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Hi this sarath,

according to my knowledge there no much difference between first angle and third angle of projection, just only the difference in projections of the views on the the planes

first angle of projection: here object is placed in first quadrant it means object is placed in between the observer and the plane.what ever shape observed from the front u r going to project on the plane which is situated at back side of the object.

third angle of projection : here object is placed in first quadrant it means plane is placed in between the observer and the object. what ever shape observed from the front u r going to project on the plane which is situated in front of the object.

still if u didn't get clarity go through the below link

http://www.technologystudent.com/designpro/ortho1.htm

if u got more information about this topic please share with me.

CIDesigner likes this

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Difference between first angle and third angle method of projection:
1) In First angle method Object is assumed to be placed in First quadrant whereas in third angle method of projection, Object is assumed to be placed in third quadrant.
2) In First angle method Object lies between the projection screen and observer whereas in third angle method of projection, projection screen lies between the object and observer.
3) As a result, In First angle method, View from left is projected on right side and view from right is projected on left side.In third angle method, View from left is projected on left side and view from right is projected on right side.
Detailed Explaination is shown in Image...

I think that First angle method is a better practice and as a result it is mostly preferred. ( Projection screen lies rear to the object).
The symbol of first and third angle projections itself explains their significance. Symbol of first and third angle method of projection indicates a frustum of cone which is led horizontally on the surface.
In case of first angle method of projection, left view of frustum of cone is displayed on right side and in case of first angle method of projection, left view of frustum of cone is displayed on left side.
For more details, please visit:

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Engineering drawing is two-dimensional depiction of various phases of actual objects. To make engineering drawings meaningful and executable, different phases of an object are depicted in two-dimension and placed in a particular way using technique of Projection .... more.

pawar Digambar likes this

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The original question was, "Why is first angle method preferred over third angle?"

I think in the long run, it all comes down to local custom and tradition. Both convery the same information, so neither it truly superior to the other.

That said, there is one basis for a good selection that might tilt in favor of one or the other. It is desireable to minimize the number of hidden lines in a drawing, so if one method results in more hidden lines than the other, the second option is preferable.

Again though, I think it is a matter of familiarity, what we are all agreed upon, all of which is known as convention.

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My perspective is.. Third angle offers the view as you would see the object from that side. i prefer third angle. It has a logic to it.

The image of a previous video explains itself. with First Angle it's Bottom view at the Top, Left view at the right, and vice versa for both. Wheres the sense of it?

 

Ist Angle.JPG

Edited by Vic Baylis

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In first angle projection the object is assumed to be placed in first quadrant(The front view is coming above xy-line and top view is below xy-line).

In third angle projection the object is assumed to be placed in third quadrant(The top view is coming above xy-line and front view is below xy-line).

Any one type of representation can be followed. But internationally, presently first angle projection is preferred, the reason might be in first angle projection the object is directly visible but in third angle projection visualize through transparent planes.

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There really can't be a preferable projection because depending on the first (fornt presumably) view, the number of transparent lines can be the same, especially if you want more than the standard three views.

I prefer third angle because that's what I was brought up on... first angle projection is just 'foreign' to me.

In the end, it really depends on who your customers and suppliers are. If you're working with American, British, Australian, or New Zealand companies, you will most likely be working in third angle. If you're working with European customers or suppliers, you'll probably be working in first angle. In Asia, it's a complete mixed bag with the standards, because they are typically suppliers to the originator and will conform to whatever standard they're working with on the day.

 

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In first angle projection the object is imagined to be in  first quadrant and object is lies between observer and plane. Plane of projection  is non-transparent . Top view comes below front view( elevation ) , right side views drawn to left side of the front view( elevation)  when the views are drawn in their relative position 

In third angle projection the object is  placed in third quadrant and plane lie between observer and object .Plane of projection  is transparent . when the views are drawn in their relative position top view (plan) comes above front view ( elevation) and right side view drawn to the right side of the front view (elevation )     

Both  methods can be followed in practice  and it depends upon end customer requirement .

 

 

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What does it mean if the cone is reversed from what is shown above? Does that mean the part is reversed or does it matter? I have a European customer that uses first angle projection, but the cone is reversed from above.

First Angle.tif

 

I do not know if the tiff shows, it says I can not see it due to permissions.

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In fact, First Angle Projection is not preferred at all. It is a 19th century practice which has become Obsolete over 40 years ago. In First Angle Projection, the View of the Object from one side is shown on the opposite side. So View of the Object from Left side is shown on the Right side. View  of the Object from the Top - the Plan View - is shown Below the Object. Third Angle Projection is the No.1 Default Choice in Engineering Drawing for over 50 years now. In Third Angle Projection, every View of the Object is placed on the side from which it is viewed. So Plan View is placed Above the Object, Left View is placed on the Left side of the Object, and so on. 

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Well being an engineer our aim is to made the job in easy and in cheaper cost as consider 1st angle  the job is in between plane and observer so it n easy task to work out but in 3rd angle the plane is in between observer and job so 1st angle drawing is an easy task 

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On 1/3/2015 at 9:01 PM, Sarath Chandra_26602 said:

Hi this sarath,

according to my knowledge there no much difference between first angle and third angle of projection, just only the difference in projections of the views on the the planes

 

first angle of projection: here object is placed in first quadrant it means object is placed in between the observer and the plane.what ever shape observed from the front u r going to project on the plane which is situated at back side of the object.

 

third angle of projection : here object is placed in first quadrant it means plane is placed in between the observer and the object. what ever shape observed from the front u r going to project on the plane which is situated in front of the object.

 

still if u didn't get clarity go through the below link

http://www.technologystudent.com/designpro/ortho1.htm

 

if u got more information about this topic please share with me.

Can you explain the symbol for first and third angle projection?

pawar Digambar likes this

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