3 Replies Latest reply on Jul 15, 2014 4:43 PM by Nathan Rollins

    small gaps - edge continuity - model accuracy...?

    Nathan Rollins

      Hi again,

       

      I am doing really well at keeping my calm - for now.  Not so well in understanding what happened, why things are bad and how to fix them...  The deadline is approaching.

       

      I have some 3D sketches I made that are simply converted from a surface's edges.  From these 3D sketches, I created a loft.  I changed some dimensions in some parent features - nothing too drastic - and now the edges of thparent surface are not continuous.  The 3D sketches do not fail, but they no longer satisfy the Loft guide curve criteria.  SWX is showing gaps of .004mm and refuses to create my loft.  The vertices in question are the result of a surface that was knitted together and then trimmed with an extruded surface. These edges should be tangent, but I am unable to select them using any tangency selection.  Zooming in on either the surfs or the curves does not show the gap.  I have tried recreating the curves and lofts - no luck.

       

      My thought is to lower the model accuracy so that a .004 gap looks like a connection (a hacker's technique from another CAD package) - I wonder if that is a possibility in SWX? 

       

      I tried to create a composite curve to use as my guide curve - but of course there is technically no continuity - according to SWX - so that doesn't work either.  From a geometry perspective, the edge in question did not change at all (dimensionally)  Obviously, if you ask the software, something DID change mathematically... Just wish I knew what.

       

      And I wish I knew better how the selection manager worked.  It LOOKS like a useful tool, but it never seems to do what I think it ought to.  Surely a case of operator error.  Any tips there?

       

      Thanks to all for reading...

       

      -Nate

        • Re: small gaps - edge continuity - model accuracy...?
          Nathan Rollins

          Well, I learned something - but it doesn't help me much.  Maybe it will help you to help me...?

           

          2014-07-15_12-27-55.jpg

          I am guessing the absence of the tangency selection breaks the edge's ability to be used as a guide curve.

          Maybe it is "just one of those things..."?

           

          I will try to create my 3D sketches before the delete face and hope that:

          #1 the Loft will work

          #2 the edge of the loft will knit to the "finger"

          #3 I eventually figure out how to drive this software

           

          Nate

          • Re: small gaps - edge continuity - model accuracy...?
            Jerry Steiger

            Nate,

             

            Why did you use 3D sketches and not the edges? Any time you Convert Entities or use something other than the edge itself you introduce the chance of errors creeping in.

             

            Are you quite certain that there isn't a very short edge (like 0.004 mm) introduced between the two original edges?

             

            Boundary Surfaces are usually more robust than Lofts. I think about the only place where a Loft still makes sense is when you can do a Centerline Loft. No doubt there are individual cases where the general rule doesn't work and a Loft works best. I suspect that this has nothing to do with your problem, but it is a good rule of thumb to keep in mind.

             

            There is no way to change the accuracy of the SolidWorks model. There is at least one place where you can do something like this, the Knitting tolerance under Gap Control on the Knit Surface, but that is the only one I can remember now.

             

            I don't really understand why SoldiWorks sometimes struggles with accuracy issues. We just have to live with it.

             

            Jerry S.

              • Re: small gaps - edge continuity - model accuracy...?
                Nathan Rollins

                Jerry,

                Can I come and work next to you for a week?

                 

                I chose not to use the actual edges because I only need half of the edge to create the surf I am looking for. see:

                 

                2014-07-15_16-13-10.jpg

                 

                I did try to use boundary, but I had trouble with the outer edge not wanting to be selected.  I am not certain there is not a very small edge - but I did zoom "all the way" in to look closely at the vertices.  I will take your comments to heart and continue to hone my skills.  I prefer boundary blends over sweeps and lofts in Pro/E, so doing the same here will be easy.  Another similarity between the two CAD's : strange struggles with accuracy...   Nothing new under the sun.

                 

                Thanks for your input...

                -Nate