First angle projection and third angle projection are the vocabularies of technical drawings. These are the latest standards used in engineering drawings to communicate design intent among different stockholders. Let’s learn more about 1st angle projection and 3rd angle projection in this article.
It’s very common for beginners who just passed out of colleges to get confused between first-angle projection vs third-angle projection. In fact, it’s a matter of confusion among experienced engineers also.
In simple words, 1st angle projection and 3rd angle projection are the types of Orthographic Projection system which is used to project three-dimension objects into two-dimensional projection view.
Must Read: What Is Orthographic Projection
Orthographic projection works on the principle of projecting views to imaginary planes which are called reference planes. In 2D drafting, you can have two planes perpendicular to each other and normal to the human eye.
One plane is in the X- Direction and the other is in Y Direction. These two reference planes, when placed at the perpendicular, creates a four-quadrant where you can place a 3D object to project views.
What Is First Angle Projection
In the first angle projection, the object is placed in the 1st quadrant. The object is positioned at the front of a vertical plane and top of the horizontal plane. First angle projection is widely used in India and European countries.
In the first angle projection, the object is placed between the observer and projection planes. The plane of projection is taken solid in 1st angle projection.
What Is Third Angle Projection
In the third angle projection, the object is placed in the third quadrant. The object is placed behind the vertical planes and the bottom of the horizontal plane. Third angle projection is widely used in the United States.
In the third angle projection, the projection planes come between the object and observer. The plane of projection is taken as transparent in the 3rd angle projection.
Difference between first angle projection vs third angle projection
We all might know that in Orthographic Projection there are mainly six views ( Front, Back, Top, Bottom, Right, Left). Out of these six views, three views ( Front, Top, Right) are important and most of the drawings usually have these three views.
First angle projection and third angle projection can be broadly differentiate based on a couple of criteria as mentioned below.
Object Placement
In the first angle projection, the object is placed between the object and projection planes. In the third angle projection, the object is placed behind the projection planes.
Projection Plane Placement
In the first angle projection, the projection planes are at the behind and bottom of the object. In the case of third angle projection, projection planes are front and top of the object.
Symbol
When you look at a drawing, for a moment you may not diagnose whether it’s a first angle projection or a third angle projection. The only way to figure it out is by looking at the projection symbol. It’s a mandatory requirement for drawing to have a projection symbol.
View Placement
The view Placement differs in 1st angle projection and 3rd angle projection due to the different positions of projection planes. But before that, we should know the rule of Orthographic Projection
The Orthographic Projection states that you have to virtually rotate the horizontal plane clockwise to project the views in a 2D drawing.
In the first angle projection, the front view is placed above the unfolded line and the top view is placed below. The right side view is placed on the left side of the front view. The left side view is placed on the right side.
In the third angle projection, the front view is placed below the unfolded line and the top view is placed above. The right side view is placed on the right side and the left side view is placed on the left of the front view.
Snippet Of 1st Angle Projection Vs 3rd Angle Projection
| First Angle Prpjection | Third Angle Projection |
|---|---|
| Objects are placed in 1st Quadrant | Objects are placed in the third quadrant |
| Projecion planes comes behind the object | Projection planes shows up front of object |
| Plane of projection is non transparent | Transparent plane of projection |
| Front view is at the top of the horizontal axis | Front view at the bottom of the horizontal axis |
| Top view at the bottom of the horizontal axis | Top view at the top of horizontal axis |
| Right view is at the left side of vertical axis | Right view is at the right side of vertical axis |
| Left view is at the right side of vertical axis | Left view is at the left side of vertical asxis |
| Preffered choice in India and asian countries | Widely used in United State and Australia |
Conclusion
To sum up, first angle projection and third projection are just two types of orthographic projection types that are widely used to create a two-dimensional drawing. These are standards that every company follows so that they don’t face any issues in communicating the design intent across the globe.
If you have any questions regarding first angle projection vs third angle projection, then do ask in the comment section and I will be happy to respond. Also if you do feel that I missed something to add here, you can raise that in the comment section.
