Technical Graphics - Projection Systems - Orthographic

3^rd Angle Projection

3^rd Angle Orthographic Projection is used mostly in the United States but it is also very useful to know in this part of the world, especially with the improvements in communication.

If we go back to our "Glass Box", for 3^rd Angle Projection the object is placed in the third section of the box.

Now if we remove the external panes of "glass" we are left with the vertical and horizontal planes between us and the object.

We project the points and edges of the object in the same way as we did with 1^st Angle Projection but as you can see in the next picture the box we are left with looks quite different.

With 1^st Angle Projection we folded the box away from us so that it was flat, but in this case we fold the box toward us. So the red section is at the top of the drawing as in the picture below.

So now you have the 3^rd Angle Orthographic Projection of the object.


Do you think there's much of a difference ?

Well there is, with 3^rd Angle Projection whatever side of the object the drawing is on is the side that is being viewed. If you check back to 1st Angle projection you may notice the difference.