Engineering Drawing Symbols

Understanding engineering drawing symbols is crucial in Computer Aided Drafting and Design. These symbols, like dimension lines and hidden lines, help convey precise information about objects, ensuring clarity and accuracy in technical drawings for effective communication in engineering.

1. Dimension lines and arrows

   • Indicate the extent and direction of a dimension.
   • Arrows point to the feature being measured.
   • Must be clear and not cross other lines to avoid confusion.

2. Center lines

   • Represent the center of circles, arcs, and symmetrical objects.
   • Typically shown as alternating long and short dashes.
   • Used for locating features and dimensions.

3. Hidden lines

   • Indicate edges or surfaces not visible in the current view.
   • Shown as dashed lines, typically with a specific dash pattern.
   • Essential for conveying complete information about the object.

4. Section lines

   • Used to indicate the cut surface in sectional views.
   • Typically shown as closely spaced parallel lines.
   • Help differentiate between different materials or parts in a section.

5. Break lines

   • Indicate that a portion of the drawing has been omitted for clarity.
   • Shown as a jagged or wavy line.
   • Useful for reducing the size of a drawing while maintaining essential details.

6. Leader lines

   • Connect a note or dimension to a specific feature.
   • Typically drawn as a straight line with an arrowhead.
   • Help clarify annotations and dimensions in the drawing.

7. Cutting plane lines

   • Indicate where a section view is taken from the object.
   • Shown as a thick line with arrows at both ends.
   • Essential for understanding the internal features of the object.

8. Phantom lines

   • Represent alternate positions of parts or adjacent objects.
   • Shown as a long dash followed by two short dashes.
   • Useful for illustrating movement or assembly relationships.

9. Datum symbols

   • Indicate a reference point, line, or surface for measurements.
   • Essential for ensuring consistency in dimensions and tolerances.
   • Help in establishing a common reference for manufacturing.

10. Geometric Dimensioning and Tolerancing (GD&T) symbols

    • Provide a standardized way to communicate tolerances and relationships.
    • Include symbols for flatness, parallelism, and concentricity, among others.
    • Essential for ensuring parts fit together correctly in assembly.

11. Weld symbols

    • Indicate the type and location of welds on a drawing.
    • Include information on weld size, length, and finish.
    • Critical for manufacturing and assembly processes.

12. Surface finish symbols

    • Specify the required surface texture or finish of a part.
    • Indicate roughness, lay, and other surface characteristics.
    • Important for ensuring proper function and aesthetics of the part.

13. Thread symbols

    • Indicate the type and specifications of threads on fasteners.
    • Include information on diameter, pitch, and thread form.
    • Essential for ensuring proper assembly and function of threaded components.

14. Material symbols

    • Represent the type of material used for a part or assembly.
    • Help in identifying material properties and specifications.
    • Important for manufacturing processes and material selection.

15. Revision symbols

    • Indicate changes made to a drawing after its initial release.
    • Typically shown with a revision number and date.
    • Essential for maintaining accurate and up-to-date documentation.