Geometric Dimensioning and Tolerancing GDT

1. Pat McQuistion Pat McQuistion

6. Geometric Dimensioning & Tolerancing (GD&T) GD&T is a means of dimensioning & tolerancing a drawing which considers the function of the part and how this part functions with related parts. This allows a drawing to contain a more defined feature more accurately, without increasing tolerances.

7. GD&T cont�d GD&T has increased in practice in last 15 years because of ISO 9000. ISO 9000 requires not only that something be required, but how it is to be controlled. For example, how round does a round feature have to be? GD&T is a system that uses standard symbols to indicate tolerances that are based on the feature�s geometry. Sometimes called feature based dimensioning & tolerancing or true position dimensioning & tolerancing GD&T practices are specified in ANSI Y14.5M-1994.

8. For Example Given Table Height However, all surfaces have a degree of waviness, or smoothness. For example, the surface of a 2 x 4 is much wavier (rough) than the surface of a piece of glass. As the table height is dimensioned, the following table would pass inspection. If top must be flatter, you could tighten the tolerance to � 1/32. However, now the height is restricted to 26.97 to 27.03 meaning good tables would be rejected.

9. Example cont�d. You can have both, by using GD&T. The table height may any height between 26 and 28 inches. The table top must be flat within 1/16. (�1/32)

10. WHY IS GD&T IMPORTANT Saves money For example, if large number of parts are being made � GD&T can reduce or eliminate inspection of some features. Provides �bonus� tolerance Ensures design, dimension, and tolerance requirements as they relate to the actual function Ensures interchangeability of mating parts at the assembly Provides uniformity It is a universal understanding of the symbols instead of words Quotes from Geo Metric III FosterQuotes from Geo Metric III Foster

11. WHEN TO USE GD&T When part features are critical to a function or interchangeability When functional gaging is desirable When datum references are desirable to insure consistency between design When standard interpretation or tolerance is not already implied When it allows a better choice of machining processes to be made for production of a part Quotes from Geo Metric III Foster Quotes from Geo Metric III Foster

12. TERMINOLOGY REVIEW Maximum Material Condition (MMC): The condition where a size feature contains the maximum amount of material within the stated limits of size. I.e., largest shaft and smallest hole. Least Material Condition (LMC): The condition where a size feature contains the least amount of material within the stated limits of size. I.e., smallest shaft and largest hole. Tolerance: Difference between MMC and LMC limits of a single dimension. Allowance: Difference between the MMC of two mating parts. (Minimum clearance and maximum interference) Basic Dimension: Nominal dimension from which tolerances are derived. Quotes from Geo Metric III Foster Pat McQuistion Quotes from Geo Metric III Foster Pat McQuistion

13. Pat McQuistion Pat McQuistion

14. Pat McQuistion Pat McQuistion

16. Pat McQuistion Pat McQuistion

17. Pat McQuistionPat McQuistion

20. Characteristics & Symbols cont�d. Maximum Material Condition MMC Regardless of Feature Size RFS Least Material Condition LMC Projected Tolerance Zone Diametrical (Cylindrical) Tolerance Zone or Feature Basic, or Exact, Dimension Datum Feature Symbol Feature Control Frame

22. Feature Control Frame Uses feature control frames to indicate tolerance Reads as: The position of the feature must be within a .003 diametrical tolerance zone at maximum material condition relative to datums A, B, and C.

23. Feature Control Frame Uses feature control frames to indicate tolerance Reads as: The position of the feature must be within a .003 diametrical tolerance zone at maximum material condition relative to datums A at maximum material condition and B.

24. The of the feature must be within a tolerance zone. The of the feature must be within a tolerance zone at relative to Datum . The of the feature must be within a tolerance zone relative to Datum . The of the feature must be within a zone at relative to Datum . The of the feature must be within a tolerance zone relative to datums . Reading Feature Control Frames

25. Placement of Feature Control Frames

26. Placement of Feature Control Frames Cont�d.

27. Basic Dimension A theoretically exact size, profile, orientation, or location of a feature or datum target, therefore, a basic dimension is untoleranced. Most often used with position, angularity, and profile) Basic dimensions have a rectangle surrounding it.

28. Basic Dimension cont�d.

29. Form Features Individual Features No Datum Reference Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

30. Form Features Examples Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

31. Form Features Examples Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

33. Verification of Flatness

34. Features that Require Datum Reference Orientation Perpendicularity Angularity Parallelism Runout Circular Runout Total Runout Location Position Concentricity Symmetry Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

35. Datum Datums are features (points, axis, and planes) on the object that are used as reference surfaces from which other measurements are made. Used in designing, tooling, manufacturing, inspecting, and assembling components and sub-assemblies. As you know, not every GD&T feature requires a datum, i.e., Flat

36. Datums cont�d. Features are identified with respect to a datum. Always start with the letter A Do not use letters I, O, or Q May use double letters AA, BB, etc. This information is located in the feature control frame. Datums on a drawing of a part are represented using the symbol shown below.

38. Placement of Datums Datums are generally placed on a feature, a centerline, or a plane depending on how dimensions need to be referenced.

39. Placement of Datums Feature sizes, such as holes Sometimes a feature has a GD&T and is also a datum

41. Example Datums Datums must be perpendicular to each other Primary Secondary Tertiary Datum

42. Primary Datum A primary datum is selected to provide functional relationships, accessibility, and repeatability. Functional Relationships A standardization of size is desired in the manufacturing of a part. Consideration of how parts are orientated to each other is very important. For example, legos are made in a standard size in order to lock into place. A primary datum is chosen to reference the location of the mating features. Accessibility Does anything, such as, shafts, get in the way?

43. Primary Datum cont�d. Repeatability For example, castings, sheet metal, etc. The primary datum chosen must insure precise measurements. The surface established must produce consistent Measurements when producing many identical parts to meet requirements specified.

45. Secondary & Tertiary Datums All dimension may not be capable to reference from the primary datum to ensure functional relationships, accessibility, and repeatability. Secondary Datum Secondary datums are produced perpendicular to the primary datum so measurements can be referenced from them. Tertiary Datum This datum is always perpendicular to both the primary and secondary datums ensuring a fixed position from three related parts.

50. Size Datum(CIRCULAR)

51. Orientation Tolerances Perpendicularity Angularity Parallelism Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

52. PERPENDICULARITY: is the condition of a surface, center plane, or axis at a right angle (90�) to a datum plane or axis. Ex:

53. Practice Problem Plane 1 must be perpendicular within .005 tolerance zone to plane 2.

54. Practice Problem Plane 1 must be perpendicular within .005 tolerance zone to plane 2

55. Practice Problem

56. PERPENDICULARITY Cont�d. Location of hole (axis)

57. 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.

58. 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.

59. Material Conditions Maximum Material Condition (MMC) Least Material Condition (LMC) Regardless of Feature Size(RFS)

60. Maximum Material Condition MMC This is when part will weigh the most. MMC for a shaft is the largest allowable size. MMC of �0.240�.005? MMC for a hole is the smallest allowable size. MMC of �0.250�.005? Permits greater possible tolerance as the part feature sizes vary from their calculated MMC Ensures interchangeability Used With interrelated features with respect to location Size, such as, hole, slot, pin, etc. Foster�s textFoster�s text

61. Least Material Condition LMC This is when part will weigh the least. LMC for a shaft is the smallest allowable size. LMC of �0.240�.005? LMC for a hole is the largest allowable size. LMC of �0.250�.005?

62. Regardless of Feature Size RFS Requires that the condition of the material NOT be considered. This is used when the size feature does not affect the specified tolerance. Valid only when applied to features of size, such as holes, slots, pins, etc., with an axis or center plane. Foster�s textFoster�s text

63. Location Tolerances Position Concentricity Symmetry Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country. Why symbols? The symbol has uniform meaning. A note can be stated inconsistently, with a possibility of misunderstanding. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies Symbols can be made by computer or with a template & retain legibility when reproduced. Symbols provide international language. Notes may need to be translated if used in another country.

64. 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.

65. Coordinate System Position Consider the following hole dimensioned with coordinate dimensions: The tolerance zone for the location of the hole is as follows: Several Problems: Two points, equidistant from true position may not be accepted. Total tolerance diagonally is .014, which may be more than was intended.

66. Coordinate System Position Consider the following hole dimensioned with coordinate dimensions: The tolerance zone for the location (axis) of the hole is as follows: Several Problems: Two points, equidistant from true position may not be accepted. Total tolerance diagonally is .014, which may be more than was intended. (1.4 Xs >, 1.4*.010=.014)

67. Position Tolerancing Consider the same hole, but add GD&T: Now, overall tolerance zone is: The actual center of the hole (axis) must lie in the round tolerance zone. The same tolerance is applied, regardless of the direction.

68. Bonus Tolerance Here is the beauty of the system! The specified tolerance was:

69. Bonus Tolerance Example This system makes sense� the larger the hole is, the more it can deviate from true position and still fit in the mating condition!

72. What if the tolerance had been specified as: Since there is NO material modifier, the tolerance is RFS, which stands for regardless of feature size. This means that the position tolerance is .010 at all times. There is no bonus tolerance associated with this specification. VIRTUAL CONDITION: The worst case boundary generated by the collective effects of a size feature�s specified MMC or LMC material condition and the specified geometric tolerance.

73. PERPENDICULARITY Cont�d.