Geometric dimensioning and tolerancing (GD&T)

Gd&t, Geometric contains, Limit of Size, Feature control Frame, Tolerance, flatness, straightness, Roundness, Locations, MMC, LMC, And More

1. GD&T (Geometric Dimensioning & Tolerancing)

2. Unit II ( 13½ Hours) Geometric Dimensioning & Tolerancing (GD&T) -Introduction -Dimensioning and Tolerancing Fundamentals – Dimensioning Features – Features Control Frame – Datum Feature – Dimensioning Characteristics & Symbols, - Form - Orientation- Position, General - Position, Location- Position, Coaxiality- Concentricity and Symmetry- Runout- Profile – Rules to GD&T - Strategy for tolerancing Parts-tolerance of various mould elements, Cost impact on GT. Context DPMT SEMESTER – VI

3. Increased under s tanding Mfg Design Quality

4. It is the science of the properties and relations of lines, surfaces and solids. Geometry It is a measurable extent, as length, breadth and depth. A numerical value expressed in appropriate units of measure and used to define the size, location geometric characteristics or surface texture of a part. Dimension 3 PDF created with pdfFactory Pro trial version www.pdffactory.com

5. Dimension It is a allowable variation in any measurable property. The total amount that features of the part are permitted to vary from the specified dimension. The tolerance is the difference between the maximum and minimum limits. Two common methods to specify tolerances limit tolerances plus-minus tolerances Tolerance 4 PDF created with pdfFactory Pro trial version www.pdffactory.com

6. Limit tolerances Plus Minus Tolerances 5 PDF created with pdfFactory Pro trial version www.pdffactory.com

7. Dimension Anatomy ASME Y14.5M-1994 - The national standard for dimensioning and tolerancing in the United States. ASME stands for American Society of Mechanical Engineers. The Y14.5 is the standard number. "M" is to indicate the standard is metric, and 1994 is the date the standard was officially approved. What is GD&T 6 PDF created with pdfFactory Pro trial version www.pdffactory.com

8. Geometric Dimensioning and tolerancing (GD&T) is a language used on mechanical engineering drawings composed of symbols that are used to efficiently and accurately communicate geometry requirements for associated features on component and assemblies. A method to specify the shape of a piece of hardware on an engineering drawing. What is GD&T A set of fourteen symbols used in the language of GD&T. It consists of well- defined of symbols, rules, definitions and conventions, used on engineering drawings to accurately describe a part. GD&T is a precise mathematical language that can be used to describe the size, form, orientation, and location of part features. GD&T is also a design philosophy on how to design and dimension parts. What is GD&T 7 PDF created with pdfFactory Pro trial version www.pdffactory.com

9. What is GD&T 8 PDF created with pdfFactory Pro trial version www.pdffactory.com

10. 9 PDF created with pdfFactory Pro trial version www.pdffactory.com

11. Use of this language or tool “can provide economic and technical advantage” stated the ASME. Maximizes quality of the products. Provides uniformity of specification and interpretation (reducing guesswork and controversy) Advantages of GD&T Geometric dimensioning dramatically reduces the need for drawing notes to describe complex geometry requirements on a component or assembly by the use of standard symbolog y. Notes Vs Symbols 10 PDF created with pdfFactory Pro trial version www.pdffactory.com

12. Have multiple sources on various parts of an assembly. Make valid engineering calculations. Have common parts across similar assemblies. Design subassemblies in different locations and have them function correctly. Do tolerance analysis to study the effect of part tolerances on the assembly. Use state of the art software tools to analyze parts in an assembly. Use state of the art software tools to inspect the parts. Reduce the risk caused by vague specifications. And finally saves money. Other Advantages 01 Key Terms Feature The general term applied to a physical portion of a part, such as a surface, pin, hole, or slot. Feature of size One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces, associated with a size dimension. Examples: Cylinder, sphere, slot, etc. 15 PDF created with pdfFactory Pro trial version www.pdffactory.com

13. Geometric Characteristic Symbols Form Tolerances Profile Tolerances Orientation Tolerances Runout Tolerances Location Tolerances 3

14. Foundations of Mechanical Accuracy The Four Mechanical Arts Geometry Standards of Length Dividing the Circle Roundness Wayne R. Moore 1 5

15. Key Definitions Datum – Theoretically exact point, axis, or plane derived from the true geometric counterpart. Datum Feature – Actual feature on a real part used to establish a datum. Datum Feature Simulator – A surface of sufficient precision to establish a simulated datum. Simulated Datum – A point, axis, or plane established by processing or inspection equipment. Datum Target – A specified point, line, or area on a part used to establish the datum scheme. 21

16. Key Definitions Feature of Size – A cylindrical or spherical surface, or two opposing elements or parallel surfaces. Least Material Condition – This occurs where a feature of size contains the least material allowed by the stated limits of size. Maximum Material Condition – This occurs where a feature of size contains the most material allowed by the stated limits of size. Regardless of Feature Size – A term that indicates that a geometric tolerance or datum reference applies for any increment of size within its size tolerance. 22

17. 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. True Geometric Counterpart – The theoretically perfect boundary or best fit (tangent) plane of a specified datum feature. 23

18. 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. 24

19. Fundamental Rules Dimension materials made to gage numbers. 9 o a p pl y w h en fe a t u r e s a r e s h o w n as . 90 o apply when centerlines are shown . Dimensions apply at 20 o C (68 o F). Dimensions apply in a free state. Tolerances apply for full size of feature. Dimensions and tolerances only apply at the drawing level where they were specified. 25

20. Limits of Size Actual Size is a general term for the size of a feature as produced. It has two interpretations. Actual Local Size is the value of the individual distance at any cross section of any feature of size. Actual Mating Size is the dimensional value of the actual mating envelope. Limits of Size are the specified minimum and maximum values for a feature of size. 26

21. Feature Control Frame Symbols Statistical Tolerance Tangent Plane Free State Projected Tolerance Zone Least Material Condition Maximum Material Condition Spherical Diameter D i a m e t e r Feature Control Frame D es c rip t i o n Sy m b o l . 010 A B C S M L P F T ST 45

22. Feature Control Frame Elements Label the elements of the feature control frame using the following terms: Datum Modifier Geometric Characteristic Diameter Symbol Primary Datum Feature Modifier Secondary Datum Feature Tolerance Tertiary Datum .014 M A B M C 46

23. Feature Control Frame Placement Locate the Feature Control Frame below or attached to the leader-directed dimension or callout. Run the leader from the frame to the feature. Attach a side or an end of the frame to an extension line from the feature. Attach a side or an end of the frame to an extension of the dimension line related to the feature in question. 4 9

24. Form Tolerances Flatness Straightness Circularity C y l i nd r i c i t y 55

25. Form Tolerances Datum references are never made for form tolerances. Rule #1 says that limits of size control variation in form. Generally, form tolerances are only necessary to refine (require a tighter tolerance) limits of size. Form tolerances are often applied to features to qualify them as acceptable datum features. 56

26. F l a t n e s s Definition Flatness exists when a surface has all of its elements in one plane. Tolerance Zone Two parallel planes within which the surface must lie. 57

27. Checking for Flatness 58

28. Proper Application of Flatness No datum is referenced. It is applied to a single planar feature. No modifiers are specified. Tolerance value is a refinement of other geometric tolerances or Rule #1. 59

29. Straightness Definition Straightness exists when an element of a surface or an axis is a straight line. Tolerance Zone Two parallel lines in the same plane for two-dimensional applications. A cylindrical tolerance zone that contains an axis for three-dimensional applications. 60

30. Checking for Straightness 61

31. Proper Application of Straightness applied to a Surface Element No datum is referenced. It is applied to a surface element. It is applied in a view where the element to be controlled is shown as a line. No modifiers are specified. Tolerance value is a refinement of other geometric tolerances or Rule #1. 62

32. Straightness of a Feature of Size When straightness is applied to a feature of size: Tolerance zone applies to the axis or centerplane. Rule #1 does not apply. The tolerance value may be larger that the limits of size for the feature of size. 63

33. Proper Application of Straightness applied to a Feature of Size No datum is referenced. It is applied to a planar or cylindrical feature of size. If a planar feature of size, the diameter symbol is not used. If a cylindrical feature of size, the diameter symbol is used. T , and L modifiers are not specified. Tolerance value is a refinement of other geometric tolerances. P , 64

34. Circularity (roundness) 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. 65

35. Checking for Circularity 66

36. Proper Application of Circularity No datum is referenced. It is applied to a circular feature. No modifiers are specified. Tolerance value is a refinement of limits of size on the diameter or of other specified geometric tolerances. 67

37. 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. 68

38. Checking for Cylindricity 69

39. Proper Application of Cylindricity No datum is referenced. It is applied to a cylindrical feature. No modifiers are specified. Tolerance value is a refinement of limits of size on the diameter or of other specified geometric tolerances. 70

40. Decisions for Form Tolerances Form T ol e ra n ces Consider Limits of Size Flatness Straightness C i rcu l ari ty C yl i ndr i city Surface E l eme n t s Axis or Center Plane Consider Material Condition MMC R FS 71

41. Orientation Tolerances Angularity Perpendicularity Parallelism 72

42. Orientation Tolerances Datum references are always used for orientation tolerances. Orientation tolerances applied to a surface control the form of toleranced surface. Only a tangent plane may need control. Orientation tolerances may be applied to control both features of size and features without size. Orientation tolerances do not control size or location. Generally, profile tolerances are used to locate features without size and position tolerances are used to locate features of size. 73

43. A n g u l a r i t y Definition Angularity exists when all of the points on a surface create a plane or a feature axis is at the specified angle, when compared to a reference plane or axis. Tolerance Zone Two parallel planes at the true angle to a reference plane and contain the entire surface surface. Note: Applies to median planes and axes too. Datum Feature Datum Plane 74

44. Checking for Angularity 75

45. Proper Application of Angularity Datum reference is specified. Surface applications may use tangent plane modifier. Feature of size applications may use MMC, LMC, diameter, of projected tolerance zone modifiers. Basic angle defines perfect geometry between the datum reference and the toleranced feature. Specified tolerance is a refinement of other geometric tolerances that control angularity of the toleranced feature. 76

46. Perpendicularity Definition Perpendicularity exists when all of the points on a surface, median plane, or axis are at a right angle to a reference plane or axis. Tolerance Zone Two parallel planes that are perpendicular to a reference plane and contain the entire surface surface. Note: Applies to median planes and axes too. Datum Feature Datum Plane 77

47. Checking for Perpendicularity 78

48. Proper Application of Perpendicularity Datum reference is specified. Surface applications may use tangent plane modifier. Feature of size applications may use MMC, LMC, diameter, of projected tolerance zone modifiers. Basic angle defines perfect geometry between the datum reference and the toleranced feature. Specified tolerance is a refinement of other geometric tolerances that control the perpendicularity of the toleranced feature. 79

49. P a r a ll e li s m Definition Parallelism exists when all of the points on a surface, median plane, or axis are equidistant to a reference plane or axis. Tolerance Zone Two parallel planes that are parallel to a reference plane and contain the entire surface surface. Note: Applies to median planes and axes too. Datum Feature Datum Plane 80

50. Checking for Parallelism 81

51. Proper Application of Parallelism Datum reference is specified. Surface applications may use tangent plane modifier. Feature of size applications may use MMC, LMC, diameter, of projected tolerance zone modifiers. Basic angle defines perfect geometry between the datum reference and the toleranced feature. Specified tolerance is a refinement of other geometric tolerances that control parallelism of the toleranced feature. 82

52. Decisions for Orientation Tolerances O r i e n t a t i on T o ler a nc e s Parallelism A ng u la r i t y Perpendicularity Consider Limits of Size Consider Limits Of Location F e a t u re of Size Plane S u r f a ce Consider Material Condition MMC R FS L MC 83

53. Location Tolerances True Position Symmetry C on c e n tr i c ity 84

54. Location Tolerances Datum references are always used for location tolerances. Location tolerances are reserved for tolerancing applications on features of size. They are always located by basic dimensions back to the datum scheme. Location tolerances shown on the same centerline are assumed to have a basic dimension of zero. Symmetry and concentricity application are centered about the datum scheme specified for the controlled feature. 85

55. True Position Definition True position is the exact intended location of a feature relative to a specified datum scheme. Tolerance Zone Most frequently, the tolerance zone is a cylinder of specified diameter within which the true axis of the feature must lie. Note: True position can also be applied to median planes relative to specified datums. 86

56. Positional Tolerancing Traditional tolerancing (say + .005”) consist of 2-D rectangular boundaries. A circular boundary with the same worst-case conditions increases the area of the tolerance zone by 57%, prior to any bonus tolerance. 87

57. Traditional Fastener Tolerances Threaded Fastener 3/8 – 16 Clearance Hole 13/32 1/64 = .0156 . 00 1 5 Perfect Condition Worst-Case Condition 88 C le a rance

58. 8 9 Bonus Tolerances When tolerancing features of size, bonus tolerances may be applicable. With MMC, as the size of a hole increases, so does the acceptable tolerance zone, provided the hole does not exceed its limits of size. Hole at MMC O r i g i n a l T ol e ra n c e Z one L arg e r H o le L arg e r T ol e ra n ce Z o n e Larger H o le

59. Maximum Material Condition (MMC) Largest permissible external feature. Outside Diameter External Feature Size Key Smallest permissible internal feature. Holes Slots Key Way 90

60. Maximum Material Condition B C .014 M A B C . 76 . 75 S i z e 91 T o l e r an c e MM C 4 X Note: Datum feature A is the back surface.

61. Least Material Condition (LMC) Smallest permissible external feature. Outside Diameter External Feature Size Key Largest permissible internal feature. Holes Slots Key Way 92

62. Least Material Condition B C . 01 4 L A B C . 7 6 . 7 5 S i z e 93 Tolerance L M C 4 X Note: Datum feature A is the back surface.

63. R e g a r d l e s s of F e a t ur e S i ze ( R F S) RFS is no longer documented except in rare cases where it is required for clarity. RFS is assumed for features of size when neither MMC nor LMC are specified. 94

64. Regardless of Feature Size B C . 1 4 A B C . 76 . 75 S i z e 95 Tolerance 4 X Note: Datum feature A is the back surface.

65. Applications of Material Condition Modifiers Maximum Material Condition Used for clearance application. Least Material Condition Used for location applications. Used to protect wall thickness. Regardless of Feature Size Used when size and location do not interact. M L 96

66. Applications for Least Material Condition . 503 . 501 . 002 L . 500 . 499 97 The purpose of the hole is to locate the PLP pin below. Worst Case Scenario Hole diameter at .503 (LMC) Pin diameter at .499 (LMC) Clearance is .004 Pin can shift .002 in any direction Tolerance for hole location is Ø .002 at LMC Hole can be off location .001 in any direction Pin can be off location .003 in any direction

67. Applications for Least Material Condition . 503 . 501 . 002 L . 500 . 499 98 The purpose of the hole is to locate the PLP pin below. Hole at MMC – Pin at LMC Hole diameter at .501 (MMC) Pin diameter at .499 (LMC) Clearance is .002 Pin can shift .001 in any direction Tolerance for hole location is Ø .004 at MMC Hole can be off location .002 in any direction Pin can be off location .003 in any direction

68. Applications for Least Material Condition . 503 . 501 . 002 L . 500 . 499 99 The purpose of the hole is to locate the PLP pin below. Hole at MMC – Pin at MMC Hole diameter at .501 (MMC) Pin diameter at .500 (MMC) Clearance is .001 Pin can shift .0005 in any direction Tolerance for hole location is Ø .004 at MMC Hole can be off location .002 in any direction Pin can be off location .0025 in any direction

69. Proper Application of Position Position control is applied to a feature of size. Datum references are specified and logical for the application. Basic dimensions establish the desired true position of the feature of size. Tangent plane modifier is not used. Diameter symbol is used to specify axis control. Diameter symbol is not used to specify center plane control. MMC, LMC, or RFS may be specified. 119

70. 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 120

71. Set Up for Symmetry 121

72. Proper Application of Symmetry A planar feature of size to be controlled uses the same center plane as the datum scheme. Diameter symbol is never used to specify the symmetry tolerance. MMC, LMC, tangent plane, and projected tolerance zone modifiers may not be specified. 122

73. 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. A 123

74. Checking for Concentricity 124

75. Proper Application of Concentricity The surface of revolution to be controlled is coaxial to the axis of the datum scheme. Diameter symbol is used to specify the concentricity tolerance. MMC, LMC, tangent plane, and projected tolerance zone modifiers may not be specified. 125

76. Decisions for Location Tolerances Location T ol e ra n ces P o s i t i on Concentricity Symmetry Center P l ane Axis D e t ermi n e Tolerance For Position Only Consider Material Condition MMC R FS LMC 127

77. Profile Tolerances Profile of a Line Profile of a Surface 2-D Application 3-D Application 128

78. Profile Tolerances Profile tolerances are used to control multiple coplanar surfaces. Perfect geometry must be defined via basic dimensions. The default interpretation for the tolerance zone is bilateral and equal about the true perfect geometry. Profile tolerances are not used to control features of size so MMC, LMC, and RFS do not apply. Profile features can be used as datum features or they must be related to a defined datum scheme. 129

79. Profile Definition Profile defines the theoretically exact position of a surface (3-D) or the cross section of a surface (2-D). Tolerance Zone A uniform boundary on either side of the true profile that must contain either the surface or line. 3-D Application 130 2-D Application

80. Profile for Cam Application 131

81. Functional Gaging of Profile 132

82. Proper Application of Profile Tolerances Profile features are used as datum features or related to a defined datum scheme. and Basic dimensions relate the true profile back to the datum scheme. or The profile tolerance value must be a refinement of dimensions used to locate the true profile. 133

83. Decisions for Profile Tolerances Profile T ol e ra n ces Consider Limits of Size Profile of a S u r f a ce Profile of a L ine Consider Tolerance Zone B il a t e ral Unilateral I ns i de O u tsi d e Equal Unequal 134

84. Runout Tolerances Circular Runout Total Runout 2-D Application 3-D Application 135

85. R un o ut 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. 3-D Application 2-D Application 136

86. Checking for Runout 137

87. Proper Application of Runout The surface to be controlled is either coaxial or perpendicular to the axis of the datum scheme. Diameter symbol is never used to specify a runout tolerance. MMC, LMC, tangent plane, and projected tolerance zone modifiers may not be specified for a runout tolerance. 138

88. Decisions for Runout Tolerances Runout T o ler a nc e s Consider Limits of Size Total R u n o ut C i r c ul a r Runout 139

89. Geometric Characteristics for Round Features Circularity (roundness) Evaluates cross section of surface to its own axis Cylindricity Evaluates entire surface to its own axis Runout Evaluates cross section of surface to a defined axis Total Runout Evaluates entire surface to a defined axis Concentricity Evaluates best fit axis of feature to a defined axis 140

90. Reference Planes (The Point of Known Return) Ted Busch, 1962 Define the datum reference frame. Use of mutually perpendicular planes. The goal is the replication of measurements. Immobilize the part in up to six degrees of freedom. 143

91. Theoretically Perfect Geo m e t ry Three mutually perpendicular planes. D a t um 144 P o i nt 3 Datum Planes define the Origin of Measurement

92. Criteria for Selecting Datum Features Geometric Relationship to Toleranced Feature Geometric Relationship to Design Requirements Accessibility of the Feature Sufficient in Size to be Useful Readily Discernable on the Part 145

93. Designating Precedence of Datums Alphabetical order is not relevant. Order of precedence is shown in the feature control frame. Consider function first. Then, consider the process next. Finally, consider measurement processes. 146

94. Datum Features of Size MMC callouts on a datum features of size can allow a datum shift on the exact location of the datum feature. This applies to: Cylindrical Surfaces (internal or external) Spherical Surfaces A Set of 2 Opposing Elements or Parallel Planes A Pattern of Features such as a Bolt Hole Pattern 147

95. Decisions for Datum Selection Select Datum Feature F e a t u re of Size S u r f a ce Axis C e n t e r Plane Consider Material Condition MMC R FS L MC Are Other Datums Required? 148

96. Rational Strategy 149 for Datum Selection It is reasonable to prioritize the datum selection process as follows: 1. Functional Requirements 1. Production Requirements • Measurement Requirements

97. What Are We Really Interested In? 150 • Error in Geometric Forms • Size for Features of Size • Location of Features

98. Introduction to Datum Workshop Select datums based on function. Some features are leaders, others are followers. Sequence of considerations: Establish the datum reference frame (DRF). Qualify the datum features to the DRF. Relate remaining features to the DRF. For consistency, assume .005” tolerance zones unless otherwise specified. Select and qualify the datum features and identify the datum point as specified in the following examples. 151

99. D a tum It is a theoretically exact plane from which a dimensional measurement is made Datum system is a set of symbols which is used to describe the function and dimensions to the user Datum plane, Datum axis and Datum center plane are used to make measurements of a part

100. Datum symbols

101. Section 5 157 Tolerancing Strategies

102. Process for Tolerance Analysis Establish Performance Requirements Develop a Loop Diagram Convert Dimensional Requirements to Target Values with Equal Bilateral Tolerances Determine the Target Value for Requirement Select the Method of Analysis Calculate Variation for Performance Requirement 158

103. Modifiers and its symbols They are symbols which defines conditions for the tolerance zone of a geometric tolerance. There are six modifiers. The symbols of modifiers and their meaning is shown

104. Additional Symbols

105. Feature Control Frame It is a rectangular box which is divided into compartments within which symbols, modifiers, tolerances, etc… are placed. Below is an example for feature control frame

106. © Professor Britton 1996 -2000 When to use geometric tolerancing not needed if dimensional tolerances and the manufacturing process provide adequate control is needed when part features are critical to function or interchangeability when errors of shape & form must be held within tighter limits than normally expected from the manufacturing process when functional gauging techniques are to be used when datum references are required to ensure consistency between design, manufacture and verification operations when computerization techniques in design and manufacture are used Use of GD&T to control form of a part increases cost because ext ra control is required for the manufacturing processes and additional inspection is required to ensure compliance. Thus it should only be used when necessary. In order to apply GD&T properly a designer must know about and understand the manufacturing processes that will be used to make the part. All processes provide geometric control to some degree. The decision to apply GD&T or not depends to a large degree on whether the normal control provided by a process meets the design functional requirements: if it can meet requirements do not use GD&T, otherwise use GD&T. In addition GD&T could be used to ensure consistency of datum references between design, manufacture and verification operations, and also when computer tools are used during design and manufacture.