General GDT Information

8/18/2019 General GDT Information

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Geometric Dimensioning

and Tolerancing

Course Number

Instructor’s name

Planchard Copyright 2013


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hat is Geometric Dimensioning

and Tolerancing !GDT"# It is a system o$ symbols% rules and de$initions

used to de$ine the shape &Roundness,

Flatness, Cylindricity% etc'( and design Intent

&parallel, perpedicular, concentric% et'( o$ themodel'



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)b*ecti+es o$ GDT

# De$ine parts based on $unction

# Include geometric as ,ell as si-e

tolerances

# .acilitate inspection and /uality control

# educe need $or notes

# Capture design intent# Clari$y tolerances $or international use

# liminate tolerance stacup



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)b*ecti+es o$ GDT)rthogonal Datum Planes !321" ule

3 points o$ contact

1 point o$ contact

4 rule that de$ines the

minimum number o$ contact

points necessary to properly

locate a part ,ithin the datum

re$erence $rame' The primary

datum re/uires three

points% the secondary datum

t,o points% and the tertiarydatum one point'

2 points o$ contact



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5imple Part ,ith GDT

Dimension tolerance does not say anything about the shape o$ the part6

GDT controls the shape and the initial design intent'

Tolerance o$ the

$eature

Design Intent

oundness symbol o$

the $eature

Primary datum5econdary datum

Tolerance o$

the dimension

Design Intent

Perpendicularity

symbol o$

$eature



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Tertiary datum

5econdary datum

Primary datum

.latness symbol

o$ the $eature

Perpendicularity symbolo$ the $eature

Position symbol

o$ the $eature7 8ole


GDT controls the shape and the initial design intent'

Tolerance o$

the dimension

Tolerance o$ the datum

$eature



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oundness7 &459 :1;'


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oundness7 &459 :1;'


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:esNo

Perpendicularity symbol

o$ the $eature


o$ the $eature

.latness symbol

o$ the $eaturePrimary Datum plane



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4ngularity symbol

o$ the $eature

?ie, the selected Datum

planes% the angularity symbol

,as added a$ter,ards6


o$ the $eature



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Note7 The di$$erent Datum planes selected

to display the 4ngularity symbol

o$ the $eature $rom the pre+ious slide6

4ngularity symbol

o$ the $eature

.latness symbol

o$ the $eature


o$ the $eature



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GDT controls the shape and the initial design intent

Datum C is the $ace o$ the $eature7 5imple 8ole

Position symbol

o$ the $eature

.latness symbolo$ the $eature

)$$set% arro,s ,ill not $it'



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GDT controls the shape and the initial design intent

Position symbol

o$ the $eature

.latness symbol

o$ the $eature



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Parts Do Not Have Center Lines - Features Have Axes

Center lines are a dra$ting con+enience' 4ssociate the datum $eature symbol

,ith datum $eatures6

Total runout symbolo$ the $eature

No !.or Construction" Centerline6



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Coaxial Diaeters T,o &or more( diameters that are sho,n on the

dra,ing as being on the same centerline &a@is('

e+ol+ed Aase .eature 7 4@is o$ re+olutions?s' @truded Aase .eature'

Circular runout symbol

o$ the $eature

Circular runout symbol

o$ the $eature



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Pro$ile o$ a 5ur$ace symbol

o$ the $eature

Tertiary Datum

Primary Datum

5econdary Datum



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GDT 5ymbols

http7BB,,,',isconline'comBob*ectsBinde@t*'aspob*IDENG1FF0;



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De$ault Document Datum

Tolerances &Dimpert(



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9aterial Condition 5ymbols

# 9a@imum 9aterial Condition &99C(

H largest sha$t% smallest hole

# east 9aterial Condition &9C(

H smallest sha$t% largest hole

# egardless o$ .eature 5i-e &.5(

9

5



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Tolerance Jones ,ithout GDT

9eans this6

The tolerance area or boundary ,ith that $orms the

.eature may +ary ,hen no tolerance o$ the $eature is pro+ided



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GDT ule 1

# Indi+idual .eature o$ 5i-e

H here only a tolerance o$ si-e is speci$ied%

the limits o$ an indi+idual $eature prescribe the

e@tent to ,hich +ariations in its geometric$orm% as ,ell as si-e% are allo,ed'



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ocation Controls

# Position

# Concentricity

# unout



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GDKT True Positioning

Note circular tolerance -ones



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5traightness



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.latness

The sur$ace must be ,ithin the

tolerance o$ si-e and must lie bet,eent,o parallel planes7 0'2< apart &$eature

tolerance(

5ymbol

Tolerance o$

the $eature



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oundness

ach circular element o$ the 5ur$ace in any

plane perpendicular to 4 common a@is must

be ,ithin the speci$ied tolerance o$ si-e' It also

must lie bet,een t,o concentric circles H one

ha+ing a radius o$ 0'2< larger than the other6

5ymbolTolerance o$

the $eature



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Cylindricity

The cylindrical sur$ace must be ,ithin the

speci$ied tolerance o$ si-e% in this e@ample 0'2<and must lie bet,een t,o Concentric cylinders H

one ha+ing a radius o$ 0'2< larger than the

other'

5ymbol

Tolerance o$

the $eature



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)rientation Controls

# Perpendicularity

# Parallelism

# 4ngularity# ine Pro$ile

# 5ur$ace Pro$ile



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Parallelism $or Planes

The sur$ace must be ,ithin the speci$iedTolerance &0'12( o$ si-e and must lie

bet,een t,o planes &0'12( apart ,hich are

parallel to Datum Plane 4'

5ymbol

Tolerance o$ $eature

Datum Plane



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Parallelism $or 4@is and Plane

The $eature a@is must be ,ithin the speci$ied

tolerance &0'12( o$ location and must lie bet,een

t,o planes &0'12( apart ,hich are parallel to the

datum plane &4( regardless o$ the $eature si-e6



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Parallelism $or T,o 4@es

The $eature a@is must be ,ithin the speci$ied tolerance&0'0


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Perpendicularity o$ 4@is +s'

Plane

The $eature a@is must be ,ithin the speci$ied

tolerance&0'0


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4ll parts are not created e/ual

Pro$ile o$ a line is a $unny control' It ,ors ,ell $or parts lie e@trusions ,here

indi+idual slices ,ill be checed' 8o,e+er% ,hen you start adding datum

re$erences% it can turn into a pro$ile o$ a sur$ace control

CNC issues6


General GDT Information

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