Projections

Lecture Overview

  • Title: Orthographic Projection

  • Professor: Fabiola E. Buitrago G., Ph.D.

  • Contact: fabiola.buitrago@upr.edu

Objectives

  • Assigned readings from "Technical Drawing with Engineering Graphics, 15th edition" covering Chapter 6.

Key Objectives:

  1. List Principal Views: Six principal views of projection.

  2. Sketch Views: Top, front, and right-side views of an object with various surfaces.

  3. Transfer Dimensions: Identify dimensions transferable between views.

  4. Projection Symbols: Recognize and sketch the symbol for third-angle projection.

  5. Transfer Depth: Accurately transfer depth between views.

  6. Construct Missing View: Using two views, derive a missing view.

  7. Isometric Sketch: Produce an isometric sketch from orthographic projections.

Overview of Projections

  • A projection represents a view of an object graphically.

  • Projection theory allows the depiction of 3D objects onto 2D media.

  • Multiple views from different angles provide a complete description of an object's shape.

Projection Methods

  • Types of Projections:

    • Perspective

    • Parallel

    • Oblique

    • Orthographic

    • Axonometric

    • Multiview

Orthographic Projection

  • Definition: A parallel projection where lines of sight are perpendicular to the projection plane.

  • Types:

    1. Multiview Drawing: Displays each view in 2D.

    2. Axonometric Drawing: Captures all three dimensions in one view.

Multiview Projection

  • Characteristics:

    • Displays three principal dimensions: width, height, and depth.

    • Each view provides specific information regarding the object.

Axonometric Projection

  • Definition: Technique from descriptive geometry showing a hydrographic image of a 3D object.

  • Types:

    • Isometric: user-friendly but texture distortion occurs (e.g., circular holes appear as ellipses).

Six Standard Views

  • Principal Viewing Directions:

    • Top

    • Bottom

    • Front

    • Back

    • Right Side

    • Left Side

Projection Planes

  • Specific names assigned to the planes of projection:

    • Frontal Plane: Front View

    • Horizontal Plane: Top View

    • Profile Plane: Side View

Multiview Drawing Considerations

  • Advantages: Accurate shape and sizing.

  • Disadvantages: Requires practice to understand.

  • Multiview drawing might need additional vertical or partial views for complex objects.

Depth Dimension Transfer

  • Ensure depth dimensions between top and side views match.

  • Use dividers, scales, or 45° miter lines for transferring dimensions accurately.

Creating Orthographic Projections

  • Draw features of the front view first, then use projectors for top and right-side views.

  • Important to draw centerlines where necessary.

Orthographic Projection Types: First vs. Third Angle

  • First Angle Projection: Common in Europe.

  • Third Angle Projection: Prevalent in North America and Japan.

  • Method details the positioning of views related to the object.

Line Precedence in Drawings

  • Continuous Line: Over hidden lines

  • Hidden Line: Over center lines

Center Line Practice

  • Short dashes should intersect at center line points.

  • Center lines should be presented with a thin continuous line for small holes.

Isometric Representations

  • Circles depicted as ellipses in isometric drawings.

  • Four-Center Method: Steps to draw isometric ellipses with proper geometry.

Oblique Projection Types

  • Cavalier: Full scale depth, may create excessive visual distortion.

  • Cabinet: Shows depth at half scale, reduces distortion.

  • General: Uses custom scales for more natural appearance.

Exercises and Examples

  • Multiple exercises exist to build skills in sketching missing views and creating isometric projections from orthographic views.

  • Importance of visual recognition in identifying identical top views among different blocks discussed.

Review Section

  • Assess skills in converting orthographic views to isometric and understanding projection principles.