Why first angle and third angle projection method is used in machine design and why second and fourth angle method is not used?
Aditya Korde commented on saurabhjain's blog entry in Mechanical Engineering QuestionsHi, It is very simple, first consider this, 1.viewer's position is fixed. that is at right corner looking towards left for front view and at topside looking down for top view, 2. picture planes(p.p.) are either transparent or opaque , not mixed. so if you are considering p.p. as opaque then only first view can be drawn as object is visible from both sides in first quadrant only and not in any other ( for second quadrant vertical opaque plane is between object and viewer hence front view can not be drawn & for fourth quadrant opaque horizontal plane is between object and viewer hence top view cant be drawn. hence in first angle where p.p. are opaque only first quadrant can be used same logic is applied to third angle where p.p. are transparent. (note changing viewer's position will also change the orientation of quadrants. Aditya Korde