Understanding First Angle Projection vs. Third Angle Projection in Engineering Drawings

First Angle Projection vs. Third Angle Projection in Engineering Drawings

The primary method of graphic communication utilized in engineering construction is multi-view orthographic projection.  

Engineering Drawings are used to communicate concepts, dimensions, shapes, and methods for the creation of an object or the development of a system. All descriptive geometry techniques are built on the orthographic projection. 

Multi-view or an Orthographic projection is a technique that can be used to fully describe an object’s shape and dimensions utilizing two or more views that are often projected at 900 to each other, or at specific angles. The completed drawing is then copied and delivered to the shop or job site. 

The orthographic projection system is used to illustrate a 3D object using parallel lines to project 3D object views onto a 2D plane. 

What is an Orthographic Projection?  

Orthographic Projection

Orthographic projections are a type of technical drawing in which different views of an object are projected on various reference planes while viewing perpendicular to each reference plane. 

The reference planes include:  

  • Horizontal Plane (HP) 
  • Vertical Plane (VP) 
  • Side or Profile Plane (PP) 

The viewpoints include: 

  • Top View (TV) – Projected on HP 
  • Front View (FV), Projected on VP 
  • Side View (SV) – Projected on PP 

There are two types of drawings that the orthographic projection technique can create:  

  1. Multiview drawings where each view depicts an item in two dimensions. 
  1. Axonometric drawings that display all three dimensions of an item in a single view. 

Often, a three-dimensional object must be precisely represented on a plane surface. Pictorial representations of a three-dimensional object on a plane are adequate only when the object is simple; however, for more complex objects, a different method of representation must be used to show the true shapes of their surfaces. 

Read Related >> Guide to Understanding Projections in Engineering Drawings

It can be seen by observing the shadows of objects cast by light sources that an object can be ‘projected’ onto a two-dimensional surface (i.e., a plane of projection) by projecting points of the object onto the surface and joining them in order. 

The orthographic projection system is used to illustrate a 3D object using parallel lines to project 3D object views onto a 2D plane.  

Projection systems – First Angle Projection vs. Third Angle Projection 

Projection systems in Engineering Drawings

The conventional three orthographic viewpoints of a part or assembly are visible in both third angle and first angle projection. The design of the component on the sheet is the primary distinction between the first angle and the third angle projection. 

What is a First Angle Projection in Engineering Drawings? 

First Angle Projection

One of the most popular ways to acquire engineering drawings, mostly for orthographic projections, is using this method. Orthographic projection is a graphic technique for converting three-dimensional objects or buildings into various views of perspective projection. The top view, front view, and side view make up the orthographic view most frequently. One technique for sketching orthographic projections is first angle projection, which is accepted everywhere else but in the United States. The object is positioned in the first quadrant, in front of the vertical plane, and above the horizontal plane using this projection technique. 

Characteristics of First Angle Projection in Engineering Drawings 

  • Typically used In Europe, India, and Canada 
  • The object is positioned in the first quadrant  
  • The object is positioned between the projection plane and the observer 
  • The plane of projection is opaque 
  • The top of the horizontal axis represents the front perspective 
  • The top view is at the base of the horizontal axis 
  • Right view is on the vertical axis’ left side 
  • Left view is on the right side of the vertical axis  

What is a Third Angle Projection in Engineering Drawings? 

Third Angle Projection in Engineering

A sequence of two-dimensional perspectives is employed in this perspective projection technique to depict three-dimensional objects. The 3D object to be projected is positioned in the third quadrant, behind the vertical plane and below the horizontal plane, and is positioned in third angle projection. The projection planes in third angle projection are transparent, as opposed to first angle projection, when they are supposed to be opaque. Japan requires the use of a third angle projection schema for industrial designs for product manufacture, and the United States is the primary country that employs this projection technique. 

Characteristics of Third Angle Projection in Engineering Drawings 

  • Typically used in the US and Australia 
  • The object is positioned in the third quadrant 
  • The projection plane is positioned between the object and the observer  
  • The plane of projection is transparent 
  • The bottom of the horizontal axis represents the front perspective 
  • The top view is at the top of the horizontal axis 
  • Right view is on the vertical axis’s right side  
  • Left view is on the left side of the vertical axis  

The undeniable reason for the importance of graphics or drawing is that it is the language of the designer, technician, sanitarian, and engineer, used to communicate designs and construction details to others. Graphics language is written in the form of drawings that depict the shape, size, and specifications of physical objects. The language is read by interpreting drawings so that physical objects can be built exactly as the designer intended. 

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