8/9/2019 ME 407 - Introduction to GD&T (v1.3)
1/81
ME 407
Introduction toGeometric Dimensioning &
Tolerancing (GD&T)Dr. Melik Dölen
Middle East Technical UniversityDepartment of Mechanical Engineering
Ankara 06531, TURKEY1956
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
2/81
ME 407
Outline• Definition and Background
– + /- Tolerancing vs. GeometricTolerancing
– Features
– Datums
– Material Conditions Modifiers
– Feature Control Frames
• Major Categories of Tolerances
– 14 Tolerance Measurements
• Bonus Tolerance
• Virtual Conditions
• GD&T with Solidworks
• Summary
2
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
3/81
ME 407
What is GD&T?
3
• GD&T is a symbolic language used to specify the size, shape,
form, orientation, and location of features on a part.
– Design tool for communicating design requirements.
• Like other languages, GD&T uses special punctuation andgrammar rules.
– Must be used properly in order to prevent misinterpretation.
– Comparable to learning a new language!
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
4/81
ME 407
What is GD&T? (Cont’d)
• GD&T has developed as a method to question and
measure the truth about the form, orientation,
and location of manufactured parts.
– Considers the function of the part and how this part
functions with related parts.
– Allows a drawing to contain a more defined feature
more accurately without increasing tolerances.
4
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
5/81
ME 407
Standards
• Standards on GD&T comefrom two organizations: – ASME (American Society of
Mechanical Engineering)
– ISO (International Organization for
Standardization)
• ASME Y14.5M and ISO
1101 are the written
standards. – Standards are nowhere complete. – Continuously evolving since WWII!
5
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
6/81
ME 407
When to Use GD&T?
• Designers should specify tolerance for the parts
with GD&T when
– Drawing delineation and interpretation need to be the
same, – Features are critical to function or interchangeability,
– Automated manufacturing/inspection equipment is
utilized,
– Functional gauging is required, – It is important to increase productivity.
6
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
7/81
ME 407
Dimensioning
• Dimensioning can be divided into
three categories:
– General dimensioning
• Used since 1800s.
– Limit dimensioning
– Plus/minus dimensioning
– Geometric dimensioning
– Surface texture
7
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
8/81
ME 407
Plus/Minus Tolerancing
• Plus/ Minus tolerancing, or limit
tolerancing is a two-dimensional system.
• When the designer draws the part, using
CAD tools, the lines are straight, angles
are perfect, and the holes are perfectly
round.
• When the part is produced in a
manufacturing process, there will be
errors.
• The variations in the corners and surfaces
will be undetectable to the human eye.
– They can be picked up using precise
measurements such as a Coordinate Measuring
Machine (CMM).
8
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
9/81
ME 407
Plus/Minus Tolerancing (Cont’d)
• In a plus/minus tolerancing system, the datums are
implied and therefore, are open to interpretations.
• Plus/minus tolerancing works well when individual
features are considered.
– However, one can not understand the relationship between
individual features.
• With the dawn of CAD systems and CMMs, it has become
increasingly important to describe parts in three
dimensions (i.e. solid geometric models), and plus/minustolerancing is simply not precise enough.
9
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
10/81
ME 407
Example - Dimensional Tolerancing
10
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
11/81
ME 407
Example – Produced Part
11
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
12/81
ME 407
Example - GD&T Specs
12
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
13/81
ME 407
Example - Feature Control via GD&T
13
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
14/81
ME 407
Example
• Consider the given Table. – Assume all four legs will be cut to
the length at the same time.
• All surfaces have a degree of
waviness (smoothness). – The surface of a 2 by 4 is much
wavier (rough) than the surface of apiece of glass.
– As the table height is dimensioned,the following table would passinspection.
14
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
15/81
ME 407
Example (Cont’d) • 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.
• 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”)
15
26
.06
27
.06
28
.06
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
16/81
ME 407
Review of Terminology
• Basic Dimension: Nominal dimension from which tolerancesare derived.
• With Size: A feature said to be “with size” if it is associatedwith a size dimension. It can be cylindrical or spherical orpossibly a set of two opposing parallel surfaces.
• Without Size: A plane surface where no size dimensions areindicated.
• Feature Control Frames: Probably the most significantsymbol in any geometric tolerancing system. Provides theinstructions and requirements for its related feature.
• Radius: Two types of radii can be applied. The radius (R)distinguishes general applications. The controlled radius(CR) defines radius shapes that require further restrictions.
16
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
17/81
ME 407
Terminology - Feature
• Real, geometric shapes thatmake up the physical
characteristics of a part.
– May include one or more elements:
• Holes, Screw threads, Profiles, Faces,Slots
• Can be individual or may be
interrelated.
• Any feature can have manyimperfections and variations
17
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
18/81
ME 407
Material Condition Modifiers
• Have tremendous impact on stated tolerance ordatum reference.
• Can only be applied to features and datums that
specify size (holes, slots, pins, tabs). If applied to
features that are without size, they have noimpact.
• There are three material condition modifiers:
– Maximum material condition (MMC) – Least material condition (LMC)
– Regardless of feature size (RFS)
18
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
19/81
ME 407
Maximum Material Condition M
• This is when part will weigh the most.
– MMC for a shaft is the largest allowable size.• MMC of Ø.250±.005?
– MMC for a hole is the smallest allowable size.
• MMC of Ø.250±.005?
• Permits greater possible tolerance as thepart feature sizes vary from theircalculated MMC
• Ensures interchangeability
• Used with interrelated features with
respect to location: – Size, such as, hole, slot, pin, etc.
19
.255
.250 + .005
.245
.250 + .005
M
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
20/81
ME 407
Least Material Condition L
• This is when part will weighthe least.
– LMC for a shaft is the
smallest allowable size.
• LMC of Ø.250±.005?
– LMC for a hole is the largest
allowable size.
• LMC of Ø.250±.005?
20
.245
.250 + .005
.255
.250 + .005
L
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
21/81
ME 407
Regardless of Feature Size
• Requires that the condition of the
material NOT be considered.
• This is used when the size feature doesnot affect the specified tolerance.
• Valid only when applied to features of
size, such as holes, slots, pins, etc.,with an axis or center plane.
21
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
22/81
ME 407
Limits of Size
THIS MEAN?
WHAT DOES
SIZE DIMENSION
2.007
2.003
• A variation in form isallowed between the
least material condition
(LMC) and the maximum
material condition(MMC).
• Envelope (Taylor)
Principle defines the size
and form relationships
between mating parts.
22
SIZE DIMENSION
MMC
LMC
ENVELOPE OF SIZE
(2.003)
(2.007)
ENVELOPE PRINCIPLE
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
23/81
ME 407
Limits of Size (Cont’d)
• The actual size of the feature
at any cross section must be
within the size boundary.
• No portion of the feature
may be outside a perfect
form barrier at maximummaterial condition (MMC).
23
ØMMC
ØLMC
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
24/81
ME 407
Controlled Features
24
INDIVIDUAL
(No Datum
Reference)
INDIVIDUAL or
RELATED
FEATURES
RELATEDFEATURES
(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
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
25/81
ME 407
Some Common Symbols
25
Feature Control Frame
Datum Reference Frame
Diametral (Cylindrical) Tolerance
Zone or Feature
Basic- or Exact Dimension
Least Material Condition (LMC)
Maximum Material Condition (MMC)
.003 M A
A
.500
M
L
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
26/81
ME 407
Feature Control Frame
26
GEOMETRIC SYMBOL
TOLERANCE INFORMATION
DATUM REFERENCES
THE
MUST BE WITHIN
OF THE FEATURE
RELATIVE TO
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
27/81
ME 407
Example - Frame Control Frame
• Reads as “ The (true) position of the
feature must be within a .01”
diametric tolerance zone at
maximum material conditionrelative to datums A, B (at
maximum material condition), and
C.”
27
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
28/81
ME 407
Application of FCFs
• May be attached to a side, end
or corner of the symbol box to
an extension line or could be
applied to a surface or an axis.
• May be below or closely
adjacent to the dimension ornote pertaining to that feature.
28
Ø .500±.005
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
29/81
ME 407
Basic Dimension
• A theoretically exact size,
profile, orientation, orlocation of a feature or
datum target, therefore, a
basic dimension is non-
toleranced.
• Most often used with
position, angularity, and
profile• Basic dimensions have a
rectangle surrounding it.
29
1.000
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
30/81
ME 407
Datum Reference Frame
• GD&T positions every part within a “DatumReference Frame” (DRF).
• The DRF is by far the most important
concept in the geometric tolerancingsystem.
• The skeleton, or frame of reference to
which all requirements are connected.
• Understanding the DRF is critical in order to
grasp the concepts of position and profile.
30
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
31/81
ME 407
DRF (Cont’d)
• Engineering, manufacturing,
and inspection all share acommon “three planes”
concept.
• These three planes are: – Mutually perpendicular
(orthogonal)
– Perfect in dimension and
orientation• This concept is called the
Datum Reference Frame.
31
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
32/81
ME 407
DRF (Cont’d)
• The three main features of the DRF
are the planes, axes, and points.
• The DRF consists of three imaginary
planes, similar to the X, Y, & Z axes
of the traditional coordinate
measuring system.• The planes exist only in theory and
make up a perfect, imaginary
structure that is mathematically
perfect.• All measurements originate from
the simulated datum planes.
32
This flat, granite surface plate
and the angle block sitting on
it, can represent two of thethree datum planes.
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
33/81
ME 407
DRF (Cont’d)
• The Datum Reference Frame will
accommodate both rectangularand cylindrical parts.
• A rectangular part fits into the
corners represented by the
intersection of the three datum
planes.
• The datum planes are imaginary
and therefore perfect.
• The parts will vary from these
planes, even though the variations
will not be visible to the naked eye.
33
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
34/81
ME 407
DRF (Cont’d)
• The most important concept to understandis that when the part is placed into an
inspection apparatus, it must make contact
with its planes in the order specified by thefeature control frame.
– Primary, then secondary, then tertiary!
• This is the only way to assure uniformity inthe measurement of different parts.
34
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
35/81
ME 407
DRF (Cont’d)
• A cylindrical part rests on the flat
surface of the primary plane and
the center of the cylinder aligns
with the vertical datum axis
created by the intersection of
the planes.• In this case, it becomes very
important to be able to establish
the exact center of the part,
whether it is the center of a solid
surface, or the center of a hole.
• Cylindrical parts are more
difficult to measure.
35
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
36/81
ME 407
Implied Datums
• The order of precedence in the
selection and establishment of
datums is very important.
• The picture shows a part with
four holes, located from the
edges with basic dimensions.• The datums are not called out in
the feature control frame, but
they are “implied” by the
dimensions and by the edges
from which those dimensionsoriginate. Thus, we imply that
these edges are the datums.
36
( )
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
37/81
ME 407
Implied Datums (Cont’d)
• Problems with implied datums: – We do not know the order in which they are
used.
– We know the parts are not perfect.
– None of the edges are perfectly square.
– The 90o corners will not be perpendicular.
• In theory, even if the corners were out of
perpendicularity by only .0001, the part would still“rock” back and forth in the “theoretically perfect”
datum reference frame.
37
d f
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
38/81
ME 407
Order of Datums
• GD&T instructions designate which feature of the
part will be the “primary, secondary, or tertiary”
datum references.
• These first, second and third datum features
reflect an order of importance when relating toother features that don’t touch the planes
directly.
• Datum orders are important because the same
part can be inspected in several different ways,
each giving a different measurement.
38
d f ( ’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
39/81
ME 407
Order of Datum (Cont’d)
• Creating a Datum Reference
Frame and an order of
importance is mandatory in
order to achieve
interchangeable parts.• Improper positioning could
result in measurement errors
unless the preferred
positioning in the inspectionfixture is indicated in the
drawing.
39
d f ( ’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
40/81
ME 407
Order of Datums (Cont’d)
•The primary datum feature
must have at least three points
of contact with the part and
contacts the fixture first.
• The secondary has two pointsof contact and the tertiary hasthree points of contact with
the part.
• This process correctly mirrors
the datum reference frameand positions the part the way
it will be fitted and used.
40
A li i f D
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
41/81
ME 407
Application of Datums
• Datums are ideal features (points,
lines, circles, planes spheres,cylinders, cones) on the object that
are used as references from which
other measurements are made.
– Used in designing, tooling,manufacturing, inspecting, and
assembling components and sub-
assemblies.
– Not every GD&T feature requires a
datum!
• Datums are imaginary . They are
assumed to be exact for the purpose
of computation or reference.
41
1.000
D (C ’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
42/81
ME 407
Datum (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.
42
.003 M A
Pl f D
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
43/81
ME 407
Placement of Datums
• Feature sizes, such as
holes
• Sometimes a feature
has a GD&T and is also
a datum
43
A Ø .500±.005
A
Ø .500±.005 Ø .500±.005
I ti i CMM
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
44/81
ME 407
Inspection via CMM
44
Z
DATUM
REFERENCE
FRAME
SURFACE
PLATE
GRANITE
PROBE
BRIDGE DESIGN
F F t
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
45/81
ME 407
Form Features
• Individual features
• No datum (reference) is required.
45
Flatness Straightness
CylindricityCircularity
Fl t
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
46/81
ME 407
Flatness
• Flatness is a three-dimensionalversion of straightness tolerance.
• Requires a surface to be within two
imaginary (perfectly flat & parallel)
planes.
– Only the surface of the part (not the
entire thickness) is referenced to the
planes.
– Most often used on rectangular or
square parts. – If used as a primary datum, flatness must
be specified in the drawing.
46
V ifi ti f Fl t
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
47/81
ME 407
Verification of Flatness
47
St i ht
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
48/81
ME 407
Straightness
• Straightness is a two-dimensional
tolerance.
• Edge must remain within two
imaginary parallel lines to meet
straightness tolerance.• Distance between lines is
determined by size of specified
tolerance.
– Most rectangular parts have a straightnesstolerance.
– Edge or center axis of a cylinder may have a
straightness tolerance.
48
Ci l it
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
49/81
ME 407
Circularity
• Circularity (or roundness) is atwo-dimensional tolerance.
– Demands that any two-dimensional
cross-section of a round feature
must stay within the tolerance zone
created by two concentric circles.
– Most often used on cylinders.
• Also applies to cones and spheres.
– Most inspectors check multiple
cross-sections.• Each section must meet the tolerance on
its own.
49
C li d i it
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
50/81
ME 407
Cylindricity
• Cylindricity specifies the roundnessof a cylinder along its entire length.
– All cross-sections of the cylinder must
be measured together, so cylindricity
tolerance is only applied to cylinders.
• Circularity and cylindricity cannotbe checked by measuring various
diameters with a micrometer.
• Part must be rotated in a high-
precision spindle. – Best method would be to use a CMM.
50
The thickness of the wall of a pipe represents
the cylindricity tolerance zone.
C lindricit (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
51/81
ME 407
Cylindricity (Cont’d)
51
Examples of Form Features
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
52/81
ME 407
Examples of Form Features
52
Flatness as stated on drawing:
The flatness of the feature must
be within 0.06” tolerance zone.
Straightness applied to a flat
surface: The straightness of the
feature must be within 0.003” tolerance zone.
.003
0.500 ±.005
.0030.500 ±.005
Examples (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
53/81
ME 407
Examples (Cont’d)
53
Straightness applied to the
surface of a diameter: The
straightness of the feature must
be within .003 tolerance zone.
Straightness of an axis at MMC:
The derived median line
straightness of the feature
must be within a diametric
zone of .030 at MMC.
.003
0.5000.505
.0300.5000.505 M
1.0100.990
Features Requiring Reference
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
54/81
ME 407
Features Requiring Reference
• Unlike form features, the
followings necessitate datumreference:
– Orientation• Perpendicularity, Angularity, Paralellism
– Profile• Line (Curve), Surface
– Run-out
• Circular Run-out, Total Run-out
– Location• Position, Concentricity, Symmetry
54
Perpendicularity
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
55/81
ME 407
Perpendicularity• Perpendicularity is the condition of a surface,
center plane, or axis at a right angle (90°) to adatum plane or axis.
55
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.
Example Perpendicularity
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
56/81
ME 407
Example - Perpendicularity
56
This means the hole (i.e. its axis)
must be perpendicular within a
diametrical tolerance zone of.010 relative to datum A
Angularity
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
57/81
ME 407
Angularity
• Angularity is a three-dimensional
tolerance.
• Shape of the tolerance zone
depends on the feature:
– If applied to flat surface, tolerancezone becomes two imaginary planes,
parallel to ideal angle.
– If applied to a hole, it is referenced
to an imaginary cylinder existing
around the ideal angle and center
of the hole must stay within that
cylinder.
57
Parallelism
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
58/81
ME 407
Parallelism
• It is the condition of a surface or center plane
equidistant at all points from a datum plane, oran axis.
• The distance between the parallel lines, or
surfaces, is specified by the geometric tolerance.
58
±0.01
Line (Curve) Profile
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
59/81
ME 407
Line (Curve) Profile
• A profile is an outline of the part
feature in one of the datum planes. – They control orientation, location, size
and form.
• The two versions of profile
tolerance.
– Both can be used to control features
such as cones, curves, flat or irregular
surfaces, or cylinders.
• The profile of a line is a two-
dimensional tolerance. – It requires the profile of a feature to fall
within two imaginary parallel lines that
follow the profile of the feature.
59
Profile of a Surface
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
60/81
ME 407
Profile of a Surface
• Profile of a Surface is three-dimensional version of the
line profile.
– Often applied to complex and
curved contour surfaces suchas aircraft and automobile
exterior parts.
– The tolerance specifies that
the surface must remain
within two three-dimensional
shapes.
60
Circular Runout
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
61/81
ME 407
Circular Runout
• Circular and Total Runout are three-
dimensional and apply only to cylindricalparts.
– Both tolerances reference a cylindrical
feature to a center datum-axis, and
simultaneously control the location, form
and orientation of the feature.
• Circular runout can only be inspected
when a part is rotated.
– Calibrated instrument is placed against the
surface of the rotating part to detect the
highest and lowest points.
– The surface must remain within twoimaginary circles, having their centers
located on the center axis.
61
Total Runout
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
62/81
ME 407
Total Runout
• Total Runout is similar to circular
runout except that it involvestolerance control along the entire
length of, and between, two
imaginary cylinders, not just at
cross sections. – By default, parts that meet total
runout tolerance automatically satisfy
all of the circular runout tolerances.
– Runout tolerances, especially total
runout, are very demanding andpresent costly barriers to
manufacturing and inspection.
62
Position Tolerance
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
63/81
ME 407
Position Tolerance
• Position is one of most common location tolerances:
– A three-dimensional, related tolerance.
– Ideal, exact location of feature is called true position.
– Actual location of a feature is compared to the ideal trueposition.
– Usually involves more than one datum to determine where
true position should be.
– Has nothing to do with size, shape, or angle, but rather“where it is.”
63
Position Tolerance (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
64/81
ME 407
Position Tolerance (Cont d)
• A position tolerance is the total permissible variation inthe location of a feature about its exact true position.
• For cylindrical features, the position tolerance zone istypically a cylinder within which the axis of the featuremust lie.
• For other features, the center plane of the feature mustfit in the space between two parallel planes.
• The exact position of the feature is located with basicdimensions.
• The position tolerance is typically associated with the sizetolerance of the feature.
• Datums are required.
64
Position (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
65/81
ME 407
Position (Cont d)
• In the case of holes, the tolerance
involves the center axis of the hole andmust be within the imaginary cylinder
around the intended true position of
the hole.
• If toleranced feature is rectangular,
the zone involves two imaginaryplanes at a specified distance from the
ideal true position.
• Position tolerance is easy to inspect
and is often done with just a functional
gage (go / no-go gage).
65
Concentricity
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
66/81
ME 407
Concentricity
• Concentricity is a three-dimensional tolerance.
– It relates a feature to one
or multiple datums.
– Difficult to measure!
– The shaft is measured in
multiple diameters to
ensure that they share a
common center-axis.
66
Symmetry
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
67/81
ME 407
Symmetry
• Symmetry is much like
concentricity. – Difference is that it controls
rectangular features and involves
two imaginary flat planes, much like
parallelism. – Both symmetry and concentricity
are difficult to measure and
increase costs of inspection.
– When a certain characteristic, such
as balance, is important, thesetolerances are very effective.
67
Example - Symmetry
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
68/81
ME 407
Example Symmetry
68
Issues in Position Tolerancing
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
69/81
ME 407
Issues in Position Tolerancing
• Consider the following holedimensioned with coordinate
dimensions.
• The tolerance zone for the
location of the hole is as
shown.
• There exist several problems: – Two points, equidistant from
true position may not beaccepted.
– Total tolerance diagonally is.014, which may be more thanwas intended.
69
2.000
. 7 5 0
Issues (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
70/81
ME 407
Issues (Cont d)
• Consider the same hole, but add GD&T.
• Now, the actual center of the hole (axis) must lie in
the round tolerance zone. The same tolerance is
applied, regardless of the direction.
70
MMC = .500 - .003 = .497
Bonus Tolerance
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
71/81
ME 407
Bonus Tolerance
• Material condition
modifiers giveinspectors a
powerful method of
checking shafts andholes that fit
together.
• Both MMC and LMCmodifiers allow for
bonus tolerance.
71
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.
.010 M A
Example - Bonus Tolerance
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
72/81
ME 407
Example Bonus Tolerance
72
• This system makes sense:the larger the hole is, the
more it can deviate from
true position and still fit
in the mating condition!
Actual Hole Size Bonus Tolerance 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 ? ?
Virtual Condition
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
73/81
ME 407
Virtual Condition
• Depending upon its intended purpose, afeature may be controlled by multiple
geometric tolerances.
• The combined effects of these factorsdetermine the clearances between mating
parts and they establish gage feature sizes.
• The collective effect of these factors is called“virtual condition.”
73
Example - Virtual Condition
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
74/81
ME 407
Example Virtual Condition
• Regardless of its position (or
angle) the pin must lie withinthe .002 boundary.
• Tolerance for perpendicularity
allows a margin of .005.
• If the part were produced atMMC to .252 and it deviated
from perpendicularity by .005,
the total virtual size of the pin
would be.257 in relation todatum A.
74
The size tolerance for the pin
(.250 ± .002) along with the location
and perpendicularity tolerances are listedin the Feature Control Frame.
Example (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
75/81
ME 407
Example (Cont d)
• Position tolerance of .010
combined with the sizetolerance of .002 would
produce a virtual size of .262 in
relation to datums A, B and C.
• This means that an inspectiongage would have to have a hole
of .262 to allow for the
combined tolerances
• Therefore, three inspections
would be necessary in order to
check for size, perpendicularity,
and location.
75
Exercise - Virtual Sizes
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
76/81
ME 407
Exercise Virtual Sizes
76
.192
.186
.387
.379
Calculate the virtual sizes for the indicated features.
(Answers are in red!)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
77/81
GD&T with SolidWorks
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
78/81
ME 407
GD&T with SolidWorks
• Among other things,
the dimension expert
(DimXpert ) tool allows
its users to work with
GD&T: – This feature has been
added to the SW after
2008.
• Lots videos areavailable on Youtube.
– Check it out!
78
Summary
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
79/81
ME 407
Summary
• GD&T is an international design (and drafting)standard.
• Uses consistent approach and compact symbols
to define and control the features of
manufactured parts.
• Is derived from the two separate standards of
ASME Y14.5M and ISO 1101.
• Helps inspectors improve their methods byemphasizing fit, form, and function.
79
Summary (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
80/81
ME 407
Summary (Cont d)
• Compares the physical, imperfect features of a
part to its perfect, imaginary form specified in the
design drawing.
• Controls flatness, straightness, circularity,cylindricity, and four form tolerances that
independently control a feature.
• Other tolerances, such as location, runout, and
orientation must be referenced to another datum.
80
Summary (Cont’d)
8/9/2019 ME 407 - Introduction to GD&T (v1.3)
81/81
Summary (Cont d)
• The profile tolerances can define a featureindependently.
• A related datum can further define the orientation
and location.
• A series of internationally recognized symbols are
organized into a feature control frame.
• The control frame specifies the type of geometric
tolerance, the material condition modifier, andany datums that relate to the feature.