gd & t raghu nxpowerlite

8/6/2019 GD & T Raghu NXPowerLite

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Appreciation program in

Geometric Dimensioning and

Tolerancing


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When to use GD&T

When drawing and its interpretation must be same

When features are critical to function or

interchangeability

When it is important to avoid scrapping of

perfectly good parts

When it is important to reduce drawing changes

When functional gauging is required When it is important to increase productivity


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CO ORDINATE TOLERANCINGSYSTEM

Part feature is located (or defined) by means ofrectangulardimensions with given tolerances.


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THREE MAJOR SHORTCOMING OFCOORDINATE DIMENSIONING

1. Square orrectangulartolerance zones.

2. Fixed-size tolerance zones.

3. Ambiguous instruction for inspection.


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1.Square (or illogical )Tolerance Zones.

Diagonally more tolerance (0.707) than vertical andhorizontal direction (0.5)

More logical and functional approach is to allow sametolerance on all sides, creating cylindrical tolerance

zone.


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COMPARISION BETWEEN GD&TAND COORDINATE TOLERANCING.


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Cylindrical vs. RectangularTolerance Zones


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GEOMETRIC DIMENSIONING ANDTOLERANCING.


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0Rectangular Tolerancing


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Geometric Tolerancing


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2.Fixed-Size Tolerance zones

Function ofahole in assembly is , hole location iscritical when the hole is at minimum limit (MMC).


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Co-ordinate tolerancing does not allow

for cylindrical tolerance zones and

tolerance hole that increase with thehole size, lengthy notes have to be

added.

LMC

MMC

10.5


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3.AMBIGUOUS INSTRUCTION FORINSPECTORS


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Different ways to hold the part for inspection,confusion forthe inspectorwhich surface to touch

the gage equipment first, second and third.

Consequence:

Good parts could be rejected or,Bad parts could be accepted.


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3 Benefits of GD & T

A. Cylindrical tolerance zones.

B. Maximum Material Condition.

C. Datums specified in order of precedence.


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Type of dimension Appropriate

use

Pooruse

Size

Chamfer

Radius

Locating part feature

Controlling angularrelationships

Defining the form of

part feature

COORDINATE DIMENSIONING USAGE


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Symbols, Terms, of GD&T


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Symbols of GD & T

Geometric characteristic symbols areaset offourteen Symbols used inthelanguage ofgeometric tolerancing.

The symbols aredivided into fivecategories:

1. Form

2. Profile

3. Orientation4. Location

5. Runout


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FEATURES

A feature is ageneral term appliedtoaphysical portion ofpart, suchas asurface, hole or slots,tabs.

Aneasy way to rememberthis termis to think ofa featureas apartsurface.


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FEATURES


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FEATUREOF SIZE This is one cylindrical or spherical

surface, or set oftwo opposed elements orparallel surfaces associated with sizedimension which has an axis, center lineor center plane contained within it.

Features of size are features, which dohave diameter or thickness.

These may be cylinders, such as shafts

and holes. They may also be slots,rectangular or flat parts, where twoparallel flat surfaces are considered toform a single feature.


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How ma

ny featur

e of sizear

eth

er

e?


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FEATUREOF SIZE NONFEATUREOF SIZE


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EXTERNALAND INTERNALFOS

External FOS are comprised ofpartsurfaces that are external surfaces.

Like shaft diameter or width and

height ofa planner surfaces. Internal FOS is comprised of part

surfaces (or elements) that areinternal part surfaces.

like hole diameter or the width of aslot.


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Example:


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ACTUALMATING ENVELOPE=PERFECT FEATURECOUNTERPART.

The Actual Mating Envelope (AME) ofan external feature of size is a

similar perfect feature counterpart ofthe smallest size that can becircumscribed about the feature so it

just contacts the surfaces at thehighest points with in the tolerancezone.


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Actual Mating Envelope (AME) of an external

FOS


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ACTUALMATING ENVELOPE

=PERFECT FEATURECOUNTERPART

The actual mating envelope (AME) ofan internal feature of size is a similar

perfect feature counterpart of thelargest size that can be inscribedwithin the feature so that it justcontacts the surfaces at their highestpoints with in the tolerance zone.


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Actual Mating Envelope (AME) of an internal FOS


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Actual Mating Envelope (AME) of an internalFOS


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MATERIALCONDITIONS

A geometric tolerance can be specified toapply at the largest size, smallest size oractual size ofa feature of size.

Maximum Material Condition (MMC)Maximum material condition is thecondition in which a feature of sizecontains the maximum amount of material

everywhere within the stated limits ofsize.


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MMC

MMC ofexternal FeatureOf Size


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LEAST MATERIALCONDITION(LMC)

Least material condition is the condition inwhich a feature of size contains the leastamount of material everywhere within thestated limits of size .

LEASTMATERIALCONDITION


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Regardless of feature size(RFS)

Regardless of f eature size is the term thatindicates a geometric tolerance applies atany increment of size ofthe feature withinits size tolerance. NO Bonus tolerance

RFS applied only to size features, such ashole, shafts, pins, etc.; feature which havean axis, centerplane or centerline.

Symbol : S


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Material Condition Usage Each material condition is used for

different functional reasons.

Geometric tolerances are often specifiedto apply atMMC whenthe function ofa

FOS is assembly.

Geometric tolerances are often specifiedto apply atLMC to insureaminimum

distance onapart.

Geometric tolerances are often specifiedto apply at RFS to insure symmetrical

relationships.


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MODIFIERS

Modifiers communicateadditionalinformation aboutthedrawing or

Tolerancing ofapart.

Therearenine common modifiers

used ingeometric tolerancing.


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Eight modifiers


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PROJECTED TOLERANCE ZONE Symbol: P

The projected tolerance zone modifierchanges thelocation ofthe tolerance zone on the part.

It projects the tolerance zone above the part surface.

Height ofthe projected tolerance zone should beequal to the max. thickness ofthe mating part.


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FEATURECONTROLFRAMEWITHA

PROJECTED TOLERENCE ZONE SYMBOL


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Using a Projected Tolerance Zone

A projected tolerance zone is a tolerance zonethat is projected above the part surface.

A projected tolerance zone modifier is specified

as P


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TANGENT PLANEMODIFIER

The tangent plane modifierdenotes that only thetangent plane ofthe toleranced surface needs to bewithin this tolerance zone.


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DIAMETERMODIFIER ( )

Thediameter symbol is usedtwo ways:

inside a feature control frameas a modifierto denotethe shape ofthetolerance zone, oroutside the feature control frameto simplyreplacethe word "diameter.


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Insidethe featurecontrol frame

Outsidethe featurecontrol frame


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ReferenceModifierExample:


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RADIUS MODIFIER (R)

Arcs aredimensioned withradius symbolondrawings.

Aradius is astraight line extending fromthe center ofanarc ora circleto its

surface. The Symbol foraradius is "R.

Whenthe "R" symbol is used, it creates azonedefined by two arcs.

Thepart surface must lie withinthis zone.

Thepart surface may haveflats orreversals withinthetolerance zone.


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Radius modifier


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ControlledRadius (CR)

The symbol fora controlledradius is "CR.

it creates atolerance zonedefined by two

arcs.

Thepart surface must be withinthe

crescent-shapedtolerance zoneand beanarc without flats orreversals.


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CONTROLRADIUS


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DATUMFEATURE SYMBOL

DATUM IDENTIFYING

LETTER


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DATUMFEATURE SYMBOLSONAFEATURE

SURFACE

AN

DAN

EX

TEN

SION

L

INE


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PLACEMENT OFDATUMFEATURE SYMBOLS

ONFEATURES OF SIZE


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PLACEMENTOFDATUMFEATURE SYMBOL IN

CONJUNCTIONWITHAFEATURECONTROLFRAME


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DATUM TARGET SYMBOL


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56BASIC DIMESNSION SYMBOL


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BETWEEN SYMBOL


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COUNTERSINKSYMBOL


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DEPTH SYMBOL


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SYM

BOL

FO

RALL

A

RO

UN

D


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ECON

TROL

F

RAME


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FeatureControl Frame

Geometric tolerances are specifiedonadrawingthroughthe use ofafeature control frame.

Symbol ofGeometric Tol.

Zone ofTolerance

P.D S.D T.D

W or w/o zone Modifier


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FEATURECONTROLFRAME

INCORPORATINGADATUM REFERENCE

SYMBOL


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Feature Control Frame


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ORDEROF PRECEDENCEOFDATUM

REFERENCE


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COMBINED FEATURECONTROLFRAME

AND DATUMFEATURE SYMBOL


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Thank You


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Exercises:

1

.A slot

isa

n . Size.


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Exercises:

1

.A slot

isa

n Int

er

na

l Featur

e of Size.2. The surface ofarectangular plate is a


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2. The surface ofarectangular plate is a feature.

3. The tangent plane modifier is specified for


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3. The tangent plane modifier is specified forparallelism.

4.The projected tolerance modifier is generallyapplied to holes.


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4.The projected tolerance modifier is generallyapplied to tapped holes.

5.. Dimension is a numerical value usedto describe theoretically exact size, true profile,orientation,or location ofa feature.


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5. Basic Dimension is a numerical value used todescribe theoretically exact size, true profile,

orientation,or location ofa feature.6.A . .. is a part feature thatexists on the part & contacts a datum.


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6.A Datum Feature is a part feature that exists onthe part & contacts a datum.

7. .. Dimensions should be used to locatedatum ... Relative to each otherdatums on the part.

7 D Di i h ld b d l


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7. Datum Dimensions should be used to locatedatum Target Points Relative to each other datums

on the part.8. The symbol for Controlled Radius is .


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8. The symbol for Controlled Radius is CR.

9. In ASME Y 14.5M 1998, M stands for


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9. In ASME Y 14.5M 1998, M stands for

Metric.

10. Three major disadvantages of RectangularTolerance zones are:


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10. Three major disadvantages of RectangularTolerance zones are:

1. Square / RectangularTolerance zones

2. Fixed Size Tolerance zones

3. Ambiguous instructions for Inspection.

The End of Chapter2

gd & t raghu nxpowerlite

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