Boundary blends dependent on boundary blends? Can I lock some in place and make them independent?

[StevetS]

This weekend I was tasked with modifying a piece made almost entirely of boundary blends. Typically this wouldn't be an issue and an easy fix but this time the BB's are dependent on other BB's. My model tree is almost entirely BB's. I don't have a lot of experience with these as I'm usually designing with solids. The biggest problem here is that the surfaces that need changing are smack dab in the middle of the model tree. They are not grouped together either, for example Boundary Blend 8, 9, 13, 15, and 27 need to be changed. Is it possible to lock these BB's in place or somehow reference them to other geometry without the entire model failing?

[StevetS]

I've given up and started modeling a new piece with less dependent boundary blends.. I just tried for 4 hours to work on that and every single thing I tried resulted in more than half the model failing due to association issues.

[dschenken]

Sometimes models end up precarious.

It reminds me that one tool that is not available to Creo modelers is something used in other software development environments, fuzzing. This puts alternate values into the model to see if it is robust against changes. Alterations to dimension and other parameter values and to accuracy would discover areas that are more sensitive than expected.

I've had models that, were they buildings, could be brought down by a snowflake landing on a windowsill.

[StevetS]

That's exactly what I felt like with this one. My boss reassured me that modifying it should be no problem. After exhausting every thing I could possibly think with Creo I had to take the route of recreating the whole thing with the modifications I needed. I'm not sure it's actually possible to modify something where several changes needed to be made.. Modifying a sketch on a plane that already exists in the model is one thing, but this was modifying actual large chunks of the model.

[dschenken]

It is possible to make very significant changes, but it depends on how the part is made. What I've found is that models that are built by users making 'convenient' selections for references rather than looking at what function they want the references to serve are the ones that fail.

#1 cause - picking or allowing Creo to pick unsuitable sketch orientation references such that when an early part of the model changes the orientations in later features change in ways that cause the referencing sketches fail. If some thought is put into the orientation, the models are resilient.