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Workshop on

Geometric Dimensioning and

Tolerancing -- I

J R Karandikar

Spring 2014

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Introductions

Syllabus

My expectations for the class

Your expectations

Course Agenda

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O M K A R C o n s u l t e

c h

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InstructorJayant R Karandikar

Introduce yourself and

Tell me one expectation you have for this class.

Introduction

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What is GD&T? Types of Geometry Engineering Drawing Dimensioning and Tolerancing Philosophy

Legal Issues Pertaining to Part Definition and GD&T Basic Dimensioning Practices

Interpretation of Limits and Measurement Process Issues

What is ASME Y14.5-2009 ? Structure of the ASME Y 14.5-2009 Standard

GD&T Symbology New Symbols and Tools in ASME Y14.5-2009

Plus and Minus Dimensions and Tolerances

Feature Types Fundamental Rules and Definitions

O M K A R C o n s u l t e c h

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Course Syllabus

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Material Condition, Material Boundary, and Applicable Modifiers Defaults for Tolerancing Screw Threads, Splines and Gears

Actual Mating Envelopes

Datums and Datum Reference Frames

Form Tolerances

Virtual Condition and Resultant Condition

Center Geometry Orientation Tolerances

Location Tolerances Positional Tolerancing

Concentricity

Symmetry

Runout Tolerances Profile Tolerances


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Course Syllabus

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Geometrical Deviations

Size Deviations: The difference betweenactual size and nominal size

Waviness: Mostly more or less periodicirregularities of a work-piece surface with

spacing greater than the spacing of its

roughness

Form Deviations: The deviation of afeature (geometrical element, surface or line)from its nominal form

Roughness: Periodic or non-periodicirregularities of a work-piece surface withsmall spacing inherent of the forming process

Orientational Deviations: thedeviation of a feature from its nominal form

and orientation.

Surface Discontinuities: An isolatedimperfection of the surface like a crack, pore

or lap

Locational Deviations: The deviationof a feature (surface, line, point) from its

nominal location.

Edge Deviations: Deviations of thework-piece edge zone from the geometrical

ideal shape like burr or abraded edges instead

of sharp edges

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It is impossible to manufacture work-pieceswithout deviations from the nominal shape. Work-pieces always have deviations of size, form,orientation and location.


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Principles for Tolerancing

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O M K A R C o n s u l t

e c h

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The GOAL of GD&T: To guide all parties toward reckoning partdimensions the same, including the origin, direction, anddestination for each measurement.

GD&T achieves this goal through four simple and obvious steps. 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 ofeach surface along with specific rules for conformance.

Allow dynamic interaction between tolerances (simulating actualassembly possibilities) where appropriate to maximize tolerances.


e c h

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How Does GD&T Work?Overview

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Hearing spoken text and looking at graphics ? 91% morelearning,

Looking at graphics alone ? 63% more,

Reading printed text plus looking at graphics ? 56% more,

Listening to spoken text, reading text, and looking atgraphics ? 46% more,

Hearing spoken text plus reading printed text ? 32% more,

Reading printed text alone ? 12% more,

Hearing spoken text alone ? 7% more.

How Do We Learn?

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e c h

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ENGINEERING DRAWINGS AND

TOLERANCING

Chapter One

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e c h

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Understand what an engineering drawing is

Understand why geometric tolerancing is superior

to coordinate tolerancing

Goal

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A document thatcommunicates aprecise description ofa part.

The description willconsist of pictures,words, numbers and

symbols.

What Is An Engineering Drawing?

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http://c/Documents%20and%20Settings/Jayant/My%20Documents/Excellence/Six_sigma/GD_T/Basic_Dimensioning.pptx

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An engineering drawing may communicate thefollowing:

Geometry of the part

Critical functional relationships

Tolerances

Material, heat treat, surface coatings

Part documentation such as part number and drawing

revision number


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Note the Dimensions

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Electrical Quality/Descriptive

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Papyrus/Rock/Clay tablet Sumerian, Egyptian and other early civilizations.

Pen and Ink

Pencil

Mainframe

PC Several different software's

AutoCAD, MicroStation, Solidworks, Pro-E, Catia, etc


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Brief History of Engineering Drawing.

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WHAT WAS WRONG WITH THE

WAY WE ALWAYS MADE OURDRAWINGS?


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Drawing errors compoundthe cost of the error as youmove further from initialdesign to production.

Drawing errors cost: Money

Time

Material

Customer satisfaction

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Cost of Drawing Errors!

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Disagreements overdrawing interpretation.

Difficulty incommunicating drawingrequirements.

Can not understandthe designers intent.


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What Else Was Wrong?

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Bad parts passinginspections.

Wasting money on

parts that do not fit.


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What Else Was Wrong?

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Dimensions A numerical value

expressed in

appropriate units of

measure and used todefine the size, location,

orientation, form orother geometric

characteristics of a part


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Back To Engineering Drawings!

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Tolerance Tolerance is the total

amount a specific

dimension is permitted

to vary from thespecified dimension.

The tolerance is thedifference between the

maximum and minimumlimits.


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Engineering Drawings

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Limit Tolerance: When a dimension has a high and low limit stated.

31.75/29.21 is a limit tolerance.

Plus-Minus Tolerance

The nominal or target value of the dimension is givenfirst, followed by a plus-minus expression of tolerance.

32 0.1 is a plus-minus tolerance.


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Types of Tolerances

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Bilateral Tolerance A tolerance that allows the dimension to vary in both

the plus and minus directions.

Equal Bilateral Tolerance

Variation from the nominal is the same in bothdirections.

32 .004 is a Equal Bilateral Tolerance.


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Types of Tolerances

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Unilateral Tolerance Where allowable variation is only in one direction and

zero in the other.

32 + .004

Unequal Bilateral Tolerance

Where the allowable variation is from the target valueand the variation is not the same in both directions.


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Types of Tolerances

50+ .004

- .002

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For this class we will be using metric dimensions. Drawings must state the units used and certain other

information used in the drawing.

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Metric Dimensions

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The primary ways toindicate tolerances in adrawing are:

A general tolerance note

A note providing a tolerance

for a specific dimension A reference on the drawing

to another document thatspecifies the requiredtolerances

These are similar tospecifying dimension units

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Metric Dimensions

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All dimensioning limits are absolute That is all dimensions are considered to have a zero

after the last true digit.

Ex. 1.25 means 1.250

This interpretation is important for gauging.

A part with a dimension and tolerance of 1.0 .1would fail inspection at what Measure?

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Dimensioning Limits

D H

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History of GD&T Drawings before industrial evolution were elaborate

pictures of a part that could not be made today. Why?

Parts made were unique one of a kind that were made as the

craftsman saw the part.

The industrial revolution made manufacturersrealize that one of a kind was not economical.

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Dimensioning History

Di i i Hi

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Mass production created the need forinterchangeable parts. This meant drawings thatwere simple and standardized.

The first standard was coordinate based.

The publication of the GD&T standard ANSI Y14.5

First edition: 1966

Updates have been published in 1982, 1994 , 2004 and2009

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Dimensioning History

Fundamental Dimensioning Rules

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(a) Each dimension shall have a tolerance, except for thosedimensions specifically identified as reference, maximum, minimum,or stock (commercial stock size).

(b) Dimensioning and tolerancing shall be complete so there is fullunderstanding of the characteristics of each feature.

(c) Each necessary dimension of an end product shall be shown.

(d) Dimensions shall be selected and arranged to suit the function

and mating relationship of a part and shall not be subject to morethan one interpretation.

(e) The drawing should define a part without specifyingmanufacturing methods.

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Fundamental Dimensioning RulesRef: ANSI Y 14.5 2009


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(f) It is permissible to identify as non-mandatory certainprocessing dimensions that provide for finish allowance,shrink allowance, and other requirements, provided the finaldimensions are given on the drawing.

(g) Dimensions should be arranged to provide requiredinformation for optimum readability.

(h) Wires, cables, sheets, rods, and other materialsmanufactured to gage or code numbers shall be specified bylinear dimensions indicating the diameter or thickness.

(i) A 90 angle applies where center lines and lines depicting

features are shown on a drawing at right angles and no angleis specified.

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g

Ref: ANSI Y 14.5 2009


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(j) A 90 basic angle applies where center lines of features ina pattern or surfaces shown at right angles on the drawingare located or defined by basic dimensions and no angle isspecified.

(k) Unless otherwise specified, all dimensions are applicableat 20C (68F).

(1) All dimensions and tolerances apply in a free statecondition.

(m) Unless otherwise specified, all geometric tolerancesapply for full depth, length, and width of the feature.

(n) Dimensions and tolerances apply only at the drawinglevel where they are specified.

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g

Ref: ANSI Y 14.5 2009

I t t ti f Di R l

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l t e c h

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Interpretation of Dim Rules

I t t ti f Di R l

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Interpretation of Dim Rules

Lets Talk About Coordinate

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Coordinate tolerancingis a dimensioningsystem where a partfeature is located by a

means of rectangulardimensions with giventolerances.


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Tolerancing

Coordinate Tolerancing

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Shortcomings CT or coordinate

tolerancing, does not

have the completeness

needed today to enableefficient and economical

production of parts.


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CT shortcomings are: Square or rectangular

tolerance zones

Fixed size tolerance

zones Ambiguous instructions

for inspection


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SquareTolerance Zone

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Square Tolerance Zone

Good Use of Coordinate Dimensioning

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Good Use of Coordinate Dimensioning

Coordinate Dimension Usage

Type of Dimension Appropriate Use Poor Use

Size

ChamferRadius

Locating Part Features

Controlling angular

Relationships

Defining the Form of

Part

Features

Geometric Dimensioning and Tolerancing

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Geometric Dimensioning and Tolerancing (GD&T)is an international language that is used onengineering drawings to accurately describe a part.

GD&T is a precise mathematical language that canbe used to describe the size, form, orientation andlocation of part features.

GD&T is a design philosophy.


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Geometric Dimensioning and Tolerancing

CT and GD&T Drawing Comparison

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O M K A R C o n s

u l t e c h

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CT and GD&T Drawing Comparison

Philosophy of GD&T

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Functional Dimensioning Part is defined based upon function in final product

Works well with Concurrent Product and ProcessDevelopment (CPPD) also called Simultaneous

Engineering) Design is created with inputs from marketing, customers,

manufacturing, purchasing and any other area that has impacton the final production and use of the product.

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Philosophy of GD&T

Ultimate Goal

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To Provide the customer with what they want,when they want the product, how or the formthey want the product in and at the price theywant.

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Ultimate Goal

GD&T Benefits

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Improved Communications Design uniformity allows design, production and

inspection to all work from the same view. There is no

argument over what to do

Better Product Design Allows designers to say what they mean instead of

having engineers explain what to do

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GD&T Benefits

Benefits of GD&T

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Increased ProductionTolerance Bonus Tolerance: saves

cost of manufacturing

Tolerance based uponpart functionalrequirements. Techniquefor determining atolerance is not part of

this course.

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u l t e c h

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Benefits of GD&T

GD&T and CT Comparison

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Increased ToleranceZone

Tolerance is no longersquare but fits the

geometry of thefeature

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Fixed Size and Square Tolerance Zones Circle is 0.71 diameter

Square is 0.5 each side


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Ambiguous Instructionsfor Inspection CT allowed the inspector

to inspect the part fromwhatever perspective theinspector deemed

appropriate. GD&T givesa defined process forinspection.

GD&T uses the datumsystem to eliminate

inspection confusion.


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Great Myths of GD&T

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GD&T Raises product cost.

We do not need GD&T

GD&T and Y14.5M-1994 are confusing

GD&T drawings take too long to make

Easier to use CT GD&T should only be used on critical parts

I know GD&T

Dimensioning and tolerancing are separate steps I can learn GD&T in two days.


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Great Myths of GD&T

Great Myths of GD&T

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The misconception that geometric tolerancingraises product cost is still considered to be thegreat myth of GD&T.


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y

Summary

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We discussed engineering drawings and what theywere

Engineer drawings do what?

Cost of poor drawing

When should we catch mistakes?

What do errors cost?

Dimensions and Tolerances

What are they?


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y

Summary

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Fundamental Dimensioning Rules Coordinate Tolerancing

Do we use CT today?

Shortcomings of CT

What is GD&T

Benefits

Great Myth of GD&T


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y

Questions?

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Q

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INTRODUCTION TO GEOMETRIC

TOLERANCINGSYMBOLS AND TERMS

Chapter Two

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Goals

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Understand eight key terms and how they affectthe interpretation of a drawing.

Understand the modifiers and symbols used inGeometric Tolerancing.

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O M K A R C o n

s u l t e c h

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A feature Control Box

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O M K A R C o n

s u l t e c h

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The position of this feature shall be within diameter .005at maximum Material Condition to primary datum A andto secondary Datum B at maximum Material conditionand to tertiary Datum C at Maximum material condition

.005 A B CM MM

60.5 0.5

Key terms

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Features Feature of Size

Internal Features Of Size

External Feature of Size

Feature of Size Dimensions

Non Features of Size Dimensions

Actual Local Size

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Features

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Feature A product feature is a property possessed by a product

that is intended to meet certain customer needs and

thereby provide customer satisfaction.

A general term applied to a physical portion of a partsuch as a surface, hole or slot.

A feature may be considered a part surface.

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Features

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How many features forthis view?

6

7

8

9

NONE

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Feature of Size

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Feature of Size One cylindrical or spherical surface or a set of two

opposed elements or opposed parallel surfaces

associated with a size dimension.

What does this really say?

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Feature of Size

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s u l t e c h

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Features of Size

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How many features ofsize in the drawing?

2

3

4

5

NONE

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Internal Features of Size

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Internal FOS

Comprised of part surfaces, or elements, that areinternal part surfaces such as a hole diameter or the

width of a slot.

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s u l t e c h

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Internal Features Of Size

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How many InternalFOS are there in thedrawing?

2

3

4

5

NONE O M K A R C o n s u l t e c h

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External Feature of Size

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External FOS

Comprised of part surfaces, or elements, that areexternal surfaces such as a shaft diameter or an overall

width or height of a planar part.


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A feature of size dimension is a dimension that isassociated with a feature of size.

A non-feature of size dimension is a dimension notassociated with a feature of size.


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How many feature of

size dimensions are inthis drawing?

3

4

5

6

7

NONE


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Non-Feature of Size Dimensions

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How many non-FOSdimensions are there inthe drawing?

2

3

4

5

NONE O M K A R C o n s u l t e c h

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Actual Local Size

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n s u l t e c h

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Actual Local Size

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n s u l t e c h

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Actual Local Size

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If a hole has a dimension and tolerance of:

Diameter: 20 mm

Tolerance: +/- .5 mm

What would be three local readings that wouldallow the hole to be within specification?

O M K A R C o

n s u l t e c h

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Actual Mating Envelope

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An actual mating envelope is defined by the type of

feature of size considered. The actual mating envelope of an external feature

of size is a similar perfect feature counterpart of

the smallest size that can be circumscribed aboutthe feature so it just contacts the surfaces at thehighest points.

The AME will vary as this is based upon the actual

part. O M K A R C o

n s u l t e c h

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External Actual Mating Envelope

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n s u l t e c h

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O M K A R C o

n s u l t e c h

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The red hashed sections are the similarperfect surface

At the smallest size which just touches thehighest Points of the feature of size.

Internal Actual Mating Envelope

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The actual mating envelope of an internal featureof size is a similar perfect feature counterpart ofthe largest size that can be inscribed within thefeature so that it just contacts the surface at their

highest points.

O M K A R C o

n s u l t e c h

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Internal Actual Mating Envelope

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O M K A R C o

n s u l t e c h

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The red hashed area represents the

similar perfect surface inscribedWithin the feature of size.


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Note: The Actual Mating Envelope must be oriented relative to the

specified Datums. When an inspector merely uses the size of afeature to calculate the bonus tolerance, out of spec parts may beaccepted.

If a hole, for instance, has the following size and geometric control,and the hole measures .502. It would be incorrect to use a bonustolerance of .003 (.502 - .499(MMC)) if the hole is not perfectlyoriented to the Datums. If the hole is out of perpendicular to

datum A by .002, for instance, the bonus that may be used isreduced by that amount. The bonus would be merely .001 and theallowable position tolerance = .016. O M

K A R C o

n s u l t e c h

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Actual Mating Envelopes

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A hole is defined as: Diam. 25 mm +1,-0.

There are four local measurements of 25.2, 25.6,25.4. 25.0.

What is the AME size?

25.60 O M K A R C o

n s u l t e c h

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MATERIAL CONDITIONS

Chapter Three


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Material Conditions

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GD&T allows for certain modifiers to be used in

specifying tolerances at various part featureconditions. These conditions may be largest size,smallest size or actual size of that feature of size.

Material conditions may only be used when referringto a feature of size

In GD&T, maximum material condition (MMC) refers

to a feature-of-size that contains the greatest amount

of material, yet remains within its tolerance zone. O M K A R C o n s u l t e c h

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Material Conditions

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Material Condition Modifiers

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Profile Tolerance

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Projected tolerance Zone

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95

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Maximum Material Condition

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Points to Remember:

Maximum material condition, MMC, of an externalfeature of size is the largest size limit.

Maximum material condition, MMC, of an internalfeature of size is the smallest size limit.

O M K A R C

o n s u l t e c h

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Wh h MMC f h h l h l

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O M K A R C

o n s u l t e c h

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What is the MMC of the hole with internal

diameter of 60?


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O M K A R C

o n s u l t e c h

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Least Material Condition

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Least Material Condition is the condition in which afeature of size contains the least amount of material

everywhere within the stated limits of size.

This would be the smallest shaft diameter or thelargest hole diameter. O M K A R C

o n s u l t e c h

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P i t t R b


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Points to Remember

The least material condition, (LMC), for an externalfeature of size is the smallest size limit.

The least material condition, (LMC), for an internalfeature of size is the largest size limit.

O M K A R C

o n s u l t e c h

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Wh t i th LMC f th h l ith i t l


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What is the LMC of the hole with internal

diameter of 60?

O M K A R C

o n s u l t e c h

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O M K A R C

o n s u l t e c h

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Tangent Plane

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O M K A R C

o n s u l t e c h

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Regardless of feature is the term that indicates a

Regardless of Feature Size

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Regardless of feature is the term that indicates a

geometric tolerance applies at any increment ofsize of the feature within the size tolerance.

There is no symbol for RFS.

RFS is the default condition for all geometrictolerances.

O M K A R C

o n s u l t e c h

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In this example Regardless


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In this example Regardless

of Feature Size is implied.This is the most expensive

control. Although the sizemay not be less than 9.8mm

or greater than 10.2mm, the

hole may act like 9.5mm to10.5mm. Any holes made

from 9.5mm to 9.8mm or

from 10.2mm to 10.5mm

should be rejected for size

even though they mayfunction. O M

K A R C

o n s u l t e c h

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An early look at

rule two.

O M K A R C

o n s u l t e c h

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Every feature of size has a maximum and a least

Material Conditions and PartDimensions

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Every feature of size has a maximum and a least

material condition.

RFS is the most expensive option available ingeometric tolerancing.

O M K A R C

o n s u l t e c h

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Modifiers

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O M K A R C

o n s u l t e c h

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GD&T modifiers communicate additional

Modifiers

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GD&T modifiers communicate additional

information about the part. This information isused to better understand the meaning of thedrawing and how to manufacture that part.

We have already discussed MMC, LMC and RFS.

O M K A R C

o n s u l t e c h

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P: projected tolerance zone

Modifiers

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P: projected tolerance zone.

A tolerance zone that extends beyond a feature by aspecified distance. Projected tolerance zones help

ensure that mating parts fit during assembly.

T: tangent plane. Notes that only the tangent plane of the toleranced

surface need be within the tolerance zone.

O M K A R C

o n s u l t e c h

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R: radius and CR: controlled radius

Modifiers

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R: radius and CR: controlled radius

Used outside the feature control frame.

(): reference

Denotes that information is for reference only. Theinformation of the reference is enclosed in theparentheses.

O M K A R C

o n s u l t e c h

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Radius:

Radius

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A straight line extending from the center of an arc orcircle to its surface.

Symbol is R.

Use of the Radius creates a zone defined by twoarcs, which the actual surface must be containedwithin. The arcs are the minimum and maximumradii.


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This is a typical radius

Radius

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yp

dimension. The min and max radii

are?


115

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Controlled Radius

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Geometric Characteristic Symbols

Geometric Tolerances

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y

Fourteen symbols used in GD&T to further define thecharacteristics of the part on the drawing.

Five categories of characteristics exist:

Form

Profile

Orientation

Location

Runout


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Important as the first symbol in a feature


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p y

control frame.

Note that not all symbols use a datum

reference frame.


120

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A symbol in the second compartment is not

Feature Control Frame

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always needed. Second compartment will specifytolerance.

Third, fourth and fifth compartments will contain

datums if needed. A non-datum control will only have two

compartments.

O M K A R

C o n s u l t e c h

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What does the M in


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the circle mean?What is the implied

tolerance?

What does the orderof the datumsrepresent?

O M K A R

C o n s u l t e c h

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What does the


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geometriccharacteristic symbolmean?

Why only one datum?

O M K A R

C o n s u l t e c h

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O M K A R

C o n s u l t e c h

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Questions?

End of Chapter Two

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O M K A R

C o n s u l t e c h

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G_D_&_T_11_2014

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