why this happens?
i tried this to all extents and did not get it to fail… mostly this happens when your curves have issues. how did you produce this half cylinder? can you post the file including the curves?
with two curves
i find out what my problem is , i first fillet the corner of cylinder and after that fillet the top part
the problem is the fillet distance i should have use a small number for fillet distance
Filleting in Rhino is not robust and must be (often) fixed by hand
Or round in different order (here rounded with changed handle size on vertical edges)
i agree, but on this simple example i could not get it to fail even i tried hard
All edges sharply (unfilleted)
First fillet only vertical edges (Picture one)
Second fillet top edge (Picture one)
In two steps, this not work here
But works here with one step (different fillet size trough handle no problem) (picture two)
filleting over an existing fillet is an absolute no go if you have the chance to do it all at once.