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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?

saurabhjain

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

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Dear Sourabh, very good question.

Just because of the norms we do this.

We consider that horizontal plane rotates in clockwise direction after having projection on it. that's why we use 1st angle and 3rd angle projection. because only in this two quadrants we will get the both views after clockwise rotation of horizontal plane.

Yes we can use second angle and fourth angle projection but in that case we need to rotate horizontal plane of projection in counterclockwise direction. Thus both 1st angle and 3rd angle projection will be replaced by 2nd angle and 4th angle projection.

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Dear sourabh,

very good job. Please promote this website as a good source of knowledge in the field of mechanical engineering. Some times the questions make us to think about the topics which are not present in any book.

Also I want to suggest you that please implement this website with spelling suggestions and correction during typing. we all type fast and this increase chance of mistakes during typing. So it should be better to have a right spelling suggestion while typing.

Regards...

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First and third angle projections depict a 3D object in a 2D yet second and fourth angle projections show one view of the object. In other words first and third angle projections are more elaborate than second and fourth angle projections.

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Dear ,

Really i am interested in the giving the answer but i am not sure of the answer, i am seeing such questions after 6 years, i am working in manufacturing side but never think of that. It will be a great contribution to my knowledge, i am happy to start learning once again.

 

Regards

Aftab

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First and third angle projections are more elaborate?

Well I have never heard that thing before, Could you please provide some documentation/citation.

Thanks

First and third angle projections depict a 3D object in a 2D yet second and fourth angle projections show one view of the object. In other words first and third angle projections are more elaborate than second and fourth angle projections.

Well I have never heard that thing before, Could you please provide some documentation/citation.

Thanks

Edited by TANEJA PARVESH

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There is a rule that hp must be rotated 90 degree clockwise.

This conveys a point

1) That if this happens, both  fv and tv coincides with each other in 2 and 4 angle projection ( both view come above or below x axis) as said by abdul karim.

hence both 2 and 4 angle projections are not possible.

still I have a doubt why should hp be rotated clockwise  and why it cant be anti-clockwise?

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From Wikipedia

Multiview orthographic projection

Excerpt:

In first-angle projection, the object is conceptually located in quadrant I, i.e. it floats above and before the viewing planes, the planes areopaque, and each view is pushed through the object onto the plane furthest from it. (Mnemonic: an "actor on a stage".)

In third-angle projection, the object is conceptually located in quadrant III, i.e. it is positioned below and behind the viewing planes, the planes are transparent, and each view is pulled onto the plane closest to it. (Mnemonic: a "shark in a tank")

 

  • In first-angle projection, the "top" view is pushed down to the floor, and the "front" view is pushed back to the rear wall; the intersection line between these two planes is therefore closest to the large end of the cone, hence the first-angle symbol shows the cone with its large end open toward the donut.  It is standard throughout Europe and Asia (excluding Japan
  •  
  • In third-angle projection, the "top" view is pulled up to the ceiling, and the "front" view is pulled forward to the front wall; the intersection line between the two planes is thus closest to the small end of the cone, hence the third-angle symbol shows the cone with its large end away from the donut. USA (ASME Y14.3-2003 specifies it as the default projection system), Japan (JIS B 0001:2010 specifies it as the default projection system) Canada, and Australia
  •  

File:Convention_placement_vues_dessin_te

FIRST ANGLE LEFT 3RD ANG RIGHT.png

FIRST ANGLE LEFT  & 3RD ANGLE RIGHT

CONVENTIONAL SYMBOLS

NOTED ON PRINTS TO INDICATE PROJECTION USED

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On 1/15/2015 at 9:24 PM, sibonelonxumalo said:

First and third angle projections depict a 3D object in a 2D yet second and fourth angle projections show one view of the object. In other words first and third angle projections are more elaborate than second and fourth angle projections.

will you please elaborate???

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Thank u sir please continue this...

second and fourth angle not used because in these projections are overlap (front &top) /(plan,elevation)

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Hi, It is very simple, first consider this,

1.viewer's position is fixed. that is at right corner looking towards left  for front view and at topside looking down for top view, 2. picture planes(p.p.) are either transparent or opaque , not mixed.

so if you are considering p.p. as opaque then only first view  can be drawn as object is visible  from both sides in first quadrant only and not in any other ( for second quadrant vertical opaque plane is between object and viewer hence front view can not be drawn & for fourth quadrant opaque horizontal plane is between object and viewer hence top view cant be drawn. hence in first angle where p.p. are opaque only first quadrant can be used 

same logic is applied to third angle where p.p. are transparent. (note changing viewer's position will also change the orientation of quadrants.

Aditya Korde

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Since I started Drafting I never considered the requirements of Angular placement, Of course in some cases it must be adhered to but in some cases the observer of the drawing is not familiar with the concept. when I do drawings of complex nature I name each view such as "View in Direction 'A'" and so on. with this method you can give a drawing to anybody and they will be able to interpret what the part looks like. Sections are generally handled in the same fashion, the direction of the arrow indicates the direction into the part you wish to show.

Wm. East

 

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Ah, once again, we have a communication gap!! When I look at the quadrant labels in the original question, I see that the labelling convention at at least some of you are familiar with is not the one I know. The labelling sequence shown in the question moves clockwise from the first quadrant; the convention that I (and I suspect others in the USA at least) am familiar with is the opposite. Thus, I would exchange the labels for the 2nd and 4th quadrant. Neither is more right or wrong than the other, but it points to the need to communicate carefully. If you say "Second quadrant" to me, I have to ask, "just what do you mean?"

As to why one system is used and not the other, I think it is purely a matter of convention and long accepted practice. We can use any view that is useful to show the necessary information about a part.

DrD
 

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I recall in my early years wondering about 1st and third angle projection. What happen to number two? To practice 3D CAD programs I use a 1947 drafting text book, first published in 1911. I found the best explanation of angle projections I have even come across. "First angle was the norm until 60 years ago. Now 3rd angle is the norm in the US and Canada." I am not sure if the 60 refers to the original 1911 printing or the 7th Ed (1947) that I have. Either way it was been around before all of us even the good DrD. I took a photo of the page. The section continues onto the next page but only adds that expensive mistakes have been made confusing the two systems. Now we make those expensive mistake confusing metric and imperial units. 

IMG_3441 (768x1024).jpg

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Hey, JAG ...

You're telling me that you think you have a book older than I am? Why, when I was learning to write, it was still done with a stylus pressed into damp clay (later to be fired); papyrus and ink had not yet been invented!

DrD

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As Mr Karim has rightly answered,In second and fourth angle projection viewing and projected plane are different than that of first and third angle projection,There is possibility that the one projection may overlap the other one creating confusion to understand the drawing.

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The reason why 2nd and 4th angle are not used is that all details except the outer perimeter will be hidden lines. Not much science about it, just that it will be completely confusing.

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First of all, we use first angle and third angle projection because it is assumed that the Horizontal plane is rotated CLOCKWISE to bring them in the same plane (for drawing purpose) and if we use second or fourth angle projection , then the Horizontal and vertical views will overlap , creating confusions in their ...

Firstly,you understand the concept behind the angle projection system.  
Imagine you have VP and HP(perpendicular to each other),now we have 4 quadrants. For 1st angle projection system, we place object in 1st quadrant, for 2nd angle projection system, we place object in 2nd quadrant and so on.

The observation is done from right as indicated in Figure.Once the F.V.(front view) and T.V. (top view) are obtained, to draw it in 2d we have to bring F.V. and T.V.  into V.P.  plane. The rule for this is we move the view in H.P. in clockwise direction. 
Now answer to your question. 
In 2nd angle projection system, object is in 2nd quadrant.The plane is in between object and observer. F.V. is in V.P. and T.V. is in H.P. towards 2nd quadrant.Then we rotate the view in H.P. clockwise and observe it from right. The F.V. and T.V. will overlap.
So it is not wise to use it. 
Same will be the case for 4th angle projection system, you try it the same way you will get that views will overlap.

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