25 Replies Latest reply on Jul 29, 2015 11:51 AM by Richard Wehmeyer

    constrain sketch to edge/face of Boss

    Rolando Garza

      Just curious, how would you constrain this and why.

      Would you select the edge of the Boss or use Convert Entities first and constrain to that result?

      Or would you draw a construction line that is co-linear with the edge and constrain tot hat?

      Is it possible to constrain the sketch line to the face rather than the edge?


      Sorry if this seems very trivial to you.

      I'm trying to get back to basics and understand which approach is most stable.

        • Re: constrain sketch to edge/face of Boss
          Martin MacDonald

          The best approach is constrain to the edge. Convert entities or the construction line method is just an extra unnecessary step that would be relying on the edge anyway. Best to use the existing geometry instead of repeating yourself. You can't dimension to the face.


          Hope this helps



          • Re: constrain sketch to edge/face of Boss
            J. Mather

            Personal Account:

            .... understand which approach is most stable.

            Most stable.

            Dimension to the origin.


            BORN Technique - Base Orphan Reference Node Technique.

            As much as possible create all sketches on origin planes and dimension to the origin or origin planes.


            On most of my parts (even fairly complex parts) you could delete all of the solid or surface geometry and still have all (or most) of the information needed to create the part.  That is about as basic as it gets.

              • Re: constrain sketch to edge/face of Boss
                Robert Weller

                I disagree with this. I would actually prioritise design intent over stability in this case. If the boss was designed so that whatever mounts to it was always 5mm from the left edge, then it should be dimensioned to that edge as opposed to the origin. So that if the base plate was increased in size for whatever reason, the boss and thus the mounted component would still be positionally correct from the assembly level. If the position of the boss is relevant only to the origin, then by all means dimension it to the origin. This is the whole purpose of parametric modelling.

                Modelling to design intent saves manual labour in design checking. I don't like inter-part links due to stability issues and unintended consequences of changes, but for a plate with a boss, I think dimensioning to geometry is fine.

                • Re: constrain sketch to edge/face of Boss
                  Rolando Garza

                  I see what you're referring to J.

                  I've used something similar in the past. (Delphi's parallel modeling technique)


                  I create a secondary plane from a primary plane where that secondary plane is co-planar with the face of the box i want to constrain to.

                  I then constrain to that plane instead of the box.


                  I've done this on models where i want strict control of the update cycle and I know i'll be swapping out geometry that was created early on in the tree.

                  ...and it allows me to keep design intent.


                  But, its a lot of extra work; so, i don't use it unless I know i'm really early on in the design phase of a component I know will see a lot of changes.

                • Re: constrain sketch to edge/face of Boss
                  Bernie Daraz

                  Assuming you want the edges collinear I would just use the convert entities command where it would apply.

                  • Re: constrain sketch to edge/face of Boss
                    Jeff Mirisola

                    As others have touched upon, it comes down to design intent. How does the feature that the sketch will create relate to the base feature? It's the answer to that question that will determine how you should constrain the sketch.

                    I, too, disagree with J. Mather. Design intent overrules stability. While I do make every effort to keep a part symmetrical about the origin, I'll forego symmetry for intent.

                    • Re: constrain sketch to edge/face of Boss
                      John Stoltzfus

                      Really depends on the design intent and if you're copying an existing design or your doing a brand new product, to me that is what makes this question go both ways, there are guys that copy designs and guys that create the next new widgit.


                      Here is my rule of thumb;


                      1.  Copying an existing design; then what you did above is perfectly fine, providing it is the base plate and all that changes is the dimensions, w x d x h


                      2.  Brand new product; this is where I agree with J Mather 100% - because the inventor or designer may want the base plate oval or round, now what, I think you know what will happen, all dimensions, all sketches and features tied to the base will be screwed up.  I do a fair share of "Brand New" products/designs here, that are brought to us by outside designers and in most cases have no concept of the manufacturing process, so if I were to start a project like Personal posted, a lot of times I would have been screwed..  My best success has been using the Skeleton Sketch Part and each part is tied to a sketch within the Skeleton Sketch, so if I have to change from square to round the issues down stream are much easier to handle and change..


                      So everyone is right in their own world, and again it's design intent guys.....


                      A little portfolio of the New Designs that were done in the last year;




                      I know it's not machinery or cars etc... but the start of the design is just as critical

                      • Re: constrain sketch to edge/face of Boss
                        Richard Wehmeyer

                        The scenerio pictured looks like constrain to edge would work best.  I have gotten away from using convert as much as possible except for reverse calculations.  That being said if I was building for most stable design immune to design changes I would create a layout sketch, create the boss sketch based on the layout sketch and constrain to the layout. I think this is considered "top-down."  Overkill, but I have made some models using this technique when designing from concept to print simultaneously.


                        Edit:  John beat me to it

                        • Re: constrain sketch to edge/face of Boss
                          Mark Kaiser

                          I see we have reached the design intent vs. stability discussion.  Good one.  I've come across models that should be a 5 second change, but end up being a couple hour change, since stability sucked.  Then I've come across models that should be a 5 second change, but became a couple hour change, since I couldn't figure out what changed what, so sort of design intent.


                          Design intent, is good if it is for the part, but awesome if stable too.  Stability, wish we did not have to model for this one...  Good thing I do simple blocky parts 90% of the time.  Would need more coffee.