How to do this in Rhino? This is in Sketchup.
Why not use the same
WireCut method as the one Mitch posted here?
Well, don’t expect Rhino’s solid manipulation tools to work exactly like Sketchup’s. They don’t.
In this case, I would use SplitFace to split the face, then you can Use ExtrudeSurface from the Solid menu, setting DeleteInput=Yes and extrude the split face downward (you could also extrude it upward). This method could also work for the first example in your other post. quick vid
What is it that doesn’t work?
WireCut 1: defined line
Cutting depth 1 and 2
Finished WireCut 1
WireCut 2: cutting depth 1 and 2
Rhino 5 for SketchUp Users: