11 Replies Latest reply on Oct 11, 2016 8:04 PM by Daniel Cane

    Loft abberations

    Daniel Cane

      Hi,

       

      I'm having a problem with a loft. I'm not sure how to describe it so it's hard to search for. I'm sure you'll able to spot it pretty quickly at this link...

       

      Sketchfab_Publisher_test_003 by Daniel Cane - 3D model - Sketchfab

       

      Capture.JPG

       

      The thigh of the chicken is lofted from the torso to the knee, but it has aberrations where it's kinking.

      It's lofted from a face in the body, through three sketches. It's start constrained tangent to face - which is important to make it look as smooth as possible.

       

      vbcvbcvb.JPG

       

      dfdfdf.JPG

       

      So far I've tried:

      - Boundary loft instead

      - Converting the edge of the Face to a 3D sketch and adding points to the sketch to create a reference, then creating front and back guide curves for the loft.

      - Tweaking the dimensioning of the extruded cut which created the Face.

      - Meddling with the green toggle locations and the pink arrow values

      - Trying all start / end constraints

      - Not using the top sketch in the loft (closest to the face)

      - Adding another sketch (closer to the face)

       

      None of that helped so any thoughts I'd be very glad to hear if anyone has time please.

       

      Many thanks!!

       

      D

        • Re: Loft abberations
          Roland Schwarz

          I would do it in two steps. First loft w/ sharp corner or beyond body surface and intersect body. Then either fillet or create lofted blend.

          • Re: Loft abberations
            Christian Chu

            can you post your part here so we can take a look

              • Re: Loft abberations
                Christian Chu

                Daniel,

                This part was well done in surfacing - I'm not sure what's your issue for modeling this part?

                suggestion: instead of using loft feature,  you can use boundary feature  which you can constrain the end to the body surface - but what I see from the below image, look fine to me

                 

                Capture.PNG

                  • Re: Loft abberations
                    Daniel Cane

                    Hi Christian, thanks for getting back!!

                    I got someone to send me images to show the issue…

                    Here is the kink in the loft… (it is a normal loft and starts tangent to face)

                     

                    a.JPG

                    b.JPG

                     

                    Here is a boundary loft instead either tangent to face or curvature to face. It has the kink still, and boundary loft tangency to face, it also has a groove where the loft starts.

                     

                    c.JPG

                     

                    d.JPG

                • Re: Loft abberations
                  Pedro García

                  hello Daniel,

                  i saw your model and have some sketch mistakes,

                  01.jpg

                  this pink sketches have more points/divisions than the others points, to the loft works well you need have all the sketches with the same number of points/division, You cam add points more to the others  sketches using 2d split or use "fit spline" in the pink lines to convert and reduce number of division.

                  04.jpg

                   

                  another thing,

                  you need put all end lines to vertical or tangent if you want tangence ends:

                  02.jpg

                  and to make better planes to draw try to use splines points:

                  03.jpg

                  you can do better section planes to draw with splines perpendicular, first draw a spline in the middle, start another sketch add some points coincident to spline, after that

                  make planes using this points and the spline..

                  i hope helped.

                    • Re: Loft abberations
                      Daniel Cane

                      Hi,

                      Thanks for your response!

                      Yes indeed, some of the sketches in the body didn't have enough perpendicular relations to mirror properly. Idk why, but it was putting a perpendicular relation at only one end of the spline and not the other end, or if I moved the toggles for the spline, it didn't keep the relation. My quick remedy was to just delete and re-draw the splines. So...

                      BEFORE:

                      back1.JPG

                      AFTER:

                      back.JPG

                       

                      The mirror plane is now neater.

                       

                      As a test, I made the profile sketch splines in the 'tail' of the chicken just one spline like this:

                       

                      round feathers.JPG

                       

                      And that solved the problem with the leg loft I was having.

                       

                      round feathers 4.JPGround feathers 2.JPGround feathers 3.JPG

                       

                      So as you suggested, the issue is the more complex geometry of the 'tail' compared to the body.

                       

                      fit.JPG

                      I used Fit Spline on the three sketches on the tail that previously were two straight lines, a sketch fillet and a spline.

                       

                      They solved the problem with the leg, but created a new problem along the bottom edge of the tail.

                       

                      tail.JPGtail2.JPG

                       

                      I think I will re-create these sketches using a different technique than before which was not ideal.

                      Thank you!

                      • Re: Loft abberations
                        Daniel Cane

                        Hey,

                        So I think the mistake was in the tail loft profiles to use sketch fillets on the bottom edges.

                        They destroyed my driving dimensions, and I couldn't change them afterwards (without the spline going bananas)

                        I have replaced the spline + sketch filet with just a spline and it means I can toggle the dimensions of the bottom edge much more  easily to  soften the transition from the body to the tail.