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Fully defining a spline

john_dzielskijohn_dzielski Member Posts: 2
I am new to using OnShape.  This is basically my first project that doesn't involve training material.  The image below shows a simple spline.  I don't know how to fully constrain it.  I found some discussions on splines in the support involving people trying to fit splines to known shapes.  The spline below involves three points.  I think the locations of the end-points are constrained, and they are also constrained to be vertical and horizontal at the endpoints.

1)  What do I need to do to constrain this sketch?
2)  How does that answer change if I add points?
3)  The inner curve is an offset.  I added lines at the two ends, but they were not constrained to be equal to the offset.  Why?
4)  I used construction lines to define verticals and horizontals.  The line and the construction line at the upper-right are co-linear.  How do I select the line?  It seems to be hidden by the construction line.

Thanks, John.



  • John_P_DesiletsJohn_P_Desilets Onshape Employees, csevp Posts: 202
    Hello @john_dzielski

    Is it possible to share your example with us? It will be easier for us to see the constraints that you have applied. 

    A spline needs several constraints and dimensions to define the curve. The handles that adjust the magnitude (one at each end) need to be dimensioned as well. I did not see any dimensions on the handles in your example. 

    In addition, you can dimension the spline length by simply clicking the dimension tool and selecting the spline. 

    The offset will not be constrained until the original spline is fully defined. 

    If a sketched entity is overlapping another sketch entity, right click in the area and choose other. A filter will appear allowing you to select one entity or the other.

    If you navigate to the learning center we have an entire section on curves for Onshape. Here is a link to the Understanding Curves Course. 

    Here are a few examples of fully defined splines. Hope this helps and good luck! 

    Spline length defined

    Offset spline

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