SolidWorks 2011 Assemblies Bible - Matt Lombard [32]
Assembly-level reference geometry can be created that references component geometry instead of layout sketches. This creates a dependency that changes the usual order. For example, the planes are usually solved before the part locations, but when the plane is dependent on the part location, the plane has to be solved after the part. If a part is then mated to the plane, you are beginning to create a dependency loop, such that the plane is solved, followed by the part, then the plane again because the part has moved; and then the mate that goes to the plane has to resolve the part.
Best Practice
If you are a bit confused by all of this, don't worry. You can simply follow this rule: do not mate to anything that comes after the mates in the assembly FeatureManager tree. This includes assembly planes or sketches that are dependent on part geometry, as well as assembly features such as cuts, in-context features, component pattern instances, Hole Series, or Smart Fasteners.
This is probably a lot of information if you are a new user, but if you remember this rule, you can avoid creating models with circular references, where A is dependent on B, which is dependent on A — a never-ending loop that causes major problems for large assembly rebuild times.
Understanding parts and subassemblies
Parts and subassemblies are shown with their familiar icons in the design tree. You can reorder and group them in folders (which is covered in the next section), and also edit the hierarchy of parts and subassemblies within an upper-level assembly.
The primary task of parts and assemblies is to help you organize your data. Information that relates to the geometry of a single manufacturable item is put into a part. Information that relates to the relationships between the parts is put into an assembly.
You may hear some people argue that there is no real need for parts and assemblies to have different file types — that a part file should be able to handle both the geometric data and the relations between items. You can find CAD programs that work like this, but they tend to be either older or less powerful.
Organizing the data into different file types is actually necessary because it helps your computer know when to calculate which data. For example, if your computer had to rebuild all the features in every part as well as all the mates, rebuild times would suffer greatly.
In addition, parts in an assembly are different from bodies within a part. If you have bodies within a part, all of your features are in one big list, rather than segmented into individual lists for each part. This is important for three reasons: rebuild times, troubleshooting errors, and reusing data. Part features that are in a big list with other part features cannot be organized or separated easily for other purposes.
The advantages of trying to build an assembly as a single part are unclear, other than simplifying file management. It would be highly impractical for any assembly with more than a few simple parts.
Parts are sometimes shown with a feather icon, which indicates a lightweight part, and assemblies can have an icon that indicates a flexible subassembly. Special icons also exist for hidden and suppressed components.
Indicates a lightweight part
Indicates a flexible subassembly
Indicates a hidden component
Indicates a suppressed component
Creating folders
You can create folders to organize and group both parts and mates. (This technique is discussed in detail later in this