SolidWorks 2011 Assemblies Bible - Matt Lombard [30]
Understanding link values and global variables
Link values and global variables also work in assemblies, but they do not work between parts. Local assembly sketches can use these functions, and the parts can use them when edited in the context of the assembly, but they cannot cross any document barriers (links must remain within a single document).
Renaming
Equations update with new part names regardless of how you rename the parts. Names of subassemblies also update when you rename assembly files. This includes renaming a document using the Save As command, using SolidWorks Explorer, or using Windows Explorer. It also includes redirecting the assembly to the new part name, as well as renaming the assembly using each of these techniques. If the assembly can find the part and recognizes the part as the one that it is looking for, then the equation will work.
Some of the methods named previously for renaming parts are not recommended. SolidWorks Explorer and the Save As methods can be effective when used properly. References between files are a different issue altogether from an equation's references to local filenames.
Recommendations
While assembly equations are certainly a valid way to control part sizes, you should use assembly or part configurations, possibly with design tables, to accomplish something similar. Equations and configurations do not mix well because the two methods conflict over which one controls the dimensions. Configurations with design tables are recommended over equations.
Cross-Reference
Assembly configurations and design tables are discussed in Chapter 8.
Caution
You may have unexpected results if a single dimension is controlled from more than one location. For example, if you have a part-level equation and an assembly-level equation, then one of the equations will be automatically set to Read Only and will not be used.
Using an assembly layout sketch
SolidWorks has an assembly feature called Layout that uses a 3D sketch to lay out the major functions of an assembly, and even details of parts. The word layout also refers to a technique using 2D sketches in an assembly to do exactly the same thing. The distinction between the technique and the formal assembly feature is bound to be confusing. The Layout feature only works in assemblies, but layout techniques have been used in parts as well as assemblies for many years. This chapter describes the technique, and the Layout feature is discussed in Chapter 6.
When you look at the two functionalities, the feature is definitely intended to be used as an in-context tool, while you can more easily use the technique as a reference for controlling part position (through mating) rather than as a way to directly control the sizes and shapes of the parts. So when you see a reference to a Layout (capital), this refers to the formal feature. When you see a reference to a layout or layout sketch (lowercase), this refers to a technique where a sketch is used at the assembly level to control the assembly in some way.
Cross-Reference
The Layout feature is described in more detail in Chapter 6, while the technique using assembly sketches to lay out an assembly is described in this chapter. The material in this chapter is written as if the Layout feature does not exist, mainly to give you a straightforward view of how the technique works without worrying about two different functions at the same time.
The layout sketch is a very useful tool for laying out a mechanism in an assembly or even details on parts within the assembly. Sketches in the assembly have the same characteristics as they do in the part environment. In Figure 4.3, the assembly layout sketch is indicated with a heavy, dashed line for emphasis.
FIGURE 4.3
An assembly layout sketch controls the geometry of the frame and the overall bicycle assembly.
When combined with in-context techniques, assembly layout sketches can help to determine the shape of parts, or the location, size, or shape of features within the parts. You can also use layout sketches to