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Why first angle and third angle projection method is used in machine design and why second and fourth angle method is not used?



Why first angle and third angle method is used and why second and fourth angle method is not used?



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Dear all,  the geometry of all quadrants remain same.

But , when it needed for calculation of geometrical as well as physical property, the values are in ii angle is -x & +y, as viceversa reverse in iv angle is +x & -Y.  This coordinates of the object in I angle and III angle are same, Either negative or Positive, which makes calculation easy and understandable with meaning full. 

That is the why we used I angle and III angle.

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On 10/24/2015 at 1:56 PM, Syed Abdul Rafay Hammad said:

It doesn't matter which angle of projection is used because 2nd and 4th angle projection will resemble with 1st and 3rd


It matters at the time of calculation of the geometrical as well as physical properties of the object, as the coordinates sign are different.

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                          It is a good question. As most of the people said the overlapping could be avoided in first and third angle projection. Depends upon the requirement of our designing portion and application or requirement we can select any quadrant.  For example, if I need the layout of the car bottom area I can select third angle projection.   We can use even second angle projection to go for matching the two projections by overlapping it. 

chassis-frame-underbody-bottom-view-stock-photo_csp47243941 (1).jpg

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allow me to first introduce the law of quadrants , sin and cos create the basis of our visualization . 0 to 90 being contain all (sin and cos) and also 180 to 270 contains tan (which is sin/cos) but 90-180 and 270-360  .  in 2nd and 4th  all our visualizations are affected. So they can not be  use in Engineering Drawing.

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