12 Replies Latest reply on Sep 22, 2010 5:59 PM by Steve Ritter

    Fully Defined status

    John Sutherland

      What are the differences between Centerlines, Construction lines and Infinite lines?

       

      Are any  relevant to Fully Defined status?

        • Re: Fully Defined status
          Kelvin Lamport

          Except for their lengths, Construction lines and Infinite lines are the same. They are used in 2D sketches during the creation of a 3D model..

           

          A centreline is used (mainly) to represent the centre of a 3D feature in a 2D drawing view.

           

          They could be used to constrain a sketch into a fully defined state.

          • Re: Fully Defined status
            David Paulson

            John,

             

            I assume that you are asking this question because you are having a problem fully defining a sketch??  If that is the case, I see it this way:

             

            1.  Construction lines have to have a definite length for the sketch to be fully defined.  They cannot be of infinite length to fully define your sketch.

             

            2. Centerlines can be of infinite length and the sketch can still be fully defined.  You can dimension the end points of a centerline if you like, but I am not sure of the point in doing so.

              • Re: Fully Defined status
                John Sutherland

                Well I want to know:-

                 

                How these lines can be beneficial to me, and

                Which types of line can be disregarded when struggling to fully define a sketch.

                 

                 

                 

                "2.  Centerlines can be of infinite length ..........  You can dimension the end points of a centerline if you like........."

                 

                Where are the end points of an infinite line?

                  • Re: Fully Defined status
                    Deepak Gupta

                    John, it's up to you if you want to have the CL as of infinite length or not. If  you keep them of infinite length, then they'll have no end points. If not then definitely they'll have end points.

                     

                    Using a CL can help you define an diameter dimension for e.g.  Same can be used as axis of revolution.

                    • Re: Fully Defined status
                      David Paulson

                      John,

                       

                      SolidWorks lets you define both solid lines and centerlines as "construction lines or infinite lines".  My most common application of a centerline, either infinite or construction, is to establish symetry for sketches or for an axis of revolution.  You have to define a centerline to fully define your sketch.  My centerlines are typically defined as along x,y,z or symetric to two other lines.  It makes no difference in these cases whether they are fixed length or infinite.  But they could also be defined by two ordinate points  and that would be the use for a fixed length construction line with two points.

                       

                      You can disregard the definition of centerlines only if they are not referenced in the sketch or are the basis of a feature.

                       

                      Of more interest to me is the use of an infinite solid line....................

                  • Re: Fully Defined status
                    Krzysztof Grzebieniowski

                    I find this thread similar to my "how to fully undefine sketch"

                    thanks for starting thread , cause this was also my question

                    but I could not express  that properly

                    • Re: Fully Defined status
                      David Oustifine

                      In a sketch:

                      Construction lines (centerlines) are one and the same, you simply check or uncheck the box in the properties.

                      You can turn a solid line into a construciton and vise versa; for that matter any sketch entity can be turned into a construction line.

                      The "centerline" line tool is a bit of a misnommer, you can actually draw a solid line and check the properties box and it becomes a construction line (centerline) or draw a line with the centerline tool and uncheck it and it becomes a solid line.

                       

                      Construction geometry is used as a reference in your sketch:

                      1. for helping to line things up

                      2. for giving you a measurable edge that is horizontal or vertical for angle

                      3. for any other reason you might need to have an edge, point, or circule that is not consdered part of the sketch contour

                       

                      The term centerline in sketching is a double entendre, as far as SW is concerned it is the same thing as a construction line.

                      It is most commonly called this when dealing with the center line of a sketch for a revolved feature or in a drawing view.

                       

                      Infinite lines give you the benefit of always seeing the line regardless of zoom factor.  Admintedly I don't use them much if at all but I could see the benefit if you had a really long skinny part or something similar.  They have infinite length and will always extend off the graphics screen as you zoom in or out.

                       

                      To the best that I can tell angular position is the only thing that is required to fully define a construction line.  The length can be open and still achieve a fully defined sketch status.

                        • Re: Fully Defined status
                          John Sutherland

                          David,

                           

                          Yes, it does seem that center and construction lines are the same thing.  Is this deliberate backward compatibility or sloppiness on SW part?

                           

                          A semantic pedantic might suggest that construction lines can be fully defined with one degree of translational freedom, whereas solid lines require zero degrees of freedom for full definition.

                            • Re: Fully Defined status
                              Steve Ritter

                              I think if you really wanted to technical about it, you have to define the endpoints of a centerline for it be considered fully defined. But when you look at the bigger picture, and i hesitate to say this, but it is not necessary to fully define a sketch 100% of the time. I often use construction geometry to dimension my sketches off previous features. The only reason I change them to construction geometry is so that SW will disregard them and still auto-select the contour for my extrude or revolve or whatever feature I am working with.

                               

                              I personally believe that was the only intent behind the idea of construction geometry. The program and the operator can still utilize those objects as normal geometry in the sketch environment but once you exit the sketch, the program just kind of pushes it to the side and focuses on the "solid" lines.

                               

                              Steve