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Difference Between First Angle Projection and Third Angle Projection
First angle projection and third angle projection are two methods used in technical drawing to create a two-dimensional representation of a three-dimensional object. These two methods are very similar, but they differ in the way the object is projected onto the drawing surface. In this essay, we will explore the differences between first angle projection and third angle projection, including their history, their use in industry, and the specific ways they project objects.
What is First Angle Projection?
This is one of the most common methods used to obtain engineering drawings, mostly for orthographic projections. Orthographic projection is a graphical method used to represent three- dimensional structures or objects into different perspective projection images called views. The orthographic view typically consists of the top view, front view, and the side view.
First angle projection is one of the methods used for orthographic projection drawings and is approved internationally except the United States. In this projection method, the object is placed in the first quadrant and is positioned in front of the vertical plane and above the horizontal plane.
What is Third Angle Projection?
This is another perspective projection method used to represent three-dimensional objects using a series of two-dimensional views. In third angle projection, the 3D object to be projected is placed in the third quadrant and is positioned behind the vertical plane and below the horizontal plane.
Unlike in first angle projection where the plane of projection is supposedly opaque, the planes are transparent in third angle projection. This projection method is mainly used in the United States and Japan stipulates the use of third angle projection schema for industrial designs for product fabrication.
Differences: First and Third Angle Projection
The main difference between first angle projection and third angle projection lies in the placement of the object in relation to the projection planes. In first angle projection, the object is placed between the observer and the projection planes, with the observer looking through the object to see the planes. This means that the object appears inverted on the drawing surface, with the top of the object appearing at the bottom of the drawing and the bottom of the object appearing at the top of the drawing. In contrast, in third angle projection, the object is placed behind the projection planes, with the observer looking directly at the planes. This means that the object appears right-side-up on the drawing surface, with the top of the object appearing at the top of the drawing and the bottom of the object appearing at the bottom of the drawing.
Another difference between first angle projection and third angle projection is the location of the views on the drawing. In first angle projection, the views are placed on the opposite side of the object from the observer, which means that the views are placed above and to the left of the object on the drawing surface. In contrast, in third angle projection, the views are placed on the same side of the object as the observer, which means that the views are placed above and to the right of the object on the drawing surface.
There are several practical considerations that determine which projection method is used in industry. One consideration is the standard in the region where the object is being produced or manufactured. In Europe, first angle projection is the more commonly used standard, while in the United States, third angle projection is the more commonly used standard. Therefore, an American company manufacturing a product for sale in Europe would need to create technical drawings using first angle projection to meet European standards.
Another consideration is the size and complexity of the object being projected. For smaller objects with simple geometries, either projection method can be used. However, for larger objects with more complex geometries, third angle projection is often preferred because it allows for easier visualization of the object's features and dimensions. This is because the object is projected in the same orientation as it appears in reality, which makes it easier for engineers and designers to understand the object's geometry.
The following table highlights the major differences between First Angle Projection and Third Angle Projection −
Characteristics |
First Angle Projection |
Third Angle Projection |
|---|---|---|
Basics |
First Angle Projection is one of the ways of representing three- dimensional objects with respect to two dimensions which is commonly used in Europe and most of the world except the United States. For getting orthographic views from 3D objects, we divide the plane into four quadrants. The object is placed in the first quadrant for the first angle projection. |
United States and Australia uses the Third Angle Projection method as their default projection system. The object is placed in the third quadrant for the third angle projection. |
Representation |
Both are schemas used for multiview projection of three- dimensional objects using a series of two-dimensional drawings. The principal planes of an object are used to project different views of the same object from different points of sight. Overall six different sides can be drawn consisting of six orthographic views called as principal views. To get the first angle projection, the object is placed in the first quadrant meaning it’s placed between the plane of projection and the observer. |
For the third angle projection, the object is placed below and behind the viewing planes meaning the plane of projection is between the observer and the object. |
Plane |
Both methods of orthographic projection result in the same six principal views of the object except the arrangement of views and the state of plane of projection. In the first angle projection schema, the plane of projection is believed to be opaque or non-transparent. The object is placed in front of the planes and each view is pushed through the object which places the vertical plane behind the object and pushes the horizontal plane underneath. |
In the third angle projection method, the plane of projection is transparent and the object is placed below the horizontal plane and behind the vertical plane. |
View Sequence |
In the first angle projection method, the orthographic view is projected on a plane located beyond the object and the observer is on the left side of the object and projects the side view on a plane beyond the object. The right side view is projected to the left of the front view and the top view is projected onto the bottom of the front view. |
In third angle projection, the observer is on the right side of the object and the orthographic view is projected on a plane located between the view point and the object. The right view is projected onto the right side of the front view and the top view is projected above the front view. |
Conclusion
In conclusion, first angle projection and third angle projection are two methods used in technical drawing to create two-dimensional representations of three-dimensional objects. They differ primarily in the placement of the object in relation to the projection planes and the location of the views on the drawing surface. The choice of projection method depends on regional standards and the size and complexity of the object being projected.
By understanding the differences between these two methods, engineers and designers can create accurate and detailed technical drawings that meet industry standards and facilitate the manufacture of high-quality products.
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