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Engineering Tech GT Engineering Principals & Applications Introduction to Engineering & Technology Concepts Projection Systems: Orthographic and Isometric

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2 Objectives Orthographic Projections View Selection Glass Box Approach Line Precedence Two View Drawings Tips

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3 Orthographic Projections Advantage – Represent features of an object more accurately Example Problem

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4 Orthographic Projections Orthographic Projections are a collection of 2-D drawings that work together to give an accurate overall representation of an object.

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5 Defining the Six Principal Views or Orthographic Views

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6 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 an Auxiliary View

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8 Glass Box Approach 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

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9 Glass Box Approach Available on the FEH website: –Lecture Notes –Engineering H191 – Autumn 2005 –Glass Box Animation

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10 Glass Box Approach

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11 Glass Box Approach

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12 Glass Box Approach

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13 Glass Box Approach

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14 Glass Box Approach

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15 Glass Box Approach

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16 Third-angle Projection First-angle Projection First and Third Angle Projections First Angle – International Third Angle – U.S.

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17 Conventional Orthographic Views Height Depth Width Front View Top View Right Side View

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18 Is The Orthographic View OK?

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19 Orthographic Must Be In Projection

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20 Hidden and Center Lines 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

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21 For Example: 1. Visible 2. Hidden 3. Center

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22 Visible lines take precedence over all other lines Hidden lines and cutting plane lines take precedence over center lines Center lines have lowest precedence Precedence of Lines

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23 Example: Application of Precedence

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24 Intersecting Lines in Orthographic Projections Solid Line Intersections Dashed Line Intersections Gap

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25 Two-View Drawings Some objects can be fully described by two views, look for: –Symmetry or Bodies of Rotation Front ViewRight Side View Front View Right Side

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26 Other Two-View Examples

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27 Summary Introduced to orthographic projections We recommend the software animation exercise introduced in class. Animation can be found on my website.

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28 Review Questions Rectilinear grids are used for sketching isometric pictorials … True/False Based on the lines of sight, orthographic projection drawings are classified as ___________ projections There are ____ standard principal views of orthographic projections Each view in an orthographic projection concentrates on ____ dimensions of the object

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29 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

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30 Hints for Orthographic Projection Sketching 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! –You will lose points, if not aligned

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31 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

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32 Sketching a Circle Draw a square whose sides are the diameter of the circle. At the center of each side define the point of tangency for the circle. Draw the diagonals of the square. Orient the paper so you can draw equal arcs to construct the circle

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