PART PRODUCTION COMMUNICATION MODEL
MANAGEMENT
DESIGN
TOOLING
PRODUCTION
INSPECTION
ASSEMBLY
ROUTING
PLANNING
PRICING
SERVICE
PURCHASING
SALES
CU
STO
ME
RS
VEN
DO
RS
Geometric Dimensioning
and Tolerancing (GD&T)
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
Limit Tolerancing Applied
To An Angle Block
Geometric Tolerancing
Applied To An Angle Block
Geometric Dimensioning Geometric Dimensioning
& Tolerancing (GD&T)
� GD&T is a means of
dimensioning & tolerancing a drawing which considersthe 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.
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.
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
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
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
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 insure 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
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.
THIS MEAN?WHAT DOES
SIZE DIMENSION
2.0072.003
LIMITS OF SIZE
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.
ENVELOPE PRINCIPLE
LMC
CLEARANCE
MMCALLOWANCE
LIMITS OF SIZE
LIMITS OF SIZE
The actual size of the feature at any cross section must be within the size boundary.
ØMMC
ØLMC
No portion of the feature may be outside a perfect form barrier at maximum material condition (MMC).
LIMITS OF SIZE
PARALLEL PLANES
PARALLEL PLANES PARALLEL PLANES CYLINDER ZONE
PARALLEL LINES PARALLEL LINES PARALLEL LINES
PARALLEL PLANES PARALLEL PLANES
Other Factors I.e., Parallel Line Tolerance Zones
INDIVIDUAL
(No Datum
Reference)
INDIVIDUAL
or RELATED
FEATURES
RELATED
FEATURES
(Datum
Reference
Required)
GEOMETRIC CHARACTERISTIC CONTROLS
TYPE OFFEATURE
TYPE OFTOLERANCE
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
Characteristics & Symbolscont’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
THE
GEOMETRIC SYMBOL
TOLERANCE INFORMATION
DATUM REFERENCES
FEATURE CONTROL FRAME
COMPARTMENT VARIABLES
CONNECTING WORDS
MUST BE WITHINOF THE FEATURE
RELATIVE TO
Feature Control Frame
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 conditionrelative to datums A, B, and C.
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.
� 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
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
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
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
Basic Dimension cont’d.
Form Features
� Individual Features
� No Datum Reference
Flatness Straightness
CylindricityCircularity
Form Features Examples
Flatness as stated on drawing: The flatness of the
feature must be within .06
tolerance zone.
.003
0.500 ±.005
.0030.500 ±.005
Straightness applied to a flat surface: The
straightness of the feature must be within .003
tolerance zone.
Form Features Examples
Straightness applied to the surface of a diameter: The straightness of the feature must
be within .003 tolerance zone.
.003
0.5000.505∅
Straightness of an Axis at MMC: The derived
median line straightness of the feature must be
within a diametric zone of .030 at MMC.
.0300.5000.505∅ M∅
1.0100.990
BEZELCASE
CLAMP
PROBE
6
8
1012
10
8
6
4
22
4
Dial Indicator
Verification of Flatness
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.)
Features that Require
Datum Reference
� Orientation
– Perpendicularity
– Angularity
– Parallelism
� Runout
– Circular Runout
– Total Runout
� Location
– Position
– Concentricity
– Symmetry
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
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.
Datum Reference Symbols
� The datum feature symbol
identifies a surface or feature of size as a datum.
A
ISO
A
ANSI1982
ASME
A
1994
Placement of Datums
� Datums are generally placed on a feature, a
centerline, or a plane depending on how
dimensions need to be referenced.
A AOR
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
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
6 ROTATIONAL6 LINEAR AND
FREEDOMDEGREES OF
UP
DOWN
RIGHT
LEFT BACK
FRONT
UNRESTRICTED FREEMOVEMENT IN SPACE
TWELVE DEGREES OF FREEDOM
Example Datums
� Datums must be
perpendicular to each other
– Primary
– Secondary
– Tertiary Datum
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?
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.
FIRST DATUM ESTABLISHEDBY THREE POINTS (MIN)CONTACT WITH SIMULATEDDATUM A
Primary Datum
� Restricts 6 degrees of freedom
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.
SECOND DATUMPLANE ESTABLISHED BYTWO POINTS (MIN) CONTACTWITH SIMULATED DATUM B
Secondary Datum
� Restricts 10 degrees of freedom.
Tertiary Datum
� Restricts 12 degrees of freedom.
90°
THIRD DATUMPLANE ESTABLISHEDBY ONE POINT (MIN)CONTACT WITHSIMULATED DATUM C
MEASURING DIRECTIONS FOR
RELATED DIMENSIONS
Z
D AT U MR EF E R E N C EF R A M E
SU R F A C EP LA T E
G R A N IT E
P R O B E
B R ID G E D ES IG N
Coordinate Measuring
Machine
SIMULATED DATUM-
SMALLEST
CIRCUMSCRIBED
CYLINDER
THIS ONTHE DRAWING
MEANS THIS
PART
DATUM AXIS
A
Size Datum(CIRCULAR)
Size Datum(CIRCULAR)
SIMULATED DATUM-LARGEST
INSCRIBEDCYLINDER
THIS ONTHE DRAWING
MEANS THIS
DATUM AXIS A
PART
A
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
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.
Practice Problem
� Plane 1 must be
perpendicular within .005 tolerance zone to plane 2.
BOTTOM SURFACE
Practice Problem
� Plane 1 must be
perpendicular within .005 tolerance zone to plane 2
BOTTOM PLANE
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.
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’
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 basicdimension.
The surface is at a
45º angle with a
.005 tolerance zone
relative to datum A.
±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.
Activity 13 Cont’d.
� Complete worksheets GD&T-
2, GD&T-4, and GD&T-5
– Completely dimension.
– ¼” grid
Material Conditions
� Maximum Material Condition
(MMC)
� Least Material Condition (LMC)
� Regardless of Feature Size(RFS)
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.
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?
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.
Location Tolerances
– Position
– Concentricity
– Symmetry
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.
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.
2.000
.750
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)
2.000
.750
Center can be anywhere along the diagonal line.
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 =
.500 - .003 = .497
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 .497. If the hole is
bigger, we get a bonustolerance equal to the
difference between the
MMC size and the actual
size.
Bonus Tolerance Example
� This system makes senseY the larger the hole is, the more it can deviate from true position and still fit in the mating condition!
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 ? ?
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.
.503
.497 = BONUS 0
TOL ZONE .010
.499 - .497 = BONUS .002
BONUS + TOL. ZONE = .012
Shaft
Hole
.501 - .497 = BONUS .004
BONUS + TOL. ZONE = .014
.503 - .497 = BONUS .006
BONUS + TOL. ZONE = .016
� 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
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 =
Activity 13 Cont’d.
� Worksheet GD&T 6
