 I welcome you all for the module 3 lecture 2. In the last lecture, we started discussion on the basics of limits, fits and tolerances and we discussed about some of the terminologies used with reference to limits, fits and tolerances. We will continue with the discussion. Now, the next terminology is upper deviation. So, it is the algebraic difference between the maximum limit of size of either hole or shaft and the corresponding basic size. So, it is designated by capital E s for holes and small E s for shaft. And similarly, lower deviation it is the algebraic difference between the minimum limit of size of either hole or shaft and the corresponding basic size like capital E i for hole and small E i for shaft. And the next term is fundamental deviation. It is one of the two deviations which is nearest to the zero line for either a hole or a shaft which is chosen to define the position of the tolerance zone. And then we have another term allowance. It is the difference between the maximum metal limits on the hole and the shaft and this determines the quality of the fit. Now, in this diagram, we can understand the terms that are discussed just now. We can see we have the hole and this is the basic size of the hole and then we have the shaft. Again, the basic size of the shaft is same value and then this is the minimum size of the shaft and then maximum size of the shaft. So, this indicates the tolerance that is allowed for the shaft and this tolerance is designated by international tolerance grade or we say IT number. We will discuss this international tolerance grade in more detail after some time. And now, similarly for the hole, we have the this is the minimum size and then this is the maximum size. This difference between maximum size and minimum size gives the tolerance and this tolerance is again designated by international tolerance grade or IT number. Now, we can see that this difference between the basic size and the tolerance or the maximum size of the shaft is the upper deviation and it is designated by ES. And similarly, the difference between the basic size and the minimum size of the shaft is designated by EI, lower deviation EI, lower case EI. Similarly, for the hole, the algebra difference between this basic size and the minimum size of the hole. So, this difference is known as lower deviation and it is designated by capital EI and then the difference between the basic size and the maximum size of the hole. So, this difference is designated by capital ES, which is upper deviation. Now, there is another term fundamental deviation. It is the nearest deviation, the deviation which is nearer to the basic size is known as fundamental deviation. Now, in this case, the upper deviation is this is very close to the basic size. So, this gap is known as fundamental deviation and it is represented by lower case letters for shaft like A, B, C, D and in the case of holes, the lower deviation that is capital EI is very close to the basic size and this gap is known as fundamental deviation, which is again indicated designated by capital letters for holes like A, B, C, D, etc. This we will discuss in detail after some time. Now, there are some more terms basic shaft and basic hole. The shafts and holes that have zero fundamental deviations. Now, in the previous slide, we saw that there is some fundamental deviation for the shaft as well as for the hole. If this fundamental deviation is 0, that means the basic size of the shaft is equal to the maximum size of the shaft. If that is the case, that is known as the basic shaft. Similarly, for basic hole, if this fundamental deviation is 0, that means basic size of the hole is equal to the minimum size of the hole. If that is the case, then we say such a hole is known as basic hole. So, the shafts and holes that have zero fundamental deviations are known as basic shafts and holes. The basic hole has zero lower deviation, whereas the basic shaft has zero upper deviation. Then, we have hole designation. We use capital A, B, C, etc. to designate the holes in the I S O system by A, B up to Z and then Z A, Z B, Z C excluding I, L, O, Q, W and adding J S, these are the 25 numbers specified in the Indian standard. Similarly, for shaft designation, we use lower case letters A, B, C, etc. up to Z, then Z A, Z B, Z C excluding I, L, O, Q, W and adding J S. So, 25 shaft designations are there. In I S O, there are 28 designations are there. Then, we have maximum material condition, a short form is M, M, C. So, this is the minimum diameter of hole and maximum diameter of shaft. Now, we can understand this by using some simple sketches. So, we have a plate like this, some workpiece with a hole. This is the basic size of the hole and then we have a lower limit for the hole and then we have upper limit for the hole. This is the high limit for the hole and inner one is the lower limit for the hole. Now, when the size of the hole is equal to lower limit, then we have maximum material in this particular part. So, that is known as maximum material condition, which is equal to minimum diameter of the hole. Now, this is the size of the shaft and then we have the tolerance like this. So, this is basic size. So, this is basic size and then this is the lower limit of the shaft and then we have higher limit of the shaft. So, this is high limit and this is low limit. So, when the size of the shaft is equal to lower limit, then the material content will be least and then when the size of the shaft is equal to h higher limit, then it has maximum material condition that is equal to the maximum diameter of the shaft. Similarly, least material condition, this is equal to maximum diameter of hole. So, when the diameter of hole is equal to the maximum size, then the material content is the least and similarly, when the shaft size is equal to the lower limit, then the material content is least. So, that is known as least material condition. Now, those hole and shaft designations, we can understand here. So, this is the, this line indicates the basic size for the hole and this line indicates the basic size for the shaft and the y-axis is fundamental deviation in microns. Now, we have various designations for holes A, B, C, D, etcetera. Now, we can see here at this particular point where the hole is designated by h, the deviation is 0. So, this is taken as the basic hole and similarly, if you observe here, the deviation at this particular point is 0. So, deviation is 0. So, this h shaft is taken as the basic shaft. Now, at this corresponds to the, so these are holes, all capital letters, they correspond to holes. Now, this is the tolerance zone. This gap, this zone indicates the tolerance zone and this corresponds to the lower limit of the hole and this corresponds to the upper limit of the hole. So, this difference is the tolerance. Now, we can see here other than h, the other holes have some fundamental deviation, positive fundamental deviation for A, B, C, D, E, F, G up to this, we have positive fundamental deviation. Then, h has 0 fundamental deviation. After that, the other holes have negative fundamental deviations. So, similarly, with respect to the shafts, shaft A, B, C, D, E, F, G, they have negative fundamental deviation and the h, shaft H has 0 fundamental deviation. Then other holes like K, M and etcetera, they have positive fundamental deviation. Now, this particular drawing, it refers to the basic size of torque T and when the basic size varies, again the fundamental deviation values will vary. Then, we will move to the fit, definition of fit. It is the relationship between two parts that are assembled. This fit results from the difference between the size of shaft and size of one or any two mating parts. Now, it also refers to the mating of two mechanical components. Manufactured parts, all manufactured parts are very frequently required to mate with one another. They may be designed for slide freely. That means, the shaft size is smaller than the hole size, so that the shaft can move inside the hole freely. It can rotate in the hole or it can slide in the hole or they may be designed to bind together. That means, the shaft size is greater than the hole size, so that when we push the shaft into the hole by applying some force, the two mating parts are rigidly held. So, depending upon the application, we may use the clearance fit wherein the size of the shaft is lesser than the size of the hole or we may use interference fit, where the size of the shaft is greater than the size of the hole. There is another kind of fit known as the transition fit wherein depending upon the shaft size and the hole size, we may get either the clearance fit or interference fit. So, such things we will see after some time. Now, there are two systems of fits. The first one is hole based system and the second one is shaft based system. Now, we can observe in this picture, this is the hole based system wherein size of the hole is kept constant. The hole size is kept constant and the shaft size is varied. So, we have different shafts. Now, this is the basic size of the hole and then this difference gives the tolerance for the hole. Now, to get the different kinds of fit, whether we want the clearance fit or interference fit or transition fit, we vary the shaft size and in the second system, we have shaft based system wherein size of the shaft is kept constant. We can see in this picture, the size of the shaft is not varied. It is constant and hole size is varied to get different fits. For example, in this case, the hole is bigger than the shaft. So, we have some clearance here. So, we get the clearance fit and then here, the shaft is bigger than the hole size. So, we get the interference fit here. In between, we have a transition fit. Now, normally hole based system is preferred because, see the machining of the inner surfaces, for example, holes is always difficult and we need to have a series of tools. For example, we require different sizes of holes. Then, we should have multiple drill tools, internal grinding tools and then remers. So, if we have different hole sizes, then the inventory of tool will increase. Whereas, shaft size can be varied using a single point cutting tool in turning process or using a single grinding wheel. We can grind the different shaft sizes. So, by using the hole based system, we can always reduce the tool inventory. So, in manufacturing environment, normally hole based system is used. Now, we have three categories of fits known as clearance fit, transition fit and interference fit. Now, we will discuss about these three types of fits in detail. Now, the clearance fits are used when it is desirable for the shaft to rotate or slide freely within the hole. This is also known as sliding fit. That means, the hole size is bigger than the shaft size, so that the shaft can freely move inside the hole. In the interference fit, whenever we want to fix the shaft inside the hole rigidly, then we go for interference fit. Now, a great amount of force is needed to see the parts which are fixed using interference fit. If we want to remove them, then great amount of force is needed to separate them. Many times, they may get damaged when they are separated because they are rigidly held in the parts are rigidly held in the interference fits. In the case of transition fits, when it is desirable that the shaft is to be held securely, yet not so securely that they cannot be disassembled. That means, sometimes we want to separate the two mating parts. In such cases, we go for transition fit. This is also known as location fit. That is, by appropriately assigning the tolerance values for the shaft and the hole, we can get the desired type of fits depending upon the application. Within each category of fit, there are several classes ranging from high precision to narrow tolerance to lower precision and wider tolerance. The choice of fit is dictated by the use, what is the use or what is the application of the fit and secondly, by manufacturability. By what type of manufacturing system, whether we are using the not so precision machine tools or very high precision tools, that aspect also is taken into consideration while selecting the fit. Now, we will study the clearance fit in detail. This picture shows that we have a hole here with the minimum size of the hole and the maximum size of the hole. This algebraic difference gives the tolerance for the hole. So, this gap represents the tolerance for the hole. That means, the hole size can be anywhere between the minimum hole and maximum. It can be here or it can be here. So, it can take any size between these two limits, upper and lower limits. Similarly, we have a shaft with the maximum size and the minimum size. Now, when the shaft size is maximum and the hole size is minimum, this algebraic difference gives the minimum clearance. We get the maximum clearance when we have maximum sized holes and minimum sized shafts. So, this represents the maximum clearance. Sometimes, we need to say we have a bush bearing here. So, this is the bush bearing. Then, we have a shaft inside. So, it has to rotate or it has to move freely. So, in such cases, we go for clearance fit. So, one application is shown here. This is the shaft and this is the bush bearing. So, shaft is required to rotate freely inside. In such cases, we go for clearance fit. Then, there are different grades of clearance fits as per the American standard B 4.1. Now, they are represented by R C 1, R C 2, etcetera as the lower R C numbers. That means, 1, 2, 3, etcetera. They are very tighter fits and as the number increases like R C 5, 6, R C 6, etcetera, they represent the looser fits. So, R C 1, wherein it has tighter fit and it is used when accurate location is intended without any noticeable play and shafts are very expensive to manufacture since they have very tight tolerance and the clearance is very, very less. So, one example is H 7, G 6 combination gives us the R C 1 clearance fit. So, what is this H 7, G 6? It is the whole designation and the G is the designation for the shaft and 7 indicates the IT number, international tolerance grade for whole and the 6 represents the IT number for the shaft. We will discuss about these grades, IT grades in detail in a short while. So, then they have R C 2, this is the sliding fit and this kind of fit is intended for the accurate location, but with greater maximum clearance as compared to R C 1. Parts made to this fit turn and move easily because of this higher clearance. So, this type is not designed for free run, sliding fits in larger sizes may cease with smaller temperature changes. So, this point we should note while using the sliding fits. Similarly, we have R C 3, wherein the parts can run very freely because of higher clearances. This fit is intended for precision work at slow speed, low bearing pressures and light journal pressures and this is not suitable where noticeable temperature differences occur. If temperature rises there, then again the Caesar may occur. Then we have R C 4, close running fits. So, this is suitable for the machinery with moderate surface speed, moderate bearing pressures and journal pressures where accurate location and minimum play are desired. This has smaller clearances with higher requirements for precision fit. So, one example is this is suitable for lubricated bearings. We can get close running fit by using H 8 and F 7 combination. Then we have R C 5 and R C 6. They are known as medium running fits and they are designed for machines running at higher running speeds, considerable bearing pressures and heavy journal pressure. This has greater clearances with common requirements for precision fit. So, next we have R C 7, which is a free running fits, where accuracy is not that much essential. So, because of the more clearances, there may be a small play, may be present. So, this is suitable for great temperature variations and high running speeds. These fits are suitable to use without any special requirements for precise guiding of shafts. For example, H 9 D 10 combination gives us the free running fits and then we have R C 8 and R C 9. They are very loose running fits. They are not intended for use where wide commercial tolerances may be required in the shaft. With this fit, the parts have great amount of clearances with great tolerances. The loose running fits are exposed to effects of corrosion, contamination by dust and thermal or mechanical deformation. That means, since the clearances are more, we may, their parts are exposed to the such conditions like corrosion and dust. So, one example is, these are suitable for loose pulleys. So, we can get loose running fit by H 11 C 11 combination. Then we have interference fit. So, this we get when the minimum permitted diameter of the shaft, minimum permitted diameter of the shaft is larger than the maximum diameter of the hole. We can see in this picture, this is the maximum size of the hole. So, this is smaller than the minimum size of the shaft. In such cases, we get interference fit. So, we get minimum interference when we have the maximum sized hole and minimum sized shaft and the interference will be maximum when we have minimum sized hole and maximum sized shaft. So, when such interference fits are used, we can see in this diagram, we have a bearing housing and we want to fit this particular bearing into the bearing housing. So, this outer ring of the bearing should be tightly held in the bearing housing. There should not be any relative motion between these two. In such cases, interference fits are used. So, varying the outer diameter of this ring will be bigger than the diameter of this housing. Now, we have some more examples for interference fit. We can see here, a great amount of force or pressure is required to fit the parts to get the interference fit. We can see here vices, machine vices are used to fit this shaft into the hole and we have another example of engine block wherein we have to insert liner. So, we have to apply a great deal of pressure. We use hydraulic presses for fitting liners into the engine block. By knowing the diameter of the hole, diameter of the shaft and then their surface conditions etcetera. We can always calculate what is the amount of pressure or force required by using the equations available. Now, there are different grades of interference fit as per American standard ANSI B 4.1. So, there are force and shrink fits. So, we have F N 1, F N 2 etcetera. F N 1 is a light drive fit. So, these types of fits are those requiring light assembly pressure. So, as the number increases 1, 2, 3 etcetera, the amount of pressure required will also increase and these fits, light drive fits, they produce more or less permanent assemblies. They are suitable in cast iron external members for or for thin sections or long fits. So, H 7 P 6 combination gives us F N 1 fit and then they have F N 2 medium drive fit. These types of fits are suitable for ordinary steel parts or shrink fits on light sections and medium drive fits are about the tightest fits that can be used with high grade cast iron external members. We can get the medium drive fit by using H 7 S 6 combination and then we have F N 3 heavy drive fits and these are suitable for heavier steel parts or shrink fits in medium sections. The combination H 7 T 6 gives us the heavy drive fit and then we have F N 4 and F N 5 force drive fits. These types of fits are for parts which can be highly stressed. Now, the H 7 U 6 or H 8 X 7 combination gives us force drive fits. Now, we can understand from this picture that we have in all these examples, we are using H 7 basic hole, H 7 hole where in the deviation is 0 and this is the hole tolerance and then we are using P 6 S 6 T 6 shafts. So, we have P 6 shaft and S 6 shaft. Now, we can see here the diameter minimum diameter of. So, this represents this size represents minimum size of the shaft. So, this is greater than the maximum size of the hole. So, we get interference fit. Similarly, if you take the example of H 7 S 6, H 7 S 6 which gives medium drive fit, this is the S 6 shaft and this is H 7 hole. So, this is the minimum size of the shaft and this gives us the maximum size of the hole. You can see here there is lot of interference between these two. So, we have to apply great amount of force to get this medium drive fit and here this is the shaft tolerance and this is the hole tolerance and this distance gives the minimum interference and this gives the maximum interference. Then, we have locational interference fits that are designated by L n. These fits are used where accuracy of location is prime importance. These fits are used for parts requiring rigidity and alignment with no special requirements for pressure. The parts can be assembled or disassembled. The parts can be assembled or disassembled using cold pressing and great forces or hot pressing. That means, the hole is heated so that the diameter increases and then the shaft can be inserted and when both the shaft and hole are cooled down, we get the locational interference fit. So, shaft P 6 and with hole H 7, we can get the true interference fit. It is the standard press fit for steel cast iron or brass or brass to steel assemblies and different types of L n fits are used depending upon the application. One can use L n 1, L n 2, L n 3, etc. Now, this diagram shows that we have H 7 hole. This is the hole tolerance and then we have U 6 shaft tolerance or if you take this example H 7 P 6. So, we have H 7 hole. This is the hole tolerance and then we have P 6 shaft. So, you can understand and then we have H 7 S 6, H 7 U 6. So, this is the interference that is the minimum interference that is available. Now, we will move to the transition fit. So, the diameter of the largest allowable hole is greater than that of the smallest shaft, but the smallest hole is smaller than the largest shaft. That means, in this case, the tolerance zone of the shaft and the tolerance zone for the hole, they overlap each other. They may overlap completely or they may overlap partly as shown here. So, this is the tolerance zone for hole, tolerance for hole and then the tolerance for shaft, you can see they are overlapping in this particular case or it may partly overlap like this or like this. So, this is the tolerance for shaft. These smaller rectangles, they indicate tolerance zone for shafts. So, depending upon the actual size of hole and actual size of shaft, we may get clearance fit or we may get interference fit. Now, again there are different grades of transition fit. We say locational transition fit, LT fit as per ANSI B 4.1. So, we have LT 1, LT 2 transition fits, locational transition fits and these can be used for bearing bushings, hubs of gears, pulleys and bushings, retaining rings, etcetera, etcetera. The parts can be assembled or disassembled manually. That means, the amount of force that is needed to fit the parts is not too much and then they have LT 3 and LT 4. These are used for clutches, pulleys, manual wheels, brake disc, etcetera. The parts can be assembled or disassembled without any great force. That means, we can use rubber hammer to fit the parts and then we have LT 5 and LT 6. These can be used for armatures of electric motors on shafts, driven bushings, gear rings, flush bolts, etcetera. The parts can be assembled using low pressing forces. You may have to use little bit of pressure to get LT 5 and LT 6 pressure, which is greater than that, which can be applied by rubber hammer. You can see, we have a shaft and then we have a hole. Now, the shaft size, you can observe that the combination is two dots are there. Since the shaft size is smaller than the hole size, the shaft enters into hole very easily. Now, we have another combination wherein we have a single dot. So, this is the shaft and the holes. Now, I am putting the hole onto the shaft. Now, you can see there is a small layer of oil. Now, we have a transition fit. So, we have to apply a little bit of pressure on to this bush, so that it enters fully. So, this is an example for transition fit. Now, I will show, I will put some weight onto this bush, so that it will fully enter. So, I am applying a weight of 50 grams. Now, you can see, after applying 50 grams, it has entered fully. So, depending upon the actual size of shaft and hole, we may get different kinds of interference fits. Now, we have another experiment where this is the three dot combination. Now, in this case, I can observe, I am putting the bush onto the shaft. Now, it is not entering. Even when we apply force, it is not entering. The reason is, the shaft size is greater than the hole size. So, we have interference. We will conclude this lecture number 2. In the lecture number 2, we discussed about the different kinds of the fits, clearance fit, transition fit and interference fit. We also discussed about different the standards available with respect to the limits, fits and tolerances. In the next class, we will solve some numerical problems. Thank you.