 Hi, welcome you all for the series of lecture on metrology. Now, we will start module 5 lecture 3. In the previous session, we discussed about the various aspects of stylus type surface finish measuring instruments. Now, we will continue the discussion. So, in this lecture, we will study about the skid geometry and then stylus geometry and what are the various types of pickups used in surface finish measuring instruments and then what are the various specifications of stylus type instruments and then we will move to the mechanical roughness indicator, other device used for measurement of surface roughness. And finally, we will discuss about the comparison specimens. Now, you can see here the in the previous session, we discussed about skid-less instrument that is the reference surface is provided external to the surface under question. Whereas, in skid type instruments, the reference or datum is provided by using a skid which rests on the surface which is to be measured and this T is the stylus which moves up and down depending upon the asperities on the surface and it has a pointed end. Whereas, if you see the diagram, this skid is having a large radius so that it will simply slide on the surface. So, another arrangement is use of shoe. You can see here in this skid, we have an external convex shaped surface. In the case of shoe, we have a flat surface which is mounted to the body of the pickup. You can see here it is swivel mounted. So, whenever there is inclination of the surface because of this swivel mounting shoe will also get inclined and then it slides on the surface. Now, the radius of skid must be relatively large compared to the feature being measured. When the tops of the asperities are very close as we can see here, the peaks are very close and when we move the skid, so this is the locus of the centre point of the curvature of the skid. So, this is almost a nearer to the required profile but as the spacing increases as shown in the figure see here, the skid begins to move up and down at the same width and the vertical movement of the skid becomes equal to the vertical movement of the stylus making the measurements useless. That means, no longer the skid will provide a datum surface. So, always it is necessary that the skid radius should be too big compared to the roughness or the peak spacing. Now sometimes we need to measure the primary texture and sometimes we need to measure the charter. So, in such cases what type of stylus one should use. For measuring the roughness as shown here, so this is the roughness of the surface and we need to measure the roughness of the surface then we should use a very pointed stylus and the stylus should move in this particular direction, so that we get the surface roughness profile. When we need to measure the charter mark then it is necessary that we should use a very wider stylus and it should be moved in the direction B as shown in the picture. So, physically selecting the different kinds of stylus is very difficult and the commercially available measuring instruments only one stylus is provided. So, in order to segregate, separate the charter characteristic from roughness and to separate the waveiness and to separate the form of the workpiece, we need to use appropriate electronic filters. Now this shows the stylus geometry. Normally the cone angle of 60 or 90 degrees is used on the stylus. That means the stylus will have an angle of 60 or 90 degrees and the end will have radius of 2 microns or 5 microns or 10 microns. So, which will move on the workpiece surface. You can see here the size of the stylus tip is 2 micron by 3 micron or we can have a very narrower stylus with 1 micron wide and 2 micron longer. So, such geometries are necessary whenever we need to measure very narrow the surface roughness in the narrow places. And then relative to the surface topography, we should use a very thin stylus so that it can enter into the valleys. If the stylus is too big like this and then with the radius of 5 microns or 10 microns, then see it cannot enter into the valley because of this size, it cannot enter into the valley. So, it is necessary that we should use a very shallow or very thin stylus so that it will enter into the valleys and we get the proper surface reading. And then there is mechanical filtering effect due to the stylus geometry. Normally, a radius of 5 to 10 microns is provided at the tip of the stylus and when it is made to move on the surface, you can see the stylus, the center point locus you can see whenever there is a peak, the locus becomes very smooth. So, because of this, this will definitely affect the surface finish reading. Height is unaffected, but we do not get peaks, it gets rounded. Also, the depth gets reduced because of this shape of tip and then here you can see the traversing length through which the stylus will move. There is some allowance for run-up and there is some allowance for over travel and these two are not considered for the evaluation. So, the remaining length which is known as evaluation length is divided normally into 5 lengths. Each smaller length is called sampling length and each sampling length is analyzed for the various parameters like rp, rt, rmax etc etc. The average values are calculated and then we get the averaged ra, rrp or rmax results. Now, sometimes what happens? We have skid and then at some distance we have stylus. So, if they are in phase that means the stylus tip is also in valley and then skid is also in valley. If this is the case, we say skid and stylus they are in phase condition and if the stylus is inside the valley and the skid is on the tip of the peak then we say it is out of phase condition and this is in between condition. So, what is the effect of this out of phase on the surface profile? Now, you can see here we have the surface, this is the actual surface and this is the skid and the stylus. Now, you can see they are in out of phase condition. So, because of this we get a graph like this ok. So, which is actually distorted the actual surface is like this whereas because of out of phase condition the profile is distorted it looks as if there is some waveiness. So, we have to use appropriate software correction we should make to eliminate this out of phase condition. And then let us study about different types of pickups used. So, this picture shows a position sensitive pickup ok. This is a variable inductance pickup you can see the skid and the pointed stylus here. The stylus is mounted on a beam ok and then there is a knife edge and then the other end of the beam is connected to the armature which moves inside the coils and there is a knife edge. So, it will act as a pivot and the skid is mounted to the body of the pickup. Now, the because of the variation of roughness this stylus will move up and down and these movements are converted into when the stylus tip moves in and out the armature also will move in and out and then the induct the current characteristic will change. So, that change in the current characteristic will is amplified an amplification of 50,000 to 1 lakh are commonly used depending upon the surface roughness. So, this amplified signals are sent to the software for analysis purpose to calculate different parameters like R A, R P etc. Now, we can see here another kind of pickup this is moving coil pickup. Now, you can see here we have the stylus which moves on the surface and when the stylus moves the coil connected to the stylus will move inside a permanent magnet inducing voltage in the coil. So, the voltage that is induced depends upon the velocity of the coil if the roughness is more or if the surface is something like this. So, this up and down movement of the stylus is rapid that means there is higher velocity of movement of stylus hence the higher voltage is generated. If the asperities peaks and valleys are very small then the velocity is less and the voltage that is induced is also less. So, the voltage output is processed to get the various parameters. Now, the skid can be fixed to the housing like this is the housing in which the moving coil pickup is present or mounted. Now, we can always this is the surface roughness we can mount the skid on the mounting housing of the pickup. So, you can there are piezoelectric pickup now when the stylus moves up and down because of the geometry variations. So, the other we have a piezoelectric crystal. So, because of this movement the crystal gets compressed the geometry of this pickup this piezoelectric crystal will also change hence there will be voltage output. So, depending upon the movement of the stylus this voltage output will also vary which is connected to the computer for calculating the surface parameters. Now, here you can see a tip, a conical stylus tip the angle is 90 degree and there is a radius of about 2 to 3 microns. So, this is a magnified view of stylus tip. Now, let us move to the specifications of surface tester. So, the various parameters and the corresponding values we can see here. The instruments or surface testers are available with varying measuring ranges like measuring range is that means movement of the drive unit is 16 mm, 5.6 mm movement 25 mm, 50 mm. So, like this different ranges are available and the detector range to resolution. So, detector range is up to 360 micrometer with resolution of 0.02 are available or 100 micron detector range with a resolution of 0.006 micrometer are also available and very fine resolutions of 0.002 micrometers are also available and the measuring speed it varies from instrument to instrument the instrument with 0.25 mm per second and 0.5 mm per second, 0.75 mm per second measuring speeds are available and the retracting speed see when the stylus moves during measurement it moves very slowly with the specified speed of 0.25 mm per second or 0.5 mm per second. Whereas, while retracting to go to initial position it moves at a speed of 1 mm per second. Now, what is the force that is applied from the stylus on to the surface. So, it is very small force of 0.75 milli Newton with 60 degree cone angle stylus 4 milli Newton for 90 degree stylus and skid force is about 400 milli Newton's and various roughness parameters can be obtained by these roughness testers like r a value r y r z r max etcetera etcetera and then we can always select the number of lens or it is fixed in the instrument like one sampling length or two sample up to 20 sampling lens we can select normally 5 sampling lens are used and storage with memory card up to 10000 measured profiles can be stored and 500 display images can be stored and 500 statistical data can be stored. So, whenever required we can retrieve these data and profiles and maximum power consumption is about 50 watts they can be operated using the batteries and then the measurable hole diameters normally very thin probes are provided with skid and stylus and these can enter into holes. So, this diameter is 4.5 millimeter and very thin probes are also available and they can enter into holes with 2.8 millimeter diameter. So, with a special request we can obtain the very thin probes and special necessaries are always available probes are available to measure the surface on the gear tooth and deep groove detectors like say we have a groove like this. So, the probes can enter into such narrow grooves and they can measure the surface finish at the bottom of the narrow groove. So, they can enter into the hole or the narrow slot up to 9 millimeter down and the width is 2 millimeter. So, such special accessories are also available and support feet set for adjusting the height support feet sets are available and attachment for deep bore surface measurement if say we have a hole of depth 135 millimeter. So, probe can enter into that and it can measure the surface finish. Now, let me show an instrument stylus type instrument you can see the display of the instrument. I can see the various buttons to start the instrument switch on the instrument and there is a red button to start or stop the instrument and this display will show what is the cutoff length that is selected and it will also show what is the parameter that is selected. Now, you can see the movement of the stylus pickup is it is moving it is moving in the surface now it is retracting. Now, cutoff length selected is 0.8 millimeter and it is showing the parameter RA, RA value is 0.05 micrometer. Now, we can see another instrument you can see the various parts of the instrument stylus type instrument. This is the pickup inductive pickup yeah this is the inductive pickup you can see the stylus here with this and this is the stylus. Now, we will see how to use this instrument to measure this roughness of the given surface you can see the surface the workpiece is kept here this V block is used only to support the workpiece. Now, the pickup is moving and then now it is retracting it is going to the initial position. Now, it is showing the RA value RA value is 1.89 micrometer and cutoff length that is selected is 0.8 and also we can see how many sampling lengths are used 0.8 into 5 sampling lengths. Now, other parameters also you can see r y parameter is 11.42 micrometer to get the different values we have to operate this button parameter button. So, r y is 11.42 micrometer and r z is 11.42 micrometer and r q is 2.45 micrometer. Now, you can see another workpiece is being inspected it is moving on the yeah it is going back to initial position after tracing. Now, you can see the display it is showing r q is 0.55 micrometer you can see the various buttons here this is a start and stop button parameter button and then cutoff length selection and the filtering we have to we can select the filters and then we can use this in the two modes metric mode and inch mode. So, RA value of this particular surface is 0.45 micrometer. So, these are ground surfaces now r y is 2.62 micrometer and r z is 2.62 micrometer and r q is 0.55 micrometer. Now, you can see one more workpiece it is placed in position and now style the pickup is moving it is sensing the surface and it is going back to its initial position. Now, we can immediately it gives the readings RA value is 1.98 micrometer r y value is 10.37 micrometer r z is 10.37 micrometer and r q is 2.38 micrometer. Now, while storing it is very essential that we should retract the pickup and then we should store it now we can see the inductive pickup is being retracted it is moving inside the body and then it moves up into the proper position. Now, we will see another surface finish instrument stylus type instrument you can see the stages x y table for mounting the flat work surfaces. So, we have x micrometer and in y direction also there is a micrometer for positioning of the workpiece and there is rest a blade is provided to support the workpiece and this is the work table with ball joint this can be used to orient the tapered workpieces and now this is the drive unit pickup drive unit and you can see there is a knob for adjusting the orientation or the inclination of the pickup drive unit final adjustment of the inclination we can do here and we can select the required cutoff length and now you can see the pickup inductive pickup. So, this pickup can be moved up and down depending upon the workpiece height. So, this is for final adjustment and you can see we have a keyboard here. So, when we operate these keys up and down the keys this whole drive unit will move up and down and this is the column to guide the up and down movement of the drive unit. So, depending upon the workpiece height we can move the drive unit up and down. Now, we can see the pickup yeah this is the pickup and this is the guard for the pickup. Now, we can see the dedicated computer interface with the mechanical unit. You can see the various buttons we have the start button here and stop and return button. We can select various parameters like rz, rz1, rmax, rpm, rpi, rp1, rp, ra value, rq value, r3z value and then the waveiness parameters like wt, wt parameter, rt parameter, pt parameter and then the cutoff also we can select cutoff length. We can select 0.08 millimeter or 0.25, 0.8, 2.5 and 8 millimeter depending upon the process machining process we can select appropriate cutoff length. And we can make we can create our own program what are the various parameters we require we can enter we can enter the parameters required and then we can create our own program. And we can also select the filters different filters and what type of profile we require that also we can select whether we want roughness profile or waveiness profile. So, that we can select and this is the printing unit. So, it will give us the various it will print the various parameters also it will give the profile. So, this is the printing unit we can also select the magnifications how much vertical magnification is required how much horizontal magnification is required those things we can select. Now let us move to another contact type instrument which is known as Mccrin it is the short form of mechanical roughness indicator. So, commercially it is known as Mccrin 3 and this is used for practical shop work inspection. So, all the measuring instruments surface finish measuring instruments if it is supportable instruments are also available which can be carried to the machine shop and the surface finish of the components can be checked. And for the final inspection we have to move the work piece to the metallurgy lab where in very sophisticated metallurgical surface finish instruments will be available and surface roughness of the work piece can be checked there. So, for very critical components very fine instruments are used to check the surface finish. Now we will learn about this Mccrin 3 which can be used in the machine shop see the advantage of this instrument is measurement is possible without deburring and without unloading the work piece. You can see here in this picture a work piece is in the loaded condition it is placed between the check and the dead center and it is not removed from the setup. In the machining condition the machine is stopped and then we can take this device Mccrin 3 and then we can measure the surface roughness. So, you can see the picture here photograph here we have this black thing is the body. So, this is the body of the instrument so which has a dial. So, this dial inside we have a scale round scale which shows the roughness values in terms of grades n1, n2, n3, n4, n6 etc etc. Also the RA values in terms of micrometers like 0.025, 0.06, 0.1, 0.2 etc etc and this indicator can be rotated inside this housing it can be rotated and it can be fixed to the body at any particular orientation further a screw is provided we can rotate it as required and then we can fix it to the body using this fixing screw and now you can see there is a trigger here say the instrument is like this. So, this is the dial so inside there is a scale and then there is a pointer and then there is a screw to fix the dial in the required orientation and then there is a trigger. So, we have to pull this trigger so you can see here with one finger we can pull this trigger. So, when we pull the trigger here there is a very thin stainless steel blade the thickness is about 50 microns. So, at the end of the thin blade there is a tip with a sharp corner it is screwed to the thin blade. So, this is the thin blade of stainless steel with about 50 micron thickness and when we pull the trigger this blade will move out. So, when we pull when we keep on pulling this trigger this blade will move in and move out now how to use this macrin for measurement of surface roughness. So, initially we have to calibrate this instrument using standard surfaces provided with the instrument. So, two surfaces with N3 and N5 roughness grades are provided using those specimens we can calibrate this instrument. So, those details we will see when we conduct the experiment. Now after calibration so we have to hold the instrument on the workpiece surface which is to be inspected and see initially we should use a very small angle it should be almost like this with the trigger and then the you can see here the tip is in contact with the surface to be tested. So, in this condition we have to pull the trigger now if the tip slides smoothly then we have to increase the angle you slightly increase the angle may be by 2 to 5 degrees again you pull the trigger again the tip is made to move on the surface say it slides again. So, in that case again you increase the angle may be by 5 degrees again. So, you keep on doing this till the tip does not slide. So, in that case this blade will bend like this. So, the blade that is available here that is placed here it bends like this. So, that we can observe here through this window. So, when we conduct the experiment you can see that bending of blade. So, that angle is called critical angle. So, at that angle so what is the value indicated by this pointer that we should note down. So, that indicated value is the roughness of the surfaces. So, now it is showing a value between 0.8 and 1.2. So, the surface roughness is roughly about 0.9 micrometer or 1 micrometer r a. So, we can get very fine finish of about 0.9 micrometer r a or 1 micrometer r a in turning by suitably adjusting the machining parameters. That means if the surface is very fine the critical angle will be removed and if the surface is very rough then the critical angle will less. So, the advantage of this is without deburring the workpiece we can use we can measure the surface roughness and without unloading we can measure the roughness. Just we have to stop the machine we have to stop the rotation of the workpiece we have to maybe we have to clean the surface with a brush and then we can take the instrument and then we can measure the roughness. So, this is if it is roughness is not up to the requirement we can adjust the finer settings the feed rate and speed rate can be adjusted and again cut can be given and again that the surface can be tested. So, like this to control the machining operation we can use this instrument. Now, let me show how we can use Macrin 3 instrument for the measurement of surface finish. This is a very handy and very light instrument which does not require any electrical power and there is no battery inside. So, inside we have a pendulum which was operated by gravity and the pointer is connected to the pendulum. Now, along with the Macrin 3 instrument a reference calibration standards standard specimens are provided. Now, we can see the calibration standard which has two standard specimens with n 3 grade and n 5 grade. The surface finish of this surface is 0.1 micrometer and finish of this surface is 0.4 micrometer. This is n 5 grade surface and this is n 3 grade surface. Using this calibration standard we have to calibrate this Macrin instrument. Now, you can see the various parts of the Macrin 3 instrument this is the dial you can see the yeah this is the screw. So, we have to unscrew this and then we have to rotate this dial for calibration purpose. You can see the scale it starts from n 1 and it goes up to n 8 and in terms of micrometer r a it starts from 0.025 and it goes up to 4.8 micrometer. This is the range of this instrument. Now, you can see the body and you can see the trigger we have to operate the trigger. Now, when we operate the trigger you can see we have a stainless steel tin stainless steel blade and at the end of the blade we have a tip with a sharp corner. So, you can see when we operate the trigger the blade is along with the tip blade is moving and at the back side of the instrument you can see here we have another screw. So, before using this instrument we have to unscrew it so that pendulum is released. So, now pendulum can move. I am showing how to calibrate the instrument. Now, you can see we have to hold the instrument on the surface and then we have to operate the trigger so that blade moves. The stylus moves on the surface. You can see stylus is moving in the surface. Now, when it slides we have to increase this angle. So, at a particular angle you can see the blade starts to bend. So, that angle at which a blade starts to bend called critical angle. Now, you can see we have used N5 surface and so we have to rotate the dial so that pointer reads N5 and then we have to lock it. We have to lock this indicator. So, now similarly we have to calibrate using this N3 another surface N3 and now the instrument is ready for measurement. Now, we have taken a ground surface. You can see I am moving the tip on the surface which is to be inspected. I am operating the trigger. So, the tip is sliding. So, now again we have to slightly increase the angle. When the blade starts to bend we have to read the dial. So, I am taking another surface. We should start from a smaller angle. Now, you can see the blade is moving sliding on the surface. So, slightly increase the angle. Again operate the trigger. So, now you can see it just starts to bend. So, reading is between N5 and N6 or between 0.6 and 0.8. So, we can take it to be 0.7 micrometer rA. The surface finish of this surface is 0.7 micrometer rA. So, this is another ground surface. Again, you can see how to use this instrument. So, we have to keep a smaller angle and then we have to operate the trigger. Now, the tip is now it has started to bend. Now, the reading is between 0.025 and 0.05. Now, we will move to the measurement of surface evaluation by standard specimens. So, you can see a set of standard specimens. So, you can see the some surface, some specimens are convex and some surfaces are concave. Now, concave surfaces can be used to compare the surface roughness of drilled or honed holes. And these convex surfaces can be used to check or to compare the roughness with turned surfaces or cylindrical ground surfaces or cylindrical surfaces. Now, this set and this set and this set, they are flat surfaces. That means, so, these are these six surfaces, there are totally six surfaces. So, these six surfaces, they are produced by grinding process. And again, we have three flat surfaces produced by flat lapping process. And these three concave surfaces are produced by rimming process. And then we have six, totally 12 standard specimens are available here. These six surfaces are produced by vertical milling. You can see the tool marks. And these six specimens are produced by horizontal milling process. You can see the charter mark. So, now we can also see, we have a component whose surface is to be evaluated. And this is turned surface, cylindrical surface. So, we have to compare this with these convex specimens. Now, the skill of the operator is involved here. Personal factor is involved. A very skilled operator, I will be able to compare the surface of the workpiece with these standard specimens. And he will be able to evaluate the roughness of this surface. Now, this shows an enlarged view of the surfaces. So, these three surfaces, these three surfaces are flat lapped surfaces. And these three concave surfaces are rimmed surfaces. You can also see these roughness grids. So, here we have four triangles. That means very fine surface finish is there on these surfaces. The value is also mentioned here. So, this is 0.05 micrometer rA. And then we have 0.1 micrometer rA and then 0.2 micrometer rA. And then these six surfaces, they are ground surfaces with these rA values. Now, I am showing a standard specimen set. This is composite pocket set number 130 made by Robert Company. Standard specimens for the horizontal milling process, vertical milling process, turning process and then flat lapping, reaming, grinding. So, those specimens are available in this set. Now, you can see the standard specimens for flat lapping as well as for reaming. You can see the top three specimens are made by, they are for comparing the flat lapped specimens. And then bottom three surfaces, they are for reaming, for comparing the specimens or workpieces produced by reaming. Now, you can see that this set, it contains both flat surfaces as well as convex surfaces produced by turning operation. And it also contains concave surfaces produced by reaming operation. So, the workpieces produced by reaming can be compared with these standard specimens. Now, you can see there are six pieces for comparing the ground specimens. So, we have another six surfaces for comparing with horizontal milled workpieces. You can see the lay and vividness and those things we can see. And these six specimens are for comparing with vertically milled surfaces. And we have another set of six pieces for comparing turned workpieces. So, you can see the feed marks. These are produced by large feed rates. And here these pieces are produced by finer feed rates. Now, we can see the RA value for these specimens. So, these specimens in this particular row, they have a roughness of 12.5 micrometer RA. And this specimen has a roughness of 6.3 micrometer RA. And next one, this particular specimen is having a roughness of 3.2 micrometer RA. And then this particular specimen, it has a roughness of 0.4 micrometer RA. Also, the readings are available in CLA micro inch. Now, we can see this side also the roughness values are mentioned for these specimens, both in micrometer RA as well as CLA micro inch. And this particular surface is having this particular specimen is having a roughness value of 0.2 micrometer RA. And this particular piece is having a roughness value of 0.1 RA micrometer. And this last piece is having a roughness value of 0.05 micrometer RA. Again, you can see the surfaces produced by different manufacturing processes. So, these specimens can be used to compare or for visual inspection to find out the roughness value of the workpieces produced. So, we can compare the roughness of the workpiece with these surfaces having known RA value. So, by visual inspection, we can find the roughness of workpiece. Also, these workpieces can be used for scratch test. Now, let me explain the scratch test. Now, we have to take the specimen of which we have to inspect and then we have to move our nail on the standard specimen also. So, what is the feel on the surface to be tested? Same feel we should get on the selected standard specimen. And then accordingly, we have to note down the reading. So, here the personal factor is involved skill of the operator is very important. The same specimen inspected by different inspectors may give different results. Now, let us conclude this session. In this session, we discussed about the different types of pickups used in stylus type instruments and the design of skids and design of stylus. And then also, we studied about the use of macrin, a mechanical roughness indicating instrument, which is a contact type measuring instrument. And then we also studied about the use of standard specimens for comparison purpose. We can compare the surface of the component with the standard specimens whose roughness values are known and then we can assess the roughness of the surface of unknown surfaces. So, with this, we will conclude this session.