Reference Viewer

[Beau1998]

Hello;

I'm new into Creo. I have created an assembly structure and some parts with geometry reference(project) from other parts. In Reference viewer it shows the root assembly as a children for the parts which have reference, Why? see attached image/

Can I set the creo options to not to have this logic?

Thanks.

BR.

[StephenW]

You have to be careful what you use for references when you work with parts in an assembly. 

There is an option to eliminate or warn when you are making references to other parts/assemblies.

In the config under file - options configuration editor, set

default_ext_ref_scope and change the setting to NONE

[Beau1998]

Thanks @StephenW

Why I should be careful about using these references? what is long or short term issues?

[dgschaefer · Accepted solution]

The parent assy defines the relationship between your source part and the target. That's why it's in the reference chain.  Without it Creo wouldn't know where to put the geometry from the source in the target.

The way to avoid this is to use an external copy geometry feature to copy directly from one part to another by aligning coordinate systems instead of using an assy.

A more robust way is to use skeleton driven top down design techniques. The skeleton defines shared geometry and that geometry is passed down by copy geometry (still creates an assy reference) or external copy geometry (no assy reference) to the parts.

[Beau1998]

@dgschaefer

Thanks so much.

Does this Skeleton method solve the issue of external references?

Where can I find some of these practices about skeleton driven methodology? Any book or reference guide?

Generally speaking, is it practical to use references from other parts (without defining skeleton env) in complex products?

BR.

[StephenW]

If you don't have some plan to control your references, your assemblies (and parts) will quickly become unmanage-able.
I don't use skeletons. I design my parts/sub-assemblies initially using references as I work through the design process. It makes making design changes along the way easier. Then as I am finalizing my design/project/drawings, I break all the external references as I go. In the end, all my parts and assemblies end up as stand-alone components that can be re-used in other assemblies as needed. This is the nature of my product and it works well. Part / assembly reuse is key to my process so it is important to me to end up with clean structures that don't have external references.
These other guys will have to elaborate on skeleton usage.

[Amanda_Conger]

Hi Stephen,

Can you elaborate on how you break the references after you create them? What you are describing is how I am used to modeling but I am having trouble finding how to break the references after the fact.

Thanks!

Amanda

[StephenW]

It's a very manual process. At some point when I am comfortable my design is not changing (much) anymore, I usually open up the parts individually and edit the features that have external references. I make reference to either existing part references or the default datums. It's also when I start thinking about how the parts are going to be detailed and I usually get my dimensioning scheme worked out since I typically try to show dimensions.

We also use modelcheck, so that helps me find external references. 

[dgschaefer]

Skeleton driven top down design is a robust way to manage and control those external references.  It's a very powerful tool that I make use of extensively.  It allows you to essentially built your design intent in the skeleton and pass it down to the parts in the assy.

If you have a support account you have access to the PTC Knowledge Base.  There's an old exercise on top down design with a skeleton that is based around an office chair.  It's old, but it has been updated several times, and it does a very nice job of illustrating the basic concepts.  My current company does not have a current maintenance contract so I can't search and find a link for you, but it shouldn't be hard to find.  I did find a PDF version here.  There are other tutorials out there, some good, some not so good.

I should mention that the use of skeleton models requires an Advanced Assembly Extension license. 

The technique of tying parts together in an assy is similar to a Solidworks technique they promote called 'in context edits" where they simply design in the context of an assembly and reference one part to another.  Frankly, I think it creates a mess in SW and it creates a bigger mess in Creo.  You can easily create circular references and a mess of parts referencing each other.  Skeletons don't prevent this, but they promote a more thoughtful process and reference management. 

When Creo regenerates an assy, it starts at the top of the tree.  It regenerates the first part and then places it, it then regenerates the second part and places it, and so on.  If part #1 has features tied to part #2, it can't regenerate part #1 until it's been placed and part #2 has been placed and regenerated, but the order says part #1 has to be regenerated before it's placed which it can't do because of the external references.  Build enough of this and you have a real mess where the assy can never be completely regenerated.

@StephenW makes a good point about part reuse.  My work is primarily in dedicated assemblies of parts not  reused often in other contexts.  So tying them to the assy's skeleton isn't a big deal.  If you are designing parts that will need to be reused, you don't really want them tied as children of the first assy they were used in and the other components in there.  The need to stand alone.

There are strategies that can be used to implement top down design in situations like that, but they require deliberate thought and planning.  Frankly, Creo will generally reward you for planning your reference selection at every step of the way, not just in top down design.  If you are intentional about tying things together that need to be tied together and avoiding unnecessary parent child relationships, you'll be rewarded with very robust parts and assemblies.

[Beau1998]

@dgschaefer @StephenW

Thanks for your explanations. 😘

BR.