geometric dimensioning and tolerancing standards

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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 distance Tolerance: On a dimension is the total permissible variation in its size, which is equal to the difference between the limits of size. 1

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  • 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 distance

    Tolerance: On a dimension is the total permissible variation in its size, which is equal to the difference between the limits of size.

    1

  • DIMENSIONS OF A PART 2

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • TOLERANCE SIZES 3

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • TYPE OF TOLERANCE 4

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • SIZES OF MATING PARTS

    5

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • 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.

    6

    Deviations

  • DEVIATIONS

    7

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • BASIC (EXACT) DIMENSIONS Are shown in a rectangle to indicate that the tolerances in the general tolerance note do not apply

    8

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • 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.

    9

    Datum

  • EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED 10

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED 11

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • A geometric tolerance is the maximum permissible variation of form, profile, orientation, location, and run-out 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

    12

    Geometric Tolerance

  • Geometric characteristic symbol

    Geometric tolerance

    Datums (if used)

    Modifiers as required (*MMC for example)

    13

    Feature Control Frame

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    STRAIGHTNESS FORM

    INDIVIDUAL

    FEATURES

    SYMBOL CHARACTERISTIC

    TYPE OF

    TOLERANCE FEATURE

    14

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    MAXIMUM

    MATERIAL

    CONDITION

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    15

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    LEAST

    MATERIAL

    CONDITION

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    16

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    PROJECTED TOLERANCE

    ZONE

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    17

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    BASIC DIMENSION

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    18

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    DATUM

    FEATURE

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    19

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • GEOMETRIC CHARACTERISTIC SYMBOLS

    DATUM

    TARGET

    SUPPLEMENTARY

    SYMBOLS

    SYMBOL CHARACTERISTIC TYPE OF

    TOLERANCE

    FEATURE

    20

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • Form tolerances control the straightness, flatness, circularity and cylindricity.

    Form tolerances apply to individual features and as such do not require locating dimensions.

    Orientation tolerances control angularity, parallelism, and perpendicularity

    21

    Form Tolerances

  • Straightness a condition in which the element of a surface or a median line is a straight line.

    Flatness of a surface is a condition in which all surface elements are in one plane.

    22

    More on Form Tolerances

  • FEATURE CONTROL FRAME

    23

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • APPLICATION OF FEATURE CONTROL FRAME

    ATTACHED USING

    A LEADER

    24

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • 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 Condition) 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.

    25

    MMC, RFS, LMC: Applies to features subject to variations in size

  • Datum is a theoretical point, line, plane, or other geometric surface from which dimensions are measured when so specified or to which geometric tolerances are referenced

    Datum 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

    26

    Datum's and the 3-plane Concept

  • The three planes constitute 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

    27

    3-plane System

  • THE DATUM PLANES 28

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • THE DATUM PLANES 29

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • THE DATUM PLANES 30

    GEOMETRIC DIMENSIONING AND TOLERANCING

  • 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 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. 31

    Orientation Tolerancing

  • 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 use.

    Functional requirements of the part may necessitate the use of only a portion of a surface as a datum feature.

    32

    Datum Targets