As I have mentioned before when pulling on faces using direct editing, the system needs to extend or shrink the adjacent faces, but should also properly take into account rounds, fillets and chamfers. This gets much more complex if the adjacent faces happen to be complex freeform b-spline surfaces. How well will the system extend or trim the surfaces? Can you get predictable and consistent results?
For this article I also created a simple video to show the example. I start with a simple cube and then using direct editing capabilities to deform several of the planar faces. If you are trying this on other CAD systems you may have to use other methods to get the complex surfaces, however it shouldn’t matter how you create the surfaces. Once you have them just add the rounds and chamfers to get the basic shape.
Hopefully the topology of your part matches the one in the picture. Pay close attention to how your CAD system creates the chamfers. Are they accurate? It’s a bit surprising how some modern CAD tools treat chamfers.
Now let’s try some direct editing.
Try this example on your favorite CAD tool. Can you get expected and predictable results? How well do the surfaces extend? Is chamfer and blend sizes maintained? Are tangencies maintained and accurate? Are the surfaces extended in a logical and predictable way? Are the chamfers and blends order dependent? Live rules and parametrics can help control change, but if you can’t get through the basics of change they add no value.
Even though I considerably increased complexity with this second example, besides adding blends and chamfers I still did not change the topology of the model. So perhaps sometime in the near future I can bring it all together, including complex topology changes, with a realistic part.