Understanding in-context references and assembly features

The ability to model features in the context of the assembly using sketch/feature references and by using the assembly features is a powerful and effective capability.

What are in-context references?

• External and defined-in-context references are SolidWorks features that allow you to reuse existing geometry to insure parts fit together during the entire product life cycle.
  
• An external" reference is created when a sketch entity is related to something external to the sketch. Dimensioning to existing geometry or offsetting an edge within the active file will create an external reference.
  
• An external reference is also created by assembly features.
  
• A defined-in context reference refers to the creation of an external reference in the context of an assembly. This is done by using the Edit Part function while in the assembly.

Figure 1 shows an example of an in-context design. The black gasket for this part was created offset to the outside profile +.03 inches in-context to the design. This means if the parent part changes, the gasket profile will update automatically.

Figure 1 – Example in-context references

So why not use in-context references all the time? The disadvantages to using in-context references include:

• Performance. When opening the gasket example, the parent part will be accessed to drive the in-context references.
  
• Availability of reference files . There is backup data stored in the child part if the parent is not found.
  
• Who's on first. When creating an in-context reference, make sure you know what you are creating and why. You could accidentally create a circular reference.
  
• Order can be important.

You should consider using in-context references when:

• Features will change
  
• Parts and sub-assemblies are not used in many other assemblies products (change management)
  
• Using multiple sub-assemblies with different contexts in the same top-level assembly

To create an in-context reference, open the assembly with the desired part. Select the part, right click and select Edit Part . The rest of the assembly components will show as transparent as shown in Figure 2. This allows for the assembly components to be referenced to create part features. The example shown in Figure 2 is the offset to the outside profile.

Figure 2 – Gasket offset being added in-context

When a in-context feature is created, there is a visual clue left in the FeatureManager design tree. Features that have a “->” after the feature or component name contain an in-context feature. An example is the Base component shown in Figure 3.

The assembly also contains the update holders within the upper level assembly. These are shown in Figure 3 at the end of the FeatureManager design tree. The update holders are the last item evaluated when rebuilding an assembly. These features are also rebuilt in the order shown.

Figure 3 – Example FeatureManager design tree with an in-context feature and update holders

When working with a design, you may not want to carry the external references once the part goes into product because you may not want references updating automatically when a design is released.

To list the external references, open the part, right click the in-context feature and select List External References . The dialog box as shown in Figure 4 will display. You can break, lock, or unlock all selected external references.

Figure 4 – External References dialog box

Instead of breaking external references, just lock them. This will have the same effect as breaking the reference, but allows for the references to be unlocked later if there is a design change or new version of the design.

A good example of how to use the API (macro) is a macro that will lock/unlock all references within a design. So you can just run the macro and either lock or unlock all external references within an assembly. Click here to download the macro.

Figure 5 – External References dialog box

Leaving the breadcrumbs

When creating in-context references, it is a good idea to document what you did and why. This way others using the design can readily understand what has been done and how they can work with the design. There are two ways to document this design intent:

1. Design Binder
2. FeatureManager design tree comments

Figure 6 – FeatureManager design tree comments

Conclusion

In-context references are a powerful feature that can make your designs more effective. Key features of in-context references:

• Know how to apply in-context and assembly features
  
• Document when you use these features
  
• Keep it simple
  
• Think about the order

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