10 Replies Latest reply on Aug 7, 2009 10:11 AM by Dale Slotman

    Sketch will not fully constrain

    Stuart Moore

      The sketch for Extrude2 has two small radii, the position of which I cannot constrain.  Any attempt to constrain them results in an overconstrained sketch.  I can pull them with the mouse but they will not be constrained.  Those features had square ends originally and they were constrained correctly. Changing them to round ends has caused the problem.  You will see that the top pattern is correctly constrained.

       

      I know I can delete the offending parts of the sketch and recreate them but I would really like to know why this sketch won't constrain.

        • Re: Sketch will not fully constrain
          Feroz Mahomed

          Stuart,

           

          Please see attached for fully defined sketch. I created new center lines for the radius 0.75 and redrew the radius.

          • Re: Sketch will not fully constrain
            Feroz Mahomed

            Stuart,

             

            I did the following to fully define the sketch:-

             

            1. Delete the 0.5mm dimension.

            2. Add the 4.10mm dimension from the origin to the center of the 0.75mm radius.

            3. Add the 4.95mm dimension from center of the 0.25 radius to the center of the 0.75mm radius.

              • Re: Sketch will not fully constrain
                Stuart Moore

                Mahomed,

                 

                Thanks for your effort but the real question is "what is wrong with the sketch such that it will not constrain".  I do not want to use the origin - I want the the angle/distance relationship as in the top half of the pattern.  I want to be able to move the entire pattern along the strip.  Yes, I know it can be done the way you have described but it does not satisfy the design intent.

                 

                I have hit this problem before where there is nothing aparently wrong with a sketch but it will not constrain in a correct, logical way.  I was rather hoping that someone would know why.

              • Re: Sketch will not fully constrain
                Dale Slotman

                Stuart,

                 

                I got it to fully constrain by putting a vertical relation between the centerpoints of the radius and the corresponding radius above it.  You will need to delete one of the tangent relations on each of the currently underconstrained radii.

                 

                Hope this works for you.

                 

                Dale

                  • Re: Sketch will not fully constrain
                    Stuart Moore

                    Sorry guys but you're missing the point.  I can get it to constrain - my question is "what is wrong with the sketch that prevents it from accepting dimension constraints".  I can pull the offending elements and put them where I like but if I try to define their position by dimensioning in the way that I want (the same way the upper arm is dimensioned), it fails.

                     

                    This has happened to me before and I would like to know if the problem is related to the way I am constructing sketches or whether it is just another SolidQuirk.

                      • Re: Sketch will not fully constrain
                        Dale Slotman

                        Stuart,

                         

                        I think it's the tangent constraints that are jacking things up.  Because both of the lines attached to the arcs are already in a defined location, and the centerpoint is constrained to a line, it doesn't like that.  I used to have overconstrain issues with sketched with basic slots in them all the time before SW2009's new slot sketch feature.  I found that deleting tangencies often helps.

                         

                        Dale

                          • Re: Sketch will not fully constrain
                            Stuart Moore

                            Dale,

                             

                            I agree with everything you say, but the fact remains that the upper arm is constrained in precisely the same way and it does exactly what you would expect it to do.  It is (should be) perfectly reasonable to have tangent constraints where those arcs meet lines.  The only thing that is unconstrained is the position of the arcs along the 45 degree construction line.  Like, I suspect everybody else, when I get towards the end of constraining a sketch and there are still blue features, I grab them and pull them about to see in what way they are not constrained and then deal with it.  This kind of behaviour is illogical, inconsistent and unreasonable don't you think?