1. GD&T Overview Class
April 24, 2019

2. 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.

3. Aspects of Metrology Reference standard metrology
Engineering Metrology

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

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

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

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

8. Specification of Linear Tolerances

9. 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.

10. 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.

11. GEOMETRIC DIMENSIONING
AND TOLERANCING
DEVIATIONS

12. GEOMETRIC DIMENSIONING
AND TOLERANCING
DIMENSIONS OF A PART

13. GEOMETRIC DIMENSIONING
AND TOLERANCING
TYPE OF TOLERANCE

14. GEOMETRIC DIMENSIONING
AND TOLERANCING
TOLERANCE SIZES

15. GEOMETRIC DIMENSIONING
AND TOLERANCING
SIZES OF MATING PARTS

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

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

18. 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

19. 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

20. Feature Control Frame Geometric characteristic symbol
Geometric tolerance
Datums (if used)
Modifiers as required (*MMC for example)

21. GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE CONTROL FRAME

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

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

24. Angular Specifications

25. Angular Tolerances

26. 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

27. 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

28. Flatness Specification

29. Flatness Tolerances

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

31. Straightness Specification

32. Straightness Tolerance

33. Circularity Specification
Checks Roundness & applies to every section

34. Circularity Tolerances

35. Surface Profile Without Datums

36. Line Profile Without Datums

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

38. Surface Profile with Datums

39. Cylindricity Specifications

40. Cylindricity Tolerances

41. Surface Texture Specification

42. Surface Texture

43. 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.

44. Perpendicularity Specification

45. Perpendicularity Measurements

46. Parallelism Specification

47. Parallelism Measurements

48. Concentricity Specification

49. Concentricity Tolerances

50. Concentricity Measurements

51. Concentricity Measurements

52. Circular Runout Specifications

53. Circular Runout Tolerances

54. Total Runout Specifications

55. Total Runout Tolerances

56. Position Specifications

57. Position Tolerances

58. 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.

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

60. Simulated Datum

61. Datum Selection

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

63. 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

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

65. 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.

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

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

68. 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

69. 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

70. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

71. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

72. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

73. Thanks for participating!
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