SolidWorks 2011 Assemblies Bible - Matt Lombard [79]
Using 3D sketch lines in each X, Y, and Z direction may be clever, but it may be a better idea to have X, Y, and Z direction axes already saved in your assembly templates for just such a purpose.
In most situations, the rebuild time penalty of using model geometry to establish pattern direction is slight. The sketch method is probably most justifiable in large, complex assemblies, or in assemblies requiring long rebuild times. Figure 9.1 also shows the PropertyManager interface for the local pattern.
FIGURE 9.1
The Assembly FeatureManager for local component pattern setup
Notice where the pattern is placed in the FeatureManager. You can reorder the pattern feature in the design tree, but you cannot move it above the mates. Interestingly, you can move the sketches after the pattern, even though the pattern is dependent on one of the sketches. Obviously, SolidWorks is working with the order behind the scenes in such a way that the user cannot make mistakes.
Patterning the seed only
All the aspects of the interface should be familiar to you, such as the direction, instances, and spacing. The Pattern seed only option is used in feature patterns.
This option is designed to allow you to create a single pattern in two directions that are separated by 180 degrees, where the internal instances do not overlap one another. For example, if you take a basic two-directional pattern and change the angle between the directions so that they are anti-parallel (parallel but going in opposite directions), then all the component instances that were between the two legs of the L created by the two directions will come to overlap one another when they are laid out in a straight line.
Figure 9.2 shows how a 5-by-4 pattern with 20 instances becomes a 1-by-8 pattern (the seed is not counted twice). To be clear, the figure shows a two-direction pattern where the angle between the directions becomes increasingly shallow, until the two directions are parallel or anti-parallel. When this happens, the other 12 instances overlap the remaining ones. When you use the Pattern seed only option, you are only patterning the two legs of the L, and not the instances in between. Having parts that overlap can cause problems with Bills of Materials (BOMs) and mass properties due to having duplicate parts.
FIGURE 9.2
Use the Pattern seed only option for two-directional patterns.
Using the Instances to Skip option
The Instances to Skip option for component patterns, shown in Figure 9.3, works just like the equivalent option for features. Click the dots in the graphics window to toggle each instance of the pattern. On the screen, the instances to keep use pink dots and the instances to skip use orange dots. The colors are almost indistinguishable at a relatively wide spacing.
FIGURE 9.3
The Instances to Skip option
Performance
For best pattern performance, you should use subassemblies as the patterned unit as much as is practical. Multiple patterns of individual components are not as efficient as a single pattern of multiple components. A single pattern of a single component, where the single component is itself a subassembly, is the best choice, if available.
Another performance issue is the fact that component patterns require external references (for the direction or center of the pattern). These external references have the potential to increase rebuild times if you do not choose them carefully. Reference geometry internal to the assembly would be the best choice.
Although you may experience performance problems with patterns, they can also significantly decrease the number of mates in an assembly, which always improves performance.
Using Mirror Components
Mirror Components leaves a feature in the assembly tree just as pattern features do. It gives you the option to align each mirrored part, and to decide which parts require