session 08- fundamentals of gd & t

M.S Ramaiah School of Advanced Studies - Bangalore

PEMP- AME501

1

Session 08

Fundamentals of Geometric

Dimensioning and Tolerancing

Based on ASME Y14.5MBased on ASME Y14.5M

Session Speaker

Dr. N S MaheshProfessor and Course Manager

Center for Manufacturing

MSRSAS


PEMP- AME501

2

Session Objectives• Introduction to Geometric Dimensioning and Tolerancing

• Components and the overall system of GD&T

• Need for GD&T and the meaning of dimensioning and

tolerancing and GD&T specifications

• Concepts of Functional Dimensioning and Tolerancing and Dimensioning and Tolerancing Philosophy

• Implications of Engineering Specifications and their effect

on all downstream processes, such as manufacturing,

inspection, assembly, service, etc.

• The coordinate tolerancing system, geometric

dimensioning and tolerancing system

• Introduction to Geometric Tolerancing Symbols and Terms


PEMP- AME501

3

What is an Engineering Drawing?• An engineering drawing is a document that

communicates a precise description of a part. This description consists of pictures, words, numbers and symbols. Together these elements communicate part information to all drawing users

• Engineering drawing information includes– Geometry (shape, size and form of the part)

– Critical functional relationships

– Tolerances allowed for proper function

– Material, heat treat, surface coatings

– Part documentation information (part number, revision level)


PEMP- AME501

4

The engineering drawing is the specification for the component or assembly and is an important

contractual document with many legal implications, every line and every comment is important


PEMP- AME501

5

Dimensioning can be divided into three categories:

•general dimensioning,

•geometric dimensioning, and

•surface texture.

The following provides information necessary to

begin to understand geometric dimensioning and

tolerancing (GD&T)

Three Categories of DimensioningThree Categories of Dimensioning


PEMP- AME501

6

Consequences of Poor Drawing• Drawing errors

cost the

organization in

four ways

– Money

– Time

– Material

– Unhappy

customers


PEMP- AME501

7

Why Do We Use GD&T?

Drawing showing distance to ideal hole location


PEMP- AME501

8

Drawing that does not use GD&T


PEMP- AME501

9

Manufactured part

that conforms to

the drawing

(previous slide)

without GD&T


PEMP- AME501

10

Drawing that uses GD&T gives no room for ambiguity and is very precise and unique


PEMP- AME501

11

• GD&T has increased in practice in last 15 years because of ISO 9000- ISO 9000 requires not only that something be required, but how it is to be controlled. For example, how round does a round feature have to be?

• GD&T is a system that uses standard symbols to indicate tolerances that are based on the feature’s geometry

– Sometimes called feature based dimensioning & tolerancing or true position dimensioning & tolerancing

• GD&T practices are specified in ANSI / ASME Y14.5M-1994


PEMP- AME501

12

What is GD&T?• ASME Y14.5M-1994 GD&T is a language of

symbols used on mechanical drawings to efficiently

and accurately communicate geometry requirements

for features on parts and assemblies.

• GD&T, both ASME Y14.5M-1994 and ISO series are

the only recognized international drawing standards

in use throughout the world.

• GD&T is the language that designers use to translate

design requirements into measurable specifications.


PEMP- AME501

13

The Geometric Dimensioning and

Tolerancing System• Geometric Dimensioning and Tolerancing (GD&T) is an

international language that is used on engineering drawings

to accurately describe a part

• GD&T language consists of a well-defined set of symbols,

rules, definitions and conventions

• GD&T is a precise mathematical language that can be used

to describe the size, form, orientation and location of part

features

• G D & T is an exact language that enables designers to

“say what they mean” through a drawing.

• GD&T is also a design philosophy on how to design and

dimension parts


PEMP- AME501

14

GD&T is a means of dimensioning & tolerancing a drawing

which considers the function of the part and how this part

functions with related parts

– This allows a drawing to contain a more defined feature more accurately,

without increasing tolerances

– Geometric Dimensioning and Tolerancing (GD&T) is an international

language that is used on engineering drawings to accurately describe a part

– GD&T language consists of a well-defined set of symbols, rules,

definitions and conventions

– GD&T is a precise mathematical language that can be used to describe the

size, form, orientation and location of part features

– G D & T is an exact language that enables designers to “say what they

mean” through a drawing

– GD&T is also a design philosophy on how to design and dimension parts


PEMP- AME501

15

WHEN TO USE GD&TWHEN TO USE GD&T

• When part features are critical to a function or interchangeability

• When functional gaging is desirable

• When datum references are desirable to insure consistency between design

• When standard interpretation or tolerance is not already implied

• When it allows a better choice of machining processes to be made for production of a part


PEMP- AME501

16

GD&T Benefits

• GD&T provides better product design

• GD&T increases tolerances with cylindrical

tolerance zones

• GD&T allows additional (bonus) tolerances

• GD&T allows the designer to communicate

more clearly

• GD&T eliminates confusion at inspection


PEMP- AME501

17

Coordinate Tolerancing System

• Coordinate Tolerancing is a dimensioning system where a part feature is located (or defined) by means of rectangular dimensions with given tolerances


PEMP- AME501

18


PEMP- AME501

19

Notes required to make coordinate

dimensional equivalent to GD&T

Drawing


PEMP- AME501

20

Comparison between GD&T and

Coordinate Tolerancing


PEMP- AME501

21

Using English to

control part features


PEMP- AME501

22

Shortcomings of Coordinate

Tolerancing

• Coordinate Tolerancing has three

shortcomings

1. Square or rectangular tolerance zones

2. Fixed-size tolerance zones

3. Ambiguous instructions for inspection


PEMP- AME501

23

Coordinate Tolerancing and Square

Tolerance Zones


PEMP- AME501

24

Coordinate Tolerancing and Ambiguous

Instructions for Inspection


PEMP- AME501

25

Cylindrical vs square Tolerance Zone


PEMP- AME501

26

10.25 +/- 0.5

10.25 +/- 0.5

8.5 +/- 0.1

Rectangular

Tolerance Zone

Circular Tolerance Zone

Coordinate Vs Geometric Tolerancing Methods

Coordinate Dimensioning Geometric Dimensioning

Increased Effective Tolerance

10.25

10.25

8.5 +/- 0.1

B

A

C

1.4 A B C


PEMP- AME501

27

COORDINATE V/s ROUND

TOLERANCE ZONE


PEMP- AME501

28

COORDINATE V/s ROUND TOLERANCE

ZONE


PEMP- AME501

29

ROUND TOLERANCE ZONE


PEMP- AME501

30

Rectangular Tolerance Zone Circular Tolerance Zone

1.4

+/- 0.5

+/- 0.5

57% Larger

Tolerance Zone

Circular Tolerance Zone

Rectangular Tolerance Zone


PEMP- AME501

31


PEMP- AME501

32


PEMP- AME501

33

Training all relevant personnel to the mechanical drawing

industry standard (geometric dimensioning and tolerancing) will

reduce confusion, increase available tolerance and save time and

money.


PEMP- AME501

34

Coordinate Tolerancing Vs. GD&T

Condition

The datum system communicates one

set up for inspection

Results

Clear instructions for inspection

Eliminates disputes over part

acceptance

Condition

Implied datum allows choices for set up when inspecting

the part

Results

Multiple inspectors may get different results

Good parts scrapped

Bad parts accepted

Ease of

inspection

Condition

Use of MMC modifier allows tol zones

to increase under certain conditions

Results

Functional parts used

Lower operating costs

Condition

Tol zone is fixed in size

Results

Functional parts scrapped

Higher operating costs

Tolerance

zone

flexibility

Condition

Can use diameter symbol to allow round tol zones

Results

57% more tol for hole location

Lower manufacturing costs

Condition

Square or rectangular tol zones for hole locations

Results

Less tolerance available for hole

Higher manufacturing costs

Tolerance

zone shape

Geometric TolerancingCoordinate TolerancingDrawing

concept


PEMP- AME501

35

How Does GD&T Work?• Identify part surfaces to serve as origins and provide

specific rules explaining how these surfaces establish the starting point and direction for measurements.

• Convey the nominal (ideal) distances and orientations from origins to other surfaces.

• Establish boundaries and/or tolerance zones for specific attributes of each surface along with specific rules for conformance.

• Allow dynamic interaction between tolerances (simulating actual assembly possibilities) where appropriate to maximize tolerances.


PEMP- AME501

36

Symbols

• Anyone, regardless of his or her native tongue, can

read and write symbols.

• Symbols mean exactly the same thing to everyone.

• Symbols are so compact they can be placed close to

where they apply, and they reduce clutter.

• Symbols are quicker to draw and easier for computers

to draw automatically.

• Symbols are easier to spot visually.


PEMP- AME501

37

Introduction to Geometric

Tolerancing Symbols and Terms


PEMP- AME501

38

Contents

• Introduction to Geometric Tolerancing Symbols and

Terms: Definitions, concepts of LMC, MMC and

RFS

• Rules and Concepts of GD& T: Rules, Virtual

Conditions, Resultant Conditions, Applications of

virtual and resultant condition boundaries, Bonus

Tolerance


PEMP- AME501

39

THIS MEAN?WHAT DOES

SIZE DIMENSION

2.0072.003

LIMITS OF SIZELIMITS OF SIZE


PEMP- AME501

40

SIZE DIMENSION

MMC

LMC

ENVELOPE OF SIZE

(2.003)

(2.007)

ENVELOPE PRINCIPLE

LIMITS OF SIZELIMITS OF SIZEA variation in form is allowed between the least material condition (LMC) and the maximum material condition (MMC)

Envelop Principle defines the

size and form relationships

between mating parts.


PEMP- AME501

41

ENVELOPE PRINCIPLE

LMCCLEARANCE

MMCALLOWANCE



PEMP- AME501

42


The actual size of the feature at any cross section must be within the size boundary

ØMMC

ØLMC


PEMP- AME501

43

No portion of the feature may be outside a perfect form barrier at maximum material condition (MMC)



PEMP- AME501

44

Maximum Material Condition (MMC)

Least Material Condition (LMC)


PEMP- AME501

45

Maximum Material Condition (MMC)

• Maximum Material Condition (MMC)

– The condition in which a feature of size contains

the maximum amount of material within the stated

limits of size – for example, minimum hole

diameter, maximum shaft diameter.


PEMP- AME501

46

Maximum Material Condition


PEMP- AME501

47

Least Material Condition (LMC)

• Least Material Condition (LMC)

– The condition in which a feature of size contains

the least amount of material within the stated limits

of size – for example, maximum hole diameter,

minimum shaft diameter.


PEMP- AME501

48

Examples of Least Material Condition (LMC)


PEMP- AME501

49

Maximum and least material conditions


PEMP- AME501

50

PARALLEL PLANES

PARALLEL PLANES PARALLEL PLANES CYLINDER ZONE

PARALLEL LINES PARALLEL LINES PARALLEL LINES

PARALLEL PLANES PARALLEL PLANES

Other Factors i.e., Parallel Line Tolerance Zones

Other Factors i.e., Parallel Line Tolerance Zones


PEMP- AME501

51

Feature and Feature Of Size (FOS)

• Feature

– The general term applied to a physical portion of a

part, such as a surface, pin, tab, hole, or slot

• Feature of Size (FOS)

– One cylindrical or spherical surface, or a set of two

opposed elements or opposed parallel surfaces,

associated with a size dimension. An axis, median

plane or centerpoint can be derived from a feature

of size


PEMP- AME501

52

Examples of features


PEMP- AME501

53

Internal and External Features of Size


PEMP- AME501

54

Actual Local Size and Actual Mating

Envelope (AME)

• Actual Local Size is the value of any individual

distance at any cross section of a FOS

• Actual Mating Envelope (AME) is a variable

value, derived from an actual part

– For an external feature, the actual mating envelope is

the smallest perfect feature counterpart that can be

circumscribed about the feature

– For an internal feature, the actual mating envelope is

the largest perfect feature counterpart that can be

inscribed within the feature


PEMP- AME501

55

Actual Mating EnvelopeActual Mating Envelope

Internal Feature External Feature


PEMP- AME501

56

Unconstrained Actual Mating Envelope for an external feature

such as a bent cylinder is shown below:

Actual Mating EnvelopeActual Mating Envelope


PEMP- AME501

57

Actual mating envelope of an external

feature of size


PEMP- AME501

58

Actual mating envelope of an internal feature of size


PEMP- AME501

59

Using the figure, indicate if each letter is associated with a feature of

size dimension or a non-feature of size dimension.

Review Exercise - 2


PEMP- AME501

60

Material Condition Usage

• Each material condition is used for different

functional reasons

• Geometric tol are often specified to apply at

MMC when the function of a FOS is assembly

• MMC used most often (90%)


PEMP- AME501

61


PEMP- AME501

62

Regardless of Feature Size (RFS)

• Regardless of Feature Size (RFS)

– The term used to indicate that a geometric

tolerance or datum reference applies at any

increment of size of the feature within its size

tolerance.


PEMP- AME501

63

Tolerance Zone on RFS BasisTolerance Zone on RFS Basis

(Straightness of Axis)(Straightness of Axis)

0.05

0.05

0.05

0.05

0.05

0.05

0.05

0.05


PEMP- AME501

64

Tolerance Zone on MMC BasisTolerance Zone on MMC Basis(Straightness of Axis)(Straightness of Axis)

0.11


PEMP- AME501

65

Use the figure to fill the value of the MMC and LMC for each

dimension (or indicate, does not apply).

Review Exercise - 3


PEMP- AME501

66

Modifiers • Modifiers communicate additional information about the

drawing or tolerancing of a part

• There are eight modifiers used in geometric tolerancing


PEMP- AME501

67

Radius and Controlled Radius • A radius is a straight line extending from the center of an arc

or a circle to its surface

• When “R” symbol is specified, flats or reversals are allowed

• When “CR” symbol is specified, flats or reversals are not

allowed


PEMP- AME501

68

Controlled radius example

CR should only be used in special cases for eg: when the part

stresses are very high and reversals in the radiused surface would produce higher additional stresses


PEMP- AME501

69

Geometric Characteristic Symbols

• Geometric Characteristic Symbols are set of

fourteen symbols used in the language of

geometric tolerancing


PEMP- AME501

70

Geometric Characteristic Symbols


PEMP- AME501

71

FORM AND PROPORTION OF GEOMETRIC

TOLERANCING SYMBOLS


PEMP- AME501

72

FORM AND PROPORTION OF

GEOMETRIC TOLERANCING SYMBOLS


PEMP- AME501

73




PEMP- AME501

74




PEMP- AME501

75

COMPARISON OF SYMBOLS


PEMP- AME501

76



PEMP- AME501

77



PEMP- AME501

78



PEMP- AME501

79

Feature Control Frame• Feature control frame is a rectangular box that is

divided into compartments within which the

geometric characteristic symbol, tolerance value,

modifiers and datum references are placed


PEMP- AME501

80

THE

GEOMETRIC SYMBOL

TOLERANCE INFORMATION

DATUM REFERENCES

FEATURE CONTROL FRAME

COMPARTMENT VARIABLES

CONNECTING WORDS

MUST BE WITHINOF THE FEATURE

RELATIVE TO

Feature Control FrameFeature Control Frame


PEMP- AME501

81


PEMP- AME501

82


Reads as: The position of the feature must be within a .003 diametrical tolerance zone at maximum material condition relative to datums A, B, and C.

Uses feature control frames to indicate tolerance


PEMP- AME501

83


Reads as: The position of the feature must bewithin a .003 diametrical tolerance zone at maximum material condition relative to datums A at maximum material condition and B.

Uses feature control frames to indicate tolerance


PEMP- AME501

84

Placement of Feature Control FramesPlacement of Feature Control Frames

� May be attached to a side, end or corner of the symbol

box to an extension line.

� Applied to surface.

� Applied to axis


PEMP- AME501

85

Placement of Feature Control Frames Cont’d.Placement of Feature Control Frames Cont’d.

� May be below or closely adjacent to

the dimension or note pertaining to

that feature.

Ø .500±.005


PEMP- AME501

86

Placement of feature control frames


PEMP- AME501

87

Rules and Concepts of GD&T


PEMP- AME501

88

Geometric Tolerance Rule

RULE – 1 (Limits of Size Rule):

Where only a size dimension is given

a) The size dimensions at any cross section must be

within the size tolerance.

b) The surface(s) shall not extend beyond the perfect

form defined by the MMC Size.

c) The form may vary within an envelope between the

MMC and LMC.

RULE – 2

Geometric tolerances are understood to be applied RFS. If MMC or

LMC is required, it must be placed in the feature control frame.


PEMP- AME501

89

Rule#1

• There are two general rules in ASME Y14.5M-

1994. The first rule establishes default

conditions for features of size. The second rule

establishes a default material conditions for

feature control frames

• Rule#1: For features of size, where only

tolerance of size is specified, the surfaces shall

not extend beyond a boundary (envelope) of

perfect form at MMC


PEMP- AME501

90

Rule#1 Examples


PEMP- AME501

91

Rule#1 Examples


PEMP- AME501

92

Rule#1 Examples


PEMP- AME501

93

Interrelationship between features of size

ABCD four FOS, Rule #1 applies independently to each FOS. The angles b/w

these features of size (EFG) are not controlled by Rule 1


PEMP- AME501

94

• How to Override Rule#1

– A straightness control applied to a FOS

– A special note applied to a FOS

• Rule#1 Limitation

– Rule#1 does not control the location, orientation or

relationship between features of size


PEMP- AME501

95

Inspecting a Feature of Size- Go Gage and No-Go

Gage


PEMP- AME501

96

Rule#2

• Rule#2 is called “the all applicable geometric

tolerance rule”

• Rule#2: RFS applies, with respect to the

individual tolerance, datum reference or both,

where no modifying symbol is specified.

MMC or LMC must be specified on the

drawing where required


PEMP- AME501

97


PEMP- AME501

98

Basic Dimensions

• Basic Dimensions

– can be used to define the theoretically exact location, orientation or true

profile of part features or gage information

– that define part features must be accompanied by a geometric tolerance

– that define gage information do not have a tolerance shown on the print


PEMP- AME501

99

Basic DimensionBasic Dimension

• A theoretically exact size, profile, orientation, or

location of a feature or datum target, therefore, a basic

dimension is untoleranced

• Most often used with position, angularity, and profile

• Basic dimensions have a rectangle surrounding it.

1.000


PEMP- AME501

100

Basic Dimension cont’d.Basic Dimension cont’d.


PEMP- AME501

101

Basic dimension example


PEMP- AME501

102

Basic dimension used to locate datum

targets


PEMP- AME501

103

Virtual Condition and Boundary

ConditionsVirtual Condition (VC) is a worst-case boundary

generated by the collective effects of a feature of size at

MMC or at LMC and the geometric tolerance for that

material condition. The VC of a FOS includes effects of

the size, orientation and location for the FOS. The VC

boundary is related to the datums that are referenced in

the geometric tolerance used to determine the VC


PEMP- AME501

104

• Inner Boundary (IB) is a worst-case boundary generated by the smallest feature of size minus the stated geometric tolerance (and any additional tolerance, if applicable)

• Outer boundary (OB) is a worst-case boundary generated by the largest feature of size plus the stated geometric tolerance (and any additional tolerance, if applicable)

• Worst-case Boundary (WCB) is a general term to refer to the extreme boundary of a FOS that is worst-case for assembly. Depending upon the part dimensioning, a worst-case boundary can be VC, IB or OB


PEMP- AME501

105

Feature Control Frame Placement


PEMP- AME501

106

MMC Virtual Condition

• VC= MMC + Geometric Tol in the case of

external FOS such as shaft or pin

• VC= MMC - Geometric Tol in the case of

internal FOS such as hole


PEMP- AME501

107

MMC VC Examples


PEMP- AME501

108

LMC Virtual Condition

• VC= LMC - Geometric Tol in the case of


• VC= LMC + Geometric Tol in the case of



PEMP- AME501

109

LMC VC Examples


PEMP- AME501

110

RFS Inner and Outer Boundary

• OB= MMC + Geometric Tol in the case of


• IB= MMC - Geometric Tol in the case of



PEMP- AME501

111

RFS Inner and Outer Boundary Examples

???


PEMP- AME501

112

Worst-Case Boundary Formulas


PEMP- AME501

113

Bonus Tolerance

• Bonus tolerance is an additional tolerance for a

geometric control

• Bonus tolerance is only permissible when an

MMC (or LMC) modifier is shown in the

tolerance portion of a feature control frame

• Bonus tolerance comes from the FOS tolerance

• Bonus tolerance is the amount the actual

mating size departs from MMC (or LMC)


PEMP- AME501

114

Bonus Tolerance Examples


PEMP- AME501

115

Bonus Tolerance


PEMP- AME501

116

Identify Features of Size (FOS) and determine their MMC and VC size valuesReview Exercise - 4


PEMP- AME501

117

Summary

• Introduction and need for GD&T

• Terms and definitions

• Symbols and rules of GD&T

• Concept of bonus tolerance

have been studied

session 08- fundamentals of gd & t

Documents