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Parametric Related - Adding Equations.

robert_melascagliarobert_melascaglia Member Posts: 31

Lets say I placed a rectangle in a sketch, and dimensioned the short-side (w) ; could I then use an expression such as h=1.5w as the long-side?



  • Jake_RosenfeldJake_Rosenfeld Moderator, Onshape Employees, Developers Posts: 1,279

    Variables are set using the Variable feature in the Part Studio. If you create a Variable feature before the Sketch feature, you can define w as whatever length you want, and then use "#w" as width and "1.5 * #w" as the length.

    Jake Rosenfeld - Modeling Team
  • robert_melascagliarobert_melascaglia Member Posts: 31
    Thank you Jake - I will investigate; although I was sure Onshape had that covered.
  • mahirmahir Member, Developers Posts: 850 ✭✭✭✭
    The Measure Value FS is handy for things like this if you don't want to create the variable ahead of time, or your relation is based on a measurement that is not directly dimensioned.
  • robert_melascagliarobert_melascaglia Member Posts: 31
    The Measure Value FS - I will give that a try also, thanks.
  • robert_melascagliarobert_melascaglia Member Posts: 31
    Hello All

    I have another question with a graphic pertaining to "equation constraints."

    1.  I have two "construction lines (in red)" at angle "alpha (in green)."
    2.  I would like the line G-F (in blue" to be one-half the angle "alpha."

    How do I constrain the line G-F so it will always behalf as mentioned in 1 and 2 above.  Thanks for your time - Robert.

  • owen_sparksowen_sparks Member, Developers Posts: 2,225 PRO
    Hi. I'd use a variable, defined above your sketch in the feature tree, and then drive those angles in the sketch using the dimension tool.

    Cheers, Owen S.
    Production Engineer
    HWM-Water Ltd
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 2,087
    @robert_melascaglia you could also draw a construction arc (shown as a in your diagram), constrain a point to the midpoint of the arc then constrain the line to the point. 
    Neil Cooke, Director of Technical Marketing, Onshape Inc.
  • robert_melascagliarobert_melascaglia Member Posts: 31
    Neil, nice solution; I'll let you know how that goes, thanks.
  • mahirmahir Member, Developers Posts: 850 ✭✭✭✭
    Similar to @NeilCooke’s solution, you can use sector lines along with an equal constraint between them all. This would let you make one angle be any fraction of another angle. Although, I would opt for using Measure Value and a variable if it got any more complication than 1/4. 
  • robert_melascagliarobert_melascaglia Member Posts: 31
    Neil - your the man.

    The line-angle made a "mad dash" for that mid-arc point; thanks.
  • robert_melascagliarobert_melascaglia Member Posts: 31
    mahir said:
    "Similar to @NeilCooke’s solution, you can use sector lines along with an equal constraint between them all."

    How would I construct the "sector lines", and constrained them how?  I tried to work that out but somewhat confused, thanks for your assistance - Robert.

  • mahirmahir Member, Developers Posts: 850 ✭✭✭✭
    Here’s an example where the right side angle is constrained to be half of the left angle. Mind you, I would use @NeilCooke’s method for something as simple as getting half an angle. But sectors are handy for more complicated fractions. 

  • robert_melascagliarobert_melascaglia Member Posts: 31
    Okay, I see; that is also interesting and I will try, thanks.
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