Projected curves? What is the difference?

tom_auger

I'm having trouble understanding the constraints or requirements for projected curves to work properly (for the 100th time wishing Onshape's error messages were more helpful/explicit)

Here's a great example of a very simple test. Some of the edges combine perfectly as expected, some generate errors. I don't understand what's different about the two splines that cause one to work and the other to error. Can you see what I'm missing?



https://cad.onshape.com/documents/bd9cb26ea5f34944a8fc0f75/w/e88af0fbf308d8ef9dfe1e19/e/59bdf8f433ce9e7a24d01c4f

John_P_Desilets

Hello @tom_auger

After taking a closer look at your document, it looks like one of the splines is not defined properly. 

A projected curve is essentially the intersection of two surfaces. As a test, I extruded the sketches as surfaces to take a closer look at the intersection. 


The spline passes in and out of the other profile. Causing the projection to fail. 




Spline handle before.                                                                                                                      Spline handle after being vertically constrained.



Once the spline handle is defined with the vertical constraint, the projected curve is fixed. Hope this helps and good luck!

John_P_Desilets

Hello @tom_auger

After taking a closer look at your document, it looks like one of the splines is not defined properly. 

A projected curve is essentially the intersection of two surfaces. As a test, I extruded the sketches as surfaces to take a closer look at the intersection. 


The spline passes in and out of the other profile. Causing the projection to fail. 




Spline handle before.                                                                                                                      Spline handle after being vertically constrained.



Once the spline handle is defined with the vertical constraint, the projected curve is fixed. Hope this helps and good luck!

tom_auger

@John_P_Desilets you nailed it. Thank you! If the OnShape Gods are listening, a more meaningful / contextual error message would have been really helpful here.