 Hi, friends. I am Professor Prakash Sarunke, Mechanical Engineering Department from Valshan Institute of Technology, Sudapu. Today, we are gathered here to discuss the topic limit tolerance and fits third series in this particular lecture series and which comes from the subject metrology. At the end of this session, students will describe fundamental deviation, their types, which are specified by Bureau of Indian Standards. Students will also be able to identify the formulae for each type and to calculate the values of fundamental deviations for given size and specified type. Students will also be able to explain the procedure to determine minimum and maximum sizes of the component from given specifications. Let us first try to understand what do we mean by fundamental deviation. Earlier, we have seen that there are two types of deviation, upper deviation and lower deviation. Now, fundamental deviation is either upper or lower, which is nearer to the basic size or zero line. So, here we should understand that normally tolerances are specified as unilateral tolerances, in which case the tolerance zone is placed either above or below the zero line. And in that case, either lower or upper deviation will be nearer to the basic size. If the tolerance zone is placed above the zero line, then lower deviation will become the fundamental deviation nearer to the basic size. And if the tolerance zone is placed below the zero line, then the upper deviation will become the fundamental deviation. Now, how much should be the value of fundamental deviation? Because that will decide the location of tolerance zone with respect to zero line. Now, there can be innumerable choices again for the design or production engineer to locate the tolerance zone. To bring certain standardization, Bureau of Indian Standards in accordance with ISO, I mean International Standards Organization has specified 26 fundamental divisions and which are designated by later A, B, C, D capital for holes and A, B, C, D small for specifying the shafts. Now, value of particular value of fundamental division is associated with each of this type and say these values are spread around zero line as shown in the figure 3.1. So, it is like this, this figure has been taken from Bureau of Indian Standards 919-1993. You can see here that these letters A, B, C, D, E, etc., say they denote the tolerance zones of fundamental division, location of tolerance zone of fundamental divisions and A to H. So, these zones are located above the zero line for holes. These are capital letters. So, these indicate the holes and after H, so you will find the tolerance zones are located below the zero line. So, in case of A to H, it becomes the lower division as fundamental division and there onwards you will find that the upper division becomes the fundamental division. H is one where the fundamental division is zero. So, it is called as basic hole. For shafts, the trend is exactly reverse. A, B, A to H, so these tolerance zones are placed below the zero line while in case of shafts, they are placed above, I mean, sorry, holes above and for shafts, they are below and after H, the tolerance zone are placed above the zero line for shafts while in case of holes, they are placed below it. The values for both holes and shafts will have same amount or same numerical value, but their sign will be opposite to each other. Now, this ES, say that denotes the lower division, sorry, EI denotes the lower division and ES denotes the upper division. In case of shafts, say it is indicated by smaller letter ES and EI. Now, so this will illustrate us the positioning of the tolerance zone. Now, values of each FD can be calculated with the help of formulae which are given in table 3.2 shown in next slide. So, this is the table. This we shall understand later, but here you can see these are the, this is the column for shaft, this is the column for holes and these are the formulae. So, which are in terms of D where D is the geometric mean of the basic size as we have used while calculating the tolerance values. Now, in this table, the formulae for both holes and shafts are same, but the signs are opposite. It means the value of FD for holes as well as shafts will be the same, but say there it will be either positive or negative. If it is positive for holes, it will be negative for shafts and vice versa. If we see the table carefully, we will find the values that A, B, C, D. So, these are specified here later. So, this will indicate the sign. This will give us the designation. So, whether it is upper division or lower division and this will give us the formula. Now, this formulae as you can see here 265 plus 1.3D for a particular basic size. Now, for holes, so this will be opposite. If it is as I told you, upper division for shaft, it will be lower division for hole. And then it will be minus sign here. It will be plus sign. And A, that small letter here, it will be a capital letter. So, that way for each of the holes and shafts, the formulae are specified that you can see in this particular table. So, there are totally for different I mean specifications, all these formulae say they are written. And for each type, as I told you, that deviation is zero fundamental. So, it is called as basic hole or basic shaft. So, there is no question of sign. Now, how to do the calculation? While specifying the fundamental deviation, initially basic size is written. Then later showing the fundamental deviation and the grade is expressed as suffix to this particular alphabet. For example, 40B7. Here 40 will indicate the basic size. B, so it is capital. So, it will indicate that the component is hole. And it is also indicate the type of fundamental deviation. And this 7, so a suffix. So, that will indicate the grade of tolerance. Similarly, 75 here is basic size. H, say that will since it is small letter, it will indicate the shaft and say it. So, that will indicate the grade of tolerance like this. So, from the given specifications, we can calculate the maximum and minimum sizes of the component as follows. Normally, we have seen that when we get the later basic size and later for fundamental deviation. For each later, the value of fundamental deviation is given in the table, earlier table we have seen this table. So, with the help of this, I mean table with this formula for example, IT7 plus 0.63D. So, we can determine the value of fundamental. First we have to calculate the value of IT7. Again, that IT7 is the grade of tolerance. So, that will be calculated by using the earlier formula that we have seen last time. And then D is the, we have seen the geometric mean of the diameter steps in which the basic size lies. And with this, we can say find out the value of fundamental deviation. And it will be either positive, say for I mean shafts and it will be negative for holes. So, accordingly say we can determine the value of fundamental deviation first. Once we decide the value of fundamental deviation, then with the help of this grade as suffix, we can we have to determine the value of grade of I mean tolerance value. So, that tolerance value how we have to determine that we were studied earlier that formula are there. So, we determine the tolerance value and then say we use the following formula. First here, we will get either maximum size or minimum size depending upon whether the tolerance zone is located above the zero line or below the zero line. So, when the tolerance zones or fundamental deviation value is negative and the tolerance zone is plus below the zero line, then maximum size will be given by this formula maximum size equal to basic size plus fd. Now this fd will have a value negative. So, it will be basic size minus that numerical value. Now if the fundamental deviation is positive that is tolerance zone surplaced above the basic size, then we will get the minimum size. Minimum size will be equal to basic size plus fd. Here the fd will be having positive value. So, it will be directly added numerical value will be added. So, we will get either maximum size or minimum size from this fd and then say we determine other value with the help of tolerance. So, maximum size minus minimum size equal to tolerance, this formula will be useful. So, one of the size either maximum or minimum will be decided with the help of fd and other size will be decided with the help of tolerance and using this particular formula, okay. I hope you understood this particular procedure. If you have any doubts, difficulties you can contact me. So, we have taken the references for this particular topic from IS-919 part 1 1993. Thank you.