ENGR1025 - Lecture 6

  • Axonometric Projection

    • A parallel projection technique to create an object's pictorial by rotating around an axis relative to the projection or picture plane.
    • Origin: Derived from Greek; 'Axono' means Axis and 'Metric' means to Measure.
    • Key Features:
    • All three dimensions (width, height, depth) are visible in one view.
    • Displayed through a parallel projection around axis or axes.

  • Four Principal Projection Techniques:

    1. Multiview Projection (A)
    • Observer's lines of sight are parallel and perpendicular to the picture plane.
    1. Axonometric Projection (B)
    • Observer at a finite distance; lines of sight converge at the observer's eye.
    1. Oblique Projection (C)
    • Lines of sight are parallel but oblique to the picture plane.
    1. Perspective Projection (D)
    • Lines of sight converge towards a vanishing point.

  • Difference Between Multiview and Axonometric Drawing:

    • Multiview only shows two dimensions per view, while axonometric displays all three dimensions by rotating and tilting the object.

  • Classification of Axonometric Projection:

    • Based on the angles between the lines that form the axes.
    • Aesthetically pleasing and easier to draft when angle conditions are met (∡ ≠ B).

  • Isometric Projection:

    • Rotate the object 45° around the vertical axis and tilt it forward 35° 16’ until the body diagonal appears as a point in the front view.
    • Isometric Angle:
    • The three axes form equal angles of 120°.
    • Isometric Line:
    • Any line parallel to an isometric axis.
    • Isometric Plane:
    • Any plane parallel to cube faces.

  • Isometric Scale:

    • Isometric drawings are usually foreshortened.
    • Isometric scale calculation:
    • extIsometricScale=extCos(35°16′)ext(approximately0.81647)ext{Isometric Scale} = ext{Cos}(35° 16') ext{ (approximately } 0.81647)
    • Isometric drawing is approximately 1.23 times the isometric projection.
    • Preferred for technical drawings due to readability.

  • Types of Isometric Drawings:

    • Different views can be created by positioning the isometric axes:
    1. Looking up from the bottom.
    2. Looking down from the top.
    3. Looking from the right.
    4. Looking from the left.

  • Hidden Lines:

    • Use hidden lines sparingly and only when necessary to fully describe an object.
    • Select the most descriptive view available.

  • Center Lines:

    • Drawn only to indicate symmetry or for dimensioning purposes.

  • Dimensioning Guidelines (ANSI Y14.4, 1989):

    • Dimension lines, extension lines, and lines being dimensioned must lie in the same plane.
    • All dimensions should read unidirectionally from bottom upward and be located outside the view whenever possible.
    • Many isometric drawings are aimed at a non-technical audience and are not strictly for engineering.

  • Procedure for an Isometric Sketch:

    1. Establish isometric axes.
    2. Define width, depth, and height.
    3. Add dimensions and sketch overall shapes.

  • Isometric Ellipses:

    • Major and minor axes perpendicular; major axes at 60° to horizontal on profile planes.
    • Major axis aligns horizontally on the top plane; Perpendicular to hole’s axis.

  • Isometric Cylinder Drawing Process:

    1. Draw the bounding box.
    2. Sketch the end of the cylinder.
    3. Complete the sides and finalize sketch.

  • Oblique Projection:

    • A drawing where the front view is treated as the most descriptive and parallel to the projection plane.
    • Common in furniture design; can lead to distortion depending on the angle used.

  • Perspective Projection Basics:

    • Objects in the picture plane appear true size; those further back appear smaller.
    • Lines parallel to the picture plane converge toward a vanishing point, influencing overall perspective.
    • Vanishing Point:
    • Represents distance; an object at infinity appears as a point.
    • Adjusting the vanishing point alters perspective views.
    • Horizon Line Positioning affects perceived height of the observer versus the object.
    • Varying ground line position changes the perspective view dramatically.

  • Classifications of Perspective Projection:

    • Based on the number of vanishing points (1 for parallel, 2 for angular, and 3 for complex views).

  • Drawing Variables for Perspective:

    • Selection based on distance from the picture plane, station point positioning, ground line relative to horizon, and number of vanishing points.

  • Disclaimer:

    • Images and descriptions are derived from established textbooks and resources to guide educational presentations in engineering design.