yeah, I agree that connectors are useful, and I do use them, but I find GC can be more consistent, especially if I make a change.   Unfortunately, I can't just let Boundary Surface place the edge randomly as both for CFD, and stability in my part, I can't have the edge move on me when I make a small change higher in the tree, and then rebuild it.