Parts can be created and built from within the assembly. These parts can also be inserted into the assembly as new parts and built using converted edges, offset edges and standard techniques. They are called Virtual or In-context parts. In-context modeling can be a great time-saver in the design phase of most projects. By using in-context features, you will be required to do much less work when changing dimensions of individual parts and features as the in-context relationships carry the changes through the in-context features in a predictable way. Generally accepted best practice is to remove in-context references before parts are released to manufacturing to avoid unintended changes from occurring; however, the point at which this occurs is not absolute. In some industries, in-context relationships may be left intact and locked if the customer is known to require changes after manufacturing has begun. When building parts in context, you can take advantage of other parts that exist. You can copy geometry, offset from it, add sketch relations to it, or simply measure to it.
While there are many advantages to using in-context features in your models, they can cause slower performance when solving the model and can create confusion for people working on the model later in the process. Additionally, creating in-context parts in an assembly can cause the part origin to be someplace other than the most desirable location.
Note: One of the things to consider before deciding to model a part in the context of an assembly is where that part will be used. In-context features and parts are best used for “one-of-a-kind” parts that will be used only in the assembly where they are modeled. Parts that will be used in more than one assembly should probably not be modeled in context. The reason for this is that the external references created by the in-context features are stored in and controlled by the assembly in which the references were established.
If a virtual or in-context part is to be reused in other assemblies, it is possible, with some work, to make a copy of the part and remove all of the external references. The part can also be created by purposely borrowing geometry but with no external references created.
In-Context Modeling and Performance
How do in-context features affect performance? With in-context features, the relationship between the current feature and the entity it is referencing is maintained at the assembly level. This is required because the relationships depend on the positions of the parts which are controlled by mates. In the assembly, we see these relationships as Update Holders. Therefore, in-context features create additional work when the assembly is solved. While one or two properly constructed in-context relationships may not make a noticeable difference in assembly rebuild speed, the more you have, the greater the slowdown could be. So, in addition to the other reasons for removing in-context relationships, we must consider the performance of the assembly.