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Offset Issue

eric_borden595eric_borden595 Member Posts: 19
I have been working on this drawing: https://cad.onshape.com/documents/254de3cb7943e51f789a4ebb/w/bcf9f589e3aaece018525e29/e/6793e296358d8401df5d22f1
Please don't judge my drafting capabilities as I fully admit, I don't have any!
I'm trying to "Offset" the edges of my drawing but I'm having issues with red lines showing up once the Offest is created.  I understand due to curvature, one can't easily offset the entire edge of the drawing so I did split it before I tried the Offset.  If you look at my 2d sketch, I have created "pieces".  If you look at the piece labled with "2" at the bottom left you will see the red line result I'm talking about.  I have looked for what this red line means but can't find an answer. 
If I try Offset on sections of the "mouth" and "eyes" I don't get red lines and it seems to work well.  What did I do wrong with the outline of the tree that is keeping me from using Offset on even the smaller less curved segments?

Thank you.

Best Answer

  • Ste_WilsonSte_Wilson Member Posts: 74 EDU
    Accepted Answer
    If you're getting 'red' lines that means something is over-constrained, for example, you have said line a is equal to line b AND you have dimensions on both lines.  The dimension on line b is not needed.  Christmas tree looks good :)

Answers

  • Ste_WilsonSte_Wilson Member Posts: 74 EDU
    Accepted Answer
    If you're getting 'red' lines that means something is over-constrained, for example, you have said line a is equal to line b AND you have dimensions on both lines.  The dimension on line b is not needed.  Christmas tree looks good :)
  • eric_borden595eric_borden595 Member Posts: 19
    Thank you for the help!
  • eric_borden595eric_borden595 Member Posts: 19
    You answered my question and it made perfect sense. However, I removed any and all consraints from the section I split out of the spline and tried to offset and still got the red line.  I get no warnings when I do the offset. Just the red line result.
    I thought, hey, lets copy the split segment and paste it back in and try to offest that.  Interestingly, I got the segment I split and all the spline handles for the entire tree outline when pasted.  This makes me think the offset is failing because it is actually trying to offset the entire spline, not just the segment I split.
  • GlenDGlenD Member, OS Professional Posts: 231 PRO
    Unfortunately your link leads me back to this forum page instead of your document so I'm only guessing at what may be happening.
    There are some things that don't offset well such as my example using a spline. OS can't keep up with the math for this or is trying to loop back on it's self.
    Sketch 1 works ok but sketch 2 gives this message.

  • eric_borden595eric_borden595 Member Posts: 19
    I think I figured it out.  I have way too many spline handles.  If I use less of them, I can get the offset to work...at least thus far.
  • matthew_stacymatthew_stacy Member Posts: 234 PRO
    @eric_borden595, also be aware that there is a limit to how far you can offset to the inside of a curve or vertex.  I don't know if this is related to the issue you encountered but the wheels may fall-off-the-bus when the offset goes beyond any local center of curvature.



    And you are on the right track with reducing the number of spline points.  That is generally good practice for sketching curves anyway.  Extra spline points inevitably result in unintended inflection points that will result in ugly surfaces when extruding, lofting, or filling.  The curvature comb tool is particularly useful for visualizing curve continuity.  Think of the old boat-builders' trick of using a batten to lay out fair curves.  This next screenshot shows the curvature discontinuities that can result from using too many spline points.


  • eric_borden595eric_borden595 Member Posts: 19
    Thank you for the feedback.  I believe it was the number of spline points.  I have things going nicely now.
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