The Geometrical Tolerancing Desk Reference: Creating and Interpreting ISO Standard Technical Drawings

By Paul Green

Chapter 6: Datum Symbols

When the toleranced feature is related to a datum, a datum letter(s) is shown in the tolerance frame. The datum is represented on the drawing in the following way:

Figure 6.1: Datum symbol

Location of the Datum Triangle

The location of the datum triangle can be represented on the drawing in the following ways:

Example 1a: When the datum is a plane or line

Example 1b: When the datum is a plane or line

Example 2: When the datum is an axis

Example 3: When the datum is a median plane

Example 4: When there is insufficient space for two dimension arrowheads

Example 5: When the datum is applied to a restricted part of a feature

Example 6: When two datum features combine to make one single datum reference

Example 7: When the datum is a surface in the drawing plane

Example 8a: When the datum is one common axis (or plane) formed by two different features

Example 8b: When the datum is one common axis (or plane)

Example 9a: When the datum is without a datum letter

Example 9b: When the datum is without a datum letter

Example 10: Toleranced feature and datum are the same

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The Geometrical Tolerancing Desk Reference: Creating and Interpreting ISO Standard Technical Drawings

TABLE OF CONTENTS

Chapter 6: Datum Symbols

Location of the Datum Triangle

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