 I welcome you all for this lecture of module 2. In this session, we will study about height gauge and micrometer, the construction of height gauge and various applications of height gauge and what are the different types of height gauge, those things we will study. Similarly, in the micrometer, we will study a little bit about history of micrometer and then we will move to the construction and various uses of micrometer and then we will study the variants of micrometer. Now, let us start our discussion with height gauge. So, this photograph shows a Vernier type height gauge. I will just explain the different parts of the Vernier height gauge. This is the main scale, this is the column of the Vernier height gauge and on the column, we have main scale, one side we have metric scale and on the other side, we have English scale. Now, you can see here, we have some arrangement for lifting the scale, for sliding the scale up and down. The details of this portion is shown in this figure. We can see the screw and we can see the net. By rotating the net, the main scale can be moved up and down. This is needed for making the zero adjustment and then coming to the Vernier part, we have one side metric Vernier and on the other side English Vernier. We have a screw for clamping the measuring head to the beam and similarly there is a screw for moving the measuring jaw up and down. I can see here, carbide tipped scriber is fixed to the measuring jaw and there is a clamp for fixing the carbide tipped jaw to the measuring jaw. So, by rotating the screw, we can clamp the scriber to the measuring jaw. This is the base of the Vernier scale, Vernier height gauge and the bottom view of the Vernier height gauge, we can see. So, this is the ground finish surface. At the center, it is relieved and then this portion is the bottom of the beam and a screw by means of screw, it is fixed to the base and here you can see the clamp which is used to fix the scriber. This is the carbide tipped scriber. This scriber can be fixed to the measuring jaw with the help of this clamp. Now, we can see the closed view of Vernier height gauge. We can see the Vernier and a screw for fixing the measuring jaw to the beam and then there is a screw. We can initially, we have to screw this and then we have to operate this screw for finer adjustment of the Vernier and then we can see the scriber has been removed, clamp has been removed and now we are viewing the top surface of the measuring jaw. Now, it is very essential that the top surface and bottom surface of the measuring jaw should be parallel and these two surfaces, these two surfaces, top and bottom surfaces of the measuring jaw should be parallel to the datum surface within 10 microns. So, that we can check with the help of a dial indicator. Now, we can see the dial indicator is fixed to the column of magnetic stand and the spindle is in contact with the top surface of the measuring jaw. Now, we have to make zero adjustment when it just touches the top surface of the measuring jaw. Now, slowly we have to move this dial indicator towards the Vernier height gauge, towards the beam of the Vernier height gauge and then we should note down what is the reading. So, this reading should be less than 10 microns. Now, checking for zero error in the Vernier height gauge. Now, we can observe here the main scale zero line is here and this is the zero line of the Vernier. Now, they are not coinciding, even though the scriber is in contact with the datum surface, the scale is showing some reading. So, this should adjust by lifting the main scale as I have already discussed. Now, we can see here we have lifted, we have made some adjustments in the height of the main scale and now there is no zero error. Now, let me explain the Vernier height gauge. This shows the Vernier height gauge, this is the base of the Vernier height gauge and this is the main scale vertical bar, this is vertical bar and you can see the main scale. The resolution of this main scale is 1 millimeter. Now, we can see the range of this instrument, it is 0 to 300 millimeter and this portion is the measuring head and we have the Vernier scale here and now this is the scriber attached to the measuring head and you can see the carbide tip here and this can be used for scribing lines on the work pieces and this can also be used for measuring height of the work pieces. Now, I will explain how to use this for measurement of height of a work piece. I am taking a work piece here and we should initially check approximately what is the height of the work piece using a steel rule and then we have to adjust the gap between the datum and the bottom surface of the scriber and then we have to lock the measuring head using this screw and then this is the finer adjustment screw. I am just operating the screw so that the measuring the scriber just moves down and it just touches the work piece. So, the feel of the operator is very important here, we should not apply the over pressure here. If over pressure is applied, what happens is this base will move up as shown on the black bolt. Now, I am operating this so it is just touching the work piece. Now, I will read the scale. Now, this is the zero reference. Now, it is 40 millimeter on the main scale and now we have to see what is the coinciding division. 15th division is coinciding with a line graduation on the main scale. That means, 15 into 0.02 is 0.3. So, to the main scale reading value that is 40 millimeter, we have to add the reading of the one year that is 0.3. So, the height of this work piece is 40.3 millimeter. Now, we can see here setting of height cage using slip gauge. So, initially we have used a slip cage here and we have used a lever type dial indicator and any required height can be set using this arrangement. So, we can use this slip cage and say this is a 40 millimeter. So, now we have to adjust, we have to move the measuring jump so that this reads 0. So, in that case we have set the height cage to 40 millimeter diameter and then we can use this setting for the comparison purpose to check the height of other work pieces. In this case we are using the vernier height cage as a comparator and then we have digital height cage. You can see the base of the digital height cage and then beam of the digital height cage. Now, here instead of vernier we have a digital readout. We have hold option for holding the data point and then we can fix the tolerance values. So, we can quickly take the data point and take the readings because of the digital display. Also, there is a provision for transferring the data to a computer via RS-232C for data transmission and this will be useful for statistical quality control. Now, there are some advanced digital height cages. A photograph of advanced digital height cage is shown here. This is the base of the height cage and this is the column or beam of the height cage and then we have a wheel for height adjustment when we rotate this depending upon the direction in which we rotate the probes will move up and down. Now, you can see the measuring probes here. We have arrangement for fixing multiple probes. One more probe we can fix here. So, both the probes we can use together. Now, this is the display unit for displaying the data. Now, what are the various features of this or such a advanced digital height cage? We can see here perpendicularity measurement. This instrument can be used for measuring the perpendicular I will just write some simple sketches. Say we have some workpiece like this. So, we can fix a probe here and we have to move the probe towards the workpiece and we have to just touch the workpiece and then we have to move the probe up and again we have to just touch the workpiece. Then, if there is any difference that gives the perpendicularity measurement. Similarly, we can use this for diameter measurement. Say we have a workpiece with a hole like this. So, this is the workpiece with a hole. Now, what we can do? We can move the probe and we can make a contact here. First contact, second contact somewhere here and third contact. Then, these three data are supplied to the microprocessor attached to the instrument which will calculate the diameter of the hole and it also calculates coordinates of the center point. Then, circle pitch measurement. Say we have some 2-3 holes like this. This is first hole, this is second hole and then say we have third hole. So, now, the diameter of all the three holes we can measure and now say we want a pitch circle pitch measure. That means, what is the this is the center of first circle and this is the center of second circle and this is the center of third circle. What is the pitch? What is the distance between the centers of different circles? So, that can be calculated. The microprocessor will calculate the data and it will display the circle pitch measurement. Then, multiple probes can be used together. Now, we have fixed one probe here and we can also fix one more probe here. Together, we can use both of them together we can use for so that measurement becomes very fast. I will just write a rough sketch. So, we have some work piece like this. So, there is a projection in the work piece. Now, I want this distance to be measured. So, this is the distance to be measured. Now, what we can do? We can rotate this wheel so that this probe will make contact with the surface and then again we rotate the wheel in the other direction so that the probe that is fixed here will make contact with this. So, the difference in reading will give the distance between these two surfaces. So, for such quick measurements, we can use multiple probes and then we can also attach extra long probes. So, we have some work piece like this. This is the work piece. Now, we need to measure the diameter of this inner hole diameter of this inner hole and also we need to measure the distance between this surface and this surface that is depth of inner hole. Now, in this case we can always fix extra long probes and then that probe will come here it will make contact and then we can move the probe inside the hole. So, that difference in reading gives the depth. Also that extra long probe can be used to measure the diameter of the inner hole. So, this is about extra long probes. So, the probes are available in the length of 100 millimeter, 200 millimeter like that. Then data transfer facility is provided for statistical quality control purpose. All the data measured data can be supplied to a computer where in the SQC's offers are available. So, it can be data can be used for processing and another important feature of such a device is air cushion with built in compressor. Now, the weight of this will be like 25 kg or 30 kg. So, it becomes heavy. Lot of effort is required to move this instrument over the surface plate. So, to make it easy moving the first sliding the instrument, air cushions are provided at the bottom of the base. So, and it is built in compressor. It has its own built in compressor and the external compressor is not necessary. So, because of this arrangement, we can easily slide the worthier height cage on the surface plate. And another beautiful feature of this instrument is whenever by mistake the operator tries to move the height cage beyond the surface that is available on the surface plate. Immediately there will be air locking the instrument will be it gets clamped to the surface plate. So, that it will not fall and then we have built in battery facility depending upon the usage the its life will be like 500 hours or 1000 hours like that. And then we have swiveling display. So, this display can be swivelled it can be swivelled like this. So, that the reading becomes easy. And then measuring force adjustment facility is available in this depending upon the workpiece whether it is soft material like rubber, plastic or hard material like metal. We can adjust the measuring force it can be force can be like 1 Newton or 2 Newton or 3 Newton depending upon the workpiece we can adjust the measuring force. And another very important feature is go no go judgment is possible. So, any physical quantity for example, high diameter etcetera will have some tolerance and those tolerance values we can feed to the instrument. And then when we make the actual measurement the microprocessor will check whether that measured quantity is within the tolerance or not. If the measured quantity is within the tolerance specified then it will indicate that it is acceptable workpiece is acceptable. If it is beyond the limits then it will indicate that should be rejected by displaying some red color. So, like this we can use this instrument for quick judgment like limit gauging type of work. And then this can be used working the temperature range is from 0 to 40 degree Celsius. So, within that range we can use without making any external thermal compensation. And the mm to inch conversion is possible this can be used for measurement of distances in a metric system as well as in the inch system. Now, there are some more features perpendicularity of this height gauge is 0.006 millimeter. That means, range these instruments are available with the range of like 300 millimeter, 600 millimeter and 900 millimeter. And over the height over the full range the perpendicularity that means, this surface will be perpendicular to the vertical movement. And that error will be within 6 micrometer and then the vertical movement that is straightness of this of such an instrument will be like 4 micrometer. And 60000 data points can be stored in the memory of this such instruments and whenever required they can be retrieved and used. And the resolutions switchable resolutions are possible like 10 microns, 1 microns and 0.1 micrometer. That means, depending upon the accuracy needed we can always switch we can select the appropriate resolution. Now, let us start the discussion on another very important instrument that is micro meter. Now, let us study some points about the history of the micrometer. Now, you can see here this picture shows a micrometer designed and developed by James Watt in 1772. You can see that there are two dials are there and two pointers are there. And then we have that U shaped body of the micrometer even now we are using U shaped body of the micrometer with little variations and this is the annual fix to the body and this is the movable spindle. So, we have to keep the workpiece here and we have to move this and then by reading these two dials we can get the dimension of the workpiece. And then this micrometer is developed by Gene Palmer in 1848. That means, approximately after 70 or 75 years Gene Palmer improved the micrometer. Here you can see this is too huge we have to fix this micrometer to may be a table surface by using bolts whereas, here this is this can be hand held very small instrument. Now, let us discuss about the anatomy of outside micrometer. Now, this is the frame of the micrometer made of steel and now we can see here heat insulator is provided here a plastic material is provided here. So, when the operator holds the micrometer is body temperature will not flow heat will not flow to the body of the micrometer. So, that the thermal expansion of the body due to the body temperature of operator will be less. Now, we have a annual fix to the frame of the micrometer and then we have a spindle which can be advanced or it can be retracted inside the sleeve. This is the sleeve wherein we have to insert the spindle and the spindle has finely cut threads their ground threads the pitch of this screw is normally 0.5 millimeter. Now, these two are the measuring faces measuring faces are very important they are heat treated ground and lapped and then stabilization is required. So, that internal stresses are relieved so that they will not deform and the faces are lapped and the measuring face flatness and parallelism between these two surfaces is very very important flatness and parallelism can be checked using optical flats and normal flatness value will be 1 micron or less than that and parallelism will be 1 micron or less than that depending upon the accuracy of the micrometer and now we can see there is a clamp here spindle lock for locking this spindle at any desired location and now this is the sleeve on which we have scale graduations this is called sleeve scale or main scale and then we have the timble. So, this is the timble portion so this side of the timble right side of the timble we can see that they are knurled for easy rotation of the timble and on the left end of the timble we have again graduations we will see about this graduation after some time and then there is a nut here which is fixed to the inner sleeve. So, when we rotate the timble, timble is rigidly fixed to the screw when we rotate the timble this screw will move in and out that means the spindle can be advanced towards the anvil or it can be retracted now sometimes due to continuous usage there may be some clearance between the screw and the nut. So, we have to adjust the clearance for that there is an adjustment nut when we rotate the adjustment nut the clearance between the main nut and the screw will be reduced and then hence slackness or backlash can be eliminated and then we have a ratchet stop arrangement to apply uniform measuring force. We will see the construction of this ratchet a little later. Let me explain how to use the micrometer this is the frame of the micrometer you can see that ribbed shape ribbings are there so that it becomes rigid and then here the range is mentioned 0 to 25 millimeter and then the resolution of this instrument is 0.01 millimeter we can see the carbide tipped anvil and carbide tipped spindle the clamp for clamping the spindle the timble sleeve and ratchet now before using this micrometer we have to clean the faces anvil face and the spindle face with a clean cloth or smooth paper so that dust particles and oily layer is removed and then we have to unclamp the spindle and then slowly we have to rotate the timble like this and then we have to operate the ratchet till we get one or two clicks. Now we have to observe the reading now we can see the reference line and this is 0 on timble it is not coinciding with the 0 on the sleeve that means there is some 0 error we have to eliminate this 0 error before using this instrument further an arrangement is provided when we rotate this micrometer so this is the backside view we can see backside of the sleeve there is a small hole now a spanner is provided with the micrometer now we have to use this spanner and we have to operate the we have to rotate the sleeve in proper direction so that the 0 error is eliminated. Now we can see the 0 error is eliminated and now this instrument is ready for using now we can see the anvil surface close view of the anvil surface sometimes now the carbide tipped anvil surfaces are also available so that we are is less. Now flatness of measuring surface measuring surface as well as anvil surface is very very important they are ground and lapped and flatness error will be below less than 1 micrometer and the spindle surface and the anvil surface should be parallel if there is any taper inclination then the error will creep in so it is very essential that these two surface anvil surface and major spindle surface should be parallel and a parallelism of less than 1 micron is maintained. The parallelism and the flatness can be checked using optical flats so this shows the close view of a spindle surface so it is very essential that we should maintain all these precision instruments whenever they are not in use for a longer time we should apply a petroleum jelly to all the important parts of the moving parts of the instrument. Now we can see here since the coating was not provided there is a corrosion now crew has been removed out of the sleeve now we can observe the ground threads very fine threads are there the pitch of the matrix micrometer will be normally 0.5 millimeter and you can also clearly see the taper on the timble surface and we can also see the graduations very clearly and this is the micrometer stand and we can clamp it and the inclination of this can be adjusted by rotating this knob so whenever required we can use the micrometer stand if the workpiece is very heavy when we have to hold the workpiece with both the hands then in that case micrometer stand will be very useful. Now some inner details of the micrometer we can observe here this is the adjusting nut and then we have main nut so main nut has both internal and external thread inside also there are threads and this will be mating with the main screw of the micrometer and outside of the main nut also we have threads so when we rotate this adjusting nut we can see here the slots are provided and using the spanner we can rotate this adjusting we can rotate the adjusting nut so that and in the main nut we have slots slots are cut so when we rotate the adjusting nut the main nut gets compressed and it embraces the main screw and hence there is any clearance that is eliminated and backlash is eliminated and then the ratchet mechanism disassembly I told that ratchet is used to apply uniform measuring the force when the measuring torque exceeds a certain value which is decided by the spring we can see here there is a spring here so the spring tension decides what is the amount of force that is applied on to the workpiece normally it will be like 5 newtons 6 newtons 7 newtons and since we apply uniform pressure this ratchet mechanism is used when the torque exceeds the set limit which is decided by the spring now you can see here this these two parts one acts as ratchet and another acts as pall so when the torque exceeds this pall will slip and hence the further movement of the spindle will stop this is how the uniform pressure is applied on the workpiece now let us study how we can use the micrometer to measure the thickness of this plate now I am keeping the spring tension on the plate on the datum surface and then I am moving the micrometer towards the workpiece and then slowly we have to operate the thimble now the spindle is advancing and it is moving towards the workpiece it is moving towards the workpiece now it has just touched the workpiece and giving I am using the ratchet to apply uniform pressure and then I am clamping the spindle slowly we have to remove the workpiece now we have to take the reading now main scale or sleeve scale reading is 0 1 2 3 4 so 4 millimetre and then we have to take the on the thimble we have 0 1 second second gradation is coinciding that means second gradation means 2 into 0.01 that is 0.02 so the thickness of this plate is 4.02 millimetre now let me show how we can measure the outside diameter of workpiece I am showing you the thickness of the workpiece I am showing the measurement of o d of this portion so now the workpiece is between anvil and spindle now slowly we have to rotate the thimble in the reverse direction spindle is moving towards the workpiece now it has just touched the workpiece now let me operate the ratchet and then we have to clamp the spindle now slowly we have to remove the workpiece now we have to read the scale so this is the main scale 0 5 millimetre 10 millimetre 11 12 13 and then 13.5 13.5 and then thimble reading 45 46 so this reference line is between 46 and 47 we will take 46 46 into resolution that is 0.01 so the thimble reading is 0.46 so this 0.46 we have to add to main scale reading that is 10 millimetre 13.5 13.5 plus 0.46 that means 13.96 13.96 is the diameter of the workpiece now let us see the variants of the micrometer there are various kinds of micrometers available in the market now let us study this inside micrometer and this type micrometer and the large micrometers and dial type micrometer now this shows front view of inside micrometer I can see this is the sleeve on sleeve we have the main scale and then this is the thimble and this is the ratchet and now this jaw is fixed to the sleeve and when the spindle move when we rotate the thimble spindle moves in and out depending upon the direction of thimble so to the spindle a moving caliper or moving jaw is fixed so in this case this part of the jaw this jaw will move and this is fixed to the sleeve and now we can see the range of this instrument it is 5 millimetre to 30 millimetre that is the range and then we can see the markings on the sleeve so it is in the reverse direction so this is 10 15 20 25 30 like that so between two graduations here the spindle movement will this represents 1 millimetre and below this we have markings so this will give 0.5 millimetre readings so various ranges are available like 175 to 200 millimetre with 0.01 millimetre resolutions are available so here again thimble graduations are visible now this is a back view of inside micrometrics this is used for measuring the inside dimensions like the distance between groove or inside hole diameter for such things we can use this now what we can see in this photograph there is a guide rod and this is the guide so when we move the thimble this movable jaw will move and this is guided by this guide rod guide rod and the guides now the resolution of this instrument is 0.01 millimetre now we can observe one thing here the jaws of this instrument they are contoured or radiused so this is necessary when we want to measure the inside hole diameter so if we have a flat surfaces then the measurement will not be correct we can see the example here I will write some sketches so this is the inside so this is the hole if we have a flat jaw then the contact will be like this contact will then this much error will occur in the measurement so because of this radiused jaw the contact will be like this and then there will not be any error so this is the reason why the radius is provided on the jaws now another variant is disc type micrometer this is used for measurement of spur gears and helical gears this the details of this we will see in the appropriate module when we discuss about the gear measurement and let us learn something about large micrometer now the in the market the very large micrometers are available with the range 25 to 2000 millimetre now one thing we can observe the measuring head range remains same 0 to 25 millimetre and then we use setting masters to set the distance for example in this case the we have a setting master of say 25 millimetre length now we have to place the setting master between animal and jaw and then we have to rotate the timble so that the spindle will just touch the surface and then the setting will be 25 millimetre because we are using 25 millimetre setting master and then if the work piece is greater than 25 millimetre then we can use the this instrument that means the range of this instrument becomes 25 to 50 millimetre with this 25 millimetre setting master now we have to place the work piece here and then we have to rotate the timble and then we have to take the reading and to this reading we have to add the size of the setting master then we get the work piece size and you can observe insulating gripper is provided here so we have to hold the micrometer use at this grip insulator heat insulator so that body temperature will not transfer to the body when we hold the micrometer for a longer time like 20 minutes or 30 minutes and if heat insulator is not provided the body temperature will heat will get transferred to the body and then it expands and then the measurement error will occur now various sizes of setting masters are available in the range of 25 to 2000 millimetre size in steps of 25 millimetre so we can depend upon the work piece size we have to select the appropriate setting master and we have to set the micrometer and then we have to use again these setting masters the flatness of surface of the setting master surface is 0.3 micrometer or less than that they are ground and lapped so that the flatness very good flatness is achieved also the parallelism between this working surface and this working surface is very very important and it is maintained like 2 micrometer or less than 2 micrometer parallelism is maintained so that the we get good accurate measurement. Now, this is another variant of the micrometer wherein we have the body and then spindle anvil clamp this portion is common to our common micrometer and we have the moving anvil see the important feature of this micrometer is anvil also moves in and out and there is a slider to move the anvil in and out and at the other end a dial is fixed so the movement of anvil also can be fixed by using this clamp and then movement of spindle also can be it can be clamped using this clamp now what is the advantage of using this dial see dial can be used to maintain uniform pressure in the absence of ratchet the dials are provided so that when we rotate the thimble the now we have the work piece here when we rotate the thimble spindle moves and then the force is applied to the dial indicator and then the pointer moves. So, by noting down the amount of rotation of the pointer we can maintain uniform pressure on the work piece that is one thing other thing is dial can be used for no go go and no go judgment that means sometimes the actual size of the work piece is not required what is required is whether the work piece is acceptable or not whether it is in the within the range. So, in such cases we can insert the work piece here and then we can move the we can move the anvil inside by operating the anvil operating the slider and then we can keep the work piece here and then we can release the slider. So, that anvil moves towards the work piece and then we have to note down what is the reading if the reading is within the limits the work piece is accepted if it is beyond the work piece is rejected. We conclude this session in this session we discussed about the height cage the height different types of height cages and the construction of height cages and what are the various uses of height cages and we also discussed about the micrometer the history of the micrometer the construction of the micrometer what are the various types of micrometers in the next session we will continue the discussion on other types of micrometers. Thank you.