ENGR1025 - Lecture 5

Orthographic Projection Overview

  • Eight Rules of Orthographic Projection:
    1. Alignment of Features: Every point or feature must align in adjacent views.
    2. Distances in Related Views: Distances between points in related views must be equal.
    3. True Length and Size: Achieved when lines of sight are perpendicular to the feature.
    4. Foreshortening: Occurs when lines of sight are not perpendicular.
    5. Configuration of Planes: Similarity of areas from concurrent views unless viewed on the edge.
    6. Parallel Features: Remain parallel across all views.
    7. Edge View: Surfaces parallel to the line of sight appear as edges (represented as lines).
    8. Contiguous Planes: No two contiguous areas can lie on the same plane.

Auxiliary Views

  • Definition: Auxiliary views are orthographic views projected onto any plane that isn’t one of the six principal views.
  • Creation: Established by positioning a new line of sight relative to the object.

Techniques for Creating Auxiliary Views

1. Fold-Line Method
  • Involves visualizing a glass box with six principal views: Front, Right Side, Top, Back, Left Side, and Bottom.
  • Phantom Lines: These are fold lines connecting views, guiding the projection into the auxiliary view.
  • The object within the glass box may be repositioned to clarify the auxiliary view.
2. Reference Plane Method
  • Utilizes a plane positioned relative to the object instead of floating the object in a glass box.
  • Measurements for the auxiliary view are taken perpendicular to the reference plane.
3. Auxiliary View Classification
  • Primary Auxiliary View: Projected from one of the six principal views.
  • Secondary Auxiliary View: Projected from a primary auxiliary view.
  • Tertiary Auxiliary View: Projected from a secondary or another tertiary auxiliary view.

Depth, Height, and Width Auxiliary Views

  • Depth: Projected from the front view, showing true depth dimensions.
  • Height: Projected from the top view, displaying true height dimensions.
  • Width: Projected from the profile view, illustrating true width dimensions.

Special Auxiliary View Types

  • Partial Auxiliary View: Only shows features of interest, simplifying the drawing process when CAD is not used.
  • Half Auxiliary View: Used for symmetrical features, often simplifying the representation.
  • Successive Auxiliary Views: Allow determination of the true size and shape of oblique surfaces.

Dihedral Angles

  • Defined as the angle between two intersecting planes. Constructed by creating a point view of the line of intersection.

Application Areas for Auxiliary Views

  • Identifying true sizes and shapes of features that might appear foreshortened in principal views.
  • Reverse Construction: Establishes auxiliary views prior to pictorial views, essential in complex designs.

Construction Techniques

  • When dealing with curves or conic sections, specific tools like flexible curves are needed to create accurate representations.

Additional Notes on Labels and Conventions

  • Each fold line or reference plane can be labelled based on its views, e.g., T-F for a fold line between top and front views.
  • Lines of sight determine the projection direction used in auxiliary views.

Endnotes

  • The techniques and rules discussed are derived from standard engineering drawing and modeling frameworks, emphasizing practical skills within engineering design.