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Guia do In

Dimensiona

Geomtrico e Tole

Tho

Co-Chair of North Texas SolidW

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Anteriormente, no mundo de SolidWorks

Trs faz uma trilogia... Ou so cinco...

Em 2009, "Como formar GD & T" comeou nossa discusobre Dimensionamento Geomtrico e Tolerncia conce

se nos quatorze smbolos bsicos, utilizando o grfico F

Em 2010, "Como formar GD & T Parte II: Retaliao da

circundadas" se concentraram nos modificadores de s

GD & T. Agora em 2013, estamos prontos para o prximo captu

emocionante na Saga GD & T, onde vamos responder

"Para GD & T, o Universo e tudo mais".

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Resposta GD & T, vida e tudo.

14 smbolos, cada um com um nome, smboloe controle

14x3 = 42

Coincidncia? Acho que no ...

Srio, este um mtodo de organizar GD & T

para melhorar a curva de aprendizado.

O Chart FOPRL

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Updated

FOPRL ChartNow based on ASME

Y14.5-2009

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Rule #1 of GD&T states that the geometric

of a feature can vary so long as it stays wthe limits of its size tolerance.

Another way of saying this rule is to say si

tolerance is the primary control of a featuthat GD&T is a refinement within that tole

The f i rs t magn i tude of con trol is size.

First Lesson in G

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GD&T symbols refine the shape or geometry.

Refining implies that you first simply check the

dimensions of the part to the drawing before y

check the refinement.

The best example to illustrate this is not from t

GD&T standard but from the surface finish cal

Whats Rule #1 Me

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Surface finish is a measurement of the surfaceroughness.

Surface roughness height is measured:

microinches (millionths of an inch)

micrometers (millionths of a meter)

Roughness spacing is measured in inches ormillimeters.

Surface Rough

Surface Fi

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A Maximum Roughness Average

B Minimum Roughness Average

C Machining Allowance

D Lay Symbol

E Roughness Sampling Length

F Maximum Waviness Height Rating

G Maximum Waviness Spacing Rating

Surface Rough

Sym

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Surface Rough

Removal of Mat

Do NotRemove

MaterialMeth

No

Spec

Remove

Material

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Perpendicular to surface indicated

(wink) we like this symbol

= Parallel to surface indicated

X Angular in both directions

M Multidirectional

C Circular with center on surface indicated

R Radial with center on surface indicated

P Nondirectional, pitted, or protuberant

Surface Rough

Surface Lay Sym

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You dont start by inspecting the surface finish of a plate

Initially you would measure the length, width, and thickn

make sure the dimensions are in tolerance.

If the parts dont match the tolerances then it doesnt make

waste time checking how the surface is finished.

The last inspection step would be to check the surface f Surface Roughness is a refinement of the limits of size.

Surface Rough

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If the first rule of GD&T states that the geometric form of a

can vary so long as the feature stays within the limits of ittolerance then we better understand limits of size.

The limits of size are the minimum acceptable measure v

maximum acceptable measured value for a dimension.

Geometric tolerancing should only be added when form mmore accurately controlled or to convey functional/interch

requirements.

Rule #1 Revi

Li i f Si E

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Min Max

.625 .675

1.450 1.550

3.900 4.100

.550 .650

40 45

0 .750

.475 .525

.95 1.05

.08 .18

2.500 has no tolerance

Limits of Size Exam

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What is the difference in connotation in a limits dimensio

bilateral toleranced dimension?

Isnt .100-.150, the same as .125.025?

Answer #1: Limits of acceptable dimensions are identical

Answer #2: Manufacturing people dont target .125 when

limits but rather the tool safe side and let wear bring them

the other extreme.Answer #3: What should the CAD model show for limit dim

The average is not really the target so why not show it a

the minimum or maximum values?

Op

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Section 2.1:

If CAD/CAM database models are use

they do not include tolerances, t

tolerances must be expressed outsi

the database to reflect design

requirements.

This section clearly states that models mayi

tolerances hence paving the way to eliminconventional drawings someday!

ASME Y14.5M-1994 CAD/CAM

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In Section 1.2.1 Cited Standards now has ASME

2003 (reaffirmed in 2008) Digital Product Defin

Data Practices.

Provides guidance to 3D model with embedded dimensi

tolerances.

Numerous new citations back to this standard.

This topic came up in one of my Primer lectures and I w

mention that the embedded 3D data has been allowed

1984 but now it is really well documented.

ASME Y14.5-2009 CAD/CAM

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What if you want a straight edge?

You can tighten the linear tolerances bu

can get expensive it can cost you timeyield.

How about we control the shape?

Hey, we need some kind of ShapContro l o r maybe Geometr ic

Dimens ioning and Toleranc ing!

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Towels

Do you have yours?

Everyone knows that if you arecaught Hitchhiking through the

Galaxy with your towel then they

assume you have everything you

need.

In lieu of a towel, how about we all

learn something about GD&T toshow everyone we have everything

we need.

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Like I said, we have already discussed

symbols and modifiers, so the next stopGD&T primer train is the Tolerance Zon

Shapes station.

These sound like the same thing but the

two separate but related items for tolera

Tolerance Zones and Sha

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Cylindrical zone sounds easy - its a circ

cylinder within which the feature must rebe acceptable.

What shape is a total wide zone?

Heres where it gets complicated and onthe reasons I originally built the FOPRL

lets look at the shapes.

Tolerance Zone Sha

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Total Wide Tolerance Zone

Just a Pinch

The size of the of total

wide zone can beindicated by holding your

thumb and fore finger

together without quite

touching. The trick is how you

move your hand.

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All controls can have TOTAL WIDE TOLERANCE ZONESExcept Concentricity.

Only five can have a CYLINDRICAL TOLERANCE ZONE

Position

Orientation

Parallelism, Angularity, Perpendicularity

Straightness

Concentricity requires CYLINDRICAL TOLERANCE ZON

Tolerance Zo

Posit ion to lerance zone

and bo sses are always

tolerance zone

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Tolerance Zone Symbolog

Total wide zone is default

UNLESS...You put the diameter symbol

f .014m U

j n.002l Y

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Each geometric control has its own total wide toleshape that is suggested by its name.

Form

Straightness: between two lines

Flatness: between two planesCircularity: between two circles

Cylindricity: between two cylinders

Tolerance Zone Sh

Form Total W

C

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Form C

2D

2D

T l Z Sh

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For all three orientation controls, the surfaces musbetween two planes.

Parallel

Angularity

Perpendicular

Hold it a second, we just said flatness control was

between two planes.

Tolerance Zone Sh

Orientation Total W

O i t ti C l

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Orientation Cal

T l Z Sh

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ProfileLine: between two curves that are the shape

of the feature

Surface: between two surfaces that are the

shape of the feature

Runout

Full indicator movement

Tolerance Zone Sh

Profile / Runout Total W

P fil C

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Profile Ca

R t C

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Runout Ca

T l Z Sh

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Position: depends on the geometry it controlsBetween resultant and virtual conditions and fix

floating fastener theory, theres a days worth

topics on positional tolerances.

Symmetry: two planes

Concentricity: cylindrical

Tolerance Zone Sh

Location Controls Total W

Position Ca

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Position Ca

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Rule 1 has four (countem four) exceptions:

Stock parts : Bars, sheets, tubing, structural shapes

Parts subject to free state variation

Add note to a surface or feature: PERFECT FORM AT

NOT REQUIRED.

Straightn ess tolerance on features of size with MMapplied.

Straightness is the important exception at the e

Straightness Excep

Straightness Tolera

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Pretty much, just like it sounds.

The shaft shown below can be shaped like a sm

face and still be acceptable.

Straightness Toleraon Features of Size with MMC Ap

J

No Equ

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New Unequally Disposed Profile Symbol is a U in a circle.

This concept has always been in the standard but required you uchain lines and basic dimensions to determine the distribution of profile tolerance zone other than 50%-50% (practice still allowed

In the feature control frame you add the symbol and the value of much material you want to add.

0.5 U 0.5 means it is all added

0.5 U 0 means it can only remove material

0.5 U 0.1 means it can be 0.1 added material and no more than 0.4removed.

No Equ

How much is

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How much is

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Thi i li fl t f 1

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This implies a flatness of .1

Independe

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New Independency Symbol is an I in a circle.

Previous standard required you write out Perfect Form (or LMC) is not required.

Example: If you say a shaft is toleranced at MMC then i

straight but size may be all that is important to you so yo

This choice of symbol and wording baffles me If would

gone Old School Ghostbusters and made a circular no swith a slash through it and PF inside.

Independe

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Wrap Up

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p p

So Long and Thanks fo r all the Fish

Its not quite Vogon poetry but being made to listen to lec

GD&T is still pretty bad I hope todays discussion helps you and other of the thir

creatures on the planet get something more out of GD&T

Any questions?

I am happy to respond to most GD&T questions via em

[email protected]

Please be safely travel ing back hom
mailto:[email protected]:[email protected]

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