When a surface, center plane, or axis is at a specified angle then this condition is known as Angularity.
A geometric tolerance which helps in limiting the angle of variation of a surface, axis or center plane is known as Angularity control.
ANGULARITY TOLERANCE ZONE
The two common angularity tolerance zones are:
- Two parallel planes.
- A cylinder.
- Application of angularity to a surface.
- Application of angularity on a cylindrical FOS.
The worst case boundary (WCB) is not affected when an angularity control is applied to a surface.
The application of an angularity control on a FOS affects the worst case boundary (WCB) of a FOS.
Angularity applied to a surface
In the above figure, the most common application of angularity is shown.
The part features must be dimensioned with a basic angle with respect to the datum in an angularity application.
The following conditions are applicable when this control is stated.
- Two parallel planes is the shape of the tolerance zone.
- The distance between the planes is the angularity tolerance value.
- All the elements must be within the tolerance zone.
- Basic angle is used to specify the angle between the part surface and datum.
- Limits the flatness of the toleranced surface.
In the below figure, application of angularity control is done on a diametrical FOS.
Angularity applied to a FOS
Please note the use of a diameter symbol in the feature control frame.
The following conditions are applicable when an angularity control is stated:
- A cylinder is the tolerance zone.
- Diameter of the tolerance cylinder is the angularity tolerance value.
- Axis of the tolerance feature must be within the tolerance zone.
- Basic angle is used to dimension the angle between part surface and datum.
INDIRECT ANGULARITY CONTROLS
There are a number of geometric controls which can indirectly affect the angularity of a part feature.
Tolerance of position, total runout and profile can limit angularity.
Indirect angularity controls are not mostly inspected.
If the part feature needs to be inspected, then an angularity control should be specified.
The tolerance value must be less than any indirect angularity controls that are applicable when an angularity control is used.
LEGAL SPECIFICATION TEST FOR AN ANGULARITY CONTROL
Following conditions must be satisfied for the angularity control to be a legal specification.
- In the feature control frame, one or more datums planes, datum axis or center plane must be referenced.
- A basic angle must be stated relative to the datum.
- The tolerance value of an angularity control must be lesser than any other geometric tolerance value.
- If the angularity control is applied to a surface, then the modifiers such as (MMC, LMC or diameter) are not required to be mentioned in the feature control frame.
In the below example, let’s see how to verify angularity control.
The part is placed on the gage equipment using a sine plate.
This plate is at a basic angle where the surface of the part is placed.
A dial indicator is used to verify the surface elements are within the specified limits of angularity control.