 Welcome you for the today's lecture. This is module 4 lecture 1. Now in this lecture, we will be studying about the various geometrical measurement, geometry measurement of the workpieces. Now in the present lecture, we will be discussing about the importance of geometric integrity of workpieces. Also what are the various definitions related to the part geometry measurement and then we will be discussing about the various symbols used to represent the geometric tolerancing and also a surface plate is most commonly used in the workshops for the inspection purpose. So, which is used as a datum surface. We will see a brief description of surface plate and then we will move on to the meaning of straightness and straightness tolerancing. Afterwards, we will see what are the various straightness measurement methods. Now let us understand the importance of geometric integrity of the components. There is an increasing demand for product reliability and efficiency which prominences the geometric integrity of components and assemblies. The components are to be produced as per the designers very strict specifications so that the function as expected. The measured components invariably contain various deviations from the nominal features and these deviations must be controlled during manufacturing for functional reasons. The various kinds of irregularities on the workpieces are broadly categorized into micro irregularities and macro irregularities. The micro irregularities contain roughness and wabiness on the surface of the components and the macro irregularities encompass the errors of size and form of the components. The deviation from the ideal form normally known as form error or geometrical deviations is one of the many aspects affecting the component performance. For example, the errors of cylindrical city on the pistons used in hydraulic pistons and hydraulic motors and pumps, they affect the efficiencies of the product. If there are any deviations like out of roundness, out of cylinderity and the pistons, so they lead to increased friction or increased leakage. So, the efficiencies of these products will definitely affect. So, it is very essential that we should control the errors while manufacturing and also it is essential that we should measure the various deviations to make, to ascertain that the components are within the prescribed tolerance limits. In engineering applications, we face the problem of measurement of geometrical features such as straightness, squareness, flatness, roundness, cylindricity, parallelism, concentricity, runout, etcetera, etcetera. In this lecture, we learn the methods used to measure the various geometrical features of engineering components. Particularly in this lecture, we will be discussing about measurement of straightness. Now, let us try to understand various definitions associated with geometric deviations of the components or geometric deviation measurement of the components. So, many times we use the term feature. A feature is a general term applied to a physical portion of a component such as a surface or hole or a slot and these features are generally part surfaces. For example, if we have a component like this, so we have this particular surface and the feature means whether this particular surface is straight or cylindrical or is there any out of roundness. So, such things are known as feature of a component and a datum is theoretically exact plane or a point or an axis from which a dimension is measured. For example, when we want to measure the height of this component, it is essential that we should take this particular surface as a reference. So, normally what we do, we keep the component to be measured on the surface plate. So, this is the surface plate and then with reference to this surface, we measure the height of this component using appropriate instrumentation. So, this surface plate, top surface of the surface plate will act as a datum. Actually, the datum is a theoretically exact plane or it could be a point or an axis, but when we consider the top surface of the surface plate, again there will be variations due to manufacturing variations. Now, this top surface even though the variations are there on the top surface. Now, we try to control the deviation of deviations, manufacturing errors on the surface plate and we try to achieve a very flat surface. That means the surface plate is often used to simulate the datum. So, top surface of the surface plate is used as a datum and that surface is simulated as a datum. Now, a datum feature is nothing but a part feature that contacts a datum. Since datums are theoretically exact, we use datum features as the origin for measurements. Now, in this diagram, we can see this is the surface plate. This is the surface plate and there is a line, which is a theoretical line, which is a theoretically exact datum plane. And then on the surface, top surface of the surface plate, again there are micro irregularities and we take this top surface as simulated datum surface and now the datum surface, the part surface. On the part surface, we have the variations like this. So, the datum, that particular surface, the datum feature is on the part surface and the simulated datum is on the surface plate. Now, we should try to understand what is the meaning of datum reference frame. It is a set of 3 mutually perpendicular datum planes. Now, this datum reference frame is very essential in order to measure the component properly. Now, 3 mutually perpendicular datum planes means, so this is one reference plane and then we can keep another reference plane, vertical reference plane perpendicular to this primary reference plane. This is primary reference plane or reference plane number 1 and this angle should be 90 degree. This angle is 90 degree and then perpendicular to these two, we should provide another surface. So, this is second reference surface and this is third reference surface. All the three are mutually perpendicular. Now, we have to keep the workpiece, which is to be inspected in this frame and then we should use these three reference planes as references or datum surfaces and then we should take the measurement. For example, when we want to measure the height, so the prime, this horizontal surface is taken as the primary reference. So, when we want to measure this particular distance, so again this plane is taken as reference and then this distance is measured. Similarly, when we want to measure this distance, now this particular plane is taken as the reference and then measurement is made. So, this is the datum reference frame but how do we physically create the reference frame so that we can use it during the physical measurement. Now, you can see here we have a surface plate. So, this surface plate can be used as primary reference surface or horizontal reference surface. Now, angle plate, angle plate we have to keep on the surface plate. So, where in this inclination is 90 degree. So, now we have formed the vertical second reference surface. So, similarly we can keep one more angle plate here. So, this forms the third reference surface. Now, we can keep the component within this frame and we can make the measurement. In some cases, only one reference plane may be required. For example, we say we have the surface plate and we want to measure only the height of the object. In that case, we require only one reference plane. In some cases, two references may be required. In some cases, three reference planes may be required. The three planes provide a common reference for the origin and direction of measurement for draftman, machinist as well as inspector. For all these three personnel, the datum reference frame is required in order to draw the, in order to show the various dimensions. So, again the draftman will use a particular point as reference. With this reference, he gives all the dimensions. Also during the manufacturing in the machine shop, the operator will use the same reference point and he will measure all the dimensions or give the cuts. And similarly, during inspection, the same reference frame is used during inspection by the inspector. Now, we should understand that features on the workpiece can be external or it can be internal features. For example, external feature means the diameter of a shaft. So, this diameter is an external feature. Similarly, the height of the object is an external feature. Width of the object is an external feature or say we have some workpiece with some external feature like this, a profile. This is also an external feature. Similarly, if you take an object wherein there is some hole. So, we have some hole here. So, this hole diameter becomes the internal feature or maybe inside there is a tapered hole. So, this taper is another internal feature or say there is a slot like this. So, this is some internal feature. Now, we should understand what are the various symbols used in during geometric tolerancing. And all these tolerance symbols are as specified by various standards. You can see here the different kinds of features are there. Individual features and you can see type of tolerances, form tolerance, profile tolerance, orientation, location, run out. And in the form we have different characteristics like flatness. So, we have the flatness and this shows how the flatness is indicated on the drawings. And when we want to show the straightness horizontal line is used and whenever we require to show the circularity or roundness, a circle is used. And the cylindicity is shown by this symbol. Similarly, profile of a line can be shown like this. Profile of a surface can be shown by using this particular symbol. And whenever two surfaces are to be made perpendicular and we want to show the perpendicularity aspect, then we should use this inverted T symbol. And when angularity is to be shown, for example, we have some angular component like this, then the angularity is shown using this particular symbol. And whenever we want to show that two lines or two surfaces should be parallel, then we use this particular symbol. Similarly, for location run out these are the symbols used. And this is known as feature control frame. So, in the first box we have to write the symbol corresponding to the required characteristic. For example, here we have used the circle with a plus which indicates the position, position characteristic and the tolerance value on the diameter. And then this is the modifier, maximum material control either and which is the reference datum for achieving this position. So, that is mentioned in the last box. Now, in the machine shops normally surface plates are used as the datum surfaces. So, surface plates are mostly rectangular, they have rectangular shape having 4 is to 3 length to width ratio. These plates are rigid in the design and they are ribbed in the bottom surface. So, that no warping takes place in heavy loads are placed on that. The top surface of the plate is scraped to true flatness. A lot of care is taken during manufacturing of these surface plates, particularly the machining of the top surface of the surface plate. And many times the straight edges are used to check the flatness of the surface plates. I can see here we have this straight edge and we can always use the prussian blue. So, prussian blue can be applied to this knife edge. And then the straight edge is moved along the surface of the surface plate. Wherever there are top peak points, prussian blue gets adhered to the top peaks. And then those peaks can be removed by scraping operations like this. We should scrape the surface so that it is made flat. And for big surface plates, leveling screws are provided for adjusting the top surface truly horizontal. Now, standard available sizes of plates are sizes vary from 100 by 100 millimeter to 2000 by 100 millimeter in 13 ranges. All the 4 edges of the surface plates are finished straight and are square to each other. According to the Indian standard 2285, the cast iron surface plates, the surface plates are made by cast iron and are classified into two grades as grade 1 and grade 2. Depending upon the requirement, if it is for inspection grade, for calibration grade, we should go for grade 1. If it is for measurement of flatness or straightness, we can go for grade 2. And then surface plate is used to provide datum or a reference surface in most of the measurement activities carried out in the machine shops. Now, let us move on to the geometric feature, straightness of the component. Let us try to understand what is the meaning of straightness. You can see here, a line is set to be straight over a given length. If all points on the line remain within the two lines drawn parallel to the general direction of the line in question, separated by a tolerance amount. For example, this is the general direction of the line. And now on this line, we have many points or maybe peaks and valleys are there. Now, we have to draw two lines parallel to this general line which are separated by the tolerance amount. Say this tolerance amount is some 0.05 millimeter. Now, if all the peaks and valleys on that particular line are well within this range, then we say that line is straight. Now, the straightness tolerance, it can be applied to an axis or it can be applied to a surface. Now, we can see when it is applied to an axis, when the tolerance is applied to axis, say we have a cylindrical object like this and this is the axis and the size varies, diameter varies 12 to 12.5. So, diameter is varying from 12 to 12.5 and then the tolerance is specified like this. So, this is the symbol for straightness and then its value is 0.03 millimeter and it should be straight within this 30 microns. So, what happens is now the size of the component, now this size, the maximum it can be 12.5 as per the given tolerance on the size. So, minimum is 12 and maximum is 12.5 and then similarly here at the center also it is 12.5. Now, this total distance can go up to 12.53. That means, this is the axis and we have another axis here for this particular portion. So, this distance is 0.03 millimeter. So, this is diameter tolerance zone. So, this size can be up to 12.53. Now, when the tolerance, straightness tolerance is applied to surface then, so we have this object cylindrical object and so again the size varies from 12 to 12.5. So, this is 12 to 12.5 diameter. Now, in actual practice, this is the specified tolerance. So, when we manufacture the actual component can be like this. So, the maximum size it is 12.5 maximum material condition. So, this is 12.5 millimeter as per the given tolerance and so this tolerance on the surface. So, this is say 0.02 millimeter. Now, this is the tolerance on the size of the component and this is the tolerance on the feature that is straightness. So, this variation can be up to 0.02 millimeter and similarly here it can be up to 0.02 millimeter. At many places it is needed that work surfaces must be perfectly straight. For example, in the case of lathe the tool must move in a straight path to generate a perfect cylinder. So, this is possible only when the guideways are straight. When the guideways are straight, the carriage will move on this straight guideway and then the cutting tool will give the cut on the workpiece and then we get cylinders. If the guideways are not straight and some error is there, then the tool will also move in this fashion so that we do not get the proper cutting. We get lot of errors on the workpieces. So, now in order to check whether the machine tool guideway is straight or not, we use many instruments and methods so that we will study now. Now, we should understand what is the meaning of the straightness tolerance zone. You can see here we have a cylindrical object and on this surface the straightness tolerance is given it is 0.1 millimeter. So, what is the meaning of this? Now, we have this cylinder and we take one generator. If you take one generator on this particular cylinder, this variation should not exceed this 0.1 millimeter. This is the straightness tolerance. That means this gap is 0.1 millimeter. Like this, we have to consider many generators. We have to make measurements on many generators and in all the generators, if the error is within 0.1, then the cylinder is said to be straight. Similarly, on the flat surfaces, planar surfaces, again on the surface, the straightness tolerance is 0.01. That means on this surface if you consider a line, all the variations in the vertical plane should be within this 0.01 millimeter. If that is the case, we say this particular surface is straight. Now, having understood what is the meaning of straightness and straightness tolerance, now we will move to the measurement of straightness. So, various methods and various devices are used to measure the straightness. Some of the methods are using straight edge. We can check the straightness and straight edge along with the slip cages can be used to assess the straightness and we can also use spirit level and autocalimeters for checking the straightness. The spirit level can be used only on the horizontal surfaces whether a particular line on the horizontal surface is straight or not. Whereas, autocalimeter can be used on all different planes. It can be used for checking the straightness along horizontal axis, horizontal planes as well as vertical planes. For example, in machine tools, say we have a vertical guide ways. So, whether the vertical guide ways are straight or not, that can be checked by using autocalimeter. And recently with the advancement of CMM and computed ed inspection, CMMs are used to check the straightness. And there are some methods that test as per ASTM like gap test and then the total indicator readout TIR test and then finger roll test for checking the straightness of thin wires and rods and bars. So, we will learn some of these methods. Now, using the straight edge, how to check the straightness? Now, this straight edge is a rectangular or eye shaped device with beveled edge. So, it looks like this. So, we have this rectangular shape and then one end is beveled like this with a small radius at this place. And then the straightness of this particular edge is well within one micron depending upon the length. Now, these are made using steel or cast iron and they are available in different lengths like half meter length or 1 meter, 2 meter, 3 meter. For example, when we want to measure the straightness of machine tool guide ways. So, this is the slide of the machine tool and this is the machine bed wherein we have the guide ways. And say we want to check whether the guide way is straight or not. So, depending upon the size of the machine, this length of the guide way may be half meter or 1 meter or 2 meter. So, throughout the length, whether the guide way is straight or not that we want to check. In that case, we can use these straight edges and straight edges can be placed on the guide way and then the straightness can be checked. Now, we can use directly straight edge on the machine tool bed or guide way we can check. Or sometimes along with surface plate, the straight edge can be used for measurement of straightness. Now, according to Indian standard 2220, straight edges are provided in two grades, grade A for inspection purpose and grade B for workshop purpose. By using the pressure blue and straight edge, the irregularities on the surface plate can be found as I already explained. So, this photograph shows a eye shaped straight edge. So, this is the finished scraped surfaces. This surface is used for checking purpose and where different lengths are possible. To reduce the weight, the holes are made here and you can also see some ribbing to increase the rigidity of the straight edges. Now, for checking the straightness of the components, the straight edge is placed along the full length of the surface and the two are viewed against the bright light. Now, we can see here this is the work piece and we want to measure whether this top surface is straight or not. So, in that case we have to take this straight edge and we have to keep it on the surface and the other side we should keep a bright light source. Now, whether the light is passing between the surface plate top surface and the knife edge straight edge. So, that we have to observe light passing in the gap we should observe. If no light is passing, then the work piece surface is straight and if there is some light there is it indicates that there is some error, straightness error. A quantitative assessment can be made by observing the color of the light. So, due to interference caused by diffraction of light while passing through the gap, the color of light changes. If the color is red, it indicates a gap of 1 to 2 microns and if the color is blue the gap is 7 to 8 microns. So, in this way we can check the straightness of the work piece surfaces. Now, along with the straight edge along with the slip gauge and the straight edge, we can check the straightness. The procedure is like this. We have to use a surface plate a datum surface and then this is the component the straightness of which is to be checked. So, this could be surface plate or a straight edge. Now, here we have to keep the slip gauge say this is point number 0 and then so we have to mark. So, if this is L, so we have to support this length at airy points like this. We have to use another set of slip gauges and we have to support like this. So, that this distance is airy distance. So, that the bending is minimum. Now, we have to divide this distance into 10 equal parts. So, this is 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. So, now the height of this particular slip gauge is say 10 millimeter and height of this particular set is say 11 millimeter. So, now we can we know the height of this point number 0 is 10 millimeter and here it is 11 millimeter. Height is 11 millimeter, point number 10, but height is 11 millimeter. So, the theoretical height at this point will be 10.1 and here it is 10.2, 10.3, 10.4 and here it is 10.5, 10.5. This is 10.6, 10.7, 10.8, 10.9 and 11. So, this is height is 11. So, this is 10 and this is 11. So, theoretical heights we know. Now, we have to use slip gauges and we have to insert the slip gauges at all these points and actually what is the height we have to measure and then we can draw the graph. So, this is the position on the workpiece surface. So, this is point number 0 and up to 10. At point number 0, the height is 10 millimeter and at point number at this point the height is 11 millimeter. So, now, we can join this by means of a straight line. Now, actual distances, actual heights we have to measure by inserting the slip gauges say this is 5. So, at point number 1 say the height is 10.1 something like that and here it is second point, third point, fourth point, fifth point, sixth, eighth, ninth and this is 10 point. If we join then we get the line like this. Now, we have to draw two lines one passing through this peak and other passing through this valley. So, this gap gives us the straightness error of this particular edge. So, this is the edge to be inspected. So, what is the error in this particular edge can be obtained by this method. Now, other method is by use of spirit level we can check the straightness of the components. Spirit level consists of sealed glass tube and it is mounted in a base. The inside surface of the tube is ground to a convex barrel as shown here and this radius is large radius and then there is a scale engraved on the glass and the tube is filled with ether or alcohol and then there is a small air bubble. So, this air bubble it always tries to remain at the top most point. If the base is perfectly horizontal then the bubble will be at the center of the scale and if it is tilted, if the spirit level is tilted then it tries to occupy the top most point. It always tries to remain at the highest point of the tube. These spirit levels they are used for leveling the machine tools and they are also used to check the straightness of surfaces. Now, the test procedure is like this. The test can be carried out by using spirit level or auto collimator the procedure remains same. The straightness of any surface could be determined by either of these instruments by measuring the relative angular positions of number of adjacent sections made on the surface to be tested. So, what we have to do is we have to draw a line on the surface whose straightness is to be inspected like this. So, this is the surface to be inspected and here we have to draw a straight line and then we have to divide this straight line into number of equal parts and distance between two adjacent lines being L. So, this distance is L where L is the distance between the base the two feet on the spirit level. This is the spirit level and this is the glass tube with the bubble and two feet will be provided on the auto collimator reflector surface or the spirit level. So, this distance centered distance is equal to L. So, by knowing this L we can divide this line into equal number of parts keeping the distance between two lines equal to L. Now, the spirit level can be used only for the measurement of straightness along horizontal surfaces whereas auto collimators can be used to check the straightness on vertical and inclined surfaces also. In case of spirit level the block is moved along the line on the surface to be tested in steps equal to the pitch distance between the center lines of the feet. The angular variations are measured by the sensitive level that means in the first position what is the reading of the spirit level that should be noted down and then it is moved to the second section again what is the bubble reading that should be noted. This bubble in the spirit level reading will change when the straightness changes. So, angular variation can be correlated in terms of difference of height between two points by knowing the least count of level or least count of level and length of the base. Now, with this we will conclude this session. In this session we learnt about the importance of geometric tolerancing and what are the terms associated with dimension feature measurement and then we also learnt what are the various methods of measuring the straightness and out of those methods we started discussion on the measurement of straightness using spirit level. So, with this we will conclude in the next session we will continue the discussion on the straightness measurement by various methods. Thank you.