Download - ENGR-22_Lec-19_Sp07_GDT_Tolerancing-1
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 22
GeometricGeometricDimensioninDimensionin
gg& &
TolerancingTolerancing
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Skill-Development GoalSkill-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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Geometric?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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
History of TolerancingHistory 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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Definitions - 1GD&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.
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Definitions - 2GD&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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Definitions - 3GD&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
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Envelope PrincipleEnvelope 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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Limits of SizeLimits of Size
A variation in form is allowed between the least material condition (LMC) and the maximum material condition (MMC).
SIZE DIMENSION
MMC
LMC
ENVELOPE OF SIZE
(2.003)
(2.007)
ENVELOPE PRINCIPLE
Envelope Principle defines the size and form relationships between mating parts.
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Limits of Size LMC & MMCLimits of Size LMC & MMC
Clearance & AllowanceENVELOPE PRINCIPLE
LMCCLEARANCE
MMCALLOWANCE
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Limits of Size @ X-SectionLimits of Size @ X-Section
The ACTUAL size of the feature at ANY CROSS SECTION must be within the size BOUNDARY.
ØMMC
ØLMC
CROSS Sections are what we measure with Calipers or Micrometers
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Limits of Size - BoundaryLimits of Size - Boundary
No portion of the feature may be outside a PERFECT FORM BARRIER at maximum material condition (MMC).
Most CommonThe Surface can also be ROUGH
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GD&T Feature Control FrameGD&T Feature Control Frame
From ASME Y14.5M-1994• Some ACAD Feature-Frames from Y14.5-1982
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ANSI/ASME Y14.5 Rev.sANSI/ASME Y14.5 Rev.s
Responsibility for Maintenance of the Standard Shifted ANSI → ASME after the 1994 Version
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T – Form & ProfileGD&T – Form & Profile
INDIVIDUAL (No Datum Reference)
INDIVIDUAL or RELATED FEATURES
GEOMETRIC CHARACTERISTIC CONTROLS
TYPE OFFEATURE
TYPE OFTOLERANCE CHARACTERISTIC SYMBOL
FLATNESS
STRAIGHTNESS
CIRCULARITY
CYLINDRICITY
LINE PROFILE
SURFACE PROFILE
FORM
PROFILE
14 characteristics that may be controlled
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GD&T – Orient, RunOut, LoctnGD&T – Orient, RunOut, Loctn
RELATED FEATURES (Datum Reference Required)
GEOMETRIC CHARACTERISTIC CONTROLS
TYPE OFFEATURE
TYPE OFTOLERANCE CHARACTERISTIC SYMBOL
SYMMETRY
PERPENDICULARITY
ANGULARITY
PARALLELISM
CIRCULAR RUNOUT
TOTAL RUNOUT
CONCENTRICITY
POSITION
ORIENTATION
RUNOUT
LOCATION
14 characteristics that may be controlled
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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.
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
are THEORETICALLY Exact
Basic Dims Identified by Enclosure in a FRAME
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Std-Tol vs GD&T - 1Std-Tol vs GD&T - 1 Standard Tolerance
Not Well Known: Actual hole-ctr distances, angle of hole-ctrs
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Std-Tol vs GD&T - 2Std-Tol vs GD&T - 2 GD&T
Specs for Hole Centers and Angularity
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Cylindrical Tolerance Zone
Line Connecting the Centers of the Circles at the Top & Bottom Surfaces Must Fall Completely Within The Tolerance Cylinder
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Measure Position ToleranceMeasure Position Tolerance
.500
Acutually Need TWO Measurement Fixtures• A Go-Gage with Ø0.496 Pins
• A NoGo-Gage with Ø0.504 Pins
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Material ConditionsMaterial Conditions
Maximum Material Condition (MMC)• largest acceptable size for external feature
• smallest acceptable size for internal feature
• object weighs the most
Least Material Condition (LMC) Regardless of Feature Size (RFS)
• No “Bonus Tolerance” Applied
M
L
S
• Default when no “Circle” Modifier Applied
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Maximum Material ConditionMaximum Material Condition
Same Gage Pins for LMC Holes w/ Wide-Spacing allow Larger Pos Tol.
Holes at MMC Holes at LMC
Smallest Holes at narrow Position accept 0.493” Gage Pins
Given
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
ISO
A
ANSI1982
ASME1994
A
Datum Reference Symbols →
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
ANSI Datum FrameANSI Datum Frame
Still Widely Used• By ACAD for Example...
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Datums IllustratedDatums Illustrated
A
B
CC
AB
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FlatnessFlatness
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
StraightnessStraightness
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Circularity (Roundness)Circularity (Roundness)
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CylindricityCylindricity
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PerpendicularityPerpendicularity
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ParallelismParallelism
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Angular Tolerances Traditional
methods for tolerancing angles require that angled surfaces be veryaccurate 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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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)
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
ProfileProfile
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
RunOutRunOut 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
Circular
Total
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Industrial ExampleIndustrial Example
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Caveat → Use with CareGD&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…
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Bottom LineGD&T Bottom Line
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All Done for TodayAll Done for Today
GD&Tis Not forEveryone
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engr/Math/Physics 25
AppendiAppendixx
6972 23 xxxxf
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Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T – Datum Surfaces and FeaturesGD&T – Datum Surfaces and Features