Post on 01-Apr-2015
transcript
Engineering Tech GTEngineering Principals & Applications
Introduction to Engineering & Technology Concepts
Projection Systems: Orthographic and Isometric
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Objectives
• Orthographic Projections• View Selection• Glass Box Approach• Line Precedence• Two View Drawings• Tips
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Orthographic Projections
• Advantage – Represent features of an object more accurately
• Example Problem
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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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Defining the Six Principal Views or
Orthographic Views
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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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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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Glass Box Approach
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Glass Box Approach
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Glass Box Approach
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Glass Box Approach
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Glass Box Approach
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Glass Box Approach
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Conventional Orthographic Views
Height
Depth
Width
Front View
Top View
Right Side View
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Is The Orthographic View OK?
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Orthographic Must Be In Projection
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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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For Example:
1. Visible
2. Hidden3. Center
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• 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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Example: Application of Precedence
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Intersecting Lines in Orthographic Projections
Solid Line Intersections
Dashed Line Intersections
Gap
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Two-View Drawings
• Some objects can be fully described by two views, look for:
– Symmetry or Bodies of Rotation
Front View Right Side View
Front View
Right Side
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Other Two-View Examples
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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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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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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