Engineering Design - Projections Overview

Axonometric Projection

  • Definition: A parallel projection technique for creating a pictorial representation of an object by rotating it relative to the projection plane.
  • Origin of Term: "Axonometric" comes from Greek: "Axono" means axis, and "metric" means to measure.
  • Characteristics:
    • Displays all three dimensions (width, height, depth) in one view.
    • Allows for a clearer visualisation of three-dimensional objects.

Four Principal Projection Techniques

  • Concept Basics:
    • Multiview Projection: Only two dimensions visible in each view.
    • Axonometric Projection: Rotated view allows all three dimensions to be visible.
    • Oblique Projection: Shows the object’s most descriptive view as the front view, with significant distortion.
    • Perspective Projection: Objects converge toward a vanishing point, more realistic representation.

Classification of Axonometric Projection

  • Classification by Angles:
    • Based on angles between lines comprising the axonometric axes.
    • Isometric Projection:
    • Rotated 45° and tilted forward 35° 16', creating equal angles of 120° between axes.
    • Isometric Drawing Scale: Cos(35° 16') = 0.81647, leads to approximately 80% of true lengths.

Types of Isometric Drawings

  • Isometric Axes can be arranged for various views:
    • Looking from different perspectives (bottom, top, sides).
  • Isometric Ellipses and Features:
    • Major/minor axes perpendicular; important for cylinders.

Dimensioning Standards

  • ANSI Y14.4 1989 Standard:
    • Ensures dimension lines and notes are aligned, located outside of the view as much as possible, and unidirectional (reading top to bottom).
  • Production Note: While isometric drawings help in communication, they are often not used in engineering manufacturing.

Oblique Projection

  • Definition: A pictorial drawing where the front view is placed parallel to the projection plane.
  • Types:
    • Cavalier Projection: Full scale.
    • Cabinet Projection: Half scale.
    • General: Ranges from full to half scale, providing true size front surfaces.

Perspective Projection

  • Concept: Objects are shown true size at the picture plane, shrinking as they recede behind it. All parallel lines converge at a vanishing point.
  • Classification: Based on the number of vanishing points (1, 2, or 3).
  • Variables in Drawing:
    • Object distance from picture plane, position of station point, and ground line relative to horizon.

Summary of Drawing Techniques

  • Overall Goals: Use these techniques to effectively depict three-dimensional objects on two-dimensional surfaces, ensuring clarity and accuracy in representation. Different projections serve distinct purposes based on the context of usage (e.g., engineering design, furniture design).