8 Replies Latest reply on Mar 13, 2008 10:06 PM by Andy Schuler

    Open Surface??

    Andy Schuler
      Hi,
      My more general question comes from a specific tricky and nightmarish problem that I'm going to attempt to explain. I realize that you will probably need to play with the model itself for hours to come up with a solution, but I cannot upload it to you. Also, I cannot change the original part or how it's done. Hopefully some general pointers will help me.

      I'm working on a part that comes from the integration of some SW surface lofts and sweeps and an imported .STP (from Catia). I'm not entirely sure how the Catia surface was generated (somehow referencing the original SW part) but all we have is the surface body. It was finagled into the original SW part with a bunch of fills and some deleteface and knit features.

      That original part is imported into sub-parts and then sliced and trimmed to create individual parts that get imported into an assembly. Well, I've been trying to use surfaces to eventually create a solid body. I have the model to the point where it is finally in the net shape I want it to be (less screw holes and other minor miscellaneous features), but it is in the form of three surface bodies that will not knit together. The "Check" Tool tells me I have two "Open" Surfaces. I've tried some surface-trims to hopefully trim the bad edge and refill the planer surface, but to no avail. The planer surface will knit to either of the inside or outside surfaces, but not both together. It won't let me do two knits either.

      I'm using SW2007 Office Professional SP4.0. I'll try to upload a screenshot.
        • Open Surface??
          Charles Culp
          Well, without seeing the part in person I'm not sure I have an answer. Although, it looks like your edges are tangent, in the wrong kind of way. It looks like the thickness approaches 0. I would check, and make sure that isn't the case, you can't exactly have a solid with 0 thickness!
          • Open Surface??
            Pete Yodis
            Andy,

            Turn on the add-in for SolidWorks Utilities. Choose Utilities... Geometry Analysis... and look at the results. See if this gives you more info...
            • Open Surface??
              Andy Schuler
              Charles: I think you're right about the edge thickness, but that's not always a show stopper (I'm pretty sure I've gotten similar situations to work).

              Peter: I ran the geometry analysis and it turns out one of the points it calls an "Open Surface" is a "Knife Vertex" (the one in the screenshot I uploaded).

              I've tried a bunch of split-lines and delete-faces and tried to get rid of the places where a surface would come to a sharp point, but to no avail. I think what it might have to come down to is re-lofting everything with a bunch of cross section sketches... It's a fix that I don't like, but it might be the only way.

              That still won't answer my original question: "What the heck is an 'Open Surface'?" and why are they caused?

              Thanks guys.
                • Open Surface??
                  Charles Culp
                  Andy,

                  An open surface is one where at least one of the edges is not coincident another edge. Thus it cannot be knit. Basically, if you create a generic surface-body square, it will have 4 open edges.

                  So if you have two surfaces that are not knit together, then you will have open edges.
                  • Open Surface??
                    Pete Yodis
                    Andy, If you could upload the model - we could work on it. Also, I think using utilities if you click on the knife edge instance in the reporting box it will highlight where it is on your model so you can delete the offending surfaces and rework them. This situation probably came about because of the differences in interpetation of the data from the output engine in Catia to the input engine in SolidWorks. Standards are not so clearly defined in some cases and vendors interpret them differently. Of course the offending geometry could have actually existed in Catia - oops did I say that
                  • Open Surface??
                    Andy Schuler
                    Peter
                    Unfortunately I cannot upload the file. I'm just about positive you're right about the export/import functions of either program. I have, however, run across open faces on virgin SW models. I don't think SW is that great at mantaining surface "integrity" throughout the model. It seems to let you create surfaces that later get corrupted, or that start out corrupted.
                    • Open Surface??
                      Andy Schuler
                      Mark,
                      That makes sense. I guess the problem is just how SW imports the surface from Catia. I ended up using a number of cross-section splines and creating some lofts that are pretty close to the original surface, and it worked. I don't like doing it that way, but it got the job done. Hopefully we won't need to change the part. Thanks for your help guys.