Engineering H191 - Drafting / CAD
Orthographic Projection
Lecture 3
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 1
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 2
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 3
Engineering H191 - Drafting / CAD
From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill
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Gateway Engineering Education Coalition
Lect 3
P. 4
Engineering H191 - Drafting / CAD
First Angle Vs. Third Angle
Third-angle Projection
First-angle Projection
From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 5
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 6
Engineering H191 - Drafting / CAD
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.
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 7
Engineering H191 - Drafting / CAD
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.
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 8
Engineering H191 - Drafting / CAD
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.
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 9
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 10
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 11
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 12
Engineering H191 - Drafting / CAD
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
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 13
Engineering H191 - Drafting / CAD
Remember - Six Principal Views
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Lect 3
P. 14
Engineering H191 - Drafting / CAD
And… Set up Conventional Three-View
Width
Top View
Front View
Autumn Quarter
Depth
Right
Side
View
Gateway Engineering Education Coalition
Height
Lect 3
P. 15
Engineering H191 - Drafting / CAD
Steps in Creating the Three-View Sketch
Completed Sketch
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 16
Engineering H191 - Drafting / CAD
Assignments
• Dwg 5 – A11
– Orthographic Sketches from an Isometric
– Due tomorrow morning
• Dwg 6 – Team Agreement
– Due tomorrow morning
Autumn Quarter
Gateway Engineering Education Coalition
Lect 3
P. 17