Graphics Programs Reference
In-Depth Information
Adding Tolerance Notation
In mechanical drafting,
tolerances
are a key part of a drawing's notation. They specify the allow-
able 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're a mechanical engi-
neer 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 topic.
To use the Tolerance command, click Tolerance from the expanded Dimensions tool group,
choose Dimension
Tolerance on the menu bar, or type
TOL
↵ at the Command prompt to open
the Geometric Tolerance dialog box (Figure 11.36).
FIGURE 11.36
The Geometric Tol-
erance dialog box
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 portion of Figure 11.37 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 parallel within
0.003˝ of the lower cylinder. Note that mechanical drawings often use measurements in thou-
sandths, so 0.3 means 0.003.
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 dia-
log box contains standard symbols relating to the maximum and minimum material conditions
of a feature on the part being dimensioned.
