Engineering
Drawing and Design
Seventh Edition
Chapter 16
GD&T stands for Geometric
Dimensioning & Tolerancing
DIMENSION is a geometric
characteristic the size of which is
specified such as
length,angle,location,or center distance
TOLERANCE on a dimension is the total
permissible variation in its size, which is
equal to the difference between the
limits of size.
GEOMETRIC DIMENSIONING
AND TOLERANCING
DIMENSIONS OF A PART
GEOMETRIC DIMENSIONING
AND TOLERANCING
TOLERANCE SIZES
GEOMETRIC DIMENSIONING
AND TOLERANCING
TYPE OF TOLERANCE
GEOMETRIC DIMENSIONING
AND TOLERANCING
SIZES OF MATING PARTS
Deviations
The difference between the basic size
and the maximum and minimum sizes
are called the UPPER & LOWER
deviations.
The BASIC DIMENSION represents the
theoretical exact size or location of a
feature.
GEOMETRIC DIMENSIONING
AND TOLERANCING
DEVIATIONS
GEOMETRIC DIMENSIONING
AND TOLERANCING
BASIC (EXACT) DIMENSIONS
Are shown in a rectangle to indicate that the tolerances in the
general tolerance note do not apply
Datum
A DATUM is a theoretical exact feature from which
dimensions may be taken.
A DATUM is generally chosen as an edge or feature
which has the greatest influence in a specific
measurement.
GEOMETRIC DIMENSIONING
AND TOLERANCING
EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM
AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED
GEOMETRIC DIMENSIONING
AND TOLERANCING
EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM
AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED
Geometric Tolerance
A geometric tolerance is the maximum
permissible variation of form, profile,
orientation, location, and runout from that
indicated or specified on a drawing.
Feature control frame for an individual
feature is divided into compartments
containing, at the least, the geometric
tolerance symbol and the geometric tolerance
value
Feature control frame (fig.1616)
Geometric characteristic symbol
Geometric tolerance
Datums (if used)
Modifiers as required (*MMC for
example)
GEOMETRIC DIMENSIONING
AND TOLERANCING
TYPE OF
TOLERANCE CHARACTERISTIC
FEATURE
INDIVIDUAL
FEATURES
FORM
SYMBOL
STRAIGHTNESS
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-2
16-5
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
MAXIMUM
MATERIAL
CONDITION
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-4
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
LEAST
MATERIAL
CONDITION
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-4
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
PROJECTED
TOLERANCE
ZONE
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-9
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
BASIC
DIMENSION
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-9
16-11
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
DATUM
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-6
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE
TYPE OF CHARACTERISTIC
TOLERANCE
SUPPLEMENTARY
SYMBOLS
SYMBOL
DATUM
TARGET
GEOMETRIC CHARACTERISTIC SYMBOLS
SEE
UNIT
16-11
Form Tolerances
FORM TOLERANCES control the straightness,
flatness, circularity and cylindricity
Form tolerances apply to individual features
and as such do not require locating
dimensions.
ORIENTATION TOLERANCES control
angularity, parallelism, and perpendicularity
More on FORM TOLERANCES
Straightness-a condition in which the
element of a surface or a median line is
a straight line
Flatness of a surface is a condition in
which all surface elements are in one
plane
GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE CONTROL FRAME
GEOMETRIC DIMENSIONING
AND TOLERANCING
ATTACHED
USING
A LEADER
APPLICATION OF FEATURE CONTROL FRAME
MMC, RFS, LMC applies to features subject
to variations in size
MMC (Maximum Material Condition) is when a feature
or part is at the limit of size, which results in its
containing the maximum amount of material.
LMC (Least Material Conditon) refers to the size of a
feature that results in the part containing the
minimum amount of material. Thus it is the
minimum limit of size for an external feature.
RFS (Regardless of feature size) indicates that a
geometric tolerance applies to any size of a feature
that lies within its size tolerance.
Datums and the 3-plane concept
(16-5)
Datum is a theoretical point, line, plane,
or other geometric surface fromwhich
dimensions are measured when so
specified or to which geometric
tolerances are referenced
Datum feature is a feature of a part,
such as a surface, that forms the basis
for a datum or is used to establish its
location
3-plane system
The three planes constitue a datum
system from which measurements can
be taken. They will appear on the
drawing.
Datum feature symbol is used on the
drawing to identify these surfaces
GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES
GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES
GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES
Orientation tolerancing (16-6)
Angularity, parallelism and perpendicularity are
orientation tolerances applicable to related features
Angularity is the condition of a surface or axis at a
specified angle (other than 90⁰or 0⁰) from a datum
plane or axis
Perpendicularity is the condition of a surface at 90⁰ to
a datum plane or axis. *A perpendicularity tolerance
for a flat surface specifies a tolerance zone defined
by two parallel planes perpendicular to a datum plane
or axis
Parallelism is the condition of a surface equidistant at
all points from a datum plane. Parallelism for a flat
surface specifies a tolerance zone defined by two
planes or lines parallel to a datum plane or axis.
Datum Targets (16-11)
Datum target symbols are used to locate specific
reference positions to be used on large datum
surfaces*
the surface of a feature may be so large that a gage
designed to make contact with the full surface may
be too expensive or cumbersome to use
Functional requirements of the part may necessitate
the use of only a portion of a surface as a datum
feature
CAD APPLICATIONS
TOLERANCE DIALOG BOX
CAD APPLICATIONS
TOLERANCE SYMBOL DIALOG BOX