Transcript FEH - ENG H191 - Lecture 3 - ::Gateway Engineering

Engineering H191 - Drafting / CAD
Orthographic Projection
Lecture 3
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Today’s Activities
•
Today
– More On Multi-view Orthographic Drawings
• BTG Chap 4
– Orthographic Projection
– Teamwork Workshop
• Tomorrow
– Learn how to do isometric drawings
– First AutoCAD Lesson
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Projection Methods (BTG pg 123)
• Perspective projections
– Linear 1, 2, or 3 Vanishing points
– Aerial
• Parallel projections
– Oblique projection: cavalier, cabinet, or general
– Orthographic projection
• Axonometric
– Isometric, dimetric, or trimetric
• Multi-view
– First-angle or third-angle
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From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill
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First Angle Vs. Third Angle
Third-angle Projection
First-angle Projection
From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill
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Review - Why Multi-view? Give 3 reasons
• Most accurate description of 3-D objects for
engineering, manufacturing, and construction
• Dimensions of features are presented in true size
in one or more views
• Easy transition to 3-D database and computer
modeling
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Principals Of Orthographic Projection
• Every point or feature must be aligned on a
parallel projector in any adjacent view.
• Distances between any two points in a related
view must be equal.
• Features are true length or true size when the
lines of sight are perpendicular to the feature.
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Principals Of Orthographic Projection
• Features are foreshortened when lines of sight
are not perpendicular to the feature.
• Areas that are the same feature will always be
similar in configuration from one view to the next,
except when viewed on the edge.
- Example: Triangular surface always has three
sides in all views
• Parallel features will always appear parallel in all
views.
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Principals Of Orthographic Projection
• Surfaces that are parallel to the lines of sight will
appear as lines or edge views.
• No two contiguous (adjacent) areas can lie in the
same plane.
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Hints For Multiview Sketching
• Identify the major features and overall
dimensions of the object
• Do not use your scale 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 Multiview Sketching
• Only measure along the primary axes fi you are
working from a pictorial.
• Map inclined and oblique faces among all three
views
• Follow the precedence of lines
• Darken all visible, hidden, and center lines
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Defining 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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Precedence of Lines
VISIBLE LINES takes
precedence over hidden and
center lines
HIDDEN LINES take precedence
over center lines
CENTER LINE does not have
precedence
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Remember - Six Principal Views
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And… Set up Conventional Three-View
Width
Top View
Front View
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Depth
Right
Side
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Height
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Steps in Creating the Three-View Sketch
Completed Sketch
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Assignments
• Dwg 5 – A11
– Orthographic Sketches from an Isometric
– Due tomorrow morning
• Dwg 6 – Team Agreement
– Due tomorrow morning
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