DPT 312
METROLOGY
CHAPTER 3
MEASUREMENT AND TOLERANCES
ROSHALIZA HAMIDON (DPT 312
08/09)
Introduction
DEFINITION
1.
2.
3.
Engineering design
What is to be manufactured?
Product
What has been manufactured?
Part inspection
How we compare the product
with the engineering design?
Geometric dimensioning
and tolerancing
Ensure the most
economical and effective
production of the parts
ROSHALIZA HAMIDON (DPT 312
08/09)
Tolerance
o
o
o
The total amount that a specific dimension is
permitted to vary
In dimensional metrology, tolerances are applied to
both position (where) and size (how big) dimensions
(see figure 3.1)
Both types of dimensions must have tolerances for
economical manufacture
ROSHALIZA HAMIDON (DPT 312
08/09)
A
E
B
D
C
Figure 3.1 Tolerances apply to both dimensions of size (A,B, E) location and
dimensions of location ( C and D)
ROSHALIZA HAMIDON (DPT 312
08/09)
Geometric dimensioning and tolerancing
(GD&T)
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GD&T is a means of dimensioning and
tolerancing a drawing with respect to the actual
function or relationship of part features that
can be most economically produced
It is a language of symbols used on
mechanical drawings to efficiently, and
accurately communicate geometry
requirements for features on parts and
assemblies.
This type of dimensioning and tolerancing
should be used when:
i.
ii.
iii.
iv.
Features are critical to be functionality or
interchange ability of the part
Datum references are desirable to ensure
consistency between design, manufacturing
and inspection
Computerization techniques in design and
manufacturing are being used or are
desirable
Standard interpretation or tolerance is not
already implied
ROSHALIZA HAMIDON (DPT 312
08/09)
Key terms in GD&T
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Feature – general term applied to a physical portion of a part
such as a surface, hole or slot
Datum- a theoretically exact plane, point axis from which a
dimension is measured
Datum feature – part feature that contacts a datum (use as
the origin for measurement)
Datum reference plane- a set of three mutually perpendicular
datum planes (see figure 3.2)
Feature of size- one cylindrical or spherical surface, or a set
of two opposed parallel surface associated with a size
dimension
i. internal – the diameter of a hole or the width of a slot
ii. External – the width or length of a block or a shaft
diameter
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.2: Datum Reference Plane
ROSHALIZA HAMIDON (DPT 312
08/09)
SYMBOL AND MODIFIERS
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The language of geometric tolerancing is a set of
symbols.
This symbols are divided into five types of
dimensioning control
1.
2.
3.
4.
5.
Form
Profile
Orientation
Location
Runout
* Geometric controls of form never use a datum
reference.
*Form control (straightness, flatness, circularity or
cylindricity) are always relative to themselves and not
other features.
*some geometric controls (orietation, location, or
runout) must have a datum reference
ROSHALIZA HAMIDON (DPT 312
08/09)
1. Form tolerance

State how far an actual surface or
feature is permitted to vary from
the desired form implied by the
drawing
ROSHALIZA HAMIDON (DPT 312
08/09)
2. Profile tolerance

States how far an actual surface or
feature is permitted to vary from
the desired form on the drawing
and/ or vary relative to a datum
ROSHALIZA HAMIDON (DPT 312
08/09)
3. Orientation tolerance

States how far an actual surface or
feature is permitted to vary relative
to a datum
ROSHALIZA HAMIDON (DPT 312
08/09)
4. Location tolerance

States how far an actual size
feature is permitted to vary from
the perfect location implied by the
drawing as related to a datum or
other feature
ROSHALIZA HAMIDON (DPT 312
08/09)
5. Runout feature

States how far an actual surface or
feature is permitted to vary from
the desired form implied by the
drawing during full 360 degree
rotation of the part on a datum axis
ROSHALIZA HAMIDON (DPT 312
08/09)
Material condition
1.
Maximum material condition (MMC)

2.
Least material condition (LMC)

3.
The condition in which a feature of size
contains the materials within its stated
tolerance limit
LMC is the condition in which a feature of
size contains the least amount of material
within its permissible limits
Regardless of Feature Size (RFS)

Indicates a geometric tolerance that applies
at any increment of size of the feature within
its permissible limits.
ROSHALIZA HAMIDON (DPT 312
08/09)
APPLICATION OF GEOMETRIC
TOLERANCING
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Form tolerance

Straightness

Flatness

Flatness

Circularity (Roundness)

Cylindricity
Profile tolerance

Profile of line

Profile of surface
Orientation tolerances

Angularity

Perpendicularity

Parallelism
Location tolerance

Position

Concentricity

Symmetry
Runout tolerances

Circular runout

Total runout
ROSHALIZA HAMIDON (DPT 312
08/09)
1. Form Tolerance


State how far an actual surface or
feature is permitted to vary from
the desired for
Straightness , flatness, circularity,
and cylindricity are most frequently
applied to single features or
portions of a feature.

ROSHALIZA HAMIDON (DPT 312
08/09)
i. Straightness
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
The condition where one line
element of an axis, or surface is in
straight line. (see figure 3.3)
Straightness tolerances can be
applied to an axis or to a surface
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.3: Straightness tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
o When applied to an
axis, straightness is
specified in the view
where the axis is in
straight line
oThe tolerance zone
is a space between
two parallel straight
lines
o MMC of LMC
Figure 3.4: Straightness tolerance
applied to an axis
ROSHALIZA HAMIDON (DPT 312
08/09)
o When a surface is to be
controlled, the feature control
frame is attached to the surface
with leader or extension line
oRFS
Figure 3.5: Straightness tolerance
applied to a surface
ROSHALIZA HAMIDON (DPT 312
08/09)
ii. Flatness
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The condition of surface having all elements in
one plane
When flatness is specified, the feature control
frame is attached directly to the surface or to an
extension line of the surface
The flatness tolerance zone is defined by two
parallel planes
All points of the surface must be within the limits
of the tolerance zone defined by these two planes.
(see figure 3.6)
The smaller the tolerance zone, the flatter the
surface
Always applied RFS, no feature modifier such as
MMC or LMC are allowed
ROSHALIZA HAMIDON (DPT 312
08/09)
Flatness (cont’)
Figure 3.6: Flatness tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
iii. Circularity (roundness)
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Circularity is identified with any given cross
section taken perpendicular to the axis of a
cylinder or cone or through the center of sphere
The tolerance is bounded by two concentric circles
Each circular element of the surface must be
contained within these concentric circles
The circularity tolerance must be less than the
size tolerance, except for parts subject to free
state variation
For RFS
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.7: Circularity
tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
iv. Cylindricity
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Defined as the condition of a surface of
revolution in which all points of the
surface are equidistant from a common
axis
The tolerance zone for cylindricity is
bound by two concentric cylinder
All surface elements must lie within these
concentric circles
The tolerance applies simultaneously to
both the circular and the longitudinal
elements of the surface
For RFS
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.8:
Cylindricity
tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
2. Profile tolerance
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Allows us to control the form or shape of
a surface
A profile is the outline of an object
represented by a cross section through
the part or by and end view of the part
Basic dimensions are generally used to
define a profile
Profile tolerance can be applied as either
a profile of line, or profile or a surface
ROSHALIZA HAMIDON (DPT 312
08/09)
i. Profile of line
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

Used where parts have a change in
the cross section through the length
The tolerance zone is two
dimensional, extending along the
length of the applicable feature
See figure 3.9
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.9:
Profile of a line
with all around
symbol
ROSHALIZA HAMIDON (DPT 312
08/09)
ii. Profile of a surface


Use to control the entire surface of
single entity
The tolerance zone is three
dimensional, extending along the
total length and width or
circumference of the part or feature
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.10 Application of profile of a surface
ROSHALIZA HAMIDON (DPT 312
08/09)
3. Orientation tolerance
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Orientation tolerance control features in
relation to one another; therefore a
datum reference is required
Orientation controls can be applied to the
surface or the axis of the part feature.
Angularity, parallelism, and
perpendicularity are orientation tolerances
ROSHALIZA HAMIDON (DPT 312
08/09)
i. Angularity
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Angularity is the condition of a surface, center
plane, or axis at a specific angle from a datum
plane or axis.
The tolerance zone is established by two parallel
planes or a cylindrical zone at any specified angle
other than 90%, to a datum plane or an axis
Where angularity is applied to a surface, the
feature control frame is connected to the surface
by a leader
See figure 3.11
The angle is specified by a basic angle from the
datum plane
For RFS
ROSHALIZA HAMIDON (DPT 312
08/09)
Angularity tolerance applied to
Angularity tolerance
an axis
applied to a surface
Figure 3.11
ROSHALIZA HAMIDON (DPT 312
08/09)
ii. Perpendicularity
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Perpendicularity is the condition when a surface, center
plane or axis is at exactly 90 degree to a datum
The tolerance zone for perpendicularity is established
by two parallel planes or cylindrical zones that are 90
degree to a specified datum plane or axis
Perpendicularity can be applied to a surface or an axis
When applied to a surface, the shape of the tolerance
zone is parallel planes that are at a 90 degree angle to
a datum plane.
See figure 3.12
The tolerance value identifies the size of the tolerance
zone
All elements of the surface must lie within this
tolerance zone
For RFS
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.12
Perpendicularity
tolerance applied to
surface
Perpendicularity
tolerance applied to an
axis
ROSHALIZA HAMIDON (DPT 312
08/09)
iii. Parallelism
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Parallelism is the condition where a surface,
center plane or axis is exactly parallel to a datum.
Parallelism may be applied to a surface, resulting
in a tolerance zone of two parallel planes, or
applied to an axis resulting in a cylindrical
tolerance zone.
When surface is controlled parallel to a datum, all
elements of that surface must lie within two
parallel planes, parallel to the datum
Parallelism may be applied to the axis of two or
more features where a parallel relationship is
required.
See figure 3.13
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.13
Parallelism tolerance applied
to a surface
Parallelism tolerance
applied to an axis
ROSHALIZA HAMIDON (DPT 312
08/09)
Location tolerance
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Location tolerance are used to locate or
position features from datums
Location tolerances include position,
concentricity and symmetry
Position tolerancing provides the
maximum benefit of GD&T, allowing
increase in tolerance of the feature by
57% and reducing scrap
Location tolerances can be used to control
position, symmetry and coaxiality
ROSHALIZA HAMIDON (DPT 312
08/09)
i. Position
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Position tolerance defines a condition
where the center, axis or center plane of
a feature of size is allowed to vary from
true position
True position is the theoretically exact
location of a feature.
The location of each feature is given by
basic dimension and the location
tolerance is indicated by the position
symbol, a tolerance value, applicable
modifiers and datum references
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.14: Position tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
ii. Concentricity
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Concentricity is used to control the relationship
between the axes of two or more cylindrical
features.
When the axes of each cylinder fall on the same
centerline, they are concentric. (see figure 3.15)
The tolerance zone for concentricity is a
cylindrical tolerance zone whose axis coincide
with the axis of the datum feature
Concentricity is a relative measurement, so it
requires a datum specification
The tolerance can only be applied on an RFS basis
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.15: Concentricity tolerance. Concentricity is
defined as the condition where all median points of
diametrically
opposed
elements
ROSHALIZA
HAMIDON
(DPT 312 of a cylinder are
08/09)
congruent with the
axis of a datum feature
iii. Symmetry
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Symmetry is a positional tolerance where the
median points of all opposed elements of two or
more feature are congruent with the axis or
center plane of a datum feature
Concentricity and symmetry are similar concepts
The difference is that they are applied to different
geometric configurations- concentricity applies to
cylindrical features while symmetry is applied to
planar features
The tolerance zone is centered about the center
plane of the datum
Symmetry is always used with a datum reference
and applied on an RFS basis.
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.16: Symmetry tolerance
ROSHALIZA HAMIDON (DPT 312
08/09)
Runout tolerance
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Runout tolerance are a combination of
tolerances used to control the
relationship of one or more features of a
part to a datum axis.
The features can be surfaces
perpendicular or surfaces around the
datum axis
There are two types of runout control:
1.
2.
Circular runout
Total runout
ROSHALIZA HAMIDON (DPT 312
08/09)
Circular runout
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
Circular runout controls circularity and
coaxiality (the condition where two or
more features share a common axis)
The tolerance is measured by full
indicator movement of a dial indicator
placed at several locations while the part
is rotated 360 degree.
Circular runout is measured as a single
circular element at each measured
location
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.17: Circular runout
ROSHALIZA HAMIDON (DPT 312
08/09)
Total runout
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Total runout is used to provide total
composite control of all surface elements.
(see figure 3.18)
The total tolerance is applied to both
circular elements and the profile
When applied to the surface around and
at right angle to a datum axis, total run
out may be used to control a combination
of circularity, straightness, angularity,
taper and profile.
ROSHALIZA HAMIDON (DPT 312
08/09)
Figure 3.18: Total runout
ROSHALIZA HAMIDON (DPT 312
08/09)
References
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Dotson C.l., Fundamentals of
Dimensional Metrology, Thomson
Delmar Learning, 2006
Meadows J.D., Measurement of
Geometric Tolerance in
Manufacturing, Marcel Dekker, 1998
Griffith G.K, Geometric
Dimensioning and Tolerancing,
Prentice Hall, 2002.
ROSHALIZA HAMIDON (DPT 312
08/09)