Difference Between First Angle Projection and Third Angle Projection

The Difference Between First Angle Projection and Third Angle Projection – This is one of the most often discussed topics among mechanical engineers and designers.

Beginners who are unfamiliar with the notion of orthographic drawings often mistake the two, and you are not alone.

Any expert with hands-on experience with design and tools would tell you that this is nothing more than a method of portraying three-dimensional objects in two dimensions.

First and third-angle projections are just methods of expressing how an object appears from various angles.

This is known as orthographic projection, and orthographic refers to engineering drawings or plan views.

Now that you understand the notion of orthographic projections.

let’s compare first and third-angle projections.

What is First Angle Projection?

Difference Between First Angle Projection and Third Angle Projection

This is one of the most often used ways of obtaining engineering drawings, particularly orthographic projections.

Orthographic projection is a graphical approach for representing three-dimensional structures or objects by converting them into distinct perspective projection images known as views.

The top view, front view, and side view are the most common orthographic views.

The first-angle projection is one of the ways that may be used for orthographic projection drawings.

This method is accepted everywhere in the world with the exception of the United States.

In this projection technique, the object is put in the first quadrant, in front of the vertical plane and above the horizontal plane.

What is Third Angle Projection?

Difference Between First Angle Projection and Third Angle Projection

This is another perspective projection technique that uses a sequence of two-dimensional images to portray three-dimensional objects.

In third angle projection, the three-dimensional object to be projected is positioned in the third quadrant, behind the vertical plane and below the horizontal plane.

Unlike in first angle projection, where the plane of projection is ostensibly opaque. The planes in the third angle projection are transparent.

This projection technique is mostly utilized in the United States while Japan requires a third angle projection schema for industrial designs for product fabrication.

Difference Between First and Third-angle Projections

  • The Fundamentals of First and Third-angle Projections

First Angle Projection is a method of expressing three-dimensional objects in two dimensions that are widely used in Europe and the rest of the world except the United States.

We split the plane into four quadrants to get orthographic views of 3D objects.

For the first angle projection, the object is placed in the first quadrant.

The 3rd-angle Projection technique is the default projection system in the United States and Australia.

For the third angle projection, the object is positioned in the third quadrant.

  • First and Third Angle Projection Representation

Both are schemas for multiview projection of three-dimensional objects utilizing a sequence of two-dimensional drawings.

The principal planes of an object are used to project several perspectives of the same object from various points of view.

Six distinct sides may be drawn in total, each of which consists of six orthographic views known as principal views.

To get the first angle projection, place the object in the first quadrant, which is between the plane of projection and the observer.

The object is positioned below and behind the viewing planes for the third angle projection, implying that the plane of projection lies between the observer and the object.

  • Plane of First and Third-angle Projections

Except for the order of views and the state of the projection plane, both techniques of orthographic projection provide the same six major views of the object.

The plane of projection is assumed to be opaque or non-transparent in the 1st angle projection schema.

The object is positioned in front of the planes, and each view is pushed through it, causing the vertical plane to be pushed behind the object and the horizontal plane to be pushed beneath.

The plane of projection in the third angle projection technique is transparent, and the object is positioned below the horizontal plane and behind the vertical plane.

  • View Sequence of First and Third-angle Projections

The orthographic view is projected on a plane beyond the object in the first angle projection technique, and the observer is on the left side of the object and projects the side view on a plane beyond the object.

The top view is projected onto the bottom of the front view, while the right side view is projected to the left of the front view.

The observer is on the right side of the object in third angle projection, and the orthographic view is projected on a plane between the viewpoint and the object.

The right view is overlaid on the right side of the front view, while the top view is projected on top of the front view.

Comparison Chart for First and Third-angle Projections

First Angle ProjectionThird Angle Projection
The object is supposed to be placed in the first quadrant.The object is supposed to be placed in the third quadrant.
It puts the object between the plane of projection and the observer.It puts the plane of projection between the observer and the object.
The plane of projection is believed to be opaque.The plane of projection is believed to be transparent.
Symbol: Symbol:
The object is in front of the vertical plane and above the horizontal plane.The object is behind the vertical plane and beneath the horizontal plane.
The right view is projected onto the left of the front view and the top view is projected onto the bottom of the front view.The right view is projected onto the right side of the front view and the top view is projected above the front view.

Summary of the Difference Between First and Third-angle Projections

First angle and third angle projections are the two methods of drawing in orthographic that generally consist of three separate perspectives of an object in two dimensions. 

They are used to get engineering drawings for clarity.

The observer is positioned on the left side of the object for the first angle projection, putting the object directly between the plane of projection and the observer.

The observer is placed on the right side of the object for the third angle projection, putting the plane of projection directly between the object and the observer.

Although both are graphical techniques used in engineering drawings, they vary in how their perspectives are positioned.

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