Chapter 16 Geometric Dimensioning and Tolerancing Engineering Drawing and Design Engineering Drawing...

Chapter 16Chapter 16

Geometric Dimensioning

and Tolerancing

EngineeringDrawing and Design

EngineeringDrawing and DesignSeventh EditionSeventh Edition

GD&T stands for Geometric Dimensioning & Tolerancing

DIMENSION is a geometric characteristic the size of which is specified such as length,angle,location,or center distanceTOLERANCE on a dimension is the total permissible variation in its size, which is equal to the difference between the limits of size.

GEOMETRIC DIMENSIONING AND TOLERANCING

DIMENSIONS OF A PART


TOLERANCE SIZES


TYPE OF TOLERANCE


SIZES OF MATING PARTS

Deviations

The difference between the basic size and the maximum and minimum sizes are called the UPPER & LOWER deviations.The BASIC DIMENSION represents the theoretical exact size or location of a feature.


DEVIATIONS


BASIC (EXACT) DIMENSIONSAre 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 which dimensions may be taken.A DATUM is generally chosen as an edge or feature which has the greatest influence in a specific measurement.


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

Geometric Tolerance

A geometric tolerance is the maximum permissible variation of form, profile, orientation, location, and runout from that indicated or specified on a drawing.Feature control frame for an individual feature is divided into compartments containing, at the least, the geometric tolerance symbol and the geometric tolerance value

Feature control frame (fig.16-16)

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


GEOMETRIC CHARACTERISTIC SYMBOLS

16-216-5

STRAIGHTNESSFORMINDIVIDUAL

FEATURES

SEE UNITSYMBOLCHARACTERISTIC

TYPE OFTOLERANC

EFEATURE



16-4MAXIMUMMATERIALCONDITION

SUPPLEMENTARYSYMBOLS

SEE UNIT

SYMBOLCHARACTERISTIC

TYPE OFTOLERANC

E

FEATURE



16-4LEASTMATERIALCONDITION


SEE UNIT


TYPE OFTOLERANC

E

FEATURE



16-9PROJECTED TOLERANCE

ZONE


SEE UNIT


TYPE OFTOLERANC

E

FEATURE



16-916-11

BASIC DIMENSION


SEE UNIT


TYPE OFTOLERANC

E

FEATURE



16-6DATUMFEATURE


SEE UNIT


TYPE OFTOLERANC

E

FEATURE



16-11DATUMTARGET


SEE UNIT


TYPE OFTOLERANC

E

FEATURE

Form Tolerances

FORM TOLERANCES control the straightness, flatness, circularity and cylindricityForm tolerances apply to individual features and as such do not require locating dimensions.ORIENTATION TOLERANCES control angularity, parallelism, and perpendicularity

More on FORM TOLERANCES

Straightness-a condition in which the element of a surface or a median line is a straight lineFlatness of a surface is a condition in which all surface elements are in one plane


FEATURE CONTROL FRAME


APPLICATION OF FEATURE CONTROL FRAME

ATTACHED USING A LEADER

MMC, RFS, LMC applies to features subject to variations in size

MMC (Maximum Material Condition) is when a feature or part is at the limit of size, which results in its containing the maximum amount of material.LMC (Least Material Conditon) refers to the size of a feature that results in the part containing the minimum amount of material. Thus it is the minimum limit of size for an external feature.RFS (Regardless of feature size) indicates that a geometric tolerance applies to any size of a feature that 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 so specified or to which geometric tolerances are referencedDatum feature is a feature of a part, such as a surface, that forms the basis for a datum or is used to establish its location

3-plane system

The three planes constitue a datum system from which measurements can be taken. They will appear on the drawing.Datum feature symbol is used on the drawing to identify these surfaces


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 90 or 0 ) from a datum ⁰ ⁰plane or axis

Perpendicularity is the condition of a surface at 90 to ⁰a 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 axis

Parallelism 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 specific reference positions to be used on large datum surfaces*the surface of a feature may be so large that a gage designed to make contact with the full surface may be too expensive or cumbersome to useFunctional requirements of the part may necessitate the use of only a portion of a surface as a datum feature

CAD APPLICATIONS

TOLERANCE DIALOG BOX

CAD APPLICATIONS

TOLERANCE SYMBOL DIALOG BOX

Chapter 16 Geometric Dimensioning and Tolerancing Engineering Drawing and Design Engineering Drawing...

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