6 Replies Latest reply on Jul 23, 2017 4:39 PM by Maha Nadarasa

    Conventions and Drawings

    Maha Nadarasa

      Either first angle projection or third angle projection is a convention to place a view in the drawing sheet. But I have seen videos these conventions are violated.

       

      Are these conventions not mandatory?

       

       

      1.png

        • Re: Conventions and Drawings
          Dave Bear

          It depends on the drafting standards you are using Maha.

          Without getting too technical, ANSI is basically the American Standard and uses Third Angle projection, whilst ISO is the European Standard and uses the First Angle projection.

           

          Caution needs to be used with not getting the two confused or mixed as this could lead to parts becoming manufactured wrong from the drawing. (I've only just learnt about this myself)

           

          Dave.

          • Re: Conventions and Drawings
            J. Mather

            The 2D views in both images that you attached appear to be classical 3rd angle orthographic projection to me.  I do not see any violation of standards.  (Well I would have re-sequenced the section designations in the drawing on left.  One of my pet peeves is when users make a mistake and remove an earlier section and then don't reset the section labels.  Lazy!)

            (You might reference ANSI/ASME standard.)

             

            Keep in mind that back in the last century on the drawing board with pencil and paper - creating isometric views would be very expensive (time consuming and challenging) and not usually done.  In the 3D world of modern CAD - these views are "free".

             

            Here is a way to test yourself to see if you really understand orthographic projection - ask someone to print out some drawings with the isometric views removed.  Now see if you can visualize the geometry and create the model in SolidWorks solely from 2D orthographic views (no "3D" isometric views).

             

            Edit:

            Building on this idea of generating models strictly from 2D orthographic views -

            because I normally work in 3rd angle projection I am initially confused when looking at a 1st angle projection drawing.  But I would expect any competent machinist to recognize the true design intent even if they had never seen a 1st angle (or for the machinist used to 3rd angle, the other way around) and create the correct geometry - at least for simple parts like these.

             

            I probably have both 1st angle and 3rd angle examples from the drawing board (no isometrics) if you would like to test yourself without YouTube step-by-step instruction.

              • Re: Conventions and Drawings
                Maha Nadarasa

                Third angle projection

                Third angle projection.png

                 

                I assume that, view that is not giving any details is being avoided.

                1.png

                 

                I assume that isometric view is given to visualize a part in question. I do not think a complicated part can be visualized without an isometric view.

                  • Re: Conventions and Drawings
                    J. Mather

                    This view is labeled - it is SECTION B-B, not R side view?

                    Note that it is projected parallel/perpendicular to the cutting plane line B-B.

                    Note that the scale is different than the view from which it was projected and clearly labeled SCALE 2:1.Section View.png

                     

                     

                     

                    All of this is typically covered in a 1st semester design class and covered in great detail in any reputable book on the field of engineering design documentation.
                    I posted link to eBook that I use in earlier discussion.

                     

                    Giesecke et al. Technical Drawing with Engineering Graphics 15th Ed.

                     

                    Technical Drawing.png

                    Also see Chapter 22.

                • Re: Conventions and Drawings
                  Peter Brinkhuis

                  They are indeed conventions and not mandatory. First angle projection is used in Europe, but somehow mostly by France and Germany, the two stubborn countries. Here in the Netherlands we use third angle projection or American projection.

                   

                  That being said, I have made hundreds of drawings in my first two years and no one noticed that the drawings were in first angle while the title block said it was in third angle I guess the isometric view is indeed a big help.