22 Replies Latest reply on Feb 9, 2011 1:45 PM by perry leets

    buggered boundary surface

    perry leets

      Im modeling a helicopter fuselage with a boundary surface. Its setup like a loft (previously it was) with closed loop "profiles" and open loop "guides".

      The problem I'm having is the intermediate profiles which are being generated are getting concaves on the sides and tops. This is easiest to see in the front view. The corners are not necessarily tangent to the sides and tops. All the direction parameters are default, i.e. global/none. changing any of these parameters only seems to make things worse. Except that if I change the direction one (profiles) curve influence to "next sharp" the intermediate profiles straighten up, but the intermediate profiles of the direction 2 curves (guide curves) gets really wacked. There is also some concavity along the guide curves as veiwed from the top. There are 6 profiles and 4 guide curves.

      Can anyone provide any guidance here?

        • Re: buggered boundary surface
          Kevin Quigley

          I've come across this when modelling some the bathtubs we do- you get a "dip" between curves. The only solution I have found is to be very rigorous in your network of curves you set up but I think in your case trying to model the whole shape in one hit is probably a factor. I always find the boundary surface works best in smaller chunks.

           

          For your shape I would create extruded surfaces on the centre plane, then rebuild the boundary as a half surface, ensuring you have set curvature continuity to the extruded centre surfaces. That way the resulting boundary surface has more control acting on it so it is "tighter". You would do the same for the rest of the shape then mirror the surfaces and stitch up into a solid.

           

          Another option might be the do this as a loft. Sometimes loft works where boundary gets all dipped up.

           

          One important thing I have found is to try to make all the curves running in the same direction have the same number of control points. That way you can have a lot of control over the way the surface flows.

            • Re: buggered boundary surface
              Charles Culp

              I agree with Kevin. It looks like your shape is symmetric right/left, so I would create a straight extrusion on the right/left plane, and use that as a reference with tangency to this "reference surface". Then only do 1/2 at a time, and mirror the feature.

               

              If possible, I would even go a step further and try and do it a 1/4 at a time, using two reference surfaces.

              • Re: buggered boundary surface
                perry leets

                I originally started as a loft but that seemed even less satisfactory (but then I did the whole shebang as one loft too).

                As far as control points on the splines, I created the "profiles" and "guides" with simple lines and arcs so I could match up to top/front/side sketch pictures. I then did fit splines onto these curves so I could get a smoother surface. That being said, is there even any control points on a fit spline?

                I have heard that it is desirable to have the same number of spline points on profiles.

              • Re: buggered boundary surface
                perry leets

                Good info, thanks guys. Not sure who to mark as "correct", you both were!

                I think I will do the "model half against a reference surface and mirror" routine.

                I'll let you know how it works out.

                  • Re: buggered boundary surface
                    Kevin Quigley

                    I never use the fit spline - ever. If you want a smooth quality surface with complete control over the flow you always need to to draw the splines from scratch.Creating profiles from lines and arcs is OK for basic stuff but for good quality surfaces you should be aiming for splines with the minimum number of control points.

                      • Re: buggered boundary surface
                        Charles Culp

                        If you want good flow between two sets of sketches that must have a different number of control points, just right click on the first one and select "add connector" then adjust your connector to get the flow you need. I would consider that preferential to fit spline.

                         

                        Yes, it is best to go between two sketches that have the same number of points, but that is because it makes things easy, not because it is required. Connectors are the "hard way" to tweak your flow as you need to make it work. As Kevin mentioned, fit spline is more of a shortcut (although it does have its applications).

                        • Re: buggered boundary surface
                          perry leets

                          Well, I dont know what the problem is with fit-spline.

                          Originally, I had splines "from scratch", but the top and sides of this surface need to be horizontal and vertical.

                          I had problems with the splines inducing curvature in those areas. That is why I eventually traced over my sketch photo's with lines and arcs and then fit a spline to those. This gave me smoother transitions from the arc-to-line areas but maintained the vertical and horizontal segments, at least in the profiles.

                      • Re: buggered boundary surface
                        Jerry Steiger

                        Perry,

                         

                        In addition to the other advice, you might want to reconsider where you located your profiles front to back. You might want to move the profiles in the top view so that they line up with the ends of the "straight" center section. You might need to actually add a profile at one or the other of those points, although it is always best to use more profiles than absolutely necessary. Either Ed Eaton or Mark Biasotti gives some hints in one of their tutorials/classes on correct placement of profiles. The trick is getting profiles that match the shape nicely in both the top and side views. It might also be better to break your shape up into three boundary surfaces, one for the nose to center, one for the center, and one for the center to tail.

                         

                        Jerry Steiger

                          • Re: buggered boundary surface
                            perry leets

                            Unfortunately I do not have any reliable profiles for either the top or side of this model.

                            In fact Im really winging it (pun) for the front to back profiles. If all else fails, I may break this into

                            5 parts. Quadrants in the longitutinal axis and a "nose" fill, to prevent a "singularity" at the very front, but I have already had problems with that particular fill surface.

                            Could you tell me where I might find those tutorials you spoke of?

                            Thanks

                              • Re: buggered boundary surface
                                Jerry Steiger

                                Perry,

                                 

                                Ed Eaton's tutorials are on

                                http://www.dimontegroup.com/Tutorials/SolidWorks_Tutorials.htm

                                Look for "Curvy Stuff" and "Surfacing for Blockheads". These go back quite a ways, some of them back before the Boundary Surface was introduced, but the basics are still true. Download them during off-hours so as not to tie up their systems. 

                                 

                                I'm not sure where to get the Mark Biasotti presentations. With any luck Mark can give you some links.

                                 

                                With reference to the nose Fill Surface, did you try using some guide curves for the Fill? You can also just use a single point at the very tip as a control.

                                 

                                Jerry Steiger

                                  • Re: buggered boundary surface
                                    perry leets

                                    Thanks for the info!

                                    The first time I tried doing a fill for the nose I did use a single sketch point. That produced a very ugly nose!

                                    I ditched that and settled for building the nose as part of the overall surface, even if it does produce a "degenerate" point.

                                    I'll worry about that part later.

                              • Re: buggered boundary surface
                                perry leets

                                Well, I have tried modeling this as a "half" surface to be mirrored upon completion but have problems already.

                                I broke all the front-to-back profiles in half, then extruded a construction surface from copies of my top and bottom guides. (See picture) When I start selecting my direction 1 curves (the front-to-back profiles), all looks fine. As soon as I pick an edge from the construction surface to use as my direction 2 curve, SW just gives a completely useless error message. So no boundary surface

                                On the other hand, I can pick my edges first, as my direction 1 curves and again I see a reasonable preview, but as soon as I add any of the direction 2 curves I get the same uninformative error. I never thought this part of the project would end up so difficult.

                                I really need to get this thing right, a lot of other mechanical detail is depending on this!

                                  • Re: buggered boundary surface
                                    Kevin Quigley

                                    Perry, before you pick anything, right mouse click and select "Selection manager". This gives you a little selection pallette so you have more control over what you select. Also if you want to pick edges of surfaces rather than sketches, RMB and choose "select other" to toggle up any alternative selection options (edges, sketch curves, surfaces etc). Failing that, just post up the file - it doesn't look as though it should be that hard.

                                     

                                    Top tip for the future - if you want to get into surfacing more - buy Matt Lombard's surfacing book - well worth it.

                                    • Re: buggered boundary surface
                                      Jerry Steiger

                                      Perry,

                                       

                                      I'm guessing that you have problems because your profiles in one direction don't intersect your profiles in the other direction. What were the error messages? They may sound perfectly useless to you right now, but they could give some pretty good clues to someone more experienced with surfaces.

                                       

                                      Jerry Steiger

                                        • Re: buggered boundary surface
                                          perry leets

                                          The profiles do intersect. Each profile has 3 pierce points, one for the top guide, one for the side guide and one for the bottom guide.

                                          At least if you miss one of these SW at least says the error is due to a profile not intersecting a guide, which is helpful. The error I got was not actually a popup dialog but instead appeared in the guide curves box within the panel. Where you would normally see the name of a curve you had selected, it simply said "error" and nothing else.

                                          I'll post an image next time I do it.

                                      • Re: buggered boundary surface
                                        perry leets

                                        Thanks for all the input guys, I really appreciate it. Im sorry this post has kinda drug on and on.

                                        Im gonna put this on the back burner for a bit because theres some other aspects of this project I need

                                        to work on. BUT I'm not gonna give up on this @!#&^* thing until its right! So I will be back.

                                        Im posting the basic surf if anyone wants to look. I stripped out all the other features. Im using sketchs

                                        of the doors and windows and projecting those into split lines which create features that look fine from the side, but not quite right

                                        from the top. Something else I need to get a grip on! It is also quite possible that the sketch pictures themselves are not terribly accurate.

                                        For instance, when you look at the windshield from the front, then from the side, it doesnt look to me like those boundary lines

                                        would actually produce the 3d surface thats implied. Oh well.

                                         

                                        Thank you very much again all, I'll be back as soon as I finish some other chores

                                        • Re: buggered boundary surface
                                          Christopher Thompson

                                          Perry,

                                           

                                          I have not yet looked at your model as I need to attend a meeting. However, I have attached a ZIP file containing two separate approaches to modeling a similar wing tip or fuselage shape.

                                           

                                          The initial boundary sketches are the same in both models, but the trimming and surface features vary near the end of the model tree. Let me know if this helps

                                           

                                          Chris