Engineering 22
Geometric
Dimensioning
& Tolerancing
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering 22 – Engineering Design Graphics
1
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Skill-Development Goal
 To learn how to effectively tolerance
parts such that
• The Parts Function Correctly
• Fabrication Cost Is Kept To A Minimum
 Apply Geometric Dimensioning &
Tolerancing (GD&T); in particuluar
• Position, Size
• Flatness, Circularity
• Perpendicularity, Parallelism
Engineering 22 – Engineering Design Graphics
2
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Geometric Dims & Tolerancing
 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
 Uses “Feature Control Frames” To
Indicate Tolerance(s)
 “State of the Art” for Tolerances
Engineering 22 – Engineering Design Graphics
3
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Geometric?
 The “G” in GD&T refers to Geometric
Forms
• e.g., plane, circle, cylinder, sq, or hexagon
 Theoretically these forms are Perfect –
but any REAL Form will be Imperfect
 In GD&T The Limits of Real Variation
(tolerance) are Specified by the
Diameter/Width of a Planer, Cylindrical,
Annular, or Spherical Zone
Engineering 22 – Engineering Design Graphics
4
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
History of Tolerancing
 In the 1800’s, manufacturing used the
“cut & try, file & fit” approach.
 The plus-minus (or coordinate) system
of tolerancing was next developed.
 In the 1900’s, the first GD&T standards
came out to improve the quality & utility
of engineering drawings.
 In 1966, the united GD&T standard was
published → ANSI - Y14.5M
Engineering 22 – Engineering Design Graphics
5
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Definitions - 1
 Feature
• General term applied to a physical portion of
a part, such as a surface, hole, or slot.
 Feature of Size (FOS)
• One cylindrical or spherical surface, or a set
of parallel surfaces, associated with a size
dimension. (Can be external or internal)
 Location Dimension
• Locates the centerline or centerplane of a
part feature relative to: another part feature,
centerline, or datum.
Engineering 22 – Engineering Design Graphics
6
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Definitions - 2
 Tolerance Zones
• all geometric tolerances have imaginary
tolerance zones that are the basis for
acceptance or rejection of the product
• have specific shapes depending on the
geometric tolerance and feature being
controlled
 Actual Local Size
• the value of any individual distance at any
cross section of a FOS
Engineering 22 – Engineering Design Graphics
7
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Definitions - 3
 Actual Mating Envelope (AME)
• a similar perfect feature counterpart that
can be circumscribed/inscribed
about/within the feature so it just contacts
the surfaces at the highest & lowest points
• It is derived from an actual part
• Used When Calculating a “Bonus
Tolerance”
– More on this Next Time
Engineering 22 – Engineering Design Graphics
8
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Envelope Principle
 Proper Tolerancing establishes the
ENVELOPE of the “perfect” part
 Any deviation in FORM is acceptable,
as long as it remains within the limits of
size
Engineering 22 – Engineering Design Graphics
9
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
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)
Envelope Principle
defines the size and form
relationships between
mating parts.
LMC
(2.003)
ENVELOPE OF SIZE
Engineering 22 – Engineering Design Graphics
10
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Limits of Size LMC & MMC
 Clearance & Allowance
ENVELOPE PRINCIPLE
LMC
CLEARANCE
MMC
ALLOWANCE
Engineering 22 – Engineering Design Graphics
11
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Limits of Size @ X-Section
 The ACTUAL size of the feature at ANY
CROSS SECTION must be within the
size BOUNDARY.
ØMMC
ØLMC
Engineering 22 – Engineering Design Graphics
12
CROSS Sections are
what we measure with
Calipers or Micrometers
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Limits of Size - Boundary
 No portion of the feature may be outside
a PERFECT FORM BARRIER at
maximum material condition (MMC).
Most Common
Engineering 22 – Engineering Design Graphics
13
The Surface
can also be
ROUGH
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Feature Control Frame
 From ASME Y14.5M-1994
• Some ACAD Feature-Frames from Y14.5-1982
Engineering 22 – Engineering Design Graphics
14
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
ANSI/ASME Y14.5 Rev.s
 Responsibility for Maintenance of the
Standard Shifted ANSI → ASME after
the 1994 Version
Engineering 22 – Engineering Design Graphics
15
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T – Form & Profile
GEOMETRIC CHARACTERISTIC CONTROLS
14 characteristics that may be controlled
TYPE OF
FEATURE
TYPE OF
CHARACTERISTIC SYMBOL
TOLERANCE
FLATNESS
INDIVIDUAL
(No Datum
Reference)
STRAIGHTNESS
FORM
CIRCULARITY
CYLINDRICITY
INDIVIDUAL
or RELATED
FEATURES
LINE PROFILE
PROFILE
Engineering 22 – Engineering Design Graphics
16
SURFACE PROFILE
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T – Orient, RunOut, Loctn
GEOMETRIC CHARACTERISTIC CONTROLS
14 characteristics that may be controlled
TYPE OF
FEATURE
TYPE OF
CHARACTERISTIC SYMBOL
TOLERANCE
PERPENDICULARITY
ORIENTATION ANGULARITY
PARALLELISM
RELATED
FEATURES
(Datum
Reference
Required)
CIRCULAR RUNOUT
RUNOUT
TOTAL RUNOUT
CONCENTRICITY
LOCATION
POSITION
SYMMETRY
Engineering 22 – Engineering Design Graphics
17
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Understanding Tolerance Zones
 Traditional ± type of tolerancing describes a
SQUARE zone for acceptable locations.
 GD&T describes a CIRCULAR zone around
the theoretically exact location for the feature.
Engineering 22 – Engineering Design Graphics
18
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Basic Dimension
 A theoretically exact
dimension used to
locate features in
GD&T
• The Dimension From
Which the Limits of
Variation are Derived
 Basic dimensions are
UNtoleranced
• These NOMINAL Dims  Basic Dims Identified
by Enclosure in a
are THEORETICALLY
Exact
FRAME
Engineering 22 – Engineering Design Graphics
19
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Std-Tol vs GD&T - 1
 Standard Tolerance
Not Well Known: Actual hole-ctr
distances, angle of hole-ctrs
Engineering 22 – Engineering Design Graphics
20
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Std-Tol vs GD&T - 2
 GD&T
Specs for Hole Centers
and Angularity
Engineering 22 – Engineering Design Graphics
21
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Cylindrical Tolerance Zone
 Line Connecting the Centers of the Circles at
the Top & Bottom Surfaces Must Fall
Completely Within The Tolerance Cylinder
Engineering 22 – Engineering Design Graphics
22
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Measure Position Tolerance
.500
 Acutually Need TWO Measurement Fixtures
• A Go-Gage with Ø0.496 Pins
• A NoGo-Gage with Ø0.504 Pins
Engineering 22 – Engineering Design Graphics
23
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Material Conditions
 Maximum Material Condition (MMC) M
• largest acceptable size for external feature
• smallest acceptable size for internal
feature
• object weighs the most
 Least Material Condition (LMC) L
 Regardless of Feature Size (RFS) S
• No “Bonus Tolerance” Applied
• Default when no “Circle” Modifier Applied
Engineering 22 – Engineering Design Graphics
24
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Maximum Material Condition
Given
Holes at MMC
 Smallest Holes at
narrow Position accept
0.493” Gage Pins
Engineering 22 – Engineering Design Graphics
25
Holes at LMC
 Same Gage Pins for LMC
Holes w/ Wide-Spacing
allow Larger Pos Tol.
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Datums
 Datums are features
on the object that are
used as reference
surfaces from which
other measurements
are made.
 Not every GD&T
feature requires a
datum.
A
A
A
 Datum Reference
Symbols →
ANSI
1982
ASME
1994
ISO
Engineering 22 – Engineering Design Graphics
26
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
ANSI Datum Frame
 Still Widely Used
• By ACAD for Example...
Engineering 22 – Engineering Design Graphics
27
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Datums Illustrated
C
C
A
A
B
Engineering 22 – Engineering Design Graphics
28
B
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Flatness
Engineering 22 – Engineering Design Graphics
29
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Straightness
Engineering 22 – Engineering Design Graphics
30
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Circularity (Roundness)
Engineering 22 – Engineering Design Graphics
31
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Cylindricity
Engineering 22 – Engineering Design Graphics
32
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Perpendicularity
Engineering 22 – Engineering Design Graphics
33
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Parallelism
Engineering 22 – Engineering Design Graphics
34
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Angular
Tolerances
 Traditional
methods for
tolerancing angles
require that angled
surfaces be very
accurate near the
vertex of the angle,
but can vary more along the length of the angled
feature.
• That is, the allowable DISPLACEMENT in inches or mm
INCREASES with DISTANCE from the VERTEX
Engineering 22 – Engineering Design Graphics
35
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Angular Tolerance Zone
 In (b) Notice How the Width of the Tolerance
Zone Expands with Distance From the Vertex
 GD&T Eliminates The Zone Expansion
• Angles Typically Given as “Basic” or Theoretical (c)
• Tolerance Zones are Then CONSTANT Width (d)
Engineering 22 – Engineering Design Graphics
36
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Profile
Engineering 22 – Engineering Design Graphics
37
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Concentricity
 Similar to Cylindrical Tolerance, but
related to a DATUM Cylinder
• The ENTIRE Axis of the Concentric Feature
Must Lie within the Tolerance Zone Relative
to the Datum centerline
Engineering 22 – Engineering Design Graphics
38
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
RunOut
Circular
Total
Engineering 22 – Engineering Design Graphics
39
 Note that the
CAUSE of the
RunOut is NOT
Known
• In CIRCULAR
Case Could be
some Combo
of Circularity &
Concentricity
• In TOTAL
Case add
Straightness to
the list
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Industrial Example
Engineering 22 – Engineering Design Graphics
40
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Caveat → Use with Care
 GDT is VERY Powerful, BUT…It it can
be Quite CONFUSING and ESOTERIC
 Many Degreed Engineers, as well as
Most Drafters/Designers, and Some
Machinists have only a Vague Notion
About Meaning of GDT Symbols
• MisApplication and Confusion-Induced
Delays are COMMON
– e.g. Try asking what MMC or RFS means…
Engineering 22 – Engineering Design Graphics
41
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T Bottom Line
Engineering 22 – Engineering Design Graphics
42
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
All Done for Today
GD&T
is Not for
Everyone
Engineering 22 – Engineering Design Graphics
43
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
Engr/Math/Physics 25
Appendix
f x   2 x  7 x 
9x  6
3
2
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering 22 – Engineering Design Graphics
44
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt
GD&T – Datum Surfaces and Features
Engineering 22 – Engineering Design Graphics
45
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT-1.ppt