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Chapter 16Chapter 16

EngineeringDrawing and Design

EngineeringDrawing and Design

Seventh EditionSeventh Edition



GD&T stands for Geometric

Dimensioning & Tolerancing

DIMENSION is a geometriccharacteristic the size of which is

specified such aslength,angle,location,or center distance

TOLERANCE on a dimension is the total

permissible variation in its size, which isequal to the difference between thelimits of size.



GEOMETRIC DIMENSIONING

AND TOLERANCING

DIMENSIONS OF A PART




AND TOLERANCING

TOLERANCE SIZES




AND TOLERANCING

TYPE OF TOLERANCE




AND TOLERANCING

SIZES OF MATING PARTS



Deviations

The difference between the basic sizeand the maximum and minimum sizes

are called the UPPER & LOWERdeviations.

The BASIC DIMENSION represents the

theoretical exact size or location of afeature.




AND TOLERANCING

BASIC (EXACT) DIMENSIONS

Are shown in a rectangle to indicate that the tolerances in the

general tolerance note do not apply



Datum

A DATUM is a theoretical exact feature from whichdimensions may be taken.

A DATUM is generally chosen as an edge or featurewhich has the greatest influence in a specificmeasurement.




AND TOLERANCING

EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM

AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED



Geometric Tolerance

A geometric tolerance is the maximumpermissible variation of form, profile,

orientation, location, and runout from that indicated or specified on a drawing.

Feature control frame for an individualfeature is divided into compartments

containing, at the least, the geometrictolerance symbol and the geometric tolerancevalue



Feature control frame (fig.16-16)

Geometric characteristic symbol

Geometric tolerance

Datums (if used)

Modifiers as required (*MMC forexample)




AND TOLERANCING

GEOMETRIC CHARACTERISTIC SYMBOLS

16-2

16-5

STRAIGHTNESSFORMINDIVIDUAL

FEATURES

SEEUNITSYMBOLCHARACTERISTIC

TYPE OF

TOLERANCEFEATURE




AND TOLERANCING


16-4MAXIMUM

MATERIAL

CONDITION

SUPPLEMENTARY

SYMBOLS

SEEUNIT

SYMBOLCHARACTERISTICTYPE OF

TOLERANCE

FEATURE




AND TOLERANCING


16-4LEAST

MATERIAL

CONDITION

SUPPLEMENTARY

SYMBOLS

SEEUNIT


TOLERANCE

FEATURE




AND TOLERANCING


16-9PROJECTEDTOLERANCE

ZONE

SUPPLEMENTARY

SYMBOLS

SEEUNIT


TOLERANCE

FEATURE




AND TOLERANCING


16-9

16-11

BASICDIMENSION

SUPPLEMENTARY

SYMBOLS

SEEUNIT


TOLERANCE

FEATURE




AND TOLERANCING


16-6DATUM

FEATURE

SUPPLEMENTARY

SYMBOLS

SEEUNIT


TOLERANCE

FEATURE



More on FORM TOLERANCES

Straightness-a condition in which theelement of a surface or a median line is

a straight lineFlatness of a surface is a condition inwhich all surface elements are in one

plane




AND TOLERANCING

FEATURE CONTROL FRAME




AND TOLERANCING

APPLICATION OF FEATURE CONTROL FRAME

ATTACHED

USINGA LEADER



MMC, RFS, LMC applies to features subject

to variations in size

MMC (Maximum Material Condition) is when a featureor part is at the limit of size, which results in itscontaining the maximum amount of material.

LMC (Least Material Conditon) refers to the size of afeature that results in the part containing theminimum amount of material. Thus it is theminimum limit of size for an external feature.

RFS (Regardless of feature size) indicates that ageometric tolerance applies to any size of a featurethat lies within its size tolerance.



Datums and the 3-plane concept (16-5)

Datum is a theoretical point, line, plane,or other geometric surface fromwhich

dimensions are measured when sospecified or to which geometrictolerances are referenced

Datum feature is a feature of a part,such as a surface, that forms the basisfor a datum or is used to establish itslocation



3-plane system

The three planes constitue a datumsystem from which measurements can

be taken. They will appear on thedrawing.

Datum feature symbol is used on the

drawing to identify these surfaces




AND TOLERANCING

THE DATUM PLANES



Orientation tolerancing (16-6) Angularity, parallelism and perpendicularity are

orientation tolerances applicable to related features

Angularity is the condition of a surface or axis at a

specified angle (other than 90or 0) from a datum

plane or axis

Perpendicularity is the condition of a surface at 90 to

a datum plane or axis. *A perpendicularity tolerance

for a flat surface specifies a tolerance zone defined

by two parallel planes perpendicular to a datum plane

or axisParallelism is the condition of a surface equidistant at

all points from a datum plane. Parallelism for a flat

surface specifies a tolerance zone defined by two

planes or lines parallel to a datum plane or axis.



Datum Targets (16-11)

Datum target symbols are used to locate specificreference positions to be used on large datumsurfaces*

the surface of a feature may be so large that a gagedesigned to make contact with the full surface maybe too expensive or cumbersome to use

Functional requirements of the part may necessitate

the use of only a portion of a surface as a datumfeature



CAD APPLICATIONS

TOLERANCE DIALOG BOX



CAD APPLICATIONS

TOLERANCE SYMBOL DIALOG BOX

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