CAD and Engineering Graphics Fundamentals

Posted on Dec 27, 2025 in Electronic and Automatic Engineering

1. Introduction to CAD and Engineering Graphics

CAD Software

  • 3D: SolidWorks, Fusion 360 (Parametric, Feature-Based)
  • 2D: AutoCAD (Precise Drafting)

Design Process and Goals

  • Steps: Conceptual → Design (2D/3D, Projection, Dimensioning/Tolerancing) → Fabrication.
  • Goals: Cost-effectiveness, Reliability/Durability, Safety, Ergonomics, Sustainability, Maintainability, Visual Appeal.

Technical Drawing Tools

  • Traditional: Freehand, Instruments (Triangles, Compasses), Drawing Machines.
  • Modern: CAD Software (Digital, allows for easy modification, simulation, and integration with CAM/CAE).

Drawing Standards (ASME)

  • Paper Sizes (ISO A Series): A4 (210x297mm), A3 (297x420mm), A2, A1, A0.

  • Alphabet of Lines (Precedence)

    Precedence Order: Visible > Hidden > Cutting Plane > Center

    • Visible (Object) Line: Thick (0.6mm), represents visible edges/contours.
    • Hidden Line: Thin (0.3mm), dashed, represents edges hidden from view.
    • Center Line: Thin (0.3mm), long dash-short dash, indicates axis of symmetry or center of holes.
    • Dimension/Extension Line: Thin (0.3mm), shows measurement extent and boundaries.
    • Cutting Plane Line: Thick (0.6mm), shows where a section view is taken. Ends have arrows showing viewing direction.
    • Section Line: Thin (0.3mm), indicates cut surfaces in section views.

Line Conventions

  • Hidden Lines: Leave gap at corners, dashes meet at corners, stagger if close.
  • Center Lines: Extend about 3mm beyond feature, use “+” for center points, leave gap if extending as an extension line.

Basic 3D CAD Operations

  • Extrude/Extrude-Cut: Adds or removes material by projecting a 2D sketch perpendicularly.
  • Revolve/Revolve-Cut: Creates geometry by rotating a 2D sketch around an axis.
  • Sweep/Sweep-Cut: Creates geometry by moving a profile (cross-section) along a path.
  • Loft/Loft-Cut: Creates a smooth transition between two or more different cross-section profiles.
  • Fillet/Round: Rounds an interior or exterior corner.
  • Chamfer: Bevels an edge.
  • Shell: Hollows out a part, leaving specified wall thickness.
  • Hole: Creates standard-sized holes (countersink, counterbore, etc.).
  • Pattern: Creates multiple copies of a feature (Linear, Circular, Mirror).

2. Projections in Engineering Graphics

Projection Fundamentals

  • Three Components: Object, Plane of Projection, Observer/Projector (Lines of Sight).

Types of Projections

  • Parallel Projection: Lines of sight are parallel. Preserves parallel lines and true dimensions on planes parallel to the projection plane.

    • Orthographic: Projectors are perpendicular to the projection plane.

      • Multiview: Object’s principal faces are parallel to projection planes. Shows 2D views (Front, Top, Side). Shows true size and shape.

      • Axonometric: Object is tilted so multiple faces are visible in a single view. Principal axes are not parallel to projection planes, causing foreshortening.

        • Isometric: All three axes are equally foreshortened (same scale used for all). Angles between projected axes are 120°.
        • Dimetric: Two axes are equally foreshortened, third is different.
        • Trimetric: All three axes are unequally foreshortened.

    • Oblique: Projectors are not perpendicular to the projection plane. Front face is drawn true size.

      • Cavalier: Receding axes (depth) drawn at full scale.
      • Cabinet: Receding axes (depth) drawn at half scale (more realistic).

  • Perspective Projection: Lines of sight converge at the observer’s eye (Vanishing Points). Most realistic but not to scale.

    • 1-point, 2-point, 3-point perspective: Defined by number of vanishing points.
    • Key Elements: Horizon Line (HL), Ground Line (GL), Vanishing Point (VP).

Multiview Projection (Orthographic)

  • Third-Angle Projection (US, HK, Japan, Canada): The plane of projection is between the observer and the object. The Right-Side view is placed to the right of the Front view.
  • First-Angle Projection (Europe, Asia): The object is between the observer and the plane of projection. The Right-Side view is placed to the left of the Front view.
  • View Selection: The Front View should be the most descriptive, have the fewest hidden lines, show the object in a stable position, and its longest dimension should be the width.
  • View Alignment: Top and Front views are aligned vertically and share the same width. Front and Side views are aligned horizontally and share the same height.

  • Line Usage in Multiview:

    • Hidden Lines: Dashed; show features not visible in that view.
    • Center Lines: Long dash-short dash; mark centers of holes and axes of symmetry.

Key Fact: Different 3D objects can have identical top and bottom views.