Geometric Dimensioning Tolerancing Symbols to Know for Computer Aided Drafting and Design

Geometric Dimensioning and Tolerancing (GD&T) symbols are essential in Computer Aided Drafting and Design. They define how parts fit together, ensuring precision and functionality. Understanding these symbols helps create accurate designs that meet manufacturing standards and assembly requirements.

1. Flatness

   • Measures the extent to which a surface deviates from a perfectly flat plane.
   • Defined by two parallel planes that enclose the surface.
   • Important for ensuring proper fit and function in assemblies.

2. Straightness

   • Indicates how much a line deviates from being perfectly straight.
   • Can be applied to edges, axes, or any linear feature.
   • Essential for ensuring alignment and proper assembly of parts.

3. Circularity

   • Describes how closely a feature approaches the shape of a perfect circle.
   • Defined by two concentric circles that enclose the feature.
   • Critical for rotational parts to ensure smooth operation.

4. Cylindricity

   • Measures how closely a feature resembles a perfect cylinder.
   • Defined by two coaxial cylinders that enclose the feature.
   • Important for parts that require precise fit and function in assemblies.

5. Profile of a Line

   • Controls the contour of a feature along a specified line.
   • Defined by a tolerance zone that surrounds the true profile.
   • Useful for complex shapes where specific outlines are critical.

6. Profile of a Surface

   • Controls the overall contour of a surface in three dimensions.
   • Defined by a tolerance zone that surrounds the true surface.
   • Important for aesthetic and functional surfaces in design.

7. Perpendicularity

   • Ensures that a feature is at a right angle to a datum reference.
   • Defined by a tolerance zone that specifies the allowable deviation.
   • Critical for assembly and function where right angles are required.

8. Angularity

   • Specifies the angle between a feature and a datum reference.
   • Defined by a tolerance zone that allows for deviation from the specified angle.
   • Important for features that must meet specific angular requirements.

9. Parallelism

   • Ensures that a feature is equidistant from a datum reference at all points.
   • Defined by a tolerance zone that specifies the allowable deviation.
   • Essential for parts that must maintain consistent spacing in assemblies.

10. Position

    • Controls the location of a feature relative to a datum reference.
    • Defined by a tolerance zone that specifies the allowable deviation from the true position.
    • Critical for ensuring proper fit and function in assemblies.

11. Concentricity

    • Measures how closely a feature's center aligns with a datum reference.
    • Defined by a tolerance zone that specifies the allowable deviation.
    • Important for rotating parts to ensure balanced operation.

12. Symmetry

    • Ensures that a feature is evenly distributed around a central axis.
    • Defined by a tolerance zone that specifies the allowable deviation.
    • Important for aesthetic and functional balance in design.

13. Circular Runout

    • Measures the variation in a circular feature as it rotates around an axis.
    • Defined by a tolerance zone that specifies the allowable deviation.
    • Critical for ensuring smooth operation of rotating components.

14. Total Runout

    • Measures the variation of a feature along its entire length as it rotates.
    • Defined by a tolerance zone that encompasses the entire feature.
    • Important for ensuring overall stability and performance in rotating parts.

15. Datum Feature Symbol

    • Identifies a reference point, line, or surface used for measurement.
    • Essential for establishing a common reference for geometric tolerances.
    • Helps ensure consistency and accuracy in manufacturing.

16. Feature Control Frame

    • A rectangular box that contains geometric tolerance information.
    • Specifies the type of tolerance, the tolerance value, and the datum references.
    • Essential for clear communication of design intent in CAD drawings.

17. Maximum Material Condition (MMC)

    • Refers to the condition of a feature when it contains the maximum amount of material.
    • Important for ensuring proper fit and function in assemblies.
    • Allows for increased tolerance when parts are at their MMC.

18. Least Material Condition (LMC)

    • Refers to the condition of a feature when it contains the least amount of material.
    • Important for ensuring that parts can still function properly when at their minimum size.
    • Provides a basis for determining allowable tolerances.

19. Regardless of Feature Size (RFS)

    • Indicates that the specified tolerance applies regardless of the size of the feature.
    • Ensures that the tolerance is maintained across all sizes of the feature.
    • Important for consistent quality control in manufacturing.

20. Projected Tolerance Zone

    • Defines a tolerance zone that extends beyond the actual feature.
    • Used for features that may require additional clearance or fit considerations.
    • Important for ensuring proper assembly and function in complex designs.