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ftorabi1-Visitor
1-Visitor
March 10, 2017
Solved

How do I know my sketch is definitive ?

  • March 10, 2017
  • 5 replies
  • 32030 views

Hi All

I use Creo 2

since choosing which dimensions  could be  strong and which ones weak is completely manual in Creo, untill it goes to conflict. I would like to know, if there is anyway to understand that my sketch is definitive ( like in solidworks) , cause I am used to that, and I complete the sketch to the point that all the lines are black and can not be modified by dragging them around

    Best answer by dgschaefer

    Let's instead use Ron's image from below:

    bluedim.jpg

    All weak dims.

    Let's say I change the 202.331 dim to be 300.000.  This is what will happen:

    • The left end is constrained to the reference and therefore won't move.  So, the right hand vertical line will move to the right.
    • The vertical line below it is tied to it so it will move right too.
    • The length of that second vertical line is fixed (114.836) so it will not change.
    • That will drag the bottom angled line to the right as well.  It will not change angles because it is constrained as normal to the leftmost angled line.
    • Because the bottom most horizontal line has a fixed length (74.649), it and the short vertical line at the left will move right as well.
    • The far left bottom point is constrained to the reference and will not move.

    I also know that if that vertical reference moves right or left, this entire sketch will move with it because there are no other vertical references.

    Now, if I grab a line and drag it, Creo will allow the values of the weak dims to change. It also allows the values of string, non-locked dims to change, I believe, so no difference there.

    All predictable because Creo tells me what till happen.  Now the default scheme here creates a lot of cascading effects, but it's fully constrained and predictable.

    If we sketched the same thing in SW all the lines would be lue and there would be no dims or constraints.  I could grab and drag any line pretty freely and usually, only that line moves.  What isn't clear, however, is what happens to the sketch if the rest of the part moves.

    You mentioned below that Creo's weak dims and SW's blue sketches are the same.  The above is why I say they are not.  My point was not to critique SW (which I guess I did), but to answer the original question.  The two sketchers do not behave the same, there are differences in methods that are important to understand if you are coming from one and want to bake robust designs in the other.  There isn't really an equivalent of the "blue sketches" of SW, but I guess the image above is as close as it gets.  It still provides a lot of info on how this sketch will behave, the default SW sketch provides almost nothing.  Different ways of doing it and I strongly prefer Creo's.

    In either tool you need to master it and put in the right inputs to get good results.  Each tool, however, requires different inputs to get there.

    5 replies

    S
    23-Emerald III
    StephenW23-Emerald III
    23-Emerald III
    March 10, 2017

    One rule that helps most user is to never leave weak dimensions. Those are "arbitrary" dimensions that creo adds to keep the sketch fully constrained. The rarely correspond to design intent.

    There is one more dimension option in sketcher, LOCK. If you lock a dimension, it can not be changed by dragging.

      D
      drawlins1-Visitor
      1-Visitor
      March 13, 2017

      Steven,

      Can you explain the difference in "strong" and "lock" as it pertains to dimensions?  I've never fully understood the difference.

      Thanks

      Don

        T
        23-Emerald IV
        TomU23-Emerald IV
        23-Emerald IV
        March 13, 2017

        Weak - Dimensions automatically created by intent manager.  They will automatically be deleted if another dimension conflicts with them (without prompting the user.)

        Strong - A dimension explicitly created by the user, or a weak dimension made strong by the user.  They will not automatically be deleted if another dimension conflicts.  (The conflict manager will open instead.)  A strong dimension's value can still be changed by dragging the sketch entities.

        Lock - A dimension this is both strong and will not change value by dragging.  New values can still be manually entered.

          P
          psobejko1-Visitor
          1-Visitor
          March 10, 2017

          I suggest you set the color scheme such that weak dimensions and constraints are shown in bright red.  Your goal is to eliminate the red!

          I use this config.pro setting:

          sketcher_dimension_autolock yes

          This means that whenever I type in a value for a dimension, it will become locked (so it can't be changed by dragging the geometry around).

          If I am in the concept phase, I unlock some dimensions so that geometry can be dragged around in the 3d model, but my ultimate goal is to have all dimensions locked.

            F
            ftorabi1-VisitorAuthor
            1-Visitor
            March 14, 2017

            Thank you very much

            D
            dgschaefer21-Topaz II
            21-Topaz II
            March 10, 2017

            In SW, a sketch can be made and not constrained at all. All the sketch entities will be blue and there will be no dimensions, yet you can complete the sketch.  (How SW updates those sketches, I have no idea.)

            In Creo, all sketches are fully constrained (what I believe that you mean by "definitive") at all times.  There's no such thing as an under-defined sketch (what would be a "blue" sketch in SW) in Creo.

            Initially, however, all the dimensions and constraints (equal length, horizontal, vertical, tangent, etc) are placed by the software.  Those will be gray in color so you know that they aren't your contraints & dims, they are Creo's.  So, although the sketch is automatically fully constrained, as has been said, it isn't likely constrained as you want it.

              P
              psobejko1-Visitor
              1-Visitor
              March 10, 2017

              I've an angle about this: SW company took the time to implement ideas that enhance the user experience.

              In its sketcher, SW doesn't bother the user with what weak dimensions and constraints it imposed on the geometry behind the scenes in order to "solve the sketch".

              It instead gives the user the pertinent information by color coding the geometry that the user has "locked down" (black) and what can still be manipulated (blue).

              Creo already has all the building blocks to make its sketcher behave in the same manner - but they don't do it, maybe because of IP issues.

                D
                dgschaefer21-Topaz II
                21-Topaz II
                March 10, 2017

                Or because it's a terrible idea.

                I agree on the SW philosophy of making things simple and not giving the user info they don't think they need.  But, I need to know how you are constraining my geometry.  I hope Creo never implements anything like this. One of Creo's strength is the amount of info it gives you on the status and structure of your model.

                Best I can tell, SW simply leaves the unconstrained sketch entities at the same location relative to the part origin as the model changes.  But there's no real way to know, because SW doesn't tell you, and therefore no way to predict how your model will act.

                  T
                  tpartridge1-Visitor
                  1-Visitor
                  March 16, 2017

                  For those that have a practice or requirement to not have any weak Sketch dimensions, you could consider the following mapkey, which selects all dims and converts them to Strong.

                  ! *** mapkey for Sketch mode to select all dimensions and convert all to Strong

                  mapkey w2s @MAPKEY_NAMEselect and convert all dims to strong;\

                  mapkey(continued) @MAPKEY_LABELconvert all dims to strong;\

                  mapkey(continued) ~ Open `main_dlg_cur` `Sst_bar.filter_list`;\

                  mapkey(continued) ~ Close `main_dlg_cur` `Sst_bar.filter_list`;\

                  mapkey(continued) ~ Select `main_dlg_cur` `Sst_bar.filter_list` 1 `2`;\

                  mapkey(continued) ~ Command `ProCmdEditAll` ;~ Command `ProCmdEditWeakStrong`;;

                    F
                    ftorabi1-VisitorAuthor
                    1-Visitor
                    March 16, 2017

                    Thank you for your answer

                    Question 1 : is it Always necessary to have strong dimensions ( I mean based on principals not requirements)

                    2 : how do I use and/or apply these mapkeys and how do they work, shall you explain please?

                    D
                    drawlins1-Visitor
                    1-Visitor
                    March 16, 2017

                    Just a note from another beginner trying to learn.  I find that frequently I'll have a sketch started and change one dimension thereby making it strong.  Often this completely throws my sketch unrecognizable so bad I'll start over.  If I make the first line and then lock the dimension to the correct value then I can sketch the rest or at least part of the rest so it looks about correct.  After it looks about right then go back and either insert dimensions where I need them or modify the existing weak ones making them strong.  Maybe not the correct way but it seems effective for me.

                    T
                    TomD.inPDX17-Peridot
                    17-Peridot
                    March 16, 2017

                    Know that sneaking up on sketches is not a crime.  A lot of times I have to go through several iterations on a dimension to get to the scale I want.  Over time, you will develop techniques to make this easier.  one tip I use is to draw a 1/2" circle... or 10mm, whatever.  Let it zoom to that scale and then start the sketch.  That way I am already sketching to a relevant scale.

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