Important Point

**What Is Orthographic Projection? **

Orthographic views consist of one, two, or more separate aspects of an object taken from different directions & different sizes, generally at right angles to each other and arranged in a definite manner.

These views collectively describe the object. Orthographic views of any purpose can be represented by any one of the two systems of projection

The first angle projection and the third angle projection. It is named according to the quadrant in this which the object is imagined no place for purposes of line projection.

As far as any shape and size of the views are concerned, there is no difference between these two systems. The only difference lies in the relative positions of the various views. Indian Standards Institution recommends

(IS: 696-1972) both these systems leaving the choice to the discretion of the organization concerned. However, there are specific merits and demerits associated with each system. Students are advised to study both the methods to meet the varying demands of different industries in the country.

To meet this end. Some chapters in this book are exclusively dealt with in the first angle projection, and some in the third-angle projection.

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## Types of Orthographic Projection

Orthographic projection two different parts and also a different type of symbol as per below detail mention.

**First angle projection &****First angle projection symbol****Third angle projection****&****Third angle projection symbol**

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**First angle projection & ****First angle projection symbol **

In this, the object is imagined to be in the first quadrant. Because the observer normally looks from the right side of the quadrant to obtain the front view.

The objects will come in between the observer and the plane of projection.

Therefore, in this case, the object is to be transparent, and the projectors are imagined ta be extended from various points of the object to meet the projection plane. First, these meeting points when joined in the order form an image

**Principle first angle projection view **

This is the principle of the first angle projection. Thus in the first angle projection, any view is so placed that it represents the side of the object away from it.

First angle projection is mesurly used throughout all parts of Europe so that called **European projection.**

Most important of **First angle projection symbol **

#### First angle projection symbol

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**Third angle projection ****& ****Third angle projection symbol **

In this, the object is imagined to be placed in the third quadrant.

Again, as the observer is normally supposed to look from the right side of the quadrant to obtain the front view, in this method, the projection plane comes in between the observer and the object.

Therefore, the plane of projection has to be assumed to be transparent. The intersection of this plan with the projectors from all the points of the object would form an image on the transparent plane.

**Principle third angle projection view**

**Third angle Projection**

**symbol**

#### Third angle Projection symbol

The third angle is the system in used North America and alternatively described as American projection.

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**Making Orthographic Views **

### Front View

To draw the front view of an object in the first angle projection, the object which is assumed to be transparent is imagined to be in front of the vertical plane (first quadrant) as shown in.

**Front View Detail Drawing No 1**

The shape of the object, when viewing from the front.

Is obtained by joining in order all the meeting points of the projectors extended from the visible edges of the object. This is called a front view.

A similar treatment is repeated for the front view in the third angle projection, but with a transparent vertical plane imagined to be held in front of the object.

Here the shape of the object when viewed from the front is obtained by joining in order all the intersection points on the transparent plane of the projectors to the visible edges of the object

**Front View Detail Drawing No 2**

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### Side View

The shape of some objects cannot be interpreted completely from the from and top views only.

In such cases, more information may be needed, and for this purpose, a third plane is imagined.

This is called an auxiliary vertical plane and is placed perpendicular to the first two planes.

A view can be obtained on to this plane in a way similar to that explained above. In the first angle method, if the auxiliary vertical plane is the place to the right of the object, a view is obtained on it by looking at the object from its left side.

It is then called a left side view. On the other hand, if the auxiliary vertical plane is placed to the left of the

**Side View Detail Drawing **

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### Top View

The projection on to a plane placed horizontally below the transparent object will reveal the shape of the object as viewed from below.

#### Top View Drawing No 1

This view is called a top view, and the principle that is being followed is that of the first angle projection. Figure deals with a similar treatment in the third angle projection with a transparent plane placed horizontally below the object.

#### Top View Drawing No 2

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**Presentation of view **

For presenting the views on a drawing sheet, irrespective of the method of projection, the horizontal plane, and the auxiliary vertical plane arc rotated till they come in the plane with the original vertical plane.

Now the three views of the object will be in the same plane, viz., the plane of the paper. These three views normally provide enough information to describe the shape and size of the object.

**Presentation of view drawing No 1/ First angle projection symbol**

Above drawing shows the relative positions of the views in the first angle projection and below drawing n the third angle projection.

**Presentation of view drawing No 2/ Third angle projection symbol**

The method used for the projection is indicated by a distinctive symbol (presentation of view drawing No 1 .C and Presentation of view drawing No 2 C)

### Third Angle Projection

3rd **Angle** project is where the 3D object is seen to be in the 3rd quadrant. It is positioned below and behind the viewing planes, the planes are transparent, and each view is pulled onto the plane closest to it. The front plane of **projection** is seen to be between the observer and the object.

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