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

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)
s 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
s 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?
s 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
s GD&T practices are specified in
ANSI Y14.5M-1994.

8. For Example
s Given Table Height
Assume all 4 legs will be
cut to length at the same
time.
s 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.
or
s 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.
s 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)
.06
.06
.06
28
27
26

10. WHY IS GD&T IMPORTANT
s 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
s Ensures design, dimension, and
tolerance requirements as they
relate to the actual function
s Ensures interchangeability of
mating parts at the assembly
s Provides uniformity
s It is a universal understanding of
the symbols instead of words

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

12. TERMINOLOGY REVIEW
s 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.
s 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.
s Tolerance: Difference between MMC
and LMC limits of a single dimension.
s Allowance: Difference between the
MMC of two mating parts. (Minimum
clearance and maximum interference)
s Basic Dimension: Nominal
dimension from which tolerances are
derived.

13. LIMITS OF SIZE
SIZE DIMENSION
WHAT DOES
THIS MEAN?
2.007
2.003

14. LIMITS OF SIZE
A variation in form is allowed
between the least material
condition (LMC) and the
maximum material condition
(MMC).
SIZE DIMENSION
ENVELOPE PRINCIPLE
MMC
(2.007)
LMC
(2.003)
ENVELOPE OF SIZE
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

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

18. Other Factors
I.e., Parallel Line Tolerance Zones
GEOMETRIC DIMENSIONING TOLERANCE ZONES
PARALLEL LINES PARALLEL LINES PARALLEL LINES
PARALLEL PLANES PARALLEL PLANES PARALLEL PLANES
PARALLEL PLANES PARALLEL PLANES CYLINDER ZONE

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

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
TOLERANCE INFORMATION
DATUM REFERENCES
COMPARTMENT VARIABLES
THE
RELATIVE TO
OF THE FEATURE
MUST BE WITHIN
CONNECTING WORDS

22. Feature Control Frame
s Uses feature control frames to
indicate tolerance
s 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
s Uses feature control frames to indicate
tolerance
s 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
s The of the feature must be within a tolerance
zone.
s The of the feature must be within a
tolerance zone at relative
to Datum .
s The of the feature must be within a
tolerance zone relative to Datum .
s The of the feature must be within a
zone at
relative to Datum .
s The of the feature must be within a
tolerance zone relative to datums .

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

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

27. Basic Dimension
s A theoretically exact size, profile,
orientation, or location of a feature or
datum target, therefore, a basic
dimension is untoleranced.
s Most often used with position,
angularity, and profile)
s Basic dimensions have a rectangle
surrounding it.
1.000

28. Basic Dimension
cont’d.

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

30. Form Features Examples
Flatness as stated on
drawing: The flatness of the
feature must be within .06
tolerance zone.
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
Straightness of an Axis at MMC: The derived
median line straightness of the feature must be
within a diametric zone of .030 at MMC.
∅ 0.500
0.505 ∅ .030 M
1.010
0.990

32. Dial Indicator
DIAL INDICATOR
BEZEL
CASE
2 2
4 4
6 6
8 8
10 10
12
CLAMP
PROBE

33. Verification of Flatness

34. Activity 13
s 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
s Orientation
– Perpendicularity
– Angularity
– Parallelism
s Runout
– Circular Runout
– Total Runout
s Location
– Position
– Concentricity
– Symmetry

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

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

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

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

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

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

43. Primary Datum
s 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
s 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
PLANE ESTABLISHED
BY ONE POINT (MIN)
90° CONTACT WITH
SIMULATED DATUM C
MEASURING DIRECTIONS FOR
RELATED DIMENSIONS

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

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

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

52. Orientation Tolerances
– Perpendicularity
– Angularity
– Parallelism
s Controls the orientation of
individual features
s Datums are required
s Shape of tolerance zone: 2
parallel lines, 2 parallel planes, and
cylindrical

53. PERPENDICULARITY:
s 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. Practice Problem
s Plane 1 must be
perpendicular within .005
tolerance zone to plane 2.
BOTTOM SURFACE

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

56. Practice Problem
2.00±.01
.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.
s 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:
s 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.
The surface is at a
45º angle with a .
005 tolerance zone
relative to datum A.
s Can be applied to an axis at MMC.
s Typically must have a basic
dimension.

59. PARALLELISM:
s The condition of a surface or center plane
equidistant at all points from a datum plane, or
an axis.
s The distance between the parallel lines, or
surfaces, is specified by the geometric
tolerance.
±0.01

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

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

62. Maximum Material Condition
s MMC
s 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?
s Permits greater possible
tolerance as the part feature
sizes vary from their calculated
MMC
s Ensures interchangeability
s Used
– With interrelated features with
respect to location
– Size, such as, hole, slot, pin, etc.

63. Least Material Condition
s LMC
s 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
s RFS
s Requires that the condition of
the material NOT be
considered.
s This is used when the size
feature does not affect the
specified tolerance.
s Valid only when applied to
features of size, such as
holes, slots, pins, etc., with
an axis or center plane.

65. Location Tolerances
– Position
– Concentricity
– Symmetry

66. Position Tolerance
s A position tolerance is the total
permissible variation in the location
of a feature about its exact true
position.
s For cylindrical features, the
position tolerance zone is typically
a cylinder within which the axis of
the feature must lie.
s For other features, the center plane
of the feature must fit in the space
between two parallel planes.
s The exact position of the feature is
located with basic dimensions.
s The position tolerance is typically
associated with the size tolerance
of the feature.
s Datums are required.

67. Coordinate System Position
s Consider the following hole dimensioned with
coordinate dimensions:
s The tolerance zone for the location of the hole
is as follows:
2.000
.750
s Several Problems:
– Two points, equidistant from true position may not
be accepted.
– Total tolerance diagonally is .014, which may be
more than was intended.

68. Coordinate System Position
s Consider the following hole dimensioned with
coordinate dimensions:
s The tolerance zone for the location (axis) of the
hole is as follows:
Center can be
anywhere along
the diagonal
line.
2.000
.750
s 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)

69. Position Tolerancing
s Consider the same hole, but add
GD&T:
s Now, overall tolerance zone is:
MMC =
.500 - .003 = .497
s The actual center of the hole (axis) must lie in
the round tolerance zone. The same tolerance
is applied, regardless of the direction.

70. Bonus Tolerance
s 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 .497. 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 .497. If the
.503
hole is bigger, we
get a bonus
tolerance equal to
the difference
between the MMC
size and the
actual size.
Actual Hole Size Bonus Tol. Φ of Tol. Zone
Ø .497 (MMC) 0 .010
Ø .499 (.499 - .497 = .002) .002 (.010 + .002 = .012) .012
Ø .500 (.500 - .497 = .003) .003 (.010 + .003 = .013) .013
Ø .502 .005 .015
Ø .503 (LMC) .006 .016
Ø .504 ? ?
s 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. .497 = BONUS 0
Hole
TOL ZONE .010
Shaft
.499 - .497 = BONUS .002
BONUS + TOL. ZONE = .012

73. .501 - .497 = BONUS .004
BONUS + TOL. ZONE = .014
.503 - .497 = BONUS .006
BONUS + TOL. ZONE = .016

74. s 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.
s 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 Bonus Ø of Tol.
Size Tol. Zone
1.997
(MMC)
1.998
1.999
2.000
2.001
Vc =
2.002
2.003

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