Geometric Symbols
Geometric Dimensions and Tolerances
Geometric
Symbols
How is GTD information Conveyed on a Drawing?
• Geometric Characteristics are Specified Through
Symbols in a geometric feature control frame
• Modifiers and Tolerances Expand and Clarify
the Symbols to Ensure Drawings are
Unambiguous
Geometric Characteristics and Symbols
1. FORM
Geometric Characteristics and Symbols
2. Profile , 3. Orientation
Geometric Characteristics and Symbols
4. Runout , 5. Location
Using Notes
Using Symbols
GEOMETRIC FEATURE CONTROL FRAME
FLATNESS
FLATNESS
• The condition of a surface having all points in
one plane.
• A flatness tolerance specifies a zone defined by 2
parallel planes.
Flatness
Flatness
STRAIGHTNESS
• Straightness is the
condition where all the
points on a surface or
an axis are in a straight
line
• A straightness
tolerance specifies a
zone within which the
surface or axis must lie
STRAIGHTNESS
ROUNDNESS OF A CYLINDER
• Roundness or circularity is the condition of a
cylindrical surface in which all points on the surface
intersected by any plane perpendicular to a common
axis equidistant from the axis.
• CIRCULARITY
• Or Roundness tolerance specifies a zone
bounded by two concentric circles within which
the measured surface must lie
CIRCULARITY of A SPHERE
• The Periphery at any cross section passing
through a common center must be within
the specified tolerance of size and must be
between two concentric circles
CYLINDRICITY


Cylindricity is the condition where
all points of a surface of revolution
are equidistant from a common axis
cylindricity tolerance specifies a
zone bounded by 2 concentric
cylinders within which the
measured surface must lie.
CYLINDRICITY
CYLINDRICITY
PROFILE TOLERANCE
• PROFILE OF A LINE:
• The tolerance zone established by the profile
of a line tolerance is two dimensional
extending along the length of the considered
feature
PROFILE TOLERANCE
• PROFILE OF A SURFACE:
• The established tolerance zone is three
dimensional extending along the length and width
of the considered feature
ORIENTATION TOLERANCE
•
PERPENDICULARITY
• Is a condition of a line,
center line, axis or surface
at a right angle to a datum
plan or axis.
• Perpendicularity tolerance
specifies one of the
following:
PERPENDICULARITY
• 1. A zone defined by 2 parallel planes perpendicular
to a datum plane or axis. In the example shown,
• The surface of the feature must lie within this zone
which is 0.15mm wide and at right angles to datum A.
• 2. A zone defined by 2 parallel planes perpendicular to
the datum axis.
• In this example, the axis of the hole must lie within the
zone which is 0.3mm wide and at right angles to
datum axis A. The feature axis must also be within the
tolerance of location.
ORIENTATION TOLERANCE
ANGULARITY
• Angularity is the condition of a surface or axis at a
specified angle (other than 9O) from a datum plane or
axis.
• The tolerance zone is defined by 2 parallel
planes at the specified basic angle from a
datum plane or axis. The surface or axis of
the considered feature must lie within this
zone.
• In the example all points of the surface must
lie within the 0.5mm wide tolerance zone.
Parallelism
• Parallelism is the condition of a surface or
axis equidistant at all points from a datum
plane or axis.
• Parallelism tolerance specifies one of the
following:
• 1. A zone defined by 2 planes or lines
parallel to a datum plane or axis.
• In this example, the surface of the feature
must lie within 2 planes 0.25mm y apart
which are parallel to datum A.
• 2. A cylindrical tolerance zone whose
axis is parallel to a datum axis.
• In this example the axis of the hole must lie
within a cylindrical zone of 0.3mm diameter
parallel to datum A.