GD&T - Geometric Dimensioning and Tolerancing Form and Orientation Tolerances Questions and Answers

Question 1

Which of the following geometric tolerances is classified as a form tolerance and does NOT require a datum reference?

Accepted Answer

Flatness

Answer

Flatness is a form tolerance that controls the variation of a surface from a perfect plane. Unlike orientation tolerances (Perpendicularity, Angularity, Parallelism), form tolerances like flatness, straightness, circularity, and cylindricity do not relate to a datum; they control the feature's shape relative to itself.

Question 2

A feature control frame for a surface specifies an angularity tolerance. What is the shape of the tolerance zone?

Accepted Answer

Two parallel planes oriented at a basic angle to a datum

Answer

The tolerance zone for an angularity control applied to a surface is defined by two parallel planes. These planes are separated by the specified tolerance value and are oriented at the specified basic angle relative to the datum reference frame. All points of the controlled surface must lie within this zone.

Question 3

A drawing calls out a perpendicularity tolerance for the axis of a hole. A diameter symbol (⌀) is included before the tolerance value in the feature control frame. What does this indicate?

Accepted Answer

The tolerance zone is a cylinder within which the axis of the hole must lie.

Answer

When an orientation tolerance like perpendicularity is applied to a feature of size (such as a hole's axis), the inclusion of a diameter symbol (⌀) in the feature control frame specifies a cylindrical tolerance zone. The axis of the feature must be contained within this cylindrical zone, which is oriented perpendicular to the specified datum.

Question 4

In a scenario where a pin must assemble into a hole, applying a perpendicularity tolerance at Maximum Material Condition (MMC) to the pin offers what primary advantage?

Accepted Answer

It allows for a potential increase in the geometric tolerance, known as bonus tolerance, as the pin's size departs from MMC.

Answer

When an orientation tolerance is applied to a feature of size at MMC, it allows for a bonus tolerance. As the feature's actual size departs from its MMC size (e.g., a pin getting smaller), the difference can be added to the geometric tolerance. This functional approach ensures interchangeability and can make manufacturing less restrictive.

Question 5

What is the key difference between the application of a flatness tolerance and a parallelism tolerance to a planar surface?

Accepted Answer

Parallelism requires a datum reference, while flatness does not.

Answer

The fundamental difference is that flatness is a form control and is independent of any other feature. Parallelism is an orientation control, which by definition must relate the orientation of one feature to another (a datum). Therefore, parallelism requires a datum reference in its feature control frame, whereas flatness does not.

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

GD&T - Geometric Dimensioning and Tolerancing Form and Orientation Tolerances Questions and Answers