ch16 gd&t overview cmp-nice

8/12/2019 CH16 GD&T Overview Cmp-NICE

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Chapter 16

EngineeringDrawing and DesignSeventh Edition


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GD&T stands for GeometricDimensioning & Tolerancing

DIMENSION is a geometriccharacteristic the size of which is

specified such aslength,angle,location,or center distanceTOLERANCE on a dimension is the total

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


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GEOMETRIC DIMENSIONING

AND TOLERANCING

DIMENSIONS OF A PART


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AND TOLERANCING

TOLERANCE SIZES


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AND TOLERANCING

TYPE OF TOLERANCE


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AND TOLERANCING

SIZES OF MATING PARTS


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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.


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AND TOLERANCING

DEVIATIONS


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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.


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AND TOLERANCING

EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORMAT THE MAXIMUM MATERIAL CONDITION IS REQUIRED


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Geometric Tolerance

A geometric tolerance is the maximumpermissible variation of form, profile,orientation, location, and runout from thatindicated 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


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Feature control frame (fig.16-16)

Geometric characteristic symbolGeometric toleranceDatums (if used)Modifiers as required (*MMC forexample)


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AND TOLERANCING

GEOMETRIC CHARACTERISTIC SYMBOLS

16-216-5

STRAIGHTNESSFORMINDIVIDUALFEATURES

SEEUNITSYMBOLCHARACTERISTIC

TYPE OFTOLERANCEFEATURE


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AND TOLERANCING


16-9PROJECTEDTOLERANCE

ZONE

SUPPLEMENTARYSYMBOLS

SEEUNIT

SYMBOLCHARACTERISTICTYPE OFTOLERANCE

FEATURE


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AND TOLERANCING


16-916-11

BASICDIMENSION


SEEUNIT


FEATURE


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AND TOLERANCING


16-6DATUMFEATURE


SEEUNIT


FEATURE


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AND TOLERANCING


16-11DATUMTARGET


SEEUNIT


FEATURE


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Form Tolerances

FORM TOLERANCEScontrol the straightness,flatness, circularity and cylindricity

Form tolerances apply to individual featuresand as such do not require locatingdimensions.ORIENTATION TOLERANCEScontrolangularity, parallelism, and perpendicularity


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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


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AND TOLERANCING

FEATURE CONTROL FRAME


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AND TOLERANCING

APPLICATION OF FEATURE CONTROL FRAME

ATTACHEDUSINGA LEADER


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MMC, RFS, LMC applies to features subjectto 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.


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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


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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


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AND TOLERANCING

THE DATUM PLANES


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AND TOLERANCING

THE DATUM PLANES


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AND TOLERANCING

THE DATUM PLANES


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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 aspecified angle (other than 90 or 0 ) from a datumplane or axis

Perpendicularity is the condition of a surface at 90

toa datum plane or axis. *A perpendicularity tolerancefor a flat surface specifies a tolerance zone definedby two parallel planes perpendicular to a datum plane

or axisParallelism is the condition of a surface equidistant atall points from a datum plane. Parallelism for a flatsurface specifies a tolerance zone defined by twoplanes or lines parallel to a datum plane or axis.


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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 useFunctional requirements of the part may necessitate

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


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CAD APPLICATIONS

TOLERANCE SYMBOL DIALOG BOX

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