Adding Tolerance Notation

In mechanical drafting, tolerances are a key part of a drawing's notation. They specify the allowable variation in size and shape that a mechanical part can have. To help facilitate tolerance notation, AutoCAD provides the Tolerance command, which offers common ISO tolerance symbols together with a quick way to build a standard feature control symbol. Feature control symbols are industry-standard symbols used to specify tolerances. If you are a mechanical engineer or drafter, AutoCAD's tolerance notation options will be a valuable tool. However, a full discussion of tolerances requires a basic understanding of mechanical design and drafting and is beyond the scope of this book.

To use the Tolerance command, choose Tolerance from the Dimension toolbar, type Tol at the command prompt, or choose Dimension   Tolerance from the drop-down menu. The Geometric Tolerance dialog box appears.

This is where you enter tolerance and datum values for the feature control symbol. You can enter two tolerance values and three datum values.

In addition, you can stack values in a two-tiered fashion. Click a box in the Sym group to open the Symbol dialog box.

The top image in Figure 9.25 shows what each symbol in the Symbol dialog box represents. The bottom image shows a sample drawing with a feature symbol used on a cylindrical object. The symbols in the sample drawing show that the upper cylinder needs to be concentric within 0.0003 ² of the lower cylinder.

Figure 9.25: Position (true)

In the Geometric Tolerance dialog box, you can click a box in any of the Datum groups or a box in the right side of the Tolerance groups to open the Material Condition dialog box. This dialog box offers standard symbols relating to the maximum and minimu material conditions of a feature on the part being dimensioned.

Understanding the Power of the Properties Palette

In both this and the previous chapter, you made frequent use of the Properties palette. By now, you might have recognized that the Properties palette is a gateway to editing virtually any object. It enables you to edit the general properties of layer, color , and line type assignments. When used with individual objects, it enables you to edit properties that are unique to the selected object. For example, through this tool, you can change a spline leader with an arrow into one with straight-line segments and no arrow.

If the Properties palette does not provide specific options to edit the object, it provides a button to open a palette that will. If you edit a multiline text object with the Properties palette, for example, you can open the Multiline Text Editor. The same is true for dimension text.

Beginning with AutoCAD 2000, Autodesk has made a clear effort to make AutoCAD's interface more consistent. The text-editing tools now edit text of all types ”single-line, multiline, and dimension text ”so you don't have to remember which command or tool you need for a particular object. Likewise, using the Properties palette is a powerful way to edit all types of objects in your drawing.

As you continue with the rest of this tutorial, you might want to experiment with the Properties palette with new objects you learn about. In addition to enabling you to edit properties, the Properties palette can show you the status of an object, much like the List tool.