ORTHOGRAPHIC PROJECTION

ISSUE’S TO BE DISCUSSED

• PROJECTIONS AND ITS TYPES

• ORTHOGRAPHIC PROJECTION

• 1ST AND 3RD ANGLE PROJECTION

PROJECTION

• Any kind of representation of an object on a paper, screen or similar surface by drawing is called projection of that object.

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TYPES OF PROJECTION

• Pictorial Projection : Length, breadth and height of an object is shown in one view.

• Orthographic Projection : Projection obtained when projectors are parallel to each other but perpendicular to the plane of projection.

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• 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.

Orthographic Projections

OBSERVER MOVE AROUND

Front view Right side view

Top view

THE GLASS BOX CONCEPT

Bottom view

Left side view

Rear view

HeightWidth

De

pth

History

Defining the Six Principal Views or Orthographic Views

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Plane of projection• Principal Planes• Vertical Plane• Horizontal Plane• Auxiliary Plane• Profile Plane• Ground Line• Front View or Elevation• Top View or Plan• Side View or Profile View

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Principal planes in drawing

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Front View When the observer looks at the object from the front, the view obtained is called the front view (FV) or Elevation. FV is seen on the VP.

Top View When the observer looks at the object from above, the view obtained is called top view (TV) or plan. TV is seen on the HP.

Side Views When the observer looks at the object from side, i.e., from his left-hand side or right hand side, the view obtained is called side view (SV). SV is seen on the PP.

Left-Hand Side View When the observer views the object from his left-hand side, the view obtained is called left-hand side view (LHSV).

Right Hand Side View When the observer views the object from his right-hand side, the view obtained is called as right-hand side view (RHSV).

Bottom View When the observer looks to the object from below, the view obtained is called bottom view (BV) or bottom plan.

Rear View When the observer looks to the object from back, the view obtained is called rear view (RV) or back view or rear elevation.

ORTHOGRAPHIC VIEWS

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PROJECTION SYSTEMS

1. First angle system

2. Third angle system

First Quadrant

ThirdQuadrant

- European country

- ISO standard

- Canada, USA,

Japan, Thailand

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ORTHOGRAPHIC PROJECTION

1st angle system 3rd angle system

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ORTHOGRAPHIC VIEWS

1st angle system 3rd angle system

Foldingline

Foldingline

Foldingline

Foldingline

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ORTHOGRAPHIC VIEWS

1st angle system 3rd angle system

Front View

Front View

Right Side View

Right Side View

Top View

Top View

The relationship on plane paper of the various views in I angle

TopView

FrontView

Left View

RightView

The relationship on plane paper of the various views in III angle

TopView

FrontView

RightView

Left View

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First angle system Third angle system

PROJECTION SYMBOLS

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Difference in first and third angel projection

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First angle projection method

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Third angle projection method

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The second and fourth angel methods are not used in practice because after rotating the horizontal plane by 90° in clockwise direction the front view and top are overlapping. So we can not differentiate the front and top vies.

Why we are not using second and fourth angle projections ?

Orthographic Writing Steps

WRITING STEPS

1. Select the necessary views

2. Layout the views.

3. Project the views.

4. Dimension the views.

1. SELECT THE NECESSARY VIEWS

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152

152

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2. LAYOUT THE VIEWS

A4

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Choose anappropriate scale

1:1

PROJECT THE VIEWS

DIMENSION THE VIEWS

NOTES1. Dimensions in millimeters.2. ….

PART NAME

xx

x x

y

y

y

y

z

TRANSFERINGTHE DEPTH DIMENSION

1. Direct measurement

01

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0 1 2 3 Starting point27

TRANSFERINGTHE DEPTH DIMENSION

2. Use miter line

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Views too close

No line is formed when curved surface tangentto a plane surface.

No line

No line

TANGENT & INTERSECTION

Line is formed when curved surface intersectsa plane surface.

tangent

tangent

intersect

intersect

Orthographic Projection

of Object Features

OBJECT FEATURESEdges are lines that represent the boundary

between two faces.

Corners Represent the intersection of two or

more edges.

Edge

Corner

Edge No edge

No corner No corner

Surfaces are areas that are bounded by edges

or limiting element.

Limitingelement

is a line that represents the last visible

part of the curve surface.

Surface Surface Surface

LimitLimit

OBJECT FEATURES

Line Convention

HIDDEN LINE PRACTICEHidden line should join a visible line, except itextended from the visible line.

Correct

No !

Join

Leavespace

Hidden line should intersect to form L and Tcorners.

Correct

No !

L T

HIDDEN LINE PRACTICE

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Object

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Viewing

Direction

Picture Plane

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Viewing

Direction

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Viewing

Direction

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Drawing three views in III angle

FRONT

TOP

LEFT

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Drawing three views in III angle

FRONT

TOP

LEFT

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Drawing three views in III angle

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FRONT

TOP

LEFT

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8

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×

×