310 Quality Assurance
I
Independency Symbol (2.7.3; 3.3.24) - is applied to the size dimen-
sion in order to invoke the principle of independency to regular fea-
tures of size and override Rule #1.
M
Maximum Material Condition (MMC) (3.3.5) is that condition of
a part feature wherein it contains the maximum amount of mate-
rial within the stated limits of size. That is, minimum hole size and
maximum shaft size.
Movable Datum Targets (4.24.6) symbol may be used to indicate
movement of the datum target datum feature simulator.
5X Number of Places (1.9.6). The X is used along with a value to indicate
the number of times a dimension or feature is repeated on the drawing.
Parallelism (6.3.2) is the condition of a surface, line, or axis, which
is equidistant at all points from a datum plane or axis.
Parting Lines (3.14) are depicted on casting/forging/molded part
drawings as a phantom line extending beyond the part in applicable
views, with the parting line symbol added.
Perpendicularity (6.3.3) is the condition of a surface, axis, or line
that is 90° from a datum plane or a datum axis.
Position Tolerance (7.2) denes a zone within which the axis or
center plane of a feature is permitted to vary from true (theoretically
exact) position.
Prole of a Line (8.2.1.2) is the condition permitting a uniform
amount of prole variation, ether unilaterally or bilaterally, along a
line element of a feature.
Prole of a Surface (8.2.1.1) is the condition permitting a uniform
amount of prole variation, ether unilaterally or bilaterally, on a surface.
P
Projected Tolerance Zone (7.4.1) applies to a hole in which a pin,
stud, screw, and so on is to be inserted. It controls the perpendicu-
larity of the hole to the extent of the projection from the hole and as
it relates to the mating part clearance. The projected tolerance zone
extends above the surface of the part to the functional length of the
pin, stud, and screw relative to its assembly with the mating part.
R Radius (3.3.7) creates a zone dened by two arcs (the minimum
and maximum radii). The part surface must lie within this zone.
(50) Reference Dimension (3.3.8) is a dimension usually without
tolerance, used for information purposes only. It does not govern
production or inspection operations. (It is equivalent to auxiliary
dimension in ISO.)
RFS Regardless Of Feature Size (RFS) (1.3.48; 2.8; 2.8.1; 7.3.2) is the
condition where the tolerance of form, runout, or location must be
met irrespective of where the feature lies within its size tolerance.
311Geometric Dimensioning and Tolerancing (GD&T)
Roundness (5.4.3) describes the condition on a surface of revo-
lution (cylinder, cone, sphere) where all points of the surface inter-
sected by any plane perpendicular to a common axis in case of
cylinder and core (or passing through a common center in case
of sphere) are equidistant from the axis (or center). Since the axis
and center do not exist physically, measurement has to be made
with reference to surface of the gures of revolution, which is the
circular contour
Runout (9.4.1) is the composite deviation from the desired form of
a part surface of revolution through one full rotation (360 degrees) of
the part on a datum axis.
Slope (3.3.18) is used to indicate slope for at tapers. This symbol
is always shown with the vertical leg to the left.
SØ
Spherical Diameter (3.3.7) shall precede the tolerance value
where the specied tolerance value represents spherical zone. In
addition, a positional tolerance may be used to control the location
of a spherical feature relative to other features of a part. The symbol
for spherical diameter precedes the size dimension of the feature
and the positional tolerance value to indicate a spherical tolerance
zone.
SR Spherical Radius (3.3.7) precedes the value of a dimension or
tolerance.
SF
Spot face (1.8.14). Counter bore and spot face previously used the
same symbol. A spot face now looks like the counter bore symbol
with the addition of the letters SF.
Square (3.3.16) is used to indicate that a single dimension applies
to a square shape. The symbol precedes the dimension with no space
between.
ST
Statistical Tolerance (3.3.10) is the assigning of tolerances to
related components of an assembly on the basis of sound statistics
(such as the assembly tolerance is equal to the square root of the sum
of the squares of the individual tolerances). By applying statistical
tolerancing, tolerances of individual components may be increased,
or clearances between mating parts may be reduced. The increased
tolerance or improved t may reduce manufacturing cost or improve
the product’s performance, but shall only be employed where the
appropriate statistical process control will be used. Therefore, con-
sideration should be given to specifying the required C
p
and/or C
pk
or other process performance indices. Preference should be given to
P
p
and P
pk
.
Straightness (5.4.1) is a condition where an element of a surface or
an axis is a straight line.
312 Quality Assurance
Symmetry (7.7.2) is a condition in which a feature (or features) is
symmetrically disposed about the center plane of a datum feature.
T
Tangent Plane (3.3.21; 6.5) indicates a tangent plane is shown. The
symbol is placed in the feature control frame following the stated
tolerance.
X Target Point (4.24.2) indicates where the datum target point is
dimensionally located on the direct view of the surface.
Total Runout (9.4.2) is the simultaneous composite control of all
elements of a surface at all circular and prole measuring positions
as the part is rotated through 360°.
Datum Translation Symbol (3.3.26) indicates that a datum fea-
ture simulator is not xed at its basic location and shall be free to
translate.
U
Unilateral and Unequally Disposed Prole Tolerance (8.3.1.2)
is used to indicate that a prole of a surface tolerance is not sym-
metrical about the true prole. The rst value in the feature control
frame is the total width of the prole tolerance. The value following
the symbol is the amount of the tolerance that is in the direction
that would allow additional material to be added to the true prole.
The GD&T standard provides many symbols as opposed to notes or ver-
biage because of the following advantages:
• Symbols have uniform meaning globally.
• Symbols are recognized internationally and will not have language
barriers.
• Symbols can be quickly drawn and placed on the drawing where
required.
• Symbols are compact.
• Geometric tolerancing symbols are part of the ANSI standard.
On the other hand, the disadvantages of dening a part heavily reliant
upon notes are
• Require more space and time
• Require more explanations especially when notes originating in one
country may need to be translated for use in another country
• Require explicit and very clear verbiage because notes could be mis-
understood, depending on how the note is written
Therefore, symbols are used on drawings to help dene a part. However,
sometimes notes are necessary to clarify intent for unique situations or when
no symbol exists to represent intent.
313Geometric Dimensioning and Tolerancing (GD&T)
Types of Drawings
Generally, customers dene the types of drawings. For example, in the auto-
motive industry, you may have encountered the following three types, which
are included in the Master Data Files, which are the ofcial Documents of
Record. They are
1. CtM (3D CAD data le). This is the master. There are two ways to
establish this. (a) A CAD data le consisting of a 3D CAD geom-
etry le containing complete product manufacturing information
(PMI) annotation, and (b) a CAD data le consisting of a 3D CAD
geometry le containing complete PMI annotation and a separate,
yet associative, 3D CAD geometry le containing manufactur-
ing information annotation. (Note that PMI is also referred to as
Product Denition Data per ASME Y14.41-2003.) While there is no
physical drawing for CtM, the CAD les will contain rst frame
information, such as (a) title block, (b) revision column, and (c)
general notes.
2. DtMC (2D drawing and 3D CAD data le). This is drawing the mas-
ter with CAD content. A combination of master data les consist-
ing of a 3D CAD geometry le and a separate, yet associative, 2D
drawing that contains a customer’s title block and remaining PMI
annotation not found in the 3D CAD geometry le. It may also have
auxiliary views setup using descriptive geometry.
3. DtM (2D drawing). This is drawing the master. A 2D drawing
contains a customer’s title block and complete drawing denition
including views and PMI annotation (dimensions and tolerances). It
may also contain auxiliary views setup utilizing descriptive geom-
etry. The 2D drawings utilize (a) 3rd angle projection and (b) ortho-
graphic projection. For 3rd angle and orthographic projection, the
orthographic drawings have continuous points of view and the fol-
lowing characteristics: (a) separate views that are in line and pro-
jected with each other, (b) all views are at right angles from each
other, and (c) all projections are straight lines.
The rationale for these three types is to make sure that special characteris-
tics are identied properly and accurately. Special characteristics are identi-
ed through the design failure mode and effect analysis (DFMEA) and affect
compliance to government regulations or the safety of the product. These are
the only types of special characteristics to be identied on the drawing with
the critical characteristic (CC) symbol, for example, inverted delta. However,
in the CtM les, the verbiage Control Item can be used to replace the inverted
delta symbol.
314 Quality Assurance
Title Block and Notes
A GD&T print has a title block and a note block. The title block contains the
following information:
• Customer’s trademark
• ISO hardcopy eld protection
• Reference eld optional
• Substance restriction eld: substance restriction standard
• CAD eld, which contains CAD le number
• CAD type eld
• CAD location eld
• Drawing scale
• Master eld: Indicates which media is the master
• General information eld: Contains orthographic view projection
• Customer’s standard version eld: Contains customer’s version
number
• Title eld: Product drawing titles
• Drawing eld: Contains the engineering part number
• Sheet number eld: Sheet XXX of total number of sheets
• Left- and right-hand indicator
• Unit eld: Manufacturing unit identication number
• Operation number eld: Contains the manufacturing ID code for
process
• Division eld: Name of division to which the drawing is appointed
(if applicable)
• Plant eld: Name of plant or plant code
• Design eld: ID code of the person who designed the object
• Detail eld: ID code of the person who detailed the drawing
• Checked eld: ID code of the person who checked the drawing
• Safety eld: Contains ID code of safety personnel (manufacturing)
• Date eld: Date that drawing was started
• Control item (inverted delta [or CC] symbol)
A print with GD&T guidelines also uses notes to supply necessary infor-
mation that is not covered by dimensions. Notes are always located in the
lower right-hand corner of the drawing and to the left of the title block. They
contain
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