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Chapter 14: A. Geometric Dimensioning and Tolerancing (GD&T) 1430.5ASymbol DatumTolerancevalueStraightnessPositionFlatnessSymmetryCircularityParallelismCylindricityPerpendicityProfile of lineProfile of surfaceCoaxilityAngularityRun-outTotal run-outPart III.A.1Figure 14.7 Features that can be specified by geometric tolerancing.H<size spec><tolspec> A B2.0000A1.001.00002.00B(a) Partial specification(b) Establishing the true position of hole HFigure 14.8 Simple 2-D example of position tolerance.designate them as datums. The left-to-right ordering of A and B in the calloutblock sets the datum precedence: A is primary and B is secondary. The positiontolerance (<tolspec> in Figure 14.8a) is a small disk-shaped zone defining the allowablevariability of H’s position.

144 Part III: Inspection and Test2. TERMINOLOGY AND SYMBOLSDefine and interpret drawing views, details,etc., for product specifications or othercontrolling documents, and define and usevarious terms and symbols from the ASMEY14.5M Standard. (Application)Body of Knowledge III.A.2Part III.A.2The Y14.3-2003 Multiview and Sectional View Drawings standard published by ASMEestablishes the requirements for creating orthographic views for item description.The standard includes the multiview system of drawing, selection, and arrangementof orthographic views, auxiliary views, sectional views, details, and conventionaldrawing practices. This allows engineers to view different angles andlook at a more detailed picture of the item (ASME 2003). The different views andsymbols can be interpreted to extract the required information and the specificationsof the item. For example, orthographic views will show a top view, a frontview, and a right side view. One view will not be sufficient to describe the item indetail, additional views are required. The number of orthographic views neededto describe an object fully depends on the complexity of the object. For example,a simple metal washer can be fully described using only one orthographic view;however, an extremely complex object may require as many as six views (top, front,left side, right side, back, and bottom). Most objects can be sufficiently describedusing three views: top, front, and right side as shown in Figure 14.9.The symbols on engineering drawings have different representations basedon the ASME standards. For example, the different line styles each have their owninterpretation. Figure 14.10 shows the different line symbols that are used in engineeringdrawings.Other symbols that are used in a feature control frame to specify a feature’sdescription, tolerance, modifier, and datum(s) are shown in Table 14.1.Top viewFront viewRight side viewFigure 14.9 Top, front, and right side views of an item.

Chapter 14: A. Geometric Dimensioning and Tolerancing (GD&T) 143

0.5

A

Symbol Datum

Tolerance

value

Straightness

Position

Flatness

Symmetry

Circularity

Parallelism

Cylindricity

Perpendicity

Profile of line

Profile of surface

Coaxility

Angularity

Run-out

Total run-out

Part III.A.1

Figure 14.7 Features that can be specified by geometric tolerancing.

H

<size spec>

<tolspec> A B

2.0000

A

1.00

1.0000

2.00

B

(a) Partial specification

(b) Establishing the true position of hole H

Figure 14.8 Simple 2-D example of position tolerance.

designate them as datums. The left-to-right ordering of A and B in the callout

block sets the datum precedence: A is primary and B is secondary. The position

tolerance (<tolspec> in Figure 14.8a) is a small disk-shaped zone defining the allowable

variability of H’s position.

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