Interpretation of Geometric Dimensioning and Tolerancing

148 Pages·2011·4.698 MB·148\148

by  Puncochar, Daniel E., Evans, Ken

Interpretation of
Geometric Dimensioning
and Tolerancing
Third Edition
Based on ASME Y14.5-2009
DANIEL E. PUNCOCHAR
Third Edition prepared by
KEN EVANS
INDUSTRIAL PRESS
NEW YORK
Library of Congress Cataloging-in-Publication Data
Puncochar, Daniel E.
Interpretation of geometric dimensioning and tolerancing / Daniel E.
Puncochar. -- 3rd ed. / revised and updated by Ken Evans.
p. cm.
Includes index.
ISBN 978-0-8311-3421-1 (soft cover)
1. Engineering drawings--Dimensioning. 2. Tolerance (Engineering) I.
Title.
T357.P96 2011
620'.0045--dc22
2010029110
Industrial Press, Inc.
989 Avenue of the Americas
New York, NY 10018
Sponsoring Editor: John Carleo
Interior Text and Cover Design: Janet Romano
Developmental Editor: Robert Weinstein
Copyright © 2011 by Industrial Press Inc., New York. Printed in the United States of America.
All rights reserved. This book, or any parts thereof, may not be reproduced, stored in a retrieval
system, or transmitted in any form without the permission of the publisher.
Notice to the reader: While every possible effort has been made to ensure the accuracy of the in-
formation presented herein, the authors and publisher express no guarantee of the same. The authors and
publisher do not offer any warrant or guarantee that omissions or errors have not occurred and cannot be
held liable for any damages resulting from the use of this text by the readers. The readers accept the full
responsibility for their own safety in related activities in connection with the instructions in this text. The
reader should consult the appropriate standards that are used before any interpretations of engineering
drawings are attempted.
10 9 8 7 6 5 4 3 2 1
PREFACE
Simply put, Geometric Dimensioning and Tolerancing (GD&T) is a method for stat-
ing and interpreting design requirements. GD&T is an international system of symbolic
language, and is a crucial tool for making engineering drawings and computer-generated
three-dimensional solid models more reliable means of communication, starting with the
initial design through manufacturing and inspection. Some of GD&T’s advantages are:
uniformity in design practice, fewer misinterpretations, ensured interchangeability, and
maximum tolerance allocation. Also, with GD&T, design requirements are specified ex-
plicitly and the latest gaging techniques are accommodated to better ensure fit, form, and
function. These advantages contribute to higher production yields with less rework or
scrap.
To help the reader understand GD&T, Geometric Dimensioning and Tolerancing,
Third Edition, begins with basic principles and builds on these principles with applica-
tions-oriented concepts. Complex material is presented in a “building-block” approach,
with many graphic examples that illustrate each concept. End-of-chapter evaluations fur-
ther reinforce the explanations given in each section. It is imperative that each reader has
an adequate knowledge of basic blueprint reading methods prior to using this book. Some
examples are dimensioned and toleranced in inches and some in millimeters.
This book covers the material in ASME Y14.5-2009, but does not prescribe design
practices, state design requirements, specify inspection techniques, or specify any other
engineering practice. However, it is sometimes necessary to state how something is spec-
ified or inspected so that a concept can be discussed adequately. In addition, the drawings
in this text are not complete production drawings, but only present the concepts currently
under discussion.
It is hoped that this third edition of Interpretation of Geometric Dimensioning and
Tolerancing will assist the reader in becoming conversant in the techniques of GD&T
given in the latest ASME standard—techniques that can be integrated smoothly into engi-
neering design systems and modern inspection systems.
vii
Table of Contents
Preface vii Types 47
Acknowledgements viii Summary 49
Evaluation 49
Chapter 1 Introduction 1
History 1 Chapter 5 General Rules 51
The Importance of Standards 2 Introduction 51
Why GD&T 2 Overview 51
Evaluation 5 Rule One 51
Rule Two 53
Chapter 2 Symbols and Rule Three 54
Abbreviations 7 Rule Four 54
Introduction 7 Summary 55
Dimensioning Symbols 8 Evaluation 56
Geometric Characteristics 17
Modifying Symbols 18 Chapter 6 Form, Orientation,
Summary 25 Profile, and Runout 57
Evaluation 26 Introduction 57
Tolerances of Form 57
Chapter 3 Datums 29 Straightness 57
Introduction 29 Flatness 60
Datum Identification 29 Circularity 61
Three-Plane Concept—Flat 30 Cylindricity 62
Customized Datum Reference Frame 32 Tolerances of Orientation 64
Datum Targets 33 Perpendicularity 64
Three-Plane Concept—Circular 37 Angularity 68
Partial Datums 38 Parallelism 70
Datums of Size 38 Profile 75
Pattern of Features 40 Runout 80
Summary 41 Summary 84
Evaluation 41 Evaluation 85
Chapter 4 Feature Control Chapter 7 Virtual Condition 87
Frames 43 Introduction 87
Introduction 43 Application 87
Symbol and Definition 43 External Feature 87
Attachment 43 Parallelism 89
Content 45 Internal Feature 91
How to Read Feature Control Frames 46 Summary 91
Datum Reference Letter Precedent 46 Evaluation 91
iii
Chapter 8 Tolerances of Location 93
Introduction 93
Concentricity 93
Symmetry 94
Position Introduction 95
Position Theory 96
Position of Multiple Cylindrical Features 99
Composite Positional Tolerancing 101
Two Single-Segment Feature Control 104
Frames
Multiple Patterns Located by Basic 105
Dimensions and Related to the Same
Datums
Patterns Positions From a Datum of Size 106
Introduction
Zero Tolerancing 110
Projected Tolerance Zone 111
Noncylindrical Features 112
Bidirectional Tolerancing 113
Coaxial Features 115
Summary 118
Evaluation 119
Chapter 9 Practical Applications 121
Introduction 121
Form and Orientation Tolerances 121
Hole Pattern—Single Control 125
Hole Pattern—Composite Control 126
Non-cylindrical Features 127
Co-axial Features 127
Appendix 129
Glossary 131
Answers 139
Index 141
iv
1
INTRODUCTION
History square tolerance zone. The idea caught on and
was adopted by the military. It became part of the
During the early period of manufacturing military standards and later was a Unified Amer-
there seldom were any drawings. Aperson had an ican Standard Association standard, ASAY14.5.
idea for something that was needed for industry, This standard was released in 1956 and was ac-
farming, or mining, and made it. Usually there cepted by the military. Later, ASA became the
was only one item, and when repair was needed, American National Standards Institute (ANSI).
someone repaired or replaced the needed part ANSI published a complete system of symbology
right on the job. for geometric form and positional tolerances, Di-
Over time, complexities in manufacturing mensioning and Tolerancing.
increased, and there was an increased need for In 1983, ANSI Y14.5-1982 was released.
drawings of parts and their assemblies. With This standard clarified some of the old practices
drawings came required tolerances, that is, parts and moved a little closer to the practices of the In-
were permitted some variation rather than being ternational Organization of Standards (ISO). ISO
fitted to only one assembly. This tolerance was is primarily a European standard. In 1995, ASME
specified as a plus/minus tolerance. Y14.5-1994, from the American Standard of Me-
This plus/minus tolerancing of the coordi- chanical Engineers was released. This new stan-
nate dimensioning system worked quite well and dard further clarified requirements within the
still does for many applications. But today there standard and also moves more in line with the
is a need for interchangeability of parts and as- ISO standard. Today, geometric dimensioning
semblies manufactured around the world being and tolerancing (GD&T) is used by the majority
brought together at an assembly plant that makes of manufacturing companies in the United States
parts for industries such as aerospace, automo- and the world.
tive, energy and oil, medical, agriculture, and tool The most current standard, ASME Y14.5-
and die. These items also need replacement parts 2009 is a revision of the 1994 standard and was
that assemble readily without the need for indi- adopted in 2009. Its purpose is to further stan-
vidual fitting. dardize and state design and functional require-
As the demand for parts manufactured ments, in order to aid in manufacture on a global
around the world grew, the need for accuracy also scale. Ultimately, (plus/minus) limit dimension-
grew. Accuracy became more critical because of ing should be replaced with GD&Tfor everything
competition for parts and assemblies. The idea of except for features of size. The new ASME
positional tolerancing was introduced, which pro- Y14.5-2009 standard is further in line with the
vided a means for locating round features within needs of the ISO international community.
a round tolerance zone rather than the traditional
1
2
The Importance of Standards the American Society for Mechanical Engineers
(ASME). In the European countries and other
We live in accordance with standards all of parts of the world, the standard is maintained by
the time. Almost every aspect of life, education, the International Organization for Standards
or business operates according to some standard. (ISO). These two standards are not identical, but
Some of the standards are specified and con- with each revision the standards become more
trolled locally, whereas others are national and similar. As international companies continue to
still others are international. Standards allow us exchange drawings among themselves, the use of
to all work in the same mode of thinking and standards is imperative.
therefore, minimize errors due to ambiguity in de-
sign intent.
Why GD&T?
What Is a Standard?
GD&Tadds clarity and contributes its many
advantages to our coordinate system of dimen-
A standard is a model or rule with which
sioning. The old system of coordinate dimension-
other similar things being manufactured are to be
ing was lacking in many respects. Under the older
made or compared to. For manufacturers, GD&T
system, a part of the designer’s intent was always
symbols, principles, and rules are the model that
left to interpretation by the craftsperson (e.g., di-
is provided internationally. This system of stan-
mension origin, form profile, and orientation).
dards was created to improve communications,
Probably the most significant difference between
control, and productivity in manufacturing
the two systems is the location of round features.
throughout the world. Standards are critical to all
The coordinate system had a square or rectangu-
of us, and they have become increasingly impor-
lar (linear) tolerance zone that allowed some
tant as our technologies continue to develop.
good parts to be rejected. In our world of high
technology, high cost, and transfer of parts
Change
around the world, we cannot tolerate the misinter-
pretation that is possible with the coordinate di-
Change is one of the most constant things we
mensioning system and its square tolerance zone.
have as a society. As a result, standards change
also, especially those associated with technology.
GD&T Is Not a Replacement
GD&T is an example of a widely-used standard
that must be updated constantly to be useful to in-
The coordinate dimensioning system is not
dustry. Over time, needed improvements are
being replaced entirely with GD&T. GD&T is
identified, discussed, and evaluated. When a suf-
specified to enhance the coordinate dimensioning
ficient amount of improvements are agreed upon,
system as required per design. When the advan-
standards are changed. The most recent update to
tages of GD&Tcan be utilized, they are simulta-
the GD&T standard was adopted in 2009 titled,
neously specified. GD&T, a system of symbols,
ASME Y14.5-2009.
provides a means of completely specifying uni-
formity and describing the designer’s intent.
Universality
These symbols eliminate most drawing misinter-
pretations by minimizing the use of drawing
GD&Tis a standard throughout the world. In
notes and by giving complete descriptions of fea-
the United States, the standard is maintained by
tures and design requirements.
INTRODUCTION 33
Complete Specification
1.000±.010
..225500±.010
A complete specification of design require-
ments are made possible with symbols that com-
municate clearly the design intent. These symbols
also allow the designer to specify maximum tol-
erances for parts that must assemble with other
parts. In turn, these maximum tolerances ensure
the interchangeability of parts. The use of sym-
bols for complete specification is becoming more
important with the growing interrelated owner-
22..000000±.010
ships of companies around the world. GD&T is
an international “common symbolic language”
controlled by standards. Today, the majority of
U.S. manufacturing companies are applying
GD&Tto their drawings.
Advantages Figure 1-1: Dimensions and tolerances with
the coordinate system.
There are many reasons for specifying geo-
metric tolerancing wherever design integrity
A similar situation exists where hole or pin
must be controlled and communicated com-
locations are specified with the coordinate di-
pletely to others. Two key principles for applying
mensioning system. An example of how holes are
GD&T are the function and the relationship of
specified is shown in Figure 1-2.
parts in an assembly. Probably the most advanta-
geous part of GD&T is its method of specifying
feature location. In the past, features were located
with the coordinate dimensioning system.
The coordinate dimensioning system is a
method of tolerancing that uses a plus/minus tol-
erance. Plus and minus tolerances are specified
for lengths, widths, diameters, shapes, and loca-
tions. An illustration of how drawings may be di-
mensioned and toleranced with the coordinate
2.000±.005
system is shown in Figure 1-1. This method of
tolerancing permits the length and diameters to
vary by a plus/minus value. It also allows the
makers of the part to put the center hole wherever
they desire. By looking at the drawing, we can
only assume that the hole is centered. This is an
22..000000±..000055
example of a drawing being left open to misinter-
pretation by anyone reading it. However, with the Figure 1-2 Specifying holes with the coordi-
proper use of GD&T, ambiguity is minimized. nate dimensioning system.
4
The tolerance, as specified, establishes a
..001100
square tolerance zone based on the plus/minus
five thousandths of an inch tolerance in the X and
.010
Ydirections. There is no consideration for the ac-
..000077
tual mating part size. The tolerance zone is five
thousandths of an inch on each side of the center
location, creating a square tolerance zone regard-
less of the actual mating part size. An illustration
of how the tolerance zone appears is shown in
Figure 1-4 Radial measurement of the
Figure 1-3.
square tolerance zone.
In the coordinate dimensioning system, the
only place there is a .007 in. measurement is from
the center to any corner. That .007 in. should be
..001100 usable all around the desired true position, as il-
lustrated in the example in Figure 1-5. GD&T
.010 provides a method of specifying a tolerance zone
that takes the shape of the feature into considera-
tion, if so desired by the designer. GD&Talso al-
22..000000±..000055 lows consideration for the feature’s actual local
size for calculating total tolerance. This concept
is presented in later chapters.
2.000±..000055 ..001144
..0011 SSQQUUAARREE
Figure 1-3 Ten thousandths square
..000077
tolerance zone.
The axis of the hole or pin must be positioned
within that square zone in order for the feature to
Figure 1-5 Cylindrical tolerance zone vs.
be located properly. The feature may lean or slant
square.
an uncontrolled amount, as long as the axis stays
within the square zone. The designer assumes
only that the feature will be produced nearly per- Other advantages of GD&T include interna-
pendicular to the material it is put into. Even if the tional uniformity in describing designer intent.
center axis of the hole is in an extreme corner of The symbolic method of specifying designer in-
this zone, the feature location is still acceptable— tent eliminates most misinterpretation of drawing
that radial measurement is .007 in., as shown in notes. In the past, drawings usually contained a
Figure 1-4. list of notes that were intended to explain certain
INTRODUCTION 55
requirements. These notes were all subject to mis- ric tolerances ensures the interchangeability of
interpretation. With the available symbols, de- parts. GD&T is the common language used
signers can more readily specify complete design throughout industry internationally.
requirements. The proper application of geomet-
Chapter 1 Evaluation
1. Drawings are the primary ________ tool between designers and manufacturing.
2. GD&Tis a system made up of ________ primarily.
3. The GD&Tstandard is one of the standards maintained by the ________ .
4. GD&Tadds to the coordinate dimensioning system when specific ________ is required.
5. GD&Tdoes not ________ the coordinate dimensioning and tolerancing system.
6. GD&Tcan best be described as a ________ dimensioning and tolerancing system.
7. GD&Tis used to control the ________ of a part feature and its relationship to other features.
8. GD&Tis also used to control feature ________ and ________.
9. The key principles of GD&Tare ________ and ________.
10. Two advantages of the GD&Tsystem are maximum ________ and ensured________ of mating parts.
11. The total amount that a part size may vary is a size ________.
12. Acommon method used to specify a tolerance for the nominal size of a feature is ________ values.
13. GD&Tshould be used for all dimensioning except for features of ________ .