GD&T Angularity Definition, Symbol, Callout, Measurement, Tolerance & Angularity vs Profile

GD&T is a powerful system for defining and controlling the shape, size, location, and orientation of features on manufactured parts. Within this system, angularity stands out as a crucial control for specifying the orientation of a surface or axis relative to a datum. This article talks about GD&T angularity, exploring its definition, application, symbol, callout, tolerance zone, measurement, and differences from other GD&T symbols like profile.

GD&T Angularity Definition – What Is Angularity in GD&T?

In Geometric Dimensioning and Tolerancing (GD&T), angularity is a geometric tolerance that specifies the angular relationship between a feature and a datum. It ensures that a feature is oriented at a specified angle relative to a reference or datum feature.

Angularity is commonly used for features like holes, surfaces, and edges that must maintain a specific angle to a datum to ensure proper fit and function. If a hole must be drilled at a 30° angle relative to a base surface, the angularity tolerance would be specified to ensure that the hole’s axis remains within the acceptable limits of that angle.

Angularity Applications:

Machined Parts: Ensuring precise angles on CNC machined components, such as the angle of a bevel gear or the slope of a ramp.
Sheet Metal Fabrication: Controlling the bend angles in sheet metal parts, ensuring proper alignment and fit.
Assembly: Guaranteeing the correct angular relationship between mating parts, facilitating proper assembly and function.
Weldments: Controlling the angle of welded joints to maintain structural integrity and proper alignment.

GD&T Angularity Symbol & Callout

The symbol for angularity is an angled triangle (∠) placed next to the tolerance value in the feature control frame.

Angularity Drawing Callout:

GD&T Angularity Tolerance Zone

The angularity tolerance zone is a geometric control that specifies how much an angled surface or axis can deviate from its theoretical (basic) angle relative to a datum reference. The tolerance zone of GD& T angularity can be either Two Parallel Lines – specified without the Ø symbol, creating a 2D tolerance zone where the controlled surface must lie between two parallel lines spaced apart by the tolerance value, or Cylindrical Zone – specified with the Ø symbol, creating a 3D cylindrical boundary within which the axis or centerline of the feature must lie, with the cylinder’s diameter equal to the tolerance value. The tolerance is presented by linear distance units.

Key Components:

Basic Angle: When specifying angularity tolerance, the nominal angle must be shown as a basic dimension (typically shown in a box □ or without tolerances), and general tolerances from the title block or notes do not apply to this dimension. It represents the theoretical exact angle from which deviation is controlled.
Datum Reference: An angularity tolerance must always reference at least one datum, which serves as the geometric reference from which the specified angle is measured. This datum is typically a flat surface, centerline, or axis that establishes the orientation basis for the angular feature.

How to Measure GD&T Angularity?

Measuring GD&T angularity involves ensuring that a feature is oriented at a specified angle relative to a datum.

1. Sine Bar Method:

Setup: Place the part on a sine bar that is set to the required angle. The sine bar allows the part to be tilted to the specified angle while keeping the reference surface horizontal.
Measurement: Use a dial gauge to measure the flatness of the surface that is now horizontal. The entire surface must lie within the defined tolerance zone.

2. Coordinate Measuring Machine (CMM):

Setup: Position the part in the CMM, which can measure the angle and flatness simultaneously.
Measurement: The CMM will provide precise data on the surface’s orientation relative to the datum, ensuring that all points on the surface fall within the tolerance zone.

3. Optical Comparator:

Setup: Use an optical comparator to project the part’s profile onto a screen.
Measurement: Compare the projected image against the specified angle and tolerance zone. This method is useful for visual inspection and verification.

4. Go/No-Go Gauges:

Setup: For high-volume production, custom gauges can be designed to check if the part falls within the acceptable tolerance zone.
Measurement: These gauges provide a quick pass/fail assessment based on the angularity specifications.

Note:

Datum Reference: Angularity must always be measured relative to a datum. The datum establishes the reference angle, and any changes to the datum can affect the measurement outcome.
Tolerance Zone: The tolerance zone for angularity is not defined in angular units (degrees or radians) but rather as a linear distance between the two parallel planes or the diameter of the cylindrical zone.
Flatness Control: Angularity also implies a control over flatness. The surface must not only be at the correct angle but also flat within the specified tolerance.

GD&T Angularity vs Profile

Feature	Angularity	Profile of Surface	Profile of Line
Dimensionality	2D or 3D	3D control	2D control (cross-section)
Datum Reference	Always required	Optional	Optional
Tolerance Zone	Angular relationship to datum	3D zone around the entire surface	2D zone at any cross-section
Primary Use	Angled surfaces, chamfers, V-grooves	Complex curves, fillets, advanced shapes	Cross-sections, curved radii
Specificity	Very specific, easily recognizable	More versatile but less specific	More versatile but less specific
Control Type	Angular relationship only	Form and orientation	Form and orientation in cross-section
Measurement	Relative to the datum reference	All points must fall within the tolerance zone	Cross-sectional points within tolerance
Symbol	Angle	Curved line	Straight line

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