SolidWorks 2011 Assemblies Bible - Matt Lombard [83]
In-context modeling is also known as top-down or in-place modeling. It is a technique used to create relationships between parts in the context of an assembly in which the geometry of one of the parts is controlled by both the other part and the mates that position them relative to one another.
In-context, or top-down, modeling may be contrasted against bottom-up modeling. Bottom-up modeling involves making the parts in their own individual windows and assembling the finished parts into an assembly with mates.
In its most common form, a sketch in one part in an assembly is related to an edge in another part in the assembly. The relationship is specific to that particular assembly, and is only relevant in the context of that assembly. For example, you may create a box and put it into an assembly. You must then create a lid that is parametrically linked to the size and shape of the box. You can create a lid part in the context of the assembly such that the lid always matches the box. Sketch relationships, dimensions, and feature end conditions from the lid can reference the box. When the box changes, the lid also changes if the assembly is open.
The assembly maintains a record of each in-context reference. If the box is changed with both the assembly and the top open, then the top updates, but if the box is changed without the assembly being open, then the lid will not update until the assembly is opened. The record of the reference that the assembly maintains is held in what is called an Update Holder. In recent versions, the Update Holder is all but forgotten, and difficult to find. One Update Holder is created for every sketch or feature that contains references to other entities within that particular assembly. To show Update Holders, right-click the top-level assembly name in the FeatureManager, and select Show Update Holders.
Cross-Reference
Chapter 4 discusses in-context reference Update Holders. These pointers in the assembly hold the reference information. These holders are hidden by default and do not enable any real functionality, but they do serve as a reminder that the assembly has in-context references and can be queried to tell you what parts the in-context relations go between.
Working through a simple in-context example
Rather than discuss this topic theoretically, here is a simple set of demonstrations of in-context modeling situations. You can find the example files in the DVD folder for this chapter. You will revisit this example file throughout this chapter.
This example starts with a simple rectangular block. You have multiple options to get an in-context part into an assembly, but this example will just demonstrate one. The following steps are general, as you should already be familiar with the basics of assemblies and part modeling.
Starting a new assembly
Open a new assembly, using the template of your choice. When modeling in-context, it is especially important that the parts and the assembly use the same units. If the assembly units are different from the part units, and you edit the part in the context of the assembly, then you may be presented with one type of unit while editing the part in the assembly and another type of unit while editing the part in its own window. This difference is probably not important for library parts, but for actual design parts, it is most convenient if the units match.
The next step is to save the assembly. If you do not save the assembly before adding a new part to it, SolidWorks does not force you to save it before adding the part, but it is a good idea to save the assembly (and any file, actually) after creating it.
Inserting a new part
To insert a new part in the new assembly, choose Insert⇒Component⇒New Part and select the toolbar icon for New Part (under the Insert Component flyout toolbar).
Note
The above icon is slightly different from what most users will see as the toolbar icon for New Part. This is because from time to time, SolidWorks allows slight differences between the appearances of large and small icons. If you