1. Geometric Dimensioning and Tolerancing (GD&T)
PART PRODUCTION COMMUNICATION MODEL
MANAGEMENT
DESIGN
TOOLING
PRODUCTION
INSPECTION
ASSEMBLY
ROUTING
PLANNING
PRICING
SERVICE
PURCHASING
SALES
CUSTOMERS
VENDORS
Pat McQuistion

2. Three Categories of Dimensioning
Dimensioning can be divided into three categories:
general dimensioning,
geometric dimensioning, and
surface texture.
The following provides information necessary to begin to understand geometric dimensioning and tolerancing (GD&T)

4. Limit Tolerancing Applied To An Angle Block

5. Geometric Tolerancing Applied To An Angle Block

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 to meaning good tables would be rejected.
Assume all 4 legs will be cut to length at the same time. or

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) 28
.06 27
.06 26
.06

10. Provides “bonus” tolerance
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 Foster

11. When part features are critical to a function or interchangeability
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 ensure 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

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

13. LIMITS OF SIZE
Pat McQuistion

14. LIMITS OF SIZE
A variation in form is allowed between the least material condition (LMC) and the maximum material condition (MMC).
Pat McQuistion
Envelop Principle defines the size and form relationships between mating parts.

15. LIMITS OF SIZE
ENVELOPE PRINCIPLE
LMC
CLEARANCE
MMC
ALLOWANCE

16. LIMITS OF SIZE
The actual size of the feature at any cross section must be within the size boundary.
ØMMC
ØLMC
Pat McQuistion

17. LIMITS OF SIZE
No portion of the feature may be outside a perfect form barrier at maximum material condition (MMC).
Pat McQuistion

18. I.e., Parallel Line Tolerance Zones
Other Factors
I.e., Parallel Line Tolerance Zones

19. GEOMETRIC CHARACTERISTIC CONTROLS
14 characteristics that may be controlled
TYPE OF
FEATURE
TYPE OF
TOLERANCE
CHARACTERISTIC
SYMBOL
SYMMETRY
FLATNESS
STRAIGHTNESS
CIRCULARITY
CYLINDRICITY
LINE PROFILE
SURFACE PROFILE
PERPENDICULARITY
ANGULARITY
PARALLELISM
CIRCULAR RUNOUT
TOTAL RUNOUT
CONCENTRICITY
POSITION
INDIVIDUAL (No Datum Reference)
INDIVIDUAL or RELATED FEATURES
RELATED FEATURES (Datum Reference Required)
FORM
PROFILE
ORIENTATION
RUNOUT
LOCATION

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

21. Feature Control Frame FEATURE CONTROL FRAME GEOMETRIC SYMBOL
THE
GEOMETRIC SYMBOL
TOLERANCE INFORMATION
DATUM REFERENCES
FEATURE CONTROL FRAME
COMPARTMENT VARIABLES
CONNECTING WORDS
MUST BE WITHIN
OF THE FEATURE
RELATIVE TO

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. Reading Feature Control Frames
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

25. Placement of Feature Control Frames
May be attached to a side, end or corner of the symbol box to an extension line.
Applied to surface.
Applied to axis

26. Placement of Feature Control Frames Cont’d.
May be below or closely adjacent to the dimension or note pertaining to that feature.
Ø .500±.005

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.
1.000

28. Basic Dimension cont’d.

29. Form Features Individual Features No Datum Reference Flatness
Straightness
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.
Cylindricity
Circularity

30. Form Features Examples
Flatness as stated on drawing: The flatness of the feature must be within .06 tolerance zone.
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.
Straightness applied to a flat surface: The straightness of the feature must be within .003 tolerance zone.
.003
0.500 ±.005
.003
0.500 ±.005

31. Form Features Examples
Straightness applied to the surface of a diameter: The straightness of the feature must be within .003 tolerance zone.
.003
0.500
0.505 
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.
Straightness of an Axis at MMC: The derived median line straightness of the feature must be within a diametric zone of .030 at MMC.
.030
0.500
0.505  M
1.010
0.990

32. Dial Indicator

33. Verification of Flatness

34. Activity 13 Work on worksheets GD&T 1, GD&T 2 #1 only, and GD&T 3
(for GD&T 3 completely dimension. ¼” grid.)

35. 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.

36. 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
1.000

37. 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. Datum Reference Symbols
The datum feature symbol identifies a surface or feature of size as a datum. A
ISO
ANSI
1982
ASME
1994

39. Placement of Datums
Datums are generally placed on a feature, a centerline, or a plane depending on how dimensions need to be referenced. A OR
ASME 1994 A
ANSI 1982
Line up with arrow only when the feature is a feature of size and is being defined as the datum

40. Placement of Datums Feature sizes, such as holes
Sometimes a feature has a GD&T and is also a datum A
Ø .500±.005 A
Ø .500±.005
Ø .500±.005

41. TWELVE DEGREES OF FREEDOM
6 ROTATIONAL
6 LINEAR AND
FREEDOM
DEGREES OF UP
DOWN
RIGHT
LEFT
BACK
FRONT
UNRESTRICTED FREE
MOVEMENT IN SPACE

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

43. 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?

44. 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. Primary Datum Restricts 6 degrees of freedom FIRST DATUM ESTABLISHED
BY THREE POINTS (MIN)
CONTACT WITH SIMULATED
DATUM A

46. 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.

47. Secondary Datum Restricts 10 degrees of freedom. SECOND DATUM
PLANE ESTABLISHED BY
TWO POINTS (MIN) CONTACT
WITH SIMULATED DATUM B

48. Tertiary Datum Restricts 12 degrees of freedom. THIRD DATUM
90°
THIRD DATUM
PLANE ESTABLISHED
BY ONE POINT (MIN)
CONTACT WITH
SIMULATED DATUM C
MEASURING DIRECTIONS FOR
RELATED DIMENSIONS

49. Coordinate Measuring Machine

50. Size Datum (CIRCULAR) SIMULATED DATUM- SMALLEST CIRCUMSCRIBED CYLINDER
THIS ON
THE DRAWING
MEANS THIS
PART
DATUM AXIS A

51. Size Datum (CIRCULAR) SIMULATED DATUM- LARGEST INSCRIBED CYLINDER
THIS ON
THE DRAWING
MEANS THIS
DATUM AXIS A
PART A

52. 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.
Controls the orientation of individual features
Datums are required
Shape of tolerance zone: 2 parallel lines, 2 parallel planes, and cylindrical

53. PERPENDICULARITY:
is the condition of a surface, center plane, or axis at a right angle (90°) to a datum plane or axis.
Ex:
The perpendicularity of this surface must be within a .005 tolerance zone relative to datum A.
The tolerance zone is the space between the 2 parallel lines. They are perpendicular to the datum plane and spaced .005 apart.

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

55. Plane 1 must be perpendicular within .005 tolerance zone to plane 2
Practice Problem
Plane 1 must be perpendicular within .005 tolerance zone to plane 2
BOTTOM PLANE

56. Practice Problem 2.00±.01 Without GD & T this would be acceptable
.02 Tolerance
Without GD & T this would be acceptable
2.00±.01
.005 Tolerance Zone
.02 Tolerance
With GD & T the overall height may end anywhere between the two blue planes. But the bottom plane is restricted to the red tolerance zone.

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

58. 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.

59. 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.
±0.01

60. Activity 13 Cont’d. Complete worksheets GD&T-2, GD&T-4, and GD&T-5
Completely dimension.
¼” grid

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

62. Maximum Material Condition
MMC
This is when part will weigh the most.
MMC for a shaft is the largest allowable size.
MMC of Ø0.240±.005?
MMC for a hole is the smallest allowable size.
MMC of Ø0.250±.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 text

63. Least Material Condition
LMC
This is when part will weigh the least.
LMC for a shaft is the smallest allowable size.
LMC of Ø0.240±.005?
LMC for a hole is the largest allowable size.
LMC of Ø0.250±.005?

64. 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 text

65. 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.

66. 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.

67. 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.
.750
2.000

68. 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)
Center can be anywhere along the diagonal line.
.750
2.000

69. 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.
MMC =
= .497

70. Bonus Tolerance
Here is the beauty of the system! The specified tolerance was:
This means that the tolerance is .010 if the hole size is the MMC size, or If the hole is bigger, we get a bonus tolerance equal to the difference between the MMC size and the actual size.

71. Bonus Tolerance Example
This means that the tolerance is .010 if the hole size is the MMC size, or If the hole is bigger, we get a bonus tolerance equal to the difference between the MMC size and the actual size.
This system makes sense… the larger the hole is, the more it can deviate from true position and still fit in the mating condition!
.503
Actual Hole Size
Bonus Tol.
Φ of Tol. Zone
Ø .497 (MMC)
.010
Ø ( = .002)
( = .012)
.012
Ø .500 ( = .003)
( = .013)
.013
Ø .502
.005
.015
Ø .503 (LMC)
.006
.016
Ø .504 ?

72. .497 = BONUS 0 TOL ZONE .010 .499 - .497 = BONUS .002
Hole
Shaft
= BONUS .002
BONUS + TOL. ZONE = .012

73. = BONUS .004
BONUS + TOL. ZONE = .014
= BONUS .006
BONUS + TOL. ZONE = .016

74. 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.
GT = GEOMETRIC TOLERANCE

75. PERPENDICULARITY Cont’d.
Means “the hole (AXIS) must be perpendicular within a diametrical tolerance zone of .010 at MMC relative to datum A.”
Actual Hole Size
Bonus Tol.
Ø of Tol. Zone
1.997 (MMC)
1.998
1.999
2.000
2.001
2.002
2.003
Vc =

76. Activity 13 Cont’d.
Worksheet GD&T 6