11 Replies Latest reply on Jun 19, 2010 4:09 PM by Jerry Steiger


    Kevin De Smet
      I am looking for a feature that allows me to do the opposite of knit surface.

      I want to take a knitted surface body or a solid body, and explode its faces into separate surfaces for me to work with.
        • Unknit
          Deepak Gupta
          You can use offset surface and pick your faces in a manner that they don't connect to each other. Simultaneously, you can pick left over faces/surfaces.
          • Unknit
            Charles Culp
            For whatever reason there is no actual tool to convert a solid body to a surface body. I typically use the "delete face" tool to delete one of the faces, thus converting it into a surface body.
              • Re: Unknit

                Unknit feature would be so useful.


                The only solution right now seems to be delete face which is VERY unstable, especially early in the feature tree.

                Boundary surfaces and others surface features are touchy when it comes time to recognize the edges, when you adjust the dimensions later on of the profiles sketches.


                I faced this situation:

                -I did a surface loft with a bunch of curved surfaces (none straight)

                -I then wanted to add C3 radii on all edges, so I knited the surface loft geometry to close the volume, then knited it all

                -Then added a normal radii

                -Then comes the need to unknit. In order to create C3 radii, I have to get rid of the standard radii to replace them with boundary surface C3

                -So I have to do a delete face to remove the radii, then use the edges to do manually all the surface radii C3 using boundary surface with curvature


                What is needed is a unknit feature to explode the knited surfaces and do delete body. Why? Because delete face is not a stable feature as it can mess up the identidy of edges later on, and features like boundary surfaces will not recognize it for example. Has it happened to me lately.


                Very frustrating to use feature that are not stable... not the first time.

                  • Re: Unknit
                    Jerry Steiger



                    I agree that Delete Face is not necessarily the best tool, but I'm not sure an Unknit command would be any better or more useful. I don't see how it would help much in the example you gave. You are still quite likely to delete the left over faces (the original normal radii) when you are done. It's quite possible that the Unknit tool will have just as many problems as Delete Face, as you have still removed the same faces from the body. The reason I am hesitant about adding the Unknit tool to the software is that I would rather have the developers work on making the existing features work better instead of adding new features of questionable utility. If it is easy to make an Unknit tool and it is going to be very robust, or if it is more useful than it seems to me now, then I can't really object.


                    Jerry Steiger

                      • Re: Unknit



                        Thank you for your reply.

                        I attached a video of my issue, just to be clear as well as a screen shot of the problem.


                        I am suspicious of delete face as a fonction that once we apply some modifications on the model, SW has a tendency to renames edges or faces which down the tree affect other fonctions which were supposed to use certain edges and now are confused because the edges changed names or something. This happened to be with the Draft fonction once, the edges changed names and the Draft was applied to the wrong edges after a modification. Delete face seems to have this behaviour and that is why I usually use it at the end of the tree to patch things up rather than to create the main shape.


                        Perhaps you would argue that other features behave that way, therefore if a unknit fonction behave like this, it would of course not be a solution. It is at the very least more intuitive to have knit and unknit vs knit and delete face.


                        In this case, just changing slightly the dimension in the top profile will trickle down an error where the boundary surface cannot recognize the edges uses to recreate the radii as you can see on the video.

                          • Re: Unknit
                            Jerry Steiger



                            Thanks for attaching the video. Watching the video, it doesn't seem to me that the Delete Face feature is causing the problem, that it is more just the flaky nature of the surfacing tools. The Delete Face feature in this part is a constant, the same in the original build and in the rebuild. But I don't really see how the Boundary Surface could lose the two edges, so I obviously don't understand what is happening and could be completely wrong about the Delete Face being innocent. It would be interesting if you could use a couple of different methods to build the part and see if any of them are more robust. Unfortunately, your sacrificial fillet method is much easier than any of the other methods I can think of.


                            Jerry Steiger

                              • Re: Unknit

                                I agree the Delete face does not seem to be an evident suspect here, but based on the history of the feature, I am suspicous.


                                Perhaps there is something going on with the stability of the feature Boundary surface.


                                I changed strategy and used the Offset surface to zero then deleted the surface bodies of the fillets and redid the Boundary surface, editing the sketch after seem to not cause the problem anymore.


                                Basically a work around, not a solution.


                                The question is how stable is Boundary surface then...



                                  • Re: Unknit
                                    Jerry Steiger



                                    Very interesting experiment and result! I don't really know what it means, but it certainly must mean something to the guys who write the code. I hope someone from SolidWorks is following this thread and picks up on it.


                                    None of the surfaces seem to be very stable. Boundary Surface is newer and seems to be a little more robust in some ways than Loft, but it may be less robust in others, not having been tested as much by perverse people like users. I have certainly had lots of trouble with Lofts, Sweeps, Fills and Boundary Surfaces when the edges get lost.


                                    Jerry Steiger

                        • Re: Unknit
                          Lenny Bucholz

                          As Deepak said use the offset surface tool at zero.


                          you can pick and choose how many faces and they will be knitted together or do one at a time. the reason is that way you keep the history of the solid/surface body in the tree and when you don't need it anymore you can use delete body and then it is gone, but you can bring it back with a supress feature.


                          everything you want is already there!


                          sometimes you just have to think outside of the box, there is another way, save a iges, then open the iges, go to options and turn off the solids and knit circles and save it as a new part then in the file you are working in bring a part in a part and there you have both the solid and a surfaced part in the same file.


                          we have all sorts of tricks, us old SW abusers.


                          Message was edited by: Lenny Bucholz

                            • Re: Unknit



                              Regarding Offset surface vs possible unknit, the Offset to zero technique which is similar to Move Body to zero for solids to make a copy is an interesting idea.


                              In my example, this could actually work pretty good (see video above).


                              However I would argue that in order to let say, split a cube as such that it is splitted in 6 independent faces, you need to do Offset to zero 6 times, instead of one fonction with a possible unknit to explode all 6 surfaces. Apply this in a complexe contexte, because we all know we do not design cubes, this can add up to many more features.


                              Regardless of the above, I believe the stability of Delete Body is far superior to Delete Face as far as I know.

                                • Re: Unknit
                                  Lenny Bucholz

                                  so if they made a unknit tool it would still have to make all new surfaces as features in the tree! meaning it would have to be the exact reverse of knit. so if you had 25 face patches, you would now have 25 individual surface bodies in the tree so that you would be able to paick and choose how you want to use them.


                                  there is another way, copy the body then shell it, delete all the inside faces and now you have just the outside surfaces. it will be tied to the original solid so if you make changes to the seed the copy should update, within reason of course.


                                  these are not work arounds! it's how we have done surfacing in a history based solidmodeler for years. lets say tips and tricks. if you really need heavy surfacing you may want to look at rhino, maya that don't get caught up because of history!