SolidWorks 2011 Parts Bible - Matt Lombard [145]
Equations can cause problems if used incorrectly, but if you are familiar with how they work, you can avoid the common pitfalls and get maximum benefit by adding intelligence to your designs.
Understanding Equations
You can use equations to create mathematical relations between dimensions. You can find the Equations tool on the Tools toolbar or by choosing Tools⇒Equations from the menu. Equations are stored in a folder at the top of the FeatureManager. Figure 10.1 shows the Equations main interface along with the Add Equation window. As I have noted with other areas of the interface, Equations still uses a floating dialog box. SolidWorks has put most functions in the PropertyManager, but equations tend to be more horizontal than vertical, while the PropertyManager is more vertical than horizontal.
FIGURE 10.1
The Equations interface
Using the Equations interface, you can turn off individual equations temporarily by deselecting the Active check box to the left of the equation. Equations can also be deactivated by a design table. I will discuss design tables in more detail in Chapter 11, where I also discuss configurations.
Caution
Although I do not cover configurations until Chapter 11, I will mention part of the relationship between equations and configurations here. Equations and configurations (particularly those that are driven by a design table) should probably not be mixed. This is not because they do not work together, but is more for the sake of organization. Add to this the fact that starting in SolidWorks 2011, Global Variables are now configurable, and it certainly opens up new possibilities, but it also creates potential problems for users, as they can control dimensions from both configurations and equations. Also, equations in Excel are far more powerful than the comparatively limited equation functionality offered in SolidWorks. Of course, every user will have her own reasons for working one way or another; I am just offering a warning of a potential source of conflict.
Creating equations
Equations are easy to create and useful for many purposes. A common situation where you would use an equation is to space a pattern of holes evenly along an edge, including the gap on both ends, where the gap at the ends is half of the regular spacing. Before you write an equation, you need to take care of a few organizational details.
Naming dimensions
It is not necessary to name every entity in every SolidWorks document, but you should get in the habit of naming important features, sketches, and even dimensions. Named dimensions become particularly important when you use them in equations, configurations, and design tables. Under most circumstances, you do not use or even see dimension names, but with equations, you do.
Named dimensions make a huge difference when you want to recognize the function of an equation by simply reading it. A most obvious example would be the difference between D3@Sketch6 and Length@WindowExtrusionSketch. The first name means nothing, but the second one is descriptive if you are familiar with the part.
To name a dimension, click the dimension and go to the PropertyManager. In the Primary Value panel shown in Figure 10.2, type the new name for the dimension in the Name text box. You cannot use the symbol @ in dimension names because it is used as a delimiter between the name of the dimension and the feature or sketch to which it applies. Also, be aware that even though the software allows you to change the name of the sketch or feature in the Dimension PropertyManager, it will not accept this change.
FIGURE 10.2
Renaming a dimension
Best Practice
You should keep dimension names as short as possible while still making them unique and descriptive. This is because space in the interface is often limited, and when combined with sketch or feature names (and even part names when used in an assembly), the names can become difficult to display in a readable fashion. Also keep in mind that spaces in dimension names can be misinterpreted by Excel.
Tip
You can show dimension