GD&T Quiz

Geometric Dimensioning and Tolerancing (GD&T)

• GD&T is an international standard to specify Form, Fit, and Function of parts, following ANSI Y 14.5 and ISO 1101.
• It provides significant improvement over traditional tolerancing by focusing on 3D part geometry features in addition to 2D drawings.

Importance of GD&T

• Ensures specification of design tolerance requirements.
• Ensures interchangeability of parts during assembly.
• Provides standardization and uniformity.
• Adaptation to 3D CAD modeling leads to high productivity, less rework, and reduced cost.

Part Geometry Features to be Controlled

• Form
• Orientation
• Location
• Position
• Runout

Geometric Tolerance Symbols

• Tolerance feature frame is used to specify tolerances.

Form Tolerances

• Control the form with reference to ideal shape.
• Applies to Line, Arc, Circle, Profile, Surface.
• Tolerance is a Peak-to-Valley measure.
• Types of Form Tolerances:
  • Straightness
  • Flatness
  • Roundness (Circularity)
  • Cylindricity
  • Profile of Line
  • Profile of Surface

Orientation Tolerances

• Specifies relative orientation (attitude) between entities, such as edges, axes, surfaces, and features.
• Always need a Datum (Reference), such as a plane or feature.
• Types of Orientation Tolerances:
  • Parallelism
  • Perpendicularity
  • Angularity

Location Tolerances

• Specifies relative location (attitude) between entities, such as edges, axes, surfaces, and features.
• Always need a Datum (Reference), such as a plane or feature.
• Types of Location Tolerances:
  • Concentricity

Material Condition Modifiers

• Maximum Material Condition (MMC): largest shaft size and smallest hole size.
• Regardless of Feature Size (RFS): no size variation considered.
• ANSI/ISO recommends assuming a feature is perfect (ideal) at MMC.

Position Tolerance

• Controls position (centre or axis) of holes.
• Needs Datums, including Primary, Secondary, and Tertiary.
• Tolerance Zone: Circular or Rectangular.

Run Out Tolerance

• Primarily for cylindrical rotating parts.
• Types of Run Out:
  • Circular Run Out
  • Total Run Out

Functional Gaging

• Tests the combined effect of all tolerances, including dimensional and geometric tolerances.
• Gage: Extreme Virtual Size.