This document provides information about geometric dimensioning and tolerancing (GD&T). It begins by explaining the three categories of dimensioning and then defines GD&T as considering the function of a part and how it interacts with related parts. This allows for more precise dimensioning without increasing tolerances. The document then discusses important GD&T concepts like datums, feature control frames, and how they are used to specify tolerances and dimensions. It also provides examples of how different GD&T features like flatness and straightness are applied.

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

2. 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)
Three Categories of
Dimensioning

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. 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.
Assume all 4 legs will be
cut to length at the same
time.
or

8. 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)
27
.06
26
.06
28
.06

9. 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.
 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

10. 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

11. 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.

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

13. SIZE DIMENSION
MMC
LMC
ENVELOPE OF SIZE
(2.003)
(2.007)
ENVELOPE PRINCIPLE
LIMITS OF SIZE
A variation in form is allowed
between the least material
condition (LMC) and the
maximum material condition
(MMC).
Envelop Principle defines the
size and form relationships
between mating parts.

14. ENVELOPE PRINCIPLE
LMC
CLEARANCE
MMC
ALLOWANCE
LIMITS OF SIZE

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

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

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

18. INDIVIDUAL
(No Datum
Reference)
INDIVIDUAL
or RELATED
FEATURES
RELATED
FEATURES
(Datum
Reference
Required)
GEOMETRIC CHARACTERISTIC CONTROLS
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
FORM
PROFILE
ORIENTATION
RUNOUT
LOCATION
14 characteristics that may be controlled

19. 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

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

21. 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.

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 at
maximum material condition and B.

23.  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

24. 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

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

26. 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

27. Basic Dimension
cont’d.

28. Form Features
 Individual Features
 No Datum Reference
Flatness Straightness
Cylindricity
Circularity

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

30. Form FeaturesExamples
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.
.030
0.500
0.505
 M

1.010
0.990

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

32. Verification of Flatness

33. Features that Require
Datum Reference
 Orientation
– Perpendicularity
– Angularity
– Parallelism
 Runout
– Circular Runout
– Total Runout
 Location
– Position
– Concentricity
– Symmetry

34. 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

35. 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.

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

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

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

39. 6 ROTATIONAL
6 LINEAR AND
FREEDOM
DEGREES OF
UP
DOWN
RIGHT
LEFT BACK
FRONT
UNRESTRICTED FREE
MOVEMENT IN SPACE
TWELVE DEGREES OF FREEDOM

40. Example Datums
 Datums must be
perpendicular to each other
– Primary
– Secondary
– Tertiary Datum

41. 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?

42. 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.

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

44. 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.

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

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

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

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

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

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

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

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

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

54. 2.00±.01
.02 Tolerance
Practice Problem
Without GD & T this
would be acceptable
2.00±.01
.02 Tolerance
.005 Tolerance
Zone
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.

55. 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’

56. 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.

57. ±0.01
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.

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

59. 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.

60. 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?

61. 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.

62. Location Tolerances
–Position
–Concentricity
–Symmetry

63. 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.