G_D_&_T_11_2014
Transcript of G_D_&_T_11_2014
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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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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
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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.
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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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ENGINEERING DRAWINGS AND
TOLERANCING
Chapter One
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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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What Is An Engineering Drawing?
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What Is An Engineering Drawing?
Note the Dimensions
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What Is An Engineering Drawing?
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
Fundamental Dimensioning Rules
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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
Fundamental Dimensioning Rules
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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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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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Coordinate Tolerancing
Coordinate Tolerancing
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CT shortcomings are: Square or rectangular
tolerance zones
Fixed size tolerance
zones Ambiguous instructions
for inspection
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Coordinate Tolerancing
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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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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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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GD&T and CT Comparison
GD&T and CT Comparison
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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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GD&T and CT Comparison
GD&T and CT Comparison
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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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GD&T and CT Comparison
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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A feature Control Box
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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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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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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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Feature of Size Dimensions
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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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Feature of Size Dimensions
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Feature of Size Dimensions
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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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Actual Local Size
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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?
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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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Actual Mating Envelope
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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.
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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
87
The red hashed area represents the
similar perfect surface inscribedWithin the feature of size.
Actual Mating Envelope
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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
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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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
91
Material Conditions
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O M K A R C o n s u l t e c h
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Material Condition Modifiers
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O M K A R C o n s u l t e c h
93
Profile Tolerance
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O M K A R C o n s u l t e c h
94
Projected tolerance Zone
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O M K A R C o n s u l t e c h
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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.
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o n s u l t e c h
97
Maximum Material Condition
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
98
What is the MMC of the hole with internal
diameter of 60?
Maximum Material Condition
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O M K A R C
o n s u l t e c h
99
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
100
P i t t R b
Least Material Condition
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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
101
Wh t i th LMC f th h l ith i t l
Least Material Condition
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What is the LMC of the hole with internal
diameter of 60?
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o n s u l t e c h
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Least Material Condition
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O M K A R C
o n s u l t e c h
103
Tangent Plane
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O M K A R C
o n s u l t e c h
104
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
105
In this example Regardless
Regardless of Feature Size
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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
106
Regardless of Feature Size
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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
107
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
108
Modifiers
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O M K A R C
o n s u l t e c h
109
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
110
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
113
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.
O M K A R C o n s u l t e c h
114
This is a typical radius
Radius
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yp
dimension. The min and max radii
are?
O M K A R C o n s u l t e c h
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Controlled Radius
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O M K A R C o n s u l t e c h
117
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
O M K A R C o n s u l t e c h
118
Geometric Characteristic Symbols
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O M K A R C o n s u l t e c h
119
Important as the first symbol in a feature
Geometric Characteristic Symbols
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p y
control frame.
Note that not all symbols use a datum
reference frame.
O M K A R C o n s u l t e c h
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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
122
What does the M in
Feature Control Frame
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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
123
What does the
Feature Control Frame
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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
124
Feature Control Frame
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O M K A R
C o n s u l t e c h
125
Questions?
End of Chapter Two
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O M K A R
C o n s u l t e c h
126