Equations, Shared Values, and Design Tables

16 May, 2004 By: Greg Jankowski

SolidWorks provides three options to help drive and share values within a drawing.

Three main functions exist for driving and sharing values with SolidWorks-equations, shared values, and design tables. These powerful options can help capture and document design intent, automate design modification, and create a family of parts.

An equation creates a relationship between model dimensions using dimension names (dimension name@feature name). You can define an equation between parts within the same document or between a part and a subassembly. The scope of the equation-where it can be used-isn't limited to the document.

The Equations dialog box in figure 1 shows three examples of equations. Note the use of human-readable dimension names. You can name a dimension and a feature using the Properties dialog box.

Dimensions listed on the left side of the equation are driven by the evaluation of the right side of the equation. Trying to change a dimension listed on the left side results in a warning that this dimension is driven from the equation. Note that dimensions driven from equations can't be used as shared values.

Figure 1. Equations dialog box.

In addition to mathematical functions (+, -, *, and /), you can also use the constant value of pi and the following functions within the equations:

sin (a)		cos (a)		tan (a)	
atn (a)		abs (a)		exp (n)
log (a)		sqr (a)		int (a)
sgn (a)

Shared Values
Shared values use a variable name to link model dimension values, as shown in figure 2. You can edit any one of the linked dimensions, and all link values update. You can also create more than one variable within a document. The variable can be used only within the current document.

Figure 2. Shared Values dialog

To create a linked value, select a dimension and right-click Link Values. To create a new shared value, enter the variable name. To use an existing value, select it from the Name pull-down list. To unlink a dimension, edit the sketch, select the dimension, and right-click Unlink Value.

Design Tables
Powerful and flexible, design tables are embedded Excel spreadsheets that drive dimension parameters, feature and part suppression, and visibility. You can use configurations to create multiple versions of the same design with different features or dimension values. Or create a simplified assembly for large assemblies by breaking the subassemblies into separate configurations.

Design tables create part or assembly configurations (figure 3). To view defined configurations, select the ConfigurationManager tab at the top of the FeatureManager design tree. To go back to the FeatureManager mode, select the FeatureManager tab. These tabs are used to switch the mode (feature- or configuration-based) of the navigation tool.

Figure 3. Configuration Manager shows all defined configurations

You can create configurations either manually or by using design tables. The advantage to using design tables is that it's easier to view, edit, and understand what's different among the configurations when they can be displayed in the spreadsheet.

The design table shown in figure 4 creates three configurations for three different screw lengths. The feature, Screw Head Cut, is also not visible in two of the configurations. Also note the use of named features for the driving dimension name. If the default name were used, it would be difficult to figure out what's being controlled.

Figure 4. Design table.

Another advantage of design tables is that you can put comments in the spreadsheet. Figure 5 shows both cell and embedded comments within a design table. The cell with the red triangle in the upper right-hand corner displays the embedded cell comment when you move your mouse over it. In addition, you can place cell comments in a blank row in column A or add them to the Row 1 cell, below which all cells are comments.

Figure 5. Comments within a design table.

You can use design tables to compute dimension parameters using all functions available in a spreadsheet application (mathematical [cos, sin], or logical [if/then]). More functions are available within a design table than within equations.

What to use?
This table compares the benefits and drawbacks of the different options.

  Pros Cons
Equations • Easy to use
• Limited set of functions
• Scope not limited to current document
• Without good dimension names, can be difficult to set up
• No way to add comments
• Can't change the driving (left-side) dimension
Shared Values • Easy to use
• Ties a single value together
• Any linked valued can be changed, and the other updates
• Can provide a direct link only to another value
• Hard to understand what's been linked
• Limited scope
Design Tables • Most flexible option
• More functions available
• Scope not limited to current document
• Creates configurations; powerful and easy to view
• Inconsistent usage, default feature name, and lack of comments can make the design difficult to modify

All of these functions, used effectively, can increase your productivity and better document your design. Picking the right function for your application is key.

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