 our friend Nallin Dhamelia of B 10 he lost his A 3 sheet in fact, two of them one was a blank sheet and the other one was the one that had lab 1 work. So, if anybody in B 10 B 11 or if anybody has found those sheets please written back to Nallin otherwise you can also go to the lab and see if they are there and if not then. So, the second announcement pertains to homework number 2 I have asked you to draw sketches three hand sketches. So, there are two possibilities possibility one is you can draw them on the respective A 3 sheets the second possibility is the sketch book what do you prefer who goes for sketch book A min poolers just your hand holding a pencil over a piece of paper all right and of course, the reason is quite obvious what is the reason all right, but just in case if it was not raining today quite a few of you might still have come late. So, this is this is a game that I tend to play at times. So, given a word I try to prefix an alphabet and try to make different words. So, let us do this. So, try to prefix an alphabet and try to make different words E elate sell down guys and then before that no no no no no no no no. So, the game is about prefixing a single alphabet are late that involves an E a single alphabet just a single alphabet that is what the trick is. So, looks like the only three words possible one is elate the other one is plate and the third one is slate. Now, this is what I want you guys to do next time we meet in class come up with a reason you guys are very good at that right. So, I am late because I am late because, but there is a little constraint here in your reason you have to use these three words elate plate and slate and try to come up with the funniest excuse that you can ever make. So, you have time until Monday Tuesday let us get started. So, we are discussing this example before you know I am really very glad that you have started thinking in class which is a very nice idea this is what I would want you guys to do all right sell down thank you. So, quite a few of you guys in fact quite some of you guys had questions about the drawing that we are discussing yesterday in particular you know. So, I had drawn an arc here of fillet if I may call and a fillet here and many of you guys said well I mean if there are two fillets here then this actually happens to be a smooth surface and correspondingly there would not be any line here here and here true. So, this was a doubt now. So, let me make or let me propose a few changes in the drawing let me propose a few changes in the drawing what I do is I let go of these arcs I have a line I extend vertical lines from these points and if this is the scenario then do you think that I will be getting the corresponding lines in the other two views. So, I will be getting the corresponding lines in the other two views, but think from a realistic viewpoint is it possible for you to manufacture an object with a 90 degree angle here and here yeah is it possible for you to manufacture this object with perfect 90 degree angles yeah so no realistically there would be a little curve there would be a little curve here and a little curve here. So, let us draw that a little fillet it is probably not so discernible just a little fillet, but the corresponding lines in the other two views will still remain all right any questions yeah tell me where are these lines can you show this model to me am I impressed or am I impressed well I spent 5 minutes discussing this you prepare this in 5 minutes ok almost 10 minutes not bad all right. So, just for your benefit since you have worked quite hard what I was saying was this was the initial drawing ok and if and for in fact this was a question that was raised by you. So, these this is like a smooth surface and correspondingly there would not be lines in the other two views make sense make sense, but what I am proposing is a slight revision what I am saying is what if I let go of these smooth curves have a horizontal line extend the circular arcs to these vertical lines and I get perfect 90 degrees then I will have those lines why not in this scenario are you going to be having those lines we will there is the theoretical aspect and there is the realistic aspect of the practical aspect ok practically it will be a little difficult for you to make a perfect 90 degree angle it will be difficult ok. So, practically what we do is you will actually be seeing surfaces like this just a little fillet just a little fillet assuming that these two angles are 90 degrees assuming that these two angles are 90 degrees in the front view you will actually be seeing those lines like a vision that I proposed ok alright. So, let us get started. So, today we will study first angle projection alright. So, you have done lap 2 with third angle projection and this is example 3 in orthographic views of very familiar object victory podium let us recapitulate what we did in case of third angle projection you had a plane in between you and the object you imagined that there were light bulbs all along the edge of the object that emitted light along three orthogonal directions ok. So, this was the plane on the right again in between you and the object on top again in between you and the object these are the lights the light rays falling on the vertical plane and this is what you would see if this plane was a photographic paper this is what you would be seeing from the top and this is what you would be seeing from the side you have done this before right let us consider the same object, but we will consider a different scenario we will say instead of the plane being between me or between you and the object the plane is behind the object. So, the object is placed between you and the plane. So, this is the vertical plane that is behind the object ok the horizontal plane is to be placed below the object and the profile plane is to be again placed behind the object all that has happened is the scenario has changed the location of the plane has changed relative to you in the third angle projection the plane was in between you and the object in the first angle projection the plane is behind the object and let us do the same exercise rays falling on the plane what will these rays capture what will these rays capture the light bulbs are here ok. So, these rays will essentially capture the loop that you see now note that the loop is coming from the front the loop is going on to the plane from the front not from the rear side of the object ok once again. So, what is the impression that the horizontal plane is going to see almost same thing the loop is going to come from here from the top surface of the object this one and this one once again it is coming from the top of the object how about this right. So, what is actually happening this plane is capturing what you are seeing from here ok this one is happening actually this plane is capturing what you are seeing from here this plane is capturing what you are seeing from the top not from the rear of the object, but from the top and this plane is capturing what you are seeing from here right ok let go the object retain the impressions on the three respective planes join these guys together with that boom tear this part off and unfold it is not from the other side if this is the direction of your frontal view that plane behind the object captures the impression of the object as if you are seeing the object from this side this one is from the top this one is from here ok. So, you need to be a little careful in trying to comprehend this once again join these guys together tear this part tear this hinge and unfold where is your front view now where is your top view now does not make sense right top view at the bottom which view is this the right side view you were seeing the object from the right. So, it is the right side view ok. So, it is always a nice idea for you to get the concept. So, that you do not have to remember and if you have to remember then this is a very simple golden rule that I used to follow when I did not understand this in the first angle the top is at the bottom of the front and the right is to the left of the front just the opposite ok, but this is the concept that is important be the third angle projection or be the first angle projection you have you have been working with third angle projection you have drawn the front view the top view on the side view ok. Now, can you answer this question to me or to yourself which of the three views is the most important which of the three views is the most important have you guys heard of something called FTP FTP fire transfer protocol nah does the front view top view on the profile view. So, which one is the most important view front well the choice is yours, but conventionally conventionally we choose the front view to be the most important view ok and having said that what do we do we choose the object or we choose the placement of the object in such a way that we are able to give as much details in solid lines not hidden lines in solid lines in the front view what we try to do is we try to minimize if not eliminate the hidden lines or the presence of hidden lines in the front view ok that choice is ours right. So, the front view is the most important then the top and then the profile hence FTP front top profile you know I have never gotten somebody agreed to me like that conquering with the song ok why is this called the first angle projection why is this called the first angle projection. So, if you imagine that your drawing is divided in four quadrants your front view which is the most important amongst FTP is lying in the first quadrant and hence it is called the first angle projection why is the third angle projection called the third angle projection there your front view is here in the third quadrant right ok. So, let us draw this object in the first angle projection would you like to take five minutes to sketch or to try to sketch ok now now now now. So, before you start sketching before you start sketching this is the front view direction and you have to rotate the object like this ok. So, rotate the object like this and then view from the front and then starts sketching five minutes. So, if I were to ask you to describe this object what would you say if I were to ask you to describe this object what would you say it is a disk of some thickness with four holes mutually orthogonal to each other and then there are two extensions which are so speak semicircular with two right a disk with four holes and then there are two extensions or two appendages slightly semicircular in nature each with two holes or two voids that is not very difficult for you to imagine right take two minutes you know back in 1990 when I was in the 12th grade we used to have this concept of the class monitor right. So, you have just graduated from there from grade school to grad school. So, our monitor then was Sanjay Tiwari and we used to talk a lot we used to prepare for our JEE exams and we used to talk a lot and he used to have a hard time I mean he used to come up with list of many many students disturbing the class and he gave the list to my class teacher and she goes like Amit Raje he was my classmate and Amit Raje is like all perplexed he stands up yes ma'am why were you talking ma'am I was not talking I was thinking ok sit down do not think loudly yeah. So, do not think loudly I did not want you to sketch that box should we start it is already 229. So, I still have about 20 minutes. So, let me let me get started ok. So, start with your bottom right box fill out the details fill out the details this is the first angle projection. So, your convention of representing the first angle projection will be different can you hear me back there am I discernible am I audible. So, the convention to represent the first angle drawing will be slightly different again fruncated cone your front view is two circles a set of concentric circles what is shown on the left is what which profile ok. So, the profile on the right is shown on the left. So, in the third angle projection this guy was here in the first angle projection this guy will be here if I were to draw the orthographic projections of this how many views will I use 2 3 1 2 why not 3 why not 3 the third is the same as the second. So, although we are practicing 3 views at this time later on you will probably realize that in certain situations 3 views are redundant at times just 2 views suffice and at times 3 views are adequate and at times even 3 views are not able to resolve the uniqueness in the object or uniqueness of the object. So, we have seen that cube example in our second lecture third lecture get this convention on the top right of the bottom right box place it down here let us get started using the scale 1 is to 2 most likely I am going to be using the scaled dimensions not the true dimensions. The first thing I would do is I would start with the bounding boxes once again I have rotated this object like so and that is my frontal view direction there is no finish line there is no finish line on your t-shirt alright was the length of this box length of this box what am I drawing there what am I drawing the front view was the length of this the same as the diameter of the big circle which is 124 524 what is the width of this box or the height that is 10 plus 25 whatever this length is how much is that 25 plus 22 25 plus ok 25 plus 22 plus 10 57 good hinge line that suppress the top view from the front view projection lines that come from top in the top view you are going to be seeing a circle of 5124 since you are making a circle you have to locate the center using two dash dotted lines I am showing this circle again using dash dotted lines why is that. So, this would bear the centers the four centers of the smaller circles you know this circle is represented by PCD pitch circle diameter ok. So, hence I am using dash dotted lines let us get started bottom line shows up the vertical line shows up this is of height 10 this line shows up we complete this box. So, this represents the front view corresponding to this disc right extend the center projection line up now what am I doing here what am I doing here I am trying to draw these two appendages now they will essentially look like rectangles in the front view you will be able to figure out the dimensions. So, dimensions at this time not very important. So, the height of course is 47 and the where there is 25 right. So, this height is 47 and this where there is 25 is that right no then locate the center of these two holes they will be at the same horizontal and show the two holes using hidden lines solid lines am I done what is this node. So, I still have to sketch or I still have to worry about these circles right. But before I do that let me try to work with the top view bigger circle now what I have done is I have projected this vertical line on to the top view from here from here. So, essentially in the top view I am looking at these lines this line here the line at the back right I know the length I know that the object is symmetric about the horizontal axis I draw four rectangles sorry I draw I draw two rectangles fine. And then of course the voids within those appendages now I am locating the four circles on the pitch circle diameter I look at the centers and rest is straight forward once I have located these four circles I can take the projections of these on to the front view and show them using hidden lines right which is what I do here located centers of the two cylindrical voids and located the voids themselves in the front view right. So, far so good am I done with the two views yes or no well of course dimensioning remains, but I am not worrying about that as of now how about the profile view how about the profile view where will I show the profile view left of the front view left of the front view. So, remember I mean you relating the top view with the profile view using projection lines and a 45 degree angle yeah you remember that from this week's lab how would you do the same exercise here how would you do the same exercise here start taking the horizontal projections from the top view draw a 45 degree line go up and join the projections emanating from the front view exactly the same exercise why because this dimension has to be equal to this dimension right once you have the bounding box ready in the profile view start drawing a desk well again look like a rectangle get the projections from these if I may call flanges get the center extend them extend the lines look at the center draw a semicircle and draw the inner circle it is ok. If you want to take a quick nap and then what relate that circle to the lines in the front view where construction lines and of course the top view and from the top view get the projections corresponding to the smaller circles on the pitch circle diameter look at the centers and represent the smaller circles using hidden lines in the profile of course that is the top view at the bottom of the front view that is the front view which one right or left any questions yeah in the front view center what because the cylindrical void is like so now so this center line represents the axis of the slender axis of the cylindrical void one view is redundant why do you say that so what you are suggesting is just two views are good enough for us to represent this object you could be right what is the what perfectly conventions different people use different conventions so some people are comfortable with the first angle projections the other ones are comfortable with third angle projections can you stand up please what is your name louder louder turn around stand by my side so this friend of mine Ashish Agarwal he asked me when he was doing the second lab sir can I draw things in the first angle projection he was so eager to draw this in the third angle in the first angle projection so I thought why not why not tell you all about first angle projection so that just in case if he happens to draw in the first angle projection you guys cannot understand so there are different conventions that people use yeah yeah please any other yeah we don't draw dotted lines for smooth fillets I didn't say that you know I have a lot of anecdotes to share with you one of them goes like when I was well this is this when I was in the 10th grade I was reading a book and I read a quote by somebody some character in the story and I liked that quote very much I am without politics I am without politics please let me not behave as a politician here asking you to be quite every time okay so if one of your peers is getting up and asking a question please lend a polite here to him or her because then you will not be able to understand his or her question nor will I I wouldn't say that what I said was if I made that perfect 90-degree angle then I will have a region of discontinuity that means that two surfaces there will be stitched together in such a way that you will have a distinct line and that line is going to be shown in the other two views yeah well any feature that any feature that gives you the impression that there is some discontinuity in surface that is to be represented hold on hold on so keep that question in mind I'll come back to you we still have time so I'll come back to you okay any other question pertaining to first angle projection yeah shouldn't the top view well the choice is yours so you can choose the principal view to represent the front view the choice is yours I chose the front view to be that but you can choose differently it's perfectly fine any other question so just to emphasize this is the what first angle projection why because the front view is lying in the first quadrant okay and in the third angle projection the front view lies in the third quadrant hence the names