orthographic projection11
TRANSCRIPT
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Chapter 7: OrthographicProjections
Mechanical Sciences-I
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Introduction toOrthographic Projections
Introducing Orthographic
Projections as the language of
engineering designers
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Orthographic projections are an engineers
language for conveying the shape and size
information about the products he designs.
An orthographic projection consists of the view
obtained view when the object is viewed from
very far away, so that the resulting rays are all
parallel.
The parallel rays that are used for constructing
the views are called projectors.
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Orthographic Projections
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The three principal views are take on picture
planes which are held parallel to the three
principal faces of the object, the front, the
top and the side.
The intersections of the projectors with the
picture plane are the projections of the
points from which the projectors emanate.
The points are joined to obtain the views.
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Orthographic Projections
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Object
We consider here the development of the
orthographic views of a simple object.
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Viewing
Direction
Pictur
e
Plane
For the Top view we view from the top!
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Viewing
Direction
Point of intersection with picture plane
Projectors
Perpendicularto picture
plane
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Viewing
Direction
Intersections of allextreme points
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Top View
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Front View
Similarly, viewing from the
front with parallel projectors
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Top & Front Viewson opening up the page
Notice the
interrelation
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Similarly, the
Right Side View
Again notice the
interrelation
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Mitre
The third view can also be obtained by
taking projections from the two views,
using the mitre line, a line at 450
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Two types of projections commonly used: I &
III angle
In third angle, picture
planes in between the
viewer & object
In first angle,
picture plane
behind the object
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Opening up of the box with the various views in III angle
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The relationship on plane paper of the various
views in III angle
Top
View
Front
View
Right
View
Left
View
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The relationship on plane paper of the various
views in I angle
Top
View
Front
View
Left
View
Right
View
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Front View
Top View
Mitre
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Front
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Front View
Top View
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Front
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A Video
Engg_graphics.mpg
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A demonstration
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Gboxw31.exe
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Front
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XX X
X
XX
X
X
Front
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Notice that the oblique face of the cylinder
appears as an ellipse in right-side view, but as
lines in the front view.
Front
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Hidden Features
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Hidden Features
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Hidden Features
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Hidden Features
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Hidden Features
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Lines and Areas
Projections of lines and areas
Meaning of lines and areas in
orthographic projections
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Projection of Lines
A
B
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M i f A i
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1. A surface in true shape
2. A foreshortened surface
3. A smoothly curved surface
4. A combination of tangentsurfaces
Meaning of Areas in
Orthographic Views
M i f A i
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Surface in True shape Foreshortened Surface
Meaning of Areas in
Orthographic Views
B
B
B
M i f A i
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Curved Surface
C
C
C
Tangent Surfaces
D
D
D
Meaning of Areas in
Orthographic Views
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Projections of Areas
Some areas are
projected in true
shapes, while others
are distorted.Areas parallel to
picture planes are in
true shapes
Four types of Areas
1.A surface in true shape2. A foreshortened surface
3. A smoothly curved surface
4. A combination of tangent surfaces
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Reading Areas
An plane surface that appears as a line in
one view is normal to that view. It may ormay not appear its true shape in the other
views.
A plane surface will always appear in aprincipal view as a line or an area
An plane surface that appears as a line intwo of the principal viewsappears as a true
shape in the third view.
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Oblique surfaces
appear as areas of like
shape in all views
Reading Areas
Adjacent Areas lie in differentplanes. If two areas were in the
same plane, there will not be
any boundary between the
two.
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Reading Areas
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Reading Areas
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Three possible interpretations:Meaning of Lines in
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(Surface Limit)
p p
An edge viewof a surfaceAn intersection of two surfaces
A surface limit- reversal of
direction of a curved surface
Meaning of Lines in
Orthographic Views
Meaning of Lines in Orthographic Views
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Meaning of Lines in Orthographic Views
An edge viewof a surface
An intersection of two surfaces
A surface limit- reversal of direction of
a curved surface
Meaning of Lines in Orthographic Views
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Another Example
Meaning of Lines in Orthographic Views
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We next illustrate how to read the
orthographic drawings. This is done
by interpreting the three view todraw the represented by those
view.
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Interpretation of
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Interpretation of
Hidden Lines
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Draw the pictorial views of the
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Draw the pictorial views of theobject whose three views areshown.
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Missing Line Exercises
In the examples that follow, one or more
lines may be missing in (only) one view.
Try constructing a pictorial view todetermine what line(s) are missing.
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One or more lines may be missing in
(only) one view. Try constructing a
pictorial view to determine what
line(s) are missing.
Missing Line Exercises
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Missing Line Exercises
i i Li i
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Missing Line Exercises
Mi i Li E i
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Missing Line Exercises
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Mi i Li E i
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Missing Line Exercises
Mi i Li E i
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Missing Line Exercises
Mi i Li E i
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Missing Line Exercises
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Mi i Li E i
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Missing Line Exercises
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Mi i Li E i
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Missing Line Exercises
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Missing Line Exercises
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Missing Line Exercises
Missing Line Exercises
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Missing Line Exercises
?
Missing Line Exercises
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Missing Line Exercises
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Missing Line Exercises
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Missing Line Exercises
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Sectional Views
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Too many hidden lines
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Too many hidden lines
Too complicated to
interpret
Sectional Views
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Sectional Views
A portion of the part is cut away to reveal theinterior.
For this purpose a cutting plane is employed.
The shape of the object is clarified bydistinguishing between the areas where the
cutting plane actually cuts the solid material
and the areas where it meets voids.Wherever the cutting plane cuts the solid
material, the area is hatched
Sectional Views
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The structure of thispulley becomes
clearer if we imagine
the pulley is cut at the
meridian plane, the
material to the left of
the cutting plane is
removed and aprojection viewing
from the left is drawn.
A
A
Sectional Views
Sectional Views
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Cutting Plane
The details of the hub are now clearer.
Sectional Views
Sectional Views
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A sectional view
makes things
much clearer.
Sectional Views
Sectional Views
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Sectional Views
Sectional Views
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This does not differentiatecutand uncutportions
Note that the cutting plane
line is long dash two
short dashes line
Sectional Views
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Sectional Practices
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In the following slides we show some sectioning
practices. The principle involved in these
practices is to reduce the drawing effort as much
as possible while maintaining clarity as much aspossible.
Try reducing the number of views required.Draw as few hidden lines as possible. Use a
variety of sections as required.
Sectional Practices
Offset Sections
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Note that the sectioning plane is offset
to bring out both the hidden features in
one view
Offset Sections
Full Sections
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Full Sections
Half Sections
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In many symmetrical objects one
can show the internal & the external
feature in the same view by
Half Sections