Types Of Projection In Engineering | First Angle And Third Angle Projection

ENGINEERING DRAWING

Engineering drawing is a graphical language, a concept developed by a designer in a 2D paper with the required features, attributes, and dimensions.

Here are some common types of mechanical engineering drawings:

Orthographic Drawings: These are the most fundamental mechanical drawings, showing the object from different views (front, top, side, etc.) to provide a clear and comprehensive representation.

Isometric Drawings: These drawings represent a 3D object in a 2D format, often at an angle, to provide a more realistic and visually informative view.

Exploded Assembly Drawings: These drawings show an assembly of parts with components separated and spaced apart, making it easier to understand how they fit together.

Sectional Views: Sectional views are used to show the internal structure of an object by cutting it along a specific plane and revealing its hidden features.

Detail Drawings: These drawings provide specific information about a single part or component of a larger assembly. They often include detailed dimensions, tolerances, and notes.

Orthographic Drawings: These are the most fundamental type of mechanical drawings, showing the object from different views (front, top, side, etc.) to provide a clear and comprehensive representation.

Isometric Drawings: These drawings represent a 3D object in a 2D format, often at an angle, to provide a more realistic and visually informative view.

Exploded Assembly Drawings: These drawings show an assembly of parts with components separated and spaced apart, making it easier to understand how they fit together.

Sectional Views: Sectional views are used to show the internal structure of an object by cutting it along a specific plane and revealing its hidden features.

Detail Drawings: These drawings provide specific information about a single part or component of a larger assembly. They often include detailed dimensions, tolerances, and notes.

Pictorial Drawings: These drawings, including axonometric, oblique, and perspective drawings, offer a more artistic and visual representation of an object, which can be useful for presentations and conceptual design.

Tolerance Stack-Up Analysis: These drawings focus on defining the allowable variations in dimensions and clearances within an assembly to ensure proper functionality.

Surface Finish and Geometric Dimensioning and Tolerancing (GD&T) Drawings: These drawings specify surface finish requirements and geometric tolerances for parts, ensuring their quality and functionality.

Type of PROJECTION                                    

In mechanical drawing and engineering graphics, "projection" refers to the method used to create two-dimensional representations of three-dimensional objects. The primary purpose of projection is to convey the shape, size, and spatial relationships of an object accurately on a flat surface, such as a piece of paper or a computer screen. Basically, there are three types of projection but in mechanical engineering drawing, we use commonly two types of projection.

• Orthographic projection
• Oblique projection
• Perspective projection

ORTHOGRAPHIC PROJECTION
Orthographic projection, also known as "Multiview projection," is the most common method for creating two-dimensional representations of three-dimensional objects. In this method, an object is projected onto a series of planes (usually perpendicular to each other) to create multiple 2D views. The typical views include front, top, side, and sometimes bottom and rear views. Each view represents the object as if you were looking at it from one particular direction. By combining these views, you can accurately depict the object's shape and features in a comprehensive manner.

FIRST ANGLE PROJECTION

First-angle projection is one of the two primary methods used for creating orthographic projections, which are 2D representations of 3D objects in engineering and technical drawings. The object is placed in the first quadrant, between the observer and the projection plane.

here are some points that must be kept in mind

• First angle projections are found in the first quadrant.
• The objects are found between the observer and the plane of projection.
• When we rotate the horizontal plane in a clockwise direction, the front comes after the top view.
• When views are drawn their relative position top view comes below the front view and a right side view is drawn to the left side of the elevation same as the left side is drawn to the right side of the elevation.
• In a first angle, the plane of projection is considered as a non-transparent plane.
• the first angle projection is generally used in European countries and India.
   

THIRD ANGLE PROJECTION

In third-angle projection, the object is placed in the third quadrant of the viewing planes. The object is positioned behind the projection planes, and the views are created by projecting lines of sight from the object to the projection planes. These projection planes are typically placed between the viewer and the object, and multiple views (such as top view, front view, and side view) are created to represent different aspects of the object's shape and features.

Here is brief summary of the third-angle projection.

• Object Placement: The object is located behind the projection planes.
• Projection Planes: The projection planes are positioned between the viewer and the object.
• Views: Multiple views are generated to depict different aspects of the object's geometry and features.
• when view are drawn their relative position  front view comes below the top view and the right side view drawn to the right side
• Elevation and left side view is drawn to the left side of the elevation.   
• The plane of projection is considered as transparent plane.
• Generally, these angles are used in the USA.

Why do we not use second-angle projection and fourth-angle projection?

When we rotate the horizontal plane in clock wise direction then the top view and front view overlap to each other why we do not use the plane . But sometimes this second-angle projection and third-angle projection are used in civil engineering drawing.

Axonometric projection

In axonometric projection, the object is oriented in such a way that all three principal axes (usually the X, Y, and Z axes) are equally foreshortened. This means that the object's depth, width, and height are all represented at the same scale and without distortion. There are several common types of axonometric projections.

Basically, it is found in three types

1) Isometric Projection: In an isometric projection, all three axes are foreshortened equally at 120-degree angles from each other. This results in a drawing where the object's edges are all parallel and equally spaced.

2) Dimetric Projection: Dimetric projection uses two of the three axes with different foreshortening ratios, while the third axis remains true to scale. This creates a drawing where two sets of edges are parallel, and one set is not.

3) Trimetric Projection: Trimetric projection involves three different foreshortening ratios for each of the three axes, resulting in a drawing where none of the edges are parallel.

Axonometric projection is widely used in technical and engineering drawings, as it provides a clear and accurate representation of objects' dimensions and relationships, making it easier for designers, engineers, and architects to communicate their ideas effectively on paper or computer screens.

OBLIQUE PROJECTION

Oblique projection is a method of creating two-dimensional representations of three-dimensional objects in which the object is displayed with one axis (usually the vertical axis) in true scale and the other two axes are foreshortened at an angle to the viewer's line of sight. This results in a 2D drawing that conveys the appearance of depth and dimension without strict adherence to orthographic projection or the isometric projection's fixed 45-degree angles.

There are two main types of oblique projection:

Cavalier Projection: In cavalier projection, the depth axis (usually the z-axis) is projected at full length without any reduction. This results in a more pronounced sense of depth in the drawing but may not accurately represent the relative sizes of objects along different axes.

Cabinet Projection: In cabinet projection, the depth axis is foreshortened by a certain factor (commonly 0.5), which makes the drawing appear less distorted and provides a more realistic sense of depth compared to cavalier projection.

As compared to orthographic projection, Oblique projection is a valuable tool for quick sketches and visualizations, but it is less precise than orthographic projection for conveying accurate measurements and dimensions. As such, it is often used in conjunction with other projection methods and isometric views to provide a comprehensive representation of an object.

PERSPECTIVE PROJECTION

Perspective projection is a method of creating two-dimensional representations of three-dimensional objects in a way that simulates the natural way our eyes perceive depth and spatial relationships. In perspective projection, objects that are farther from the observer appear smaller, and parallel lines appear to converge toward a single point called the "vanishing point." This technique creates a sense of depth, dimension, and realism in drawings or images.