Orthographic Projection11

7/30/2019 Orthographic Projection11

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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
http://g/MEC101%20Padagogical/course%20material/Engg_Graphics.mpghttp://g/MEC101%20Padagogical/course%20material/Engg_Graphics.mpg


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A demonstration

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Gboxw31.exe
http://g/MEC101%20Padagogical/course%20material/GBOXW31.EXEhttp://g/MEC101%20Padagogical/course%20material/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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An edge viewof a surface

An intersection of two surfaces

A surface limit- reversal of direction of

a curved surface



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Another Example



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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.



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i i Li i


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Mi i Li E i


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Mi i Li E i


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Mi i Li E i


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Mi i Li E i


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Mi i Li E i


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Mi i Li E i


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?



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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

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Orthographic Projection11