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Mechanical

Uploaded on

18 Aug 2022

Projections Methods in CAD Drafting

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Skill-Lync

Drafting is also spelled as draughting, is popularly known as an engineering drawing. Drafting is the process of representing an object or idea through lines having various thicknesses and makeups.

 

Classification of Drafting: 

  1. Based on the usage of drafting
    1. Furniture drafting
    2. Architectural drafting 
    3. Mechanical or machine drafting
    4. Electrical and electronics drafting
    5. Structural drafting and sheet-metal drafting, etc.,
  2. Based on the function of drafting
    1. Manual drafting
    2. Computer-Aided Drafting or Designing (CAD)

 

Advantages of Manual Drafting:

 

Low Cost of Drafting Equipment: Manual drafting is created by using drafting equipment like a Pencil, Scale, Mini-Drafter, Compass, etc. The cost of drafting equipment is less compared to CAD Software Packages.

No Cutting End Technology Required: Unlike CAD Systems, you don’t need to maintain the systems with expensive maintenance services. Maintaining the Pencil and Paper is easy to do.

No Need for Subscriptions:  In the manual drafting we are not going to use CAD software. If we use CAD software, we need a subscription for the same. It will improve the cost involved in the process.

No training required: Apart from the training which we get while studying, there is no need for the designers to teach the CAD packages being used.

 

Advantages of CAD drafting:

 

Quality of Design: The CAD software has different tools to create drawings accurately as per the requirement. The quality of the CAD is better compared to Manual drafting.

Easy for Documentation: For manual drafting, we have to maintain a lot of documents. Handling and maintaining the document is a very difficult process in manual drafting. But, in CAD drafting, saving and sharing the documents is very easy. Documents can be saved in the local storage or in the cloud storage.

Modify and Reproduce Faster: Modifying the existing drawing and reproducing the drawing is very easy in CAD drafting. It is very complicated in the Manual drafting process.

Ability to Create a Drawing from 3D Models: In CAD drafting you can directly import any 3D CAD model you can create different views like Front, Side & Top, etc. in CAD drafting.

Following the Standards: Different standards are available in CAD drafting. Based on the standard which you are selecting the views and annotations are automatically added. But, In Manual drafting, you have to know about all the standards. Only then you can create proper drafting.

Time Consumption: The time consumption in CAD drafting is very less compared to manual drafting. Since most of the process is automated by tools CAD drafting will take very less time.

Use of Projections in Drafting:

  • Projection is used to represent the Complex 3D object in the 2D drawing sheet.
  • Projection is used to show the Shape and Size of the object in the Drawing or Drafting sheet.

Definition of Projections:

As an object, it has three dimensions length, width and height. The shapes and size of the object to be represented on a sheet, which has only a two-dimensional plane.

For obtaining the image of an object, various points on the contour of the object are projected on the drawing sheet by means of straight lines and curves. The figure formed by joining various points thus obtained on the plane is the image of the object and is called Projection.

We can define it as “To draw a 3D image on the 2D plane we use various contour points on the objects, plot various plane points, visual rays, straight lines, therefore, image obtained by such plot points on various points on a single 2D plane is known as Projection”.

 

Types of Projections in Drafting :

 

 

1) Parallel Projection:

  • It is a type of projection in which the lines/rays never intersect with each other.
  • The distance between the centre point of projection (COP) and the Projection point (PP) in the parallel projection is infinite.

 

 

1.1. Orthographic Projection:

  • A way to project the views on a 2D plane surface in which the projection lines are perpendicular to the surface.
  • The orthographic projection consists of projecting the essential views in a single plane.
  • The orthographic projection technique can produce either pictorial drawings that show all three dimensions of an object in one view or multiple views that show only the two dimensions of an object in a single view.

 

 

1.1.1. Multi-View Projection:

  • When more than one projection plane is used, the result is a multi-view projection.
  • Multiple projection drawings are based on the principle of orthographic projection. The views in the projection are arranged in a systematic order.
  • Projection lines are perpendicular to the plane of projection in this type of projection. Establishing an object’s height, length and width requires different views like the front, side and top views.
  • These views are created by the use of principal planes of projections. The below diagram shows the principal planes of projection.

 

 

here are two types of Multiview projection. They are given below,

  1. First Angle Projection
  2. Third Angle Projection

 

1.1.1.1. First Angle Projection:

  • The First angle or First quadrant in the principle plane of projection is used for first angle projection.
  • The following example shows the first angle projection. The front of the object is facing toward the vertical plane of projection. In the first angle projection, the front view is projected on the vertical plane, the top view on the horizontal plane and the side view on the profile plane.

 

 

In the first angle projection, the plane is beyond the object. The images show the place of the object and plane. The observer initially looks at the object the projection is projected on the plane.

As per the consideration of the drawing sheet, the six different views in the drawings are created as per the image given below,

 

 

 The common European drafting practice is first angle projection. First-angle projections are not commonly used in the United States.

 

1.1.1.2. Third Angle Projection:

  • The Third angle or Third quadrant in the principle plane of projection is used for third angle projection.
  • The following example shows the third angle projection. The front of the object is facing toward the vertical plane of projection. In the third angle projection, the front view is projected on the vertical plane, the top view on the horizontal plane and the side view on the profile plane.

 

 

In the third angle projection, the plane is before the object. The images show the place of the object and plane. The observer initially looks at the plane and the projection is projected on the plane. The plane of the position is assumed transparent in this projection.

As per the consideration of the drawing sheet, the six different views in the drawings are created as per the image given below,

 

 

The following are the annotation symbols used in the drafting to annotate the projection method used.

 

 

1.1.2. Axonometric Projection:

     Axonometric means “to measure along axes”. It is a type of projection used to draw an object when it is rotated in one or more of its axes related to the plane of projection. It has three types. These include,

  1. Isometric
  2. Dimetric
  3. Trimetric

1.2. Oblique Projection:

     Oblique Projection is a method of drawing an object a face parallel to the plane of projection as it is and the other face is drawn at any convenient angle except 90 degree. It has three types of projection. Thus are given below,

  1. Cabinet Projection
  2. Clinographic Projection
  3. Cavalier Projection

 

 

1.3. Perspective Projection:

     It is a way of projection in which the projection is drawn based on the perception of the observer. The near face of the object looks larger than the far one. This type of projection image looks realistic.

 

 

In this article, we have learned about Projection in drafting and different types of projections with suitable examples.


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Navin Baskar


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Skill-Lync

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