GD&T Overview Class April 24, 2019

Metrology Metrology is the science of measurement Dimensional metrology is that branch of Metrology which deals with measurement of “dimensions“ of a part or workpiece (lengths, angles, etc.) Dimensional measurements at the required level of accuracy are the essential link between the designers’ intent and a delivered product.

Aspects of Metrology Reference standard metrology Engineering Metrology

Basic Measurement Devices Surface Plates Test Stands Dial Gages Micrometers and Verniers Gauge Blocks

Dimensional Metrology Needs Linear measurements Angular measurements Geometric form measurements Roundness Straightness Cylindricity Flatness, etc

Dimensional Metrology Needs Geometric relationships Parallel, perpendicular, etc. Concentric, runout, etc. Controlled surface texture

Communicating Dimensional Metrology Needs Geometric Dimensioning and Tolerancing (GDT) “The language of dimensional metrology” Standard symbols, etc., on part drawings.

Specification of Linear Tolerances

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.

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.

GEOMETRIC DIMENSIONING AND TOLERANCING DEVIATIONS

GEOMETRIC DIMENSIONING AND TOLERANCING DIMENSIONS OF A PART

GEOMETRIC DIMENSIONING AND TOLERANCING TYPE OF TOLERANCE

GEOMETRIC DIMENSIONING AND TOLERANCING TOLERANCE SIZES

GEOMETRIC DIMENSIONING AND TOLERANCING SIZES OF MATING PARTS

GEOMETRIC DIMENSIONING AND TOLERANCING EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED

GEOMETRIC DIMENSIONING AND TOLERANCING EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED

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

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 Geometric characteristic symbol Geometric tolerance Datums (if used) Modifiers as required (*MMC for example)

GEOMETRIC DIMENSIONING AND TOLERANCING FEATURE CONTROL FRAME

GEOMETRIC DIMENSIONING AND TOLERANCING ATTACHED USING A LEADER APPLICATION OF FEATURE CONTROL FRAME

GEOMETRIC DIMENSIONING AND TOLERANCING BASIC DIMENSION SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

Angular Specifications

Angular Tolerances

Form Tolerances 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

More on 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

Flatness Specification

Flatness Tolerances

GEOMETRIC DIMENSIONING AND TOLERANCING STRAIGHTNESS FORM INDIVIDUAL FEATURES SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

Straightness Specification

Straightness Tolerance

Circularity Specification Checks Roundness & applies to every section

Circularity Tolerances

Surface Profile Without Datums

Line Profile Without Datums

Surface Profile with Datums Profile of a line with datums is similar

Surface Profile with Datums

Cylindricity Specifications

Cylindricity Tolerances

Surface Texture Specification

Surface Texture

Orientation 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 90⁰or 0⁰) from a datum plane or axis Perpendicularity is the condition of a surface at 90⁰ 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.

Perpendicularity Specification

Perpendicularity Measurements

Parallelism Specification

Parallelism Measurements

Concentricity Specification

Concentricity Tolerances

Concentricity Measurements

Concentricity Measurements

Circular Runout Specifications

Circular Runout Tolerances

Total Runout Specifications

Total Runout Tolerances

Position Specifications

Position Tolerances

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.

GEOMETRIC DIMENSIONING AND TOLERANCING DATUM FEATURE SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE GEOMETRIC CHARACTERISTIC SYMBOLS

Simulated Datum

Datum Selection

GEOMETRIC DIMENSIONING AND TOLERANCING DATUM TARGET SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

Datum Targets 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

GEOMETRIC DIMENSIONING AND TOLERANCING MAXIMUM MATERIAL CONDITION SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

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.

GEOMETRIC DIMENSIONING AND TOLERANCING LEAST MATERIAL CONDITION SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

GEOMETRIC DIMENSIONING AND TOLERANCING PROJECTED TOLERANCE ZONE SUPPLEMENTARY SYMBOLS SEE UNIT SYMBOL CHARACTERISTIC TYPE OF TOLERANCE FEATURE GEOMETRIC CHARACTERISTIC SYMBOLS

Datums and the 3-plane concept Datum is a theoretical point, line, plane, or other geometric surface fromwhich 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

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

GEOMETRIC DIMENSIONING AND TOLERANCING THE DATUM PLANES

GEOMETRIC DIMENSIONING AND TOLERANCING THE DATUM PLANES

GEOMETRIC DIMENSIONING AND TOLERANCING THE DATUM PLANES

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