WHy does rib fail to generate when one end is the edge of a curve

andrew_carnall

I have tried to create a rib and if the end is coincident with the edge of a curve it fails to generate, and I would like to understand why.  In the linked document I don't get why the rib through a sketch and extrusion works and the rib feature doesn't.

Any pointers?

https://cad.onshape.com/documents/1c3d44bf23c6372e72be8e42/w/f39f358e7c77dff1a16fc39e/e/e878ee492c01817c8bed6ec1

bruce_williams

with the rib sketch coincident, the edges of rib would extend above the part so it fails. by moving the sketch down as shown below, the two edges of the rib intersect the main part.  With your extruded rib you fixed the condition by 'clipping the rib to below the top.   You could add extra height to the main part and then trim after creating ribs.

andrew_carnall

Thanks for the answer, as far as it goes that makes sense - but if the rib sketch extends past the curved face it simply extrudes a rectangle down it simply extrudes a rectangle to the top face - and it can cope with this rib crossing onto the curves face:


or if the rib profile ends in line with the corner  it again extrudes a rectangular profile to the main part (construction line is perpendicular to the rib profile and co-incident with the corner of the part):


It only fails if the rib profile line is co-incident.

I can see the logic for why it fails, I just don't see why the original design couldn't be generated as the extreme case of the either of those results?