3D CAD models are represented using 2D views in drawings by different projection schemes. Horizontal and vertical projection planes divide the space into four quadrants. The object is imagined to be in 2 different quadrants i.e. first quadrant and third quadrant. The second quadrant and fourth quadrant are not used because of overlapping images/views generated while unfolding the imaginary projection box.
Separate drawing symbols are used to mention the projection scheme used in each and every drawing. This symbol is included in the title block of all drawings. Since nobody creates engineering or technical drawings using drawing tools like rulers and drafting machines these days, drafting engineers do not even care to understand the projection types.
Nowadays, parts are made in 3D using any CAD software and the same software generates the 2D drawings using the projection type that was setup. The only place it becomes critical is when the production engineers read the 2D drawings to manufacture a part/assembly etc.
Because of these easy to use CAD software, many engineers forget the correct symbols used for the first and third angle projections. Since the difference between these symbols are very minimal, it is important to remember the correct symbol.
I have explained an easy way to remember these symbols in this article.
Note: There is no engineering logic behind this explanation. I will just let you know what I imagine to remember the first angle projection symbol easily.
Imagine an observer looking at the car using binocular that is moving towards him. This single image is what I imagine to remember the symbol correctly. You will understand why I chose a moving car instead of any stationary object while reading the article Third Angle Projection Symbol – What is it – How to remember.
Now, replace the moving car with two concentric circles and the observer and binocular with a binocular icon or the front view of the conical frustum. Add the center lines and now you get the symbol for the first angle projection.
Remember the front view of the conical frustum represents the shape of the binocular directly i.e. Larger end at the right side and the smaller end at the left side.
If you remember the scene I just explained, you will never forget the correct symbol again..!
Read about third angle projection here
That’s all for this topic. Thanks.