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CLARIFICATIONS OF RULE 2 IN TEACHING GEOMETRIC DIMENSIONING AND TOLERANCING

Abstract

Geometric dimensioning and tolerancing is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation. Application cases using the concept of Rule 2 in the Geometric Dimensioning and Tolerancing (GD&T) are presented. The rule affects all fourteen geometric characteristics. Depending on the nature and location where each feature control frame is specified, interpretation on the applicability of Rule 2 is quite inconsistent. This paper focuses on identifying the characteristics of a feature control frame to remove this inconsistency. A table is created to clarify the confusions for students or designers, who can use it to justify their applications in the GD&T design.

1. Introduction

Geometric Dimensioning and Tolerancing (GD&T) has been around in one form or another since World War II. The need to define ever more complex part geometry and the need to guarantee interchangeability of parts has contributed to its widespread use. Today, it can be found in nearly all manufacturing industries, from the very small geometry found in Integrated Circuits to the very large geometry found on rockets, the Space Shuttle and the International Space Station.

It has found its greatest application in mass production, where interchangeability of blindly selected parts is essential. Just-in-time manufacturing increases the demand for parts that absolutely must fit at assembly, as it is much less likely today to have spare parts waiting in the warehouse. Parts simply must fit together at assembly.

In the engineering drawing design, GD&T is a means of specifying engineering design and drawing requirements with respect to actual “function” and “relationship” of part features. If the technique of GD&T is properly applied, it will ensure the most economical and effective production of these features, and also provides a uniform integration and interpretation of design, production, and inspection for a part1,2,3,4,5. In the United States, the governing rules of using GD&T are based on ASME 14.5M – 19946, “Dimensioning and Tolerancing”.

As shown in the first column of Table 1, there are five categories of geometric characteristics in the GD&T1: (1) Form, (2) Orientation, (3) Profile, (4) Runout, and (5) Location Tolerances. Form Tolerances include Flatness, Straightness, Circularity, and Cylindricity; Profile Tolerances include Profile of a Line and Profile of a Surface; Orientation Tolerances include Perpendicularity, Angularity, and Parallelism; Runout

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Lin, C., & Verma, A. (2007, June), Clarifications Of Rule 2 In Teaching Geometric Dimensioning And Tolerancing Paper presented at 2007 Annual Conference & Exposition, Honolulu, Hawaii. 10.18260/1-2--1651