Geometric SymbolsGeometric Symbols

Geometric Dimensions and Geometric Dimensions and TolerancesTolerances

Geometric Geometric SymbolsSymbols

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

CYLINDRICITYCYLINDRICITY

Cylindricity is the condition Cylindricity is the condition where all points of a surface of where all points of a surface of revolution are equidistant from revolution are equidistant from a common axisa common axis

cylindricity tolerance specifies cylindricity tolerance specifies a zone bounded by 2 concentric a zone bounded by 2 concentric cylinders within which the cylinders within which the measured surface must lie.measured surface must lie.

CYLINDRICITYCYLINDRICITY

CYLINDRICITYCYLINDRICITY

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 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:

Parallelism

• 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.