See CF "Surface degree (IV6)".
I've put three sets of files in CF that demonstrate native IV modeling
failures, either failed operations or failure to export and read back into IV.
The failures are related to chamfering a swept tube (elbow), shelling a swept
tube (spline path) and splitting a torus. I don't know if I'm focusing on the
wrong characteristics or qualities, but each error could be corrected by using
imported surfaces of degree 4 or 5, whereas the IV generated surfaces were
degree 2 or 3. In particular the split torus required altering the default
surface seams in order to split the shape without error, but subsequent
operations (shelling and fillets) were helped by using degree 4 or 5 surfaces
instead of degree 2 created by revolving a circle (the finished shape could be
exported as .stp and read back into IV).
Have a good one.
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