This document provides an overview of geometric dimensioning and tolerancing (GD&T). It defines GD&T as a system for defining and communicating engineering tolerances using a symbolic language on drawings. It compares GD&T standards from ISO and ASME, describing differences in their approaches. The document also outlines the structure of the ASME Y14.5M-2009 standard and provides explanations and examples of common GD&T concepts like geometric characteristic symbols, flatness, circularity, position tolerance, and more.

1. Geometric Dimensioning and
Tolerancing
By
Saravanan Kulasekaran ME.,
LLB.,
Technical Manager

2. 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.
2

3. ISO vs. ASME
3
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

4. 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 7 Tolerances of Location
Section 8 Tolerances of Profile
Section 9 Tolerances of Runout
4

5. 5

6. 6

7. 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.
7

8. Angular Units
8

9. Decimal Inch Dimensions
9

10. Millimetre Dimensions
10

11. Application of Dimensions
11

12. Grouping of Dimensions
12

13. Spacing of Dimension Lines
13

14. Staggered Dimensions
14

15. 15
Point Locations
Breaks in Extension Lines
Oblique Extension Lines

16. 16
Leader-Directed Dimensions
Minimizing Leaders
Leaders

17. 17
Overall Reference Dimension
Intermediate Reference Dimension
Reading Direction
Diameters

18. 18
Radii With Unlocated Centers
Radius With Located Center
Radii
Foreshortened Radii

19. 19
Round Holes

20. 20
Round Holes

21. 21
Round Holes

22. 22
Countersunk and Counter drilled Holes

23. 23
Internal Chamfers
Chamfers
Chamfers Between
Surfaces at Other
Than 90°
Key seats

24. 24
KNURLING

25. 25
Rectangular Coordinate Dimensioning
Rectangular Coordinate Dimensioning Without Dimension Lines

26. 26
Rectangular Coordinate Dimensioning in Tabular Form

27. Polar Coordinate Dimensioning Repetitive Features and Dimensions
Repetitive Features and Dimensions
Repetitive Features

28. Section-2 General
Tolerancing and Related
Principles

29. 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.
29

30. Limit Dimensioning

31. Plus and Minus Tolerancing

32. Tolerance Accumulation

33. Tolerance Accumulation

34. Section-03
Symbology

35. Geometric Characteristic Symbols

36. BEZEL
CASE
CLAMP
PROBE
DIAL INDICATOR
6
8
10
12
10
8
6
4
22
4
Dial IndicatorDial Indicator

37. Verification of
Flatness

38. Z
DATUM
REFERENCE
FRAME
SURFACE
PLATE
GRANITE
PROBE
COORDINATE MEASURING MACHINE
BRIDGE DESIGN
Coordinate Measuring
Machine
Coordinate Measuring
Machine

39. STRAIGHTNESS
Straightness is a condition where an element of a surface,
or derived median line, is a straight line. A straightness
tolerance specifies a tolerance zone within which
the considered element of a surface or derived median
line must lie. A straightness tolerance is applied in the
view where the elements to be controlled are represented
by a straight line.

40. STRAIGHTNESS

41. FLATNESS
Flatness is the condition of a surface or derived median plane having all
elements in one plane. A flatness tolerance specifies a tolerance zone defined by
two parallel planes within which the surface or derived median plane must lie.

42. Checking for Flatness
42

43. 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

44. Checking for Circularity
44

45. 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.

46. Checking for Cylindricity
46

47. 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.

48. PROFILE OF A SURFACE
Profile 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.

49. 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.

50. Checking for Angularity
50

51. 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.

52. 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.

53. PERPENDICULARITY
• Location of hole (axis)
This means ‘the hole (axis)
must be perpendicular
within a diametrical
tolerance zone of .010
relative to datum A’

54. Checking for Perpendicularity
54

55. ±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.

56. Checking for Parallelism
56

57. 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.

58. 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.
58
A

59. Checking for Concentricity
59

60. Runout Tolerances
• Circular Runout
• Total Runout
60
2-D Application
3-D Application

61. 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.
61
3-D Application 2-D Application

62. Checking for Runout
62

63. 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

64. Set Up for Symmetry
64

65. Geometric Characteristic Symbols

66. TO BE CONTINUED ON
SESSION 02

67. Material Source: Google
Internet