SolidWorks 2011 Parts Bible - Matt Lombard [135]
Debunking more sketch myths
People often say that it is best practice to define your sketches fully. I completely agree with this statement. However, I have heard people go to the extent to say that fully defined sketches solve faster, with the rationale being that SolidWorks has to figure out how to solve the under-defined sketch, but the fully defined sketch is already spelled out. Let's find out.
In this example, I created a sketch pattern of 4 × 4 rectangles and used the Fully Define Sketch tool to add dimensions. Then I copied and pasted the sketch and removed all the dimensions and relations. Figure 9.2 shows the Feature Statistic results.
It is safe to say that fully defined sketches are best practice, but it is not due to rebuild speed. Sketch relations are costly from a rebuild time point of view. Patterning sketch relations are even more costly. The rebuild time does not even come close to the time that it takes the Fully Define Sketch tool to create all the dimensions and relations in the first place. This combination of geometry, software, and hardware took about 30 seconds of CPU time to add the relations and dimensions.
FIGURE 9.2
Comparing rebuild times of a fully defined sketch to a completely undefined sketch
For most models that have fewer than 50 features, you may never notice this rebuild time, and the price you pay is certainly worth the peace of mind you get from having the stability of a fully defined sketch. For large models where you have hundreds of features, or features that use a lot of very busy sketches, you should pay attention to how much information you put into the sketch, and try to limit sketch patterns and even elements such as sketch fillets, using feature fillets instead where possible.
Patterning a sketch
I used the first part of this chapter to debunk some SolidWorks myths about sketches and sketch patterns. In this section, I will discuss how to use sketch patterns. Sketch patterns are an available tool, they are valid, and in a few cases, they are truly necessary.
It is best to pre-select the sketch entities that you want to pattern before using the Sketch Pattern tool. If you do not pre-select, then after the PropertyManager is open, you can only select entities to pattern one by one, because the window select is not available for this function. The right mouse button selection options, such as Select Chain, are also not available in this interface, reinforcing the need to treat sketch patterns as a pre-selection feature.
Tip
When creating a linear sketch pattern, be sure to select the Add Spacing Dimension check boxes. If these dimensions are not added, then editing the pattern becomes more difficult.
Using the Linear Sketch Pattern
The Linear Pattern PropertyManager is shown in Figure 9.3.
Unlike other PropertyManagers, the selected entities for the sketch pattern functions are found at the bottom of the PropertyManager instead of at the top. This is a little confusing. Sketch tool PropertyManagers, such as Convert Entities and Mirror, place the selection box at the top.
The Direction 1 panel works predictably by establishing the direction and spacing, and then the number. The Angle setting enables you to specify a direction that does not rely on anything outside of the sketch.
FIGURE 9.3
The Linear Pattern PropertyManager
The Direction 2 panel works a little differently. You must first specify how many instances you want, and then the other information becomes available. The spacing is grayed out until you tell it you want more than one instance in Direction 2.
Using the Circular Sketch Pattern
The Circular Sketch Pattern defaults to the sketch Origin as the center of the pattern. You can move and position this point using the numbers in the PropertyManager, but you cannot dimension it until after the pattern is created. Again, this is another feature where you need to pre-select because window selection is not available (patterned sketch entities must be selected one by one to go into the Entities to Pattern panel).