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Orthographic Projection. Lecture 09/28/04. Question of the Day. For what inventions did Charles Kettering receive patents? Where did he earn his engineering degree?. ANSWER:. The automobile self-starter and the ignition system.

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orthographic projection

Orthographic Projection

Lecture 09/28/04


Question of the Day

  • For what inventions did Charles Kettering receive patents?
  • Where did he earn his engineering degree?


  • The automobile self-starter and the ignition system

Kettering was a Buckeye and earned his engineering degree from Ohio State. His company was Delco and now is called Delphi

orthographic projections
Orthographic Projections
  • Reference: Technical Graphics, Chap 3:
  • Advantage – Represent features of an object more accurately
  • Example Problem
which views to present
Which Views to Present?

General Guidelines

  • Pick a Front View that is most descriptive of object
  • Normally the longest dimension is chosen as the width (or depth)
  • Most common combination of views is to use: Front, Top, and Side View
  • Any other view different from the Principal Views is called Auxiliary View (see 3.15 in the Technical Graphics text)
glass box approach introduction
Glass-Box Approach - Introduction
  • Most powerful technique to understand orthographic projections
  • Suspend the object with transparent strings inside a glass box
  • Freeze the view from each direction (each of the six sides of the box) and unfold the box
  • Animation illustrates glass-box approach
glass box theory
Glass Box Theory
  • This visualization tool is available on the FEH website:

Go to FEH Home Page (http://feh.eng.ohio-state.edu)  Click on “Lecture Notes”  Chose “Engineering H191” from Autumn 2004  Glass Box animation is available there

first angle international vs third angle u s projection

Third-angle Projection

First-angle Projection

First Angle (International) vs. Third Angle (U.S.) Projection

From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill

conventional orthographic views


Top View


Right Side View

Front View


Conventional Orthographic Views
defining hidden and center lines for orthographic projections

Hidden Line – used to represent features that cannot be seen in the current view

  • Centerlines – used to represent symmetry and to mark the center of circles and the axes of cylinders, and the axes of symmetrical parts, such as cylinders and bolts
Defining Hidden and Center Lines for Orthographic Projections

Center Lines

Visible Line

Hidden Lines

precedence of lines
Precedence of Lines

0.6 mm

0.3 mm

0.3 mm

conventions for intersection of lines in orthographic projections


Conventions for Intersection of Lines in Orthographic Projections

Solid Line Intersections

Dashed Line Intersections

Reference – Technical Graphics, Chapter 3

two view drawings
Two-View Drawings
  • Some objects can be fully described by two views, look for:
    • Symmetry or Bodies of Rotation

Front View

Right Side View

Right Side

Front View

  • Introduced to orthographic projections
  • We recommend the software animation exercise introduced in class. Animation can be found on WebCT – Glass Box Theory.
review questions
Review Questions
  • Rectilinear grids are used for sketching isometric pictorials … True/False
  • Based on the lines of sight, orthographic projection drawings are classified as a ____ projections
  • There are ____ standard principal views of orthographic projections
  • Each view in a orthographic projection concentrates on ____ dimensions of the object
hints for orthographic projection sketching
Hints for Orthographic Projection Sketching
  • Identify the major features and overall dimensions of the object
  • Do not use any straight-edge devices as a pencil guide when sketching by hand
  • Start by drawing bounding boxes with light construction lines.
  • Keep views aligned while sketching
tips for drawing assignments
Tips for Drawing Assignments
  • Title Information is required – follow conventions
  • Usage of construction lines is encouraged. Mandatory for circle or ellipse
  • Orthographic projection : Alignment of the views is important! Will not be graded, if not aligned
sketching a circle
Sketching a Circle
  • Draw a square whose sides are the diameter of the circle.
  • 2. At the center of each side define the point of tangency for the circle.
  • 3. Draw the diagonals of the square.
  • 4. Orient the paper so you can draw equal arcs to construct the circle
hints for orthographic projection sketching30
Hints for Orthographic Projection Sketching
  • Map inclined and oblique faces to all three views
  • Follow the precedence of lines
  • Darken all visible, hidden, and center lines
  • Drawing 7: B11 in course packet
    • Due Today
  • Drawing 8: TG 2.6 & 2.19
    • Due on next lecture day