gd&t saravanan kulasekaran 27.06.16
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Geometric Dimensioning and Tolerancing
BySaravanan Kulasekaran
ME., LLB.,Technical Manager
What is Meant by GD&T
• Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances.
• It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal geometry and its allowable variation.
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ISO vs. ASME
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Comparing the ISO and the ASME Approaches to GD&T
Issue or Topic ISO ASME
Approach
Explanation
Cost of Standards
Number of Standards
Theoretical Functional
Graphical, Few Words
700 – 1000 USD
10 - 16
Comprehensive
< 100 USD
1
ASME Y14.5M – 2009 Structure Section 1 Scope, Definitions, and General Dimensioning
Section 2 General Tolerancing and Related Principles
Section 3 Symbology
Section 4 Datum Reference Frames
Section 5 Tolerances of Form
Section 6 Tolerances of Orientation
Section 7Tolerances of Location
Section 8 Tolerances of Profile
Section 9 Tolerances of Runout
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5
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Fundamental Rules• Each dimension shall have a tolerance.
(except for those dimensions specifically identified as reference, maximum, minimum, or stock)
• Ensure full understanding of each feature.
• Show the detail needed and no more.
• Serve function needs, no misinterpretation.
• Manufacturing methods are not specified.
• Non-mandatory dimensions are OK.
• Designed of optimal readability.
• Tolerances apply for full size of feature.
• Dimensions and tolerances only apply at the drawing level where they were specified.
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Angular Units
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Decimal Inch Dimensions
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Millimetre Dimensions
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Application of Dimensions
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Grouping of Dimensions
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Spacing of Dimension Lines
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Staggered Dimensions
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Point Locations
Breaks in Extension Lines
Oblique Extension Lines
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Leader-Directed Dimensions
Minimizing Leaders
Leaders
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Overall Reference Dimension
Intermediate Reference Dimension
Reading Direction
Diameters
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Radii With Unlocated Centers
Radius With Located Center
Radii
Foreshortened Radii
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Round Holes
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Round Holes
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Round Holes
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Countersunk and Counter drilled Holes
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Internal Chamfers
Chamfers
Chamfers Between Surfaces at OtherThan 90°
Key seats
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KNURLING
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Rectangular Coordinate Dimensioning
Rectangular Coordinate Dimensioning Without Dimension Lines
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Rectangular Coordinate Dimensioning in Tabular Form
Polar Coordinate Dimensioning Repetitive Features and Dimensions
Repetitive Features and Dimensions
Repetitive Features
Section-2 General Tolerancing and Related
Principles
Key Definitions• Tolerance – The total permissible variation in size for a
specified dimension.
• Bilateral Tolerance – A tolerance zone where the boundary conditions contain the specified dimension.
• Geometric Tolerance – A general term that refers any of the 14 symbols used to control form, orientation, profile, runout, or location.
• Unilateral Tolerance – A tolerance zone that only exists on one side of the specified dimension.
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Limit Dimensioning
Plus and Minus Tolerancing
Tolerance Accumulation
Tolerance Accumulation
Section-03 Symbology
Geometric Characteristic Symbols
BEZELCASE
CLAMP
PROBE
DIAL INDICATOR
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810 12 10
8
6
422
4
Dial Indicator
Verification of Flatness
Z
DATUMREFERENCEFRAME
SURFACEPLATE
GRANITE
PROBE
COORDINATE MEASURING MACHINEBRIDGE DESIGN
Coordinate Measuring Machine
STRAIGHTNESS
Straightness is a condition where an element of a surface,or derived median line, is a straight line. A straightnesstolerance specifies a tolerance zone within whichthe considered element of a surface or derived medianline must lie. A straightness tolerance is applied in theview where the elements to be controlled are representedby a straight line.
STRAIGHTNESS
FLATNESSFlatness is the condition of a surface or derived median plane having all elements in one plane. A flatness tolerance specifies a tolerance zone defined bytwo parallel planes within which the surface or derived median plane must lie.
Checking for Flatness
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CIRCULARITY
Definition Circularity exists when all of the points on a perpendicular cross section of a cylinder or a cone are equidistant to its axis.
Tolerance Zone Two concentric circles that contain each circular element of the surface.
Note: Circularity also applies to spheres
Checking for Circularity
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CYLINDRICITY
Definition Cylindricity exists when all of the points on the surface of a cylinder are equidistant to a common axis.
Tolerance Zone Two concentric cylinders that contain the entire cylindrical surface.
Checking for Cylindricity
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PROFILE OF A LINE Profile of a line is of course closely related to profile of a surface. The difference being that profile of a line takes only the measurement at a specific cross section, and does not take into account the variance of one cross section to the next.
PROFILE OF A SURFACEProfile of a surface describes a 3-Dimensional tolerance zone around a surface, usually which is an advanced curve or shape. If it is called out on a curved surface, like a fillet on a welded part, the entire surface where the radius is has to fall within the tolerance zone.
ANGULARITY
Two parallel planes or lines which are oriented at the specified angle in relation to a datum. All points on the referenced surface must fall into this tolerance zone.
Checking for Angularity
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ANGULARITY• is the condition of a surface, axis, or median plane which
is at a specific angle (other than 90°) from a datum plane or axis.
• Can be applied to an axis at MMC.• Typically must have a Basic dimension.
The surface is at a 45º angle with a .005 tolerance zone relative to datum A.
PERPENDICULARITY
• is the condition of a surface, center plane, or axis at a right angle (90°) to a datum plane or axis.Ex:
The tolerance zone is the space between the 2 parallel lines. They are perpendicular to the datum plane and spaced .005 apart.
The perpendicularity of this surface must be within a .005 tolerance zone relative to datum A.
PERPENDICULARITY
• Location of hole (axis)
This means ‘the hole (axis) must be perpendicular within a diametrical tolerance zone of .010 relative to datum A’
Checking for Perpendicularity
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±0.01
PARALLELISM:• The condition of a surface or center plane equidistant at all points
from a datum plane, or an axis.• The distance between the parallel lines, or surfaces, is specified by
the geometric tolerance.
Checking for Parallelism
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Position Tolerance
• A position tolerance is the total permissible variation in the location of a feature about its exact true position.
• For cylindrical features, the position tolerance zone is typically a cylinder within which the axis of the feature must lie.
• For other features, the center plane of the feature must fit in the space between two parallel planes.
• The exact position of the feature is located with basic dimensions.
• The position tolerance is typically associated with the size tolerance of the feature.
• Datums are required.
Concentricity
Definition Concentricity defines the location of cylindrical features about an axis of rotation.
Tolerance Zone The tolerance zone is defined as a cylinder about the datum axis that must contain the median points of diametrically opposed elements of a feature.
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A
Checking for Concentricity
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Runout Tolerances
• Circular Runout
• Total Runout
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2-D Application
3-D Application
Runout
Definition Runout is a composite control used to specify functional relationships between part features and a datum axis.
Tolerance Zone Circular runout is a 2-D application that evaluates full indicator movement on a perpendicular cross section rotating about a datum axis. Total runout evaluates full indicator movement of the full surface rotating about a datum axis.
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3-D Application 2-D Application
Checking for Runout
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Symmetry
Definition Symmetry defines the location of non-cylindrical features about a derived median plane.
Tolerance Zone The tolerance zone is defined by two planes, equidistant to a datum center plane. The derived median points must fall within these two planes.
A
Set Up for Symmetry
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Geometric Characteristic Symbols
TO BE CONTINUED ON SESSION 02
Material Source: Google Internet
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