 I welcome you all for today's lecture module 3 and lecture 6. In this lecture, we will be studying about limit caging, what is the meaning of limit caging, why it is necessary and then what are the various kinds of gauges used, how they are manufactured and what are the materials selected for manufacture of gauges and what are the precautions to be taken while using gauges and the different kinds of gauges used for checking external features like diameter, depth, etcetera, etcetera. Also, what are the various gauges used for measuring for checking holes and then also we will study different types of gauges like pitch gauge, radius gauge, etcetera. Also, we will study about air gauge and then we will move to the design of limit gauges. Now, let us start the lecture, let us understand what is limit gauging. Now, in the mass production, the components are manufactured in large quantities and many times it is not needed to check the dimension of each and every component and if we can just check whether the work pieces are within the prescribed limits, upper limit and lower limit that will be enough and there will not be any need to check the actual size of components using measuring instruments. In such cases, to check whether the components are within the prescribed limit, we use instruments called limit gauges. Now, what is the advantage of this limit gauging? Since we are not measuring the actual size of the component and then we will be using only gauges, the inspection of the parts will be very quick and cars associated with the inspection will also be less. Now, what are gauges? These are inspection tools without a scale. There will not be any scale built into the gauges. They check the dimension of the manufactured parts and they will tell the status whether the work piece is acceptable or whether it is acceptable or not. Only that information it will give and the actual size will not be given by the gauges. Now, how these gauges are classified? There are many ways in which these gauges are classified based upon the standard, the type of limit gauges, whether it is standard gauge or limit gauge. They are classified and then based upon the use or purpose, whether they are used for working gauges or for inspection purpose or for reference or master gauges. Depending upon the elements to be checked, they are classified as gauges checking for holes and then gauges used for checking the shafts, tapers, threads and different kinds of forms and then according to the shape of the gauges, they are classified as plug gauge like full form plug gauge, segmental plug gauge and then ring gauges, snap gauges, taper gauges, thread gauges, form gauges and also thickness gauges. Now, according to their design, they are classified like whether they are single limit gauges or double limit gauges, single ended, double ended or progressive gauges, whether they are fixed gauge or adjustable gauges, whether they are replaceable gauges or reversible gauges. If there is any indicating mechanism is there, they are called indicating gauges and also if air is used for gauging purpose, we say air gauges. According to the type of work surface that is checked, they are classified as plain work surface gauges, threaded gauges, then the spline gauges and then keyway gauges. Now, what are the gauge materials used for manufacture of gauges? Different kind of materials are used like high carbon steel and then sometimes mild steel is also used, case hardened steel is used, oil hardened steel, cast iron is also used and sometimes glass and ceramic and in more are also used. And while selecting these gauge materials, there are some selection criteria like the material should be wear resistant. Since the gauge comes in contact with the work part and there is sliding motion, the gauge material should have wear resistant property. And the stability to preserve form and size, the geometric shape of the gauge and then size of the gauge should not alter because of changes in the environment. So, stability aspect is also considered and very important thing is gauges should be corrosion resistant. Since the gauges come in contact with the working environment like they come in contact with the coolant, oil etcetera, etcetera, there should not be any corrosion on the surface of the gauge. So, corrosion resistant materials are selected for manufacture of gauges. Also the machinability of the gauge material is very important, it should be possible to machine to the required size and required shape to the required accuracy level. So, the gauge material that is selected should have good machinability and also it should be thermally stable. Sometimes it comes in contact with higher temperatures like 40, 50, 60 degrees Celsius. The size of the gauge should not alter. So, it should have sufficient thermal stability. Now, sometimes the plating is also made on the gauge surfaces. For example, say we have a gauge surface like this. So, this is the surface of the gauge and then this is the gauging surface and this also gauging surface. Now, in order to improve the wear resistance, some kind of coating can be provided on these gauging surfaces. Coating like chrome plating and then carbide coating, norbide coating, sapphire tips are also used at this place and then carbide, the advantage of carbide plating is it increases the life of gauge by 5 times as compared to the only steel gauges. And carbide tips if we are using, a carbide tip can be mounted on this, which will increase the service life of the gauge by 10 to 100 times. And tin plating, titanium nitrite plating is also provided on the gauging surface, so that the service life enhances. Now, coming to the manufacture of gauges, initially the proper material should be selected and then machining to size, initial machining is made like turning operation or milling operation if it is flat surface. With some allowance machining is to be performed and then heat treatment of, if it is steel material, some kind of heat treatment is required to increase the hardness to 58 to 60 rock well sea. And then tempering is also performed on the material to get the stability and in sometimes sub zero treatment that is the gauge blanks are placed at minus 80 degree Celsius for long term stability. And then case hardening by carburizing also is sometimes performed on the gauges to improve the hardness of the gauging surfaces. So, in that case, case depth of 0.7 millimeter may be required. So, after this heat treatment the gauging surfaces are ground and then they are lopped and all sort of finishing operations are performed. And then if plating is required plating is also performed and then again after the plating is over again they are ground and lopped to get the proper size. And then after the finishing is over, we need to calibrate for example, if you take a snap gauge like this. So, what is the distance between these two surfaces? This is very important. So, now say we have finished these two surfaces and what is our requirement, whether it is 10.001 millimeter or 10.005 millimeter? We should fix up some size here, whether we have really achieved that requirement we have to check by using slip gauges. And then after calibration is over, we have to mark the specifications like what is the go size limit and what is the no go size limit and which side is, if it is some progressive type like this, then one is the go limit and other one is no go limit. So, one corresponds to the upper size of the workpiece and the other one corresponds to the lower limit of the workpiece. So, in that case, we have to properly mark the go and no go and also the manufacturer details, the manufacturer name is also marked on the gauge. And then final inspection should be carried out with respect to the marking of size of the gauges and whether all the details are provided are not the like the tolerance, what is the tolerance and what is the, which side is go, which side is no go, all such things should be marked properly. And so the inspection is carried out to check all those details and finally, they are packed. Now, what are the features of fixed gauges? So, these fixed gauges are very important fixed limiting gauge, that means the size cannot be altered. There are some limit gauges where in some slight adjustment can be made, they are known as adjustable gauges. We will be studying about those adjustable gauges in a short while. So, fixed limit gauging is most cost effective method of checking part, since the time taken to check the part is very less. So, what the operator will do? He will take the workpiece, he will clean the workpiece surface and he will take the gauge and he will take the clean the gauge surface and he will try to insert the workpiece into the gauge. If it enters the go side and if it does not enter the no go side, then the workpiece is accepted like that. So, no actual size is measured in the gauging system. So, the inspection will be very fast and then it requires very little training, since the gauges are very simple to use and not much detail training is required to train the operators. Unskilled workers can use the gauges and they can check the workpieces and no recording of the part size, no measurement is made and no recording of the workpiece is made. We just say whether the workpiece is acceptable or not and the quick checking of the parts and all these gauges, they are traceable to ISO standards and then different kinds of coating is possible to enhance the life service life of the gauges. And then also custom built gauges can be made depending upon the requirement of the user and very important thing is in order to use these gauges there is no external power needed. Only manpower operator takes the gauges and it checks the workpieces, no external power is required except air gauges where pneumatic air supply is required. Then let us move to the various kinds of gauges. Now, what is the meaning of this standard gauge? So, it is nothing but a mating power part, mating part is used as a gauge. For example, say we have a workpiece like this with a hole with some mean dimension of x. So, the mean size of this hole is x. Now, there will be a mating part for this particular hole, a shaft again with the same mean size. So, the mating part itself is used as a gauge to check whether the hole is proper or not. But in actual practice what we check using limit gauges is whether the workpiece is within the allowable limit. Some tolerance is given to the workpieces and there will be an upper limit for the workpiece and there is a lower limit for the workpiece. So, that is the status we have to check. So, this concept of standard gauge varying both the hole and shaft or the workpiece of the gauge they are made to the mean size. So, this concept is only a theoretical concept and it is not used in the practice. Now, let us move to the other types of limit gauges. So, this shows a double-ended plane plug gauge. Plane means the surface that is to be checked is plane. That means there are no threads. So, it is called the plane plug gauge. So, this is used as a plug. So, we say it is a plug gauge. Since the two gauging surfaces are there, so this is the first one, first gauging surface and this is the second gauging surface. So, we say and they are mounted on both sides of the handle. This red part is the handle. So, the gauges are mounted on both the ends of the handle. So, we say this is a double-ended plane plug gauge. Now, what we should understand here? There are two gauging ends. So, this corresponds to the maximum material limit that is this is go gauge. So, this is used for checking the holes. So, go gauge corresponds to the maximum material limit and then no go gauge corresponds to the minimum material limit or here this is used to check what is the minimum size of the hole and this is used to check the maximum size of the hole. We can see here the go end. Go end is longer than the no go end. See how we use this to check the workpiece? We will be having a workpiece with a hole and there will be always some tolerance. So, this is the tolerance for the workpiece. Now, we take this plug gauge and we try to insert go side. So, this is go side. This portion we try to enter. Go should enter the hole. So, when it enters and then we remove it and then we try to insert no go part. No go side of the gauge. No go side we try to insert into the hole. No go should not enter into the hole. Now, we can see here no go, it is slightly greater than the upper limit. So, this no go will not enter. That means when go enters into the hole and no go does not enter, then that hole is acceptable. That workpiece with that particular hole is acceptable. Then what are the other things here? You can see this is 25 h 7. So, 25 is the basic size and then h 7 is the tolerance. So, basic size is also mentioned on the handle of the gauge and what is the tolerance that is allowed that is also mentioned and actual values are also mentioned. Since this is h, the basic the fundamental deviation is 0. So, the basic size will be equal to the lower size of the hole. So, this is the lower limit of the hole will be equal to the basic size. So, this is exactly 25 millimeter and the exact 25 millimeter is always very difficult to manufacture. So, some tolerance is also provided for manufacture of gauges. They are called gauge tolerance. This we will see after some time and you can see here this is plus 21. That means the diameter of this is equal to 25.021 millimeter. That means when compared to the basic size, this is greater by 0.021 millimeter and we can also observe one more thing. The manufacturer name is marked here. So, all these things are as per Indian standard IS 3484. So, what should be the length and what should be the length of this no go portion, what should be the diameter at this place, what should be the diameter at this place, what should be the length of the handle. All those things are specified in this IS 3484. So, they are made as per this IS 3484. And most of the times a red mark is provided on no go side. So, no go is marked on the handle as well as red paint is provided at this place to indicate that it is no go side. Now, we can observe one more thing here in the handle we have a hole here. So, this is called taper lock renewable end. So, this first red gauge it is taper lock renewable end. What is the meaning of taper lock? See here this double ended this particular gauging portion it will have a tapered shank, it will have a tapered shank and there will be a mating taper in the handle. So, what we have to do we have to press this gauging gauge into this taper in the handle and then we have to press it. So, that it gets fixed into the handle and how do we remove it say we want to after sometime this is worn out and we want to replace it with new one. So, that is why it is called renewable end. So, what we have to do is we have to take a drift or a tapered part and we have to push it here into the hole and that case this gauge will come out and then we can insert a rod to remove this no go end and then new ends can be mounted on this handle. That means, handle can be reused and coming to this this is solid type. You can see here the handle and then go gauge and no go all are made in a single unit. So, this is a solid type plug gauge it is size nominal size is less we can go for solid type if nominal size is more like 25, 30, 35 then we go for renewable taper lock renewable type and what is the range of availability they are available if it is carbide coated or carbide gauges then the range is up to 2 millimeter to 40 millimeter they are available and if it is hardened steel from 2 millimeter to 250 millimeter gauges they are available also if special requirement is there they can be built as per the customer requirement. Now, in the case of go no go end that is double ended type what happens is we have to take the work piece in which there is a hole which is to be checked we have to take the double ended plug gauge we have to insert go side and then we have to remove that gauge and then we have to insert the no go. So, like this the time taken to gauge the work piece or the hole will be more. So, to save time progressive gauges are made you can see here there are two portions with the handle this is the go gauge. So, this diameter corresponds to the go limit and this one corresponds to the no go limit. So, in one insertion inspection of the hole can be completed that means time for checking the hole can be saved and another if the hole size is very less like 2 millimeter 3 millimeter 1.5 millimeter like that then they say pin gauges pin gauges are used and you can see here this is the handle and there is a green color is used. So, this will indicate that this portion is go it is also marked here go side is marked and also the color indicates that this is go and then we have red color here which indicates that this portion is no go and the limits are also what are the exact sizes are also mentioned here this is this diameter is 12.80 millimeter and this diameter is 12.9 millimeter and sometimes if the hole that is to be checked is big one like say 250 millimeter or 350 millimeter 300 millimeter it is a big hole in that case what happens is if we use a full form gauge that means the plug gauge with full form round gauge then it becomes very heavy. So, using that heavy gauge becomes difficult. So, in such cases segmental flat type gauges are used they look like this. Now, this is the segmental gauge with the handle. Now, you can see here full round form is not used. So, this much is removed and only we are using a segment part of that full form. So, they are called segmental since they are flat pieces flat type gauges the advantage is the material that is required is less and the weight is less. So, that the operator can comfortably use them also if the diameter the hole to be checked is large then we always go for single ended plug gauges in order to reduce the weight of the gauge. So, we use one gauge for checking the upper limit and one more gauge for checking the lower limit. So, they are called single ended plug gauges. Now, we can see some details of plug gauges up to 10 millimeter solid type double ended plug gauges are made and then from 10 millimeter to 30 millimeter taper lock double ended plug gauges are made in which case the ends can be renewed when the ends are worn out new ends can be replaced. From 30 to 63 millimeter phasen type double ended plug gauges are used they are not taper lock they are the ends are phasened to the handle and then from 63 to 100 millimeter single ended plug gauges are used. So, we need to have two gauges one for go limit and go and other no go and from 100 to 250 millimeter flat type single ended segmental type plug gauges are used and above 250 and above a raw type gauges or pin gauges are used with spherical ends. They look like they say we have to check a big hole and the diameter of this is say 300 millimeter. So, diameter is 300 millimeter in such cases if we use full form gauge it will be very very heavy. So, what the practice is to use pin gauges with spherical ends like this. So, the length of this is controlled there will be one pin for go the lower limit and one pin for upper limit. So, we have to insert it and then we have to rotate it or we have to remove it and again we have to insert like this some two three times we have to do like this. So, these are called pin gauges they will be very light in weight. So, easily operator can use them. Now, what are the limitations of plug gauges? Sometimes the hole conditions like tapered hole, bell mouth or out of round hole it will be very difficult to distinguish. So, it will be something like this say we have a work piece like this with a hole like this. So, it is tapered or sometimes it is bell mouth like this it is opened up like this. So, what the operator will do? He will take the plug gauge and he will just insert it. So, whether it is tapered or whether it is bell mouth and whether there is any out of roundness is there that will be very difficult to check by using the plain plug gauges. So, say we have a work piece with a hole like this and then we use the round gauge. Now, you can see here it is entering go is entering and not go is not entering, but there is some ovality in the hole. So, that cannot be checked by using these plug gauges. Then gauging surfaces and square edges that means the end of the plug gauge it will be square. So, these square edges are unprotected they are open and hence they must be handled and stored carefully. If the proper protective coating is not applied the work the gauging surfaces may get corroded and they become unusable and then they have an easy tendency to roll off or fall off from the work bench. Since the work piece the gauges are round they will roll off from the table. So, proper care should be taken to place them in the proper place so that they will not fall. If they fall then the work surface the gauging surface may get affected and they become unusable and they may get corroded if not properly protected from grease or oily layer. Whenever they are not used for a longer time it is necessary that some oily layer is put like petroleum jelly is put on the surface and then they should be stored otherwise they will get corroded. And then gauge may freeze in the hole if worker exerts undue pressure on the gauge this is very important. See we should not force the gauges into the hole what happens if we force the gauge into the hole it will enter, but it will deform the hole the hole may expand. So, undue pressure should not be exerted. So, what the operator should do is that say we have a hole like this and then the gauge side of the gauge side of the plug gauge should be just held here so that it moves inside without exerting any due to its own weight it should enter. So, that is the practice followed in the industry and undue pressure if it is not entering undue pressure should not be exerted. And if required before using we may apply some oil thin oil so that it easily flows into the hole. And then the coming to the snap gauges these are used for checking the shafts the size of the shaft. There are two types one is a fixed type snap gauge we can see here this is a fixed type double ended double ended because one side this is one working side this is another working side. So, this is called double ended fixed snap gauge. And here we have an adjustable snap gauge what happens with the fixed gauge after some usage may be after 1000 times insertion 2000 times insertion the gauging surface is subjected to wear and the size will change. See here you can see it is marked 25 J 6 25 is the basic size and J 6 is the tolerance that is allowed. So, actual size is also mentioned here minus 4 microns and plus 9 microns. So, here it is 25.009 millimeter this is go and then this is minus 25 minus 0.004. So, that is no go side. So, due to continuous usage this is this gap will change. So, in that case one thing is we can send these gauges worn out gauges for repair that means again they will quote may be chrome plating or tin coating TIN coating they will do and again they will repair it. Otherwise say the tolerance itself changes the design engineer will change the design itself the tolerance itself in such cases we cannot use such cases whereas here the adjustable gauges can be changed. If tolerance changes these anvils can be moved and they can be set to the new required sizes. We can see here the arrangement is this is the long anvil we say this is fixed and here we have movable anvils. Now, how we can move we can see here the locking screws are there and here there will be a screw and one more screw for this. So, we have to unlock these screws and we have to take a screwdriver and we have to operate these screws. So, that these anvils will move in and out and then using the slip cage we can fix we can fix what is the size that is required for go and what is the size that is required for no go and then after fixing the sizes using slip cages we have to lock these two anvils by locking these screws and then these all these screws are waxed. So, that unauthorized adjustments are not done somebody may take these gauges and they may unscrew these screws and they may adjust it. So, to avoid such things all these screws after making adjustments by proper authorized person they will lock these screws and then they are waxed. So, while using this snap gauge the operator should see whether seal is intact. If it is not intact if it is disturbed then you should not use such cases they should be sent for calibration only after calibration and waxing they should be again used and again I can see here one more type different type and this is the handle see we say since it is looking like see seed type or snap gauges and other important thing is again see the work piece will go here like this say go side. The go side should smoothly enter into the shaft there should not be any over pressure on the snap gauge if over pressure is applied then what happens is this these surfaces they move out they expand. So, it is very essential that the gauges are not forced onto the work pieces they should move smoothly and this is another fixed type snap gauge plate type snap gauge and the adjustable gauges are useful. So, that whenever the tolerance changes they can be adjusted also when the when the gauging surfaces are worn out again we can adjust the gap. So, wear adjustment is also possible in adjustable gauges by making adjustment range of diameters can be inspected. Now, double ended snap gauge they are available within this range 3 to 100 millimeter and if the diameter of the shaft increases say it is above 100 millimeter then we use a single ended progressive snap gauge. So, it looks like this. So, this is single ended that means this is go and this is no go that means the work piece will enter into go side this is go and this is no go. So, work piece will not enter into this if that is the case the work piece is accepted. So, this is a progressive snap gauge and the single snap gauges are also available like this. So, one for go and similarly one for no go like that single ended snap gauges are also available single ended progress progressive snap gauges are also available. Now, let us conclude this session in this lecture we discussed about the meaning of gauging necessity of limit gauging and then what are the various materials used to manufacture the gauges and what are the different types of gauges. We also learnt about the plug gauges different kinds of plug gauges and snap gauges in the next class we will continue the discussion on different types of limit gauges. Thank you.