First Angle vs. Third Angle Projection in Engineering Drawings: A Complete Guide

In the world of engineering, precise communication is critical, and technical drawings are one of the main ways this is achieved. Two of the most commonly used projection methods for creating these drawings are First Angle Projection and Third Angle Projection. These systems are integral to ensuring that everyone involved in the design and manufacturing process interprets the drawings in the same way. In this blog post, we’ll explore the key differences between these two types of projection, how they are used, and where each is most commonly applied.

What is Projection in Engineering Drawings?

Projection refers to the method of visually representing a 3D object on a 2D plane. In engineering drawings, projections are used to create the orthographic views of objects, allowing different perspectives like the front, top, and side views to be visualized clearly. These views give manufacturers, engineers, and designers the information they need to understand the dimensions, structure, and details of an object.

Orthographic projection can be done in various ways, but two of the most recognized standards are First Angle Projection and Third Angle Projection.

First Angle Projection

Definition:

In First Angle Projection, the object is placed between the observer and the projection plane. The views are then projected onto planes that are arranged around the object in a way that mirrors the object’s orientation.

Characteristics:

• Layout of views: In First Angle Projection, the top view appears below the front view, the left view is placed to the right of the front view, and so on. The views are essentially flipped in terms of their actual position relative to the object.
• Placement of planes: Here, the object is in the first quadrant. The projection planes are imagined to be transparent, and the views are projected behind the object.
• Symbols: The symbol for First Angle Projection is a cone with the wider end facing the left and the narrower end pointing right.
• Standard use: This method is used primarily in European and Asian countries, including India, France, and Germany.

Example:

If you want to see the top view of an object, you would imagine looking at the object from above, but the resulting view will be placed underneath the front view in the drawing. Similarly, the left side view will be positioned on the right-hand side of the front view.

Third Angle Projection

Definition:

In Third Angle Projection, the object is placed between the projection plane and the observer. The views are projected onto the planes placed around the object in a more intuitive layout.

Characteristics:

• Layout of views: In Third Angle Projection, the top view appears above the front view, the left side view is placed on the left of the front view, and so on. This layout closely resembles how the object is actually positioned in real space.
• Placement of planes: In this method, the object is in the third quadrant, meaning the projection planes are placed between the object and the observer. The views are then projected forward onto the plane.
• Symbols: The symbol for Third Angle Projection is a cone with the wider end facing the right and the narrower end pointing left.
• Standard use: This projection method is commonly used in the United States, Canada, and some other countries.

Example:

If you’re observing the top view of an object in Third Angle Projection, it will appear above the front view in the drawing, aligning more naturally with how you would visualize the object.

Key Differences Between First Angle and Third Angle Projection

AspectFirst Angle ProjectionThird Angle ProjectionPosition of the objectBetween the observer and the projection planeBetween the projection plane and the observerView arrangementTop view is below the front view, right view is on the leftTop view is above the front view, right view is on the rightCommon usageEurope, Asia (ISO Standard)USA, Canada (ANSI Standard)SymbolCone facing leftCone facing rightQuadrantFirst QuadrantThird Quadrant

How to Interpret Symbols for Projections

Symbols in engineering drawings indicate the type of projection used. Understanding these symbols ensures that engineers and manufacturers can accurately interpret the drawing, no matter where they are located globally.

• First Angle Projection Symbol: A truncated cone with the wider end on the left.
• Third Angle Projection Symbol: A truncated cone with the wider end on the right.

These symbols are typically placed in the title block of the drawing, helping users quickly identify the type of projection used.

Practical Applications

Both projection methods have their place in the engineering world, depending on regional standards and conventions.

• First Angle Projection is often the default in European and Asian countries, making it standard in industries like automotive and heavy engineering across these regions.
• Third Angle Projection is prevalent in North America, particularly in aerospace and mechanical design industries, where ANSI (American National Standards Institute) standards are followed.

Global collaboration in engineering often means engineers need to be familiar with both projection methods, as different projects may adhere to different standards.

Conclusion

Understanding the distinction between First Angle Projection and Third Angle Projection is essential for anyone involved in engineering design and manufacturing. Both methods are correct and functional, but their use depends on regional standards and industry conventions.

If you're working on international projects, becoming proficient in both projection methods ensures effective communication and interpretation of engineering drawings across different regions. Always check the projection symbol on your drawing to avoid any confusion, and you'll be well-equipped to navigate global engineering standards seamlessly