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Stokes Al
#4
Apr3-08, 06:02 PM
P: 2
First angle,third angle projection

I disagree with the statement that there are no real advantages or disadvantages to using first angle or third angle projection. Third angle projection is simpler to use than first angle projection for the reasons given below.

In engineering college I used the first angle projection for several years. Immediately after graduation, I came to the United States and had to use third angle projection exclusively.

Pretend that the object to be drawn is inside an opaque box in the first angle projection and inside a transparent box in the third angle projection.

In the first angle projection, you have to go inside the opaque box to draw the object. What is seen, you project and draw onto the wall at the rear of the object. It is like putting the object between you and the blackboard. What is seen, you project and draw onto the blackboard. Finally, to get the six views, the box is cut flat as you like.

On the other hand, in the third angle projection, you stay outside the transparent box to draw the object. You draw what you see on the transparent box. (In computer jargon:
WYSIWYG - What You See Is What You Get). It is like putting the object to be drawn behind a tracing glass table. You simply draw what you see. Finally, to get the six views, the box is cut flat as you like.

Second and fourth angle projection would be a hybrid of the above two. It would require a box with three faces opaque and three faces transparent. This would be confusing and disadvantageous.

As they say, think outside the box!!!