Extrude to opCreateBSplineSurface is not robust

brandon_furtwangler

I have a feature that adds a opCreateBSplineSurface, and then in various places I need to extrude up to this surface.  My extruded sketch is always within the XY bounds of the surface, and I'm extruding from below the whole surface up to the the surface, so this operation should never fail.

In practice, I have ~300 different unique configurations of my part & about half of them fail to extrude for unknown reasons.

For example, this configuration works just fine:


While this slight variation on the top surface shape causes the extrude to fail:



There seems to be little rhyme or reason to it - it just appears that intersections with opCreateBSplineSurface are buggy.

Here's the document.  I'm in the Talon Caps part studio & this is with the 'Homing' configuration enabled.  Feel free to use the various configuration settings as test cases for a more robust implementation.

https://cad.onshape.com/documents/0834293e74af4c6a396f8eab/w/f486ecb436e3b08b4a3a7007/e/eba3ef0267cc4c6c5161806e?configuration=List_NyThPuBqySRLMD=homing;List_f6j0re8WqI0TiW=Default;List_hn0GuVRdS6CNqY=Copy_of_edge;List_tfUVaJqjqApmxI=u1

Alex_Kempen

So, this seems more like an issue with opExtrude rather than opCreateBSplineSurface specifically. Up to next is actually handled entirely in the back end by the extrude feature (i.e. opExtrude accepts UP_TO_NEXT as a bounding type), which is different from how some of the other UP_TO options are handled (like UP_TO_FACE, which tries to make a plane on the central mate connector of the selected face). As a workaround, you could take a leaf out of the Onshape Rib Feature's playbook and make your extrude through all, split the extrude with your surface, then delete the excess. It's somewhat inefficient (which is probably why the extrude feature doesn't use it), but it should be more robust for more types of surfaces.