GD&T: Orientation Tolerances
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Questions and Answers

What is the purpose of using a sine bar or angle plate in measuring principle?

  • To orient the part on the surface plate
  • To measure the orientation tolerance of the feature
  • To control the flatness of the surface
  • To ensure the surface of the part is parallel to the surface plate (correct)

    • What is the relationship between form and orientation tolerances when applied to a single feature?

  • The form tolerance is independent of the orientation tolerance
  • The form tolerance must be less than the orientation tolerance (correct)
  • The form tolerance is equal to the orientation tolerance
  • The form tolerance must be greater than the orientation tolerance

    • What is the purpose of a parallelism tolerance for a flat surface?

  • To orient the surface parallel to a datum plane
  • To control the flatness of the surface
  • To specify a tolerance zone defined by two parallel planes (correct)
  • To measure the orientation tolerance of the feature

    • What is the role of a datum plane or axis in perpendicularity tolerance?

    <p>It acts as a reference for the perpendicularity tolerance</p> Signup and view all the answers

    What is the purpose of applying orientation tolerancing for features of size?

    <p>To control the orientation of the feature</p> Signup and view all the answers

    What is the relationship between perpendicularity tolerance and parallelism tolerance?

    <p>Perpendicularity tolerance is a subset of parallelism tolerance</p> Signup and view all the answers

    What is the purpose of controlling flatness on both sides of a feature?

    <p>To achieve a higher degree of accuracy</p> Signup and view all the answers

    What is the role of the feature control frame in orientation tolerancing?

    <p>It directs the orientation tolerance to the surface</p> Signup and view all the answers

    What is the purpose of applying a parallelism tolerance to one surface of a feature?

    <p>To make the opposite side the datum feature</p> Signup and view all the answers

    What is the relationship between orientation tolerance and form tolerance?

    <p>Form tolerance is a subset of orientation tolerance</p> Signup and view all the answers

    Study Notes

    Orientation Tolerances

    • Orientation tolerances control angularity, parallelism, and perpendicularity.
    • When applied to plane surfaces, orientation tolerances control flatness if a flatness tolerance is not specified.
    • The general geometric characteristic for orientation is termed angularity, which describes angular relationships between lines, surfaces, or features.

    Angularity Tolerance

    • Angularity is the condition of a surface or axis at a specified angle (other than 90o) from a datum plane or axis.
    • An angularity tolerance for a flat surface specifies a tolerance zone defined by two parallel planes at a specified basic angle from a datum plane or axis.
    • The surface of the considered feature must lie within this tolerance zone.

    Perpendicularity Tolerance

    • Perpendicularity is the condition of a surface at 90o to a datum plane or axis.
    • A perpendicularity tolerance for a flat surface specifies a tolerance zone defined by two parallel planes perpendicular to a datum plane or axis.
    • The surface of the considered feature must lie within this tolerance zone.

    Parallelism Tolerance

    • Parallelism is the condition of a surface equidistant at all points from a datum plane.
    • A parallelism tolerance for a flat surface specifies a tolerance zone defined by two planes or lines parallel to a datum plane or axis.
    • The line elements of the surface must lie within this tolerance zone.

    Measuring Principle

    • In theory, it is necessary to determine that every point on the centreline of the hole falls within the tolerance zone.
    • Measuring systems using a fitted gaging mandrel are usually considered acceptable.
    • The gaging mandrel must be straight and true, made of tool steel, hardened and ground, and its diameter must fit snugly in the hole.

    Applying Orientation Tolerances to Flat Surfaces

    • Orientation tolerances, when applied to plane surfaces, control angularity, parallelism, and perpendicularity.
    • The feature control frame is associated with the size dimension of the feature requiring control.

    Reference to a Datum

    • An orientation tolerance indicates a relationship between two or more features.
    • Whenever possible, the feature to which the controlled feature is related should be designated as a datum.

    Measuring Principle for Flat Surfaces

    • The part to be measured is set up on a surface plate in such a way that the surface of the part, were it perfectly formed, would be parallel with the surface plate or with an auxiliary square or angle plate.
    • When necessary, a sine bar or angle plate is used.

    Applying Form and Orientation Tolerances to a Single Feature

    • When both form and orientation tolerances are applied to a feature, the form tolerance must be less than the orientation tolerance.
    • An example is shown in the given figure where the flatness of the surface must be controlled to a greater degree than its orientation.

    Orientation Tolerance Controlling Form

    • Under certain circumstances, such as for very thin parts, it is often desirable to control flatness on both sides.
    • This is accomplished by applying a parallelism tolerance to one surface of the feature and making the opposite side the datum feature.

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    Description

    This quiz covers the concepts of orientation tolerances, including angularity and perpendicularity, in the context of geometric dimensioning and tolerancing (GD&T).

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