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### Metrology

1. 1. 5 Measurement and Metrology LabEXPERIMENT NO. 1 :MEASUREMENT WITH SCALE AND VERNIER CALIPERS Structure 1.1 Introduction Objectives 1.2 Instruments Used 1.3 Working Principle 1.4 Procedure 1.5 Precautions and Care of Instruments 1.1 INTRODUCTION In this experiment, you will be introduced to vernier caliper for taking both inside and outside measurement. It uses the vernier principle of measuring which was named after its inventor, Pierre Vernier (1588-1637), a french mathematician. The vernier caliper essentially consists of two steel rules and these can slide along each other. Objectives After performing this experiment, you should be able to • use the vernier caliper, and • read the measurement with vernier caliper. 1.2 INSTRUMENTS USED (a) Steel scale, 300 mm (b) Steel scale, 150 mm (c) Vernier caliper, size 150 mm, LC = 0.02 mm (d) Vernier caliper, size 300 mm, LC =0.02 mm (e) Surface plate, 450 mm × 450 mm (f) Magnetic base, 50 mm × 50 mm (g) Straight edge, 250 mm. 1.3 WORKING PRINCIPLE The principle of vernier was first introduced by Pierre Vernier in 1631. A vernier scale consists of a fixed scale having normal divisions like mm and another sliding scale having slightly smaller division. The sliding scale slides along the main or fixed scale. The accuracy of measurement depends upon the difference between one division of main scale and one division of sliding scale. This difference is the least length that can be measured by vernier scale and is called the least count (LC). Least count = 1 main scale division – 1 vernier scale division. Suppose 50 vernier scale division coincide with 49 divisions on main scale, and 1 MSD = 1mm.
2. 2. 6 Laboratory-IV Then 1 VSD 49 50 = Division on main scale, and LC 49 1 1 of 50 50 = − = MSD Figure 1.1 shows the details of a vernier caliper. Figure 1.2 shows 25 divisions of vernier coinciding with 24 divisions on main scale giving LC 24 1 1 25 25 = − = divisions and since one division of main scale is 0.025 hence LC 1 1000 = of main scale. 2 3 4 5 Dia Sliding Member Vernier Scale Not Shown Reading of Dia Fine Adjustment Screw Fine Adjustment Clamp Figure 1.1 : Vernier Caliper 1.4 PROCEDURE (a) Study the engineers scale, its main and subsidiary divisions and compare the scale with a straight edge. Note the length of the scale, its minimum division and observe the straightness. (b) Measure sample piece, read and record the reading in the Proforma suggested. (c) Study the vernier caliper and its constructional details; Figure 1.1 gives the important parts of the calipers. (d) Understand the vernier principle and see how the least count is calculated. Calculate and check error if any. (e) Read the instrument for at least three random vernier positions. (f) Measure the samples at indicated places and record as per standard Proforma (Figure 1.2). Figure 1.2
3. 3. 7 Measurement and Metrology Lab Reading = 2 + 0.4 + 0.025 + 0.011 (2 large division on main scale + 4 small division on main scale + 1 smallest division on main scale + 11 division on vernier scale, each division = 1/1000). Hence reading = 2.436. Figure 1.3 : Some Details of Using Vernier Caliper 1.5 PRECAUTIONS AND CARE OF INSTRUMENTS (a) The end of the scale must never be set with edge of the part to be measured because the end of the scale is usually worn out in an old scale. (b) The scale should never be laid flat on the part to be measured because by doing so the graduation of the scale are not in direct contact with the surface of the part. (c) Check if steel rule ends are worn round or unsquare before using. (d) All instruments should be thoroughly cleaned, covered with mobil oil and put in dust free covers. (e) When putting any instrument on table it should not be put violently or with a jerk. (f) While measuring length standards by above instrument error of parallax or zero error should be avoided. (g) In vernier calipers, there should be no play between sliding jaw and the fixed scale.
4. 4. 8 Laboratory-IV EXPERIMENT NO. 2 :MEASUREMENT WITH MICROMETERS – INTERNAL AND EXTERNAL Structure 2.1 Introduction Objectives 2.2 Instruments Used 2.3 Working Principle 2.4 Procedure 2.5 Precautions and Care of Instruments 2.1 INTRODUCTION Micrometer is one of the most widely used precision instruments. The instrument was invented and named by William Gascirgne. The name was derived from Greek work Mikros that means small. Micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shaft and depths of slots. Micrometers have several advantages over other types of measuring instruments. They are easy to use and their readouts are consistent. There are three types of micrometers based on their application : • External micrometer • Internal micrometer • Depth micrometer It is primarily used to measure external dimension like diameter of shaft, thickness of parts etc. to an accuracy of 0.01 mm. In this experiment, you will be introduced to the measurement of internal and external dimensions with the help of micrometer. Objectives After performing this experiment, you should be able to • measure internal dimensions with the help of micrometers, and • measure external dimensions with the help of micrometers. 2.2 INSTRUMENTS USED External Micrometers Least count = 0.1 mm, 0.001 mm (vernier type) Measuring range as below : (a) 0-25 mm (b) 25-50 mm (c) 50-75 mm (d) 75-100 mm Internal Micrometres
5. 5. 9 Measurement and Metrology Lab Least count = 0.01 mm (a) Calliper Type (5 mm-25 mm range) (b) Internal micrometer with different extension rods. 25 mm upwards measuring range. 2.3 WORKING PRINCIPLE The limits of accuracy specified on certain component involves measuring to 0.01 mm or 0.001 mm or even to finer limits which cannot be carried out by ordinary steel rule. Such measurements can be made with the help of micrometer. The micrometer consists of a precision screw in a nut. The outer cylindrical surface of nut is marked with normal scale with one division equal to say 1/2 mm. The circular edge of the screw which advances on the linear scale carries fine divisions say 50. If the screw is given one full rotation it advances by one division of linear scale which is achieved by having the pitch of the screw equal to 1/2 mm. The least count of the micrometer is the advance of screw when screw rotates by one division on circular scale. This is the least count. Least count for a micrometer of 1/2 mm pitch and 50 divisions on circular scale will be 1 0.01 mm 2 50 = = × . B Measuring Range A to B A Measuring Faces Spindle Frame 0 4.5 556 Fiducial Line Spindle Clamp Barrel Thimble Friction or Ratchet Drive Anvil Figure 2.1 : Micrometer 0 10 15 Figure 2.2 : Inside Micrometer Caliper Figure 2.3 Read 0.2 + 0.075 + 0.010 = 0.285 In the top figure as 10 Dn on thimble coincides with fiducial line. In the figure below note that only Dn 3 on thimble closely coincides with the line parallel to fiducial line on the barrel or sleeve. Hence read 0.2 + 0.050 + 0.02 + 0.0003 = 0.2703.
6. 6. 10 Laboratory-IV 2.4 PROCEDURE (a) Study the main elements of external/internal micrometer : U-frame, barrel, thimble, locknut, and ratchet. (b) Calculate the least count and note range of measurement of the instrument. (c) Read off any three positions of the main and subsidiary scale. (d) Measure the given piece and record as per standard Proforma. 2.5 PRECAUTIONS AND CARE OF INSTRUMENTS (a) The part to be measured must be held in left hand and micrometer in right hand. The way for holding the micrometer is to place the small finger and adjoining finger in the U-shaped frame. The forefingers and thimble are placed near the thimble to rotate it and middle finger supports the micrometer while holding. (b) The micrometer should be wiped clean and free from oil, dirt, dust and grit. (c) Clean the measuring surfaces of anvil and spindle for every measurement. (d) Check for zero reading. If there is no ratchet, use the pressure on thimble for checking zero error. (e) The anvil and spindle measuring surfaces should be flat and square to the anvil and spindles respectively. (f) When micrometer feels gummy, dust ribbon and thimble fail to turn freely, take the micrometer apart and thoroughly wash each component free from dirt and then assemble. Stickiness may be due to damaged threads or due to warping of frame or spindle. (g) Never leave the micrometer stored away with the spindle clamped down on empty anvil as electrolytic action takes place on contacting surfaces and measuring surfaces get corroded. (h) It is better to hold the micrometer anvil stationary and firmly against the work in one hand and take care of gauging pressure and locating the correct position of spindle by the movement of fingers of the other hand causing rotation of the spindle.
7. 7. 11 Measurement and Metrology LabEXPERIMENT NO. 3 :MEASUREMENT WITH HEIGHT AND DEPTH GAUGE Structure 3.1 Introduction Objectives 3.2 Instruments Used 3.3 Working Principle 3.4 Procedure 3.5 Precautions and Care of Instruments 3.1 INTRODUCTION Gauges are the tools which are used the checking the size, shape and relative positions of various parts. Gauges do not indicate the actual value of the impacted dimensions on the work. Gauges are, therefore, understood to be single-size fixed-type measuring tools. In this experiment, you will be introduced to the height gauge as well as the depth gauge. Objectives After performing this experiment, you should be able to • understand the fundamental of the gauges and their classifications, and • explain the working principle of height and depth gauge. 3.2 INSTRUMENTS USED (a) Height Gauge, 300 mm range, least count 0.02 mm (b) Depth Gauge, 100 mm range, least count 0.02 mm (c) Surface Plate, 450 × 450 mm, Grade I (d) V-Blocks, 30 × 30 × 50 mm. 3.3 WORKING PRINCIPLE The principle of working of height gauge is same as that of vernier calipers. It is the same simple arrangement as vernier caliper using a fixed scale and sliding scale to obtain measurement of higher accuracy, than can be obtained by an ordinary steel scale. It relies on the difference between two calibrated scales. The difference between 1 division of main scale and 1 division on vernier scale is known as the least count. Principle of working of vernier depth gauge is also the same as that of vernier caliper while the principle of the depth micrometer is same as that of a micrometer. They, however, differ in construction as can be seen in figures. Both have beam which rests on the top of the hollow to be measured.
8. 8. 12 Laboratory-IV Figure 3.1 : Vernier Height Gauge Figure 3.2 : Vernier Depth Gauge 3.4 PROCEDURE (a) Study the main elements of depth gauge, base, thimble, lock nut and depth gauge attachments. (b) Study the main elements of height gauge, main scale, vernier scale, base, movable arm, scriber, adjusting scales. (c) Calculate the least count and maximum range of measurement. (d) Read off any three positions of the main and subsidiary scale and record the readings. (e) Measure the given piece and record as per the standard proforma. 3.5 PRECAUTIONS AND CARE OF INSTRUMENT Height Gauge (a) Do not allow the instrument to come in contact with dust and dirt. It is better kept in its case. (b) Temperature rise of height gauge by room heating or by hands should be avoided while measuring and checking longer lengths. Even keeping contact with fingers for a longer time may affect the reading, especially if depth gauge attachment is long.
9. 9. 13 Measurement and Metrology Lab (c) The sliding head (with vernier mounted on its auxiliary head) and fine adjustment should be checked for squareness with beam and parallism of surface. There should be no nicks, scratches, corrosion or any other damage. (d) Check for rocking of base on surface plate at various points. (e) Check the height gauge measuring and marking arm for zero error. The zero of vernier and main scale should coincide when measuring and marking arm rests on surface plate. Depth Gauge (a) Make sure the reference surface, on which depth gauge is rested is true flat and square. (b) Make sure the gauge itself is true and square. (c) The gauge while measuring should neither be tipped forward nor backward. In case of tilted instrument, measuring end will not touch squarely on the surface to be measured and erroneous readings will be observed. (d) Too much pressure should not be applied on the beam or measuring bar as it will have lifting tendency on the slide and result in readings different from actual ones. (e) In using a depth gauge, press the slide firmly on reference surface by hand pressure on it. Manipulate the gauge beam to measure depth. Be sure to apply only standard light measuring pressures of 1/4 kg to 1/2 kg (like marking a light dot on paper with a pencil) on the beam. (f) The results are greatly affected by the “feel” of the contact between the tool and the work. Some practice is required before confidence is developed. When using long extensions, the heat of hands can be transmitted to extensions easily and thus result in incorrect reading. Hence longer extensions should be handled cautiously.
10. 10. 14 Laboratory-IV EXPERIMENT NO. 4 :MEASUREMENT WITH DIAL INDICATOR USING SURFACE PLATE AND ACCESSORIES Structure 4.1 Introduction Objectives 4.2 Instruments Used 4.3 Working Principle 4.4 Procedure 4.5 Precautions 4.6 Sources of Error 4.7 Limitations 4.1 INTRODUCTION Dial indicators are instruments used for making and checking linear measurements. These instruments are used for centering the work on machines for checking the eccentricity and for visual inspection of work. Objectives After performing this experiment, you should be able to • acquire skill of measuring with dial indicator. • know the range and the least count. • use the indicator in various shop situations with different types of holders. 4.2 INSTRUMENTS USED (a) Dial indicator – range 0 to 10 mm, LC = 0.01 mm, with stand. (b) Surface plate, 450 × 450 mm (c) V-block and C-clamp. 4.3 WORKING PRINCIPLE The linear movement of plunger is converted into rotary movement of needles on a dial. This is achieved by means of a rack and pinion, and a gear train arrangement. Figure 4.1
11. 11. 15 Measurement and Metrology Lab4.4 PROCEDURE For Checking Flatness (a) First check the accuracy of the dial indicator with some standard pieces from the box of slip gauges and record the deviations in a table. The dial gauge is fitted on the stand with dial in vertical plane. The stem of the dial gauge is also vertical. The end of the stem can be brought in contact with the job on flat surface. The stand of the dial gauge can move freely on the surface plate so the stem can be brought in contact of the surface to be checked. If deviation in dial gauge reading is not significant, then the surface is smooth and flat. (b) Place the flat piece on the surface plate. (c) Mount the dial indicator on the stand and take at least four readings on the job at different positions. (d) Record the readings in the table and note the deviations from flatness (if any). For Checking Concentricity of a Round Shaft (a) Place the round job on the V-block. (b) Mount the dial indicator on the stand and take different readings on the job by rotating it. (c) Record the readings in the table of observations and note the deviations (if any) for checking the circularity. (d) Note the maximum eccentricity. Dial Indicator Part Circle Part (a) (b) (c) Figure 4.2 : Using Dial Indicator on Round Bar 4.5 PRECAUTIONS (a) Some initial loading must be given at any given readings. (b) The plunger should not be allowed to strike the work with force otherwise the teeth of the gears and rack will be damaged. (c) The accuracy of the dial indicator may be checked with the help of slip gauges periodically.
12. 12. 16 Laboratory-IV 4.6 SOURCES OF ERROR (a) Some variations may be there in the indicator when readings are being taken. This may be avoided if the pointer movement is damped properly. (b) The operating pressure required on the measuring head to obtain zero reading may cause some error if it is not kept constant over the whole range. (c) The plunger should move only within specified limits, otherwise error will crop in. 4.7 LIMITATIONS The instrument may not be usable for a larger range. The main limitation of the instrument is its comparatively small range of measurement. The minimum reading of 0.01 mm also has its limitation.
14. 14. 18 Laboratory-IV Figure 5.1 : Combination Set 5.4 PROCEDURE For Measuring Angles (a) Fix the protractor head on the scale. (b) Place the scale on one side of the angle to be measured. (c) Adjust the protractor by rotation, so that its working surface should touch the adjacent side of the angle to be measured. (d) Lock the protractor. (e) Read the angle on the scale. For Checking Squareness (a) Fix the square head on the scale. (b) Check the spirit level for parallelism. (c) Check the surfaces for squareness by placing the job on the surface plate. For Marking Centre (a) Fix the centre head on the scale. (b) Hold the bar stock beneath the scale. (c) See that the sides of centre head are touching the bar stock. (d) Scribe a line along the scale in each position and rotate the bar stock for three positions. (e) The centre of the triangle formed will be the centre of the job. 5.5 PRECAUTIONS AND CARE OF INSTRUMENTS (a) The job should be held in the left hand and the instrument in the right hand. (b) The surfaces to be checked should be clean. (c) The edge of the scale should be straight. (d) Spirit level should be checked before taking reading. (e) See that there are no nicks and scratches on the base of heads. (f) While checking for squareness and measuring angles, stand facing the surface and light and check the light passing through the scale or base of measuring instrument. 5.6 SOURCES OF ERROR (a) The edge of scale may not be straight. (b) Zero error in the protractor scale may exist. (c) Working surfaces of different heads may be worn.
15. 15. 19 Measurement and Metrology LabEXPERIMENT NO. 6 :MEASUREMENT OF ANGLES WITH BEVEL PROTRACTOR Structure 6.1 Introduction Objectives 6.2 Instruments Used 6.3 Working Principle 6.4 Procedure 6.5 Precautions and Care of Instruments 6.6 Sources of Error 6.1 INTRODUCTION It is the simplest instrument for measuring angles between two faces. It consists of two arms and an engraved circular scale. The two arms can be set along the faces between which the angles to be measured. The level protractor can measure angles to five minutes of a degree. In this experiment, you will be introduced to the measurement of angles with bevel protractor. Objectives After performing this experiment, you should be able to • acquire the skill of measuring angles with the bevel protractor, and • know the range of measurement and to calculate the least count of the bevel protractor. 6.2 INSTRUMENTS USED Vernier bevel protractor (0 to 360o ) Least count = 5′. Surface plate 450 × 450 mm. Holding device to suit particular job. 6.3 WORKING PRINCIPLE It consists of a base plate attached to the main body and an adjustable blade attached to a circular plate containing vernier scale. Adjustable blade is capable of rotating freely about the centre of main scale engraved on the body of the instrument and can be locked in any position by using clamping nut. An attachment is provided at the top for the purpose of measuring acute angles. Least Count Fixed scale is divided into degrees and the vernier is graduated such that 12 of its divisions are equal to 23 divisions on the main or fixed scale. The divisions on the fixed scale are in degrees. The difference between one division of vernier space and two of the fixed scale is 1/12 degree. Therefore, the minimum reading of the instrument is 1/12o or 5′.
16. 16. 20 Stock Blade Blade Locking Nut Slow Motion Device Turret Body Scale Working Edge Laboratory-IV Figure 6.1 : Bevel Protractor 0 10 203040506070 80 90 80 70 60 50 40 30 20 10 0 10203040506070 80 90 8070 Figure 6.2 : Universal Bevel Protractor Figure 6.3 : Vernier Protractor Reading 20o 15′ 6.4 PROCEDURE (a) Study the bevel protractor and identify its main parts. (b) Introduce the adjustable blade in the slot of body and clamp it with the help of knob in the convenient position. (c) Place the working edge of the stock on one surface of the job and rotate the turret holding the blade so that the working edge of the blade coincides with another surface of the job. Fix the turret and read the angle.
17. 17. 21 Measurement and Metrology Lab (d) Measure the angles of the sample pieces with the bevel protractor and record the reading in the proforma suggested. 6.5 PRECAUTIONS AND CARE OF INSTRUMENT (a) Use the instrument with care. (b) While readings are taken your eyes must be in front of the matching lines. (c) Always check the tightness of clamping screws before taking reading. 6.6 SOURCES OF ERROR (a) Base plate and adjustable settings. (b) Blade and stock should be made parallel to the surfaces of the sample job otherwise the angles measured will be wrong. (c) Instrument has marking errors. (d) Parallax errors may occur.
18. 18. 22 Laboratory-IV EXPERIMENT NO. 7 :STUDY AND USE OF SLIP GAUGES Structure 7.1 Introduction Objectives 7.2 Instruments Used 7.3 Description 7.4 Precautions and Care of Instruments 7.5 Sources of Error 7.1 INTRODUCTION Slip gauges are measuring bodies of hardened steel. These gauges are of rectangular form, and are made of a high steel, hardened throughout and stabilised by means of a suitable heat treatment. It is economical to have slip-gauges made individually to all sizes of standard that are likely to be required, and they are normally slipped in carefully selected sets, the size of any required standard being made up by combining suitable slip gauges. Objectives After performing this experiment, you should be able to • acquire skill in wringing of gauge blocks, • acquire skill in selecting minimum number of gauges to make up measurements, • understand about the care and maintenance of slip gauges, and • know about the use of slip gauges in conjunction with surface plate. 7.2 INSTRUMENTS USED (a) Gauge block set (103 pcs) (b) Surface plate, 450 × 450 mm (c) Magnetic base holder (d) Steel foot rule. A number of blades (also called “slips”) of different thicknesses are assembled together in a convenient holder. It is not necessary to have slips of all thicknesses in a single holder. The common practice is to have a number of slips (blades) which can be arranged in combinations to give all the desired sizes. For instance to obtain a thicknesses of 0.125 mm slips of thickness 0.075 mm and 0.05 mm respectively can be combined. It should be ensured that surfaces maintain perfect contact in combination and for the reason only minimum number of slips should be used. The combining is known as wringing of gauges and is partly due to molecular attraction (adhesion) and partly due to pressure. The gauges will not wring if there is any dirt between them. 7.3 DESCRIPTION Slip gauges are measuring bodies of hardened steel. For measuring and testing they can be built up to various dimensions. This is accomplished by pressing together the working faces of two gauge blocks or by wringing the gauges. These are used as standards of
19. 19. 23 Measurement and Metrology Lab measurement. For wringing, the slips are first placed at right angle and then rotated through 90o under pressure of about 5 N/mm2 . Slip gauges are classified according to their accuracy : (a) ‘C’ Grade : This generally used in workshop for checking dimensions of the products. (b) ‘B’ Grade : This grade is used in factories for checking the size of the articles. (c) ‘A’ Grade : This is used for reference purpose. (d) ‘AA’ Grade : This is termed as master slip gauge and is not generally in use. Slip gauges are available in inch units and metric units as a set consisting of number of pieces. Application of Slip Gauges • Calibration and checking of precision measuring instruments. • Pre-setting of machine tools. • Pre-setting of fixtures and tools. • Building up accurate dimension. The five most commonly used sets contain 81, 49, 41, 35 and 25 pieces respectively. And in Metric units sets of 103, 76, 56, 48 and 31 pieces are available. The building up size combination for length of 2.265 mm and 38.015 mm with a set of 103 pcs is given in the “Reading Taken” sequence. As a guide for building up dimensions the range of some metric sets are given below : Metric Set Set of 103 Pieces Range Steps Pieces 1.01 – 1.49 0.01 mm 49 0.50 – 24.5 0.5 mm 49 25 – 100 25 mm 4 1.005 − 1 Total : M 103 Set of 87 Pieces (Special Set) Range Steps Pieces 1.001 – 1.009 0.001 mm 9 1.01 – 1.49 0.01 mm 49 0.5 – 9.5 0.5 mm 19 10 – 90 10 mm 9 1.005 − 1 Total : M 87 Other sets in this group are 76, 56, 48 and 31 pieces. Slip Gauge Accessories The field of application is considerably advanced by a few simple accessories viz., holders, jaws, scribers and centre point etc. (See Figure 7.1).
20. 20. 24 Laboratory-IV 25 6 5 1.005 Figure 7.1 : Gauge Blocks Figure 7.2 : A Set of Slip Gauges Reading Taken Building up size combination (sets of 103 pcs) (a) 2.265 mm (b) 38.015 mm 1st slip 1.005 mm 1st slip gauge 1.005 mm 2nd slip 1.260 mm 2nd slip gauge 1.010 mm Length 2.265 mm 3rd slip gauge 11.000 mm 4th slip gauge 25.000 mm Length = 38.015 mm 7.4 PRECAUTIONS AND CARE OF INSTRUMENTS (a) The surface of the gauge must be protected against rust with neutral petroleum jelly or some other anticorrosive preparation. (b) The gauges should be protected from dust and dirt. (c) The gauges should be used under controlled conditions of temperature and maintained at constant temperature. (d) Wipe the gauge clean with chamois leather everytime before use. (e) The excessive pressure during wringing of gauges may cause damage to the surface. (f) When building up size combination, see that you start with the minimum value of the right hand side of the decimal. (g) Never drop a slip gauge. (h) Never strike slip gauges with other metallic objects. (i) Use minimum number of gauges for building up size combination.
21. 21. 25 Measurement and Metrology Lab7.5 SOURCES OF ERROR (a) Improper wringing of the gauges. (b) Noting the dimensions incorrectly from the gauge. (c) The error may occur due to room not being maintained at proper temperature.
24. 24. 28 Whitworth 0.853 p. 0.506 p.Laboratory-IV Metric 1.01 p. 0.505 p. (d) Pitch : The lead or pitch of a single thread screw is the distance measured with the help of vernier caliper and dividing this distance by number of threads in between. Threads can also be checked by screw gauge set (Figures 8.2(a), (b), (c), (d) and (e)). (a) (b) (c) (d) (e) Figure 8.2 (e) Thread Angle : Measured by (a) Screw pitch gauge approximately and (b) Toolroom microscope accurately. P ½P 55 0 PITCH D 1/6 D 1/6 D P 45 0 ½P+0.01 0.37P P 29 0 P RAD ¼ P P 1/2
25. 25. 29 Measurement and Metrology Lab A glass template is fixed in the microscope. On this template, thread profiles are etched with high accuracy. The individual profile outlines are successively brought into the field of view. Thereby, it will be attempted to bring the outline in question into coincidence with the thread profile of the work piece and the details of thread characteristics read from the template. 8.5 PRECAUTIONS (a) When making a test, micrometer must be located at right angles to the axis of the screw being measured. (b) Threads must be fixed on the table of the microscope, so that observation is not disturbed. (c) Proper lighting of the object will assist in accurate recording of measurements. (d) Screw pitch gauge with a stopper must be used especially in case of small nuts.
26. 26. 30 Laboratory-IV EXPERIMENT NO. 9 :MARKING AND MEASURING EXERCISE WITH ALL MEASURING DEVICES Structure 9.1 Introduction Objectives 9.2 Materials Required 9.3 Instruments Used 9.4 Working Principle 9.5 Procedure 9.6 Precautions and Care of Instruments 9.7 Sources of Error 9.1 INTRODUCTION In this experiment, you will be introduced to the marking and measuring exercise with all measuring devices. Objectives After performing this experiment, you should be able to • develop skill of reading the drawings from given views, and • develop skill of transferring the dimensions from the drawing on to the job, using marking devices and measuring instruments. 9.2 MATERIALS REQUIRED (a) MS/Cl block or plate with three surfaces machined accurately and perpendicular to each other. (b) Pieces of chalk or Prussian blue paste. 9.3 INSTRUMENTS USED (a) Marking table (b) Height gauge with carbide tipped scriber (c) Ordinary scriber with magnetic base stand (d) Slip gauge set (e) Angle plate (f) Divider (g) Scale (h) Set of punches (i) Dial indicator (j) Set of parallel blocks.
27. 27. 31 Measurement and Metrology Lab9.4 WORKING PRINCIPLE Marking is based on the principle of transferring the dimensions from the measuring instruments to the job by means of scriber. 9.5 PROCEDURE (a) Clean the marking table and marking instruments. (b) Check mutual perpendicularity of the three machined surfaces of workpiece with angle plate. (c) Apply chalk or blue paste on the surfaces to be marked. (d) Place the workpiece in xy-plane on marking table. (e) Set the scriber for different dimensions parallel to xy-plane with the help of height gauge, slip gauge and scribe the respective line on the marking surface. (f) Scribe all the lines inclined with the marking table with the help of scale and scriber. (g) Make punch marks on the scribed lines. (h) Repeat marking steps of other reference planes, i.e. yz and xz. 9.6 PRECAUTIONS AND CARE OF INSTRUMENTS (a) Scriber should be fixed firmly in the height gauge. (b) Reference planes should not have any burrs and should be mutually perpendicular to each other. (c) Marking table should be leveled. (d) Scriber point should be sharp and scriber should be perpendicular to the marking surface. (e) Movement of scriber on marking table should be smooth. (f) All the dimensions should be marked carefully. (g) All the dimensions should be verified before punch marking the scribed lines. 9.7 SOURCES OF ERROR (a) Damaged base of height gauge. (b) Loose holding of scriber in the height gauge. (c) Tilting of height gauge during marking. (d) Bluntness of scriber. (e) Scribing wrong dimensions from wrong reference plane.
28. 28. 32 Laboratory-IV EXPERIMENT NO. 10 :STUDY OF INSPECTION GAUGES SUCH AS PLUG, SNAP, AND THREAD GAUGES Structure 10.1 Introduction 10.2 Go and No Go Gauging 10.1 INTRODUCTION Gauges are inspection tools of rigid design without a scale, which serve to check the dimension of manufacturing parts. Production gauges are of various types, but the majority is in the form of limit gauge. These are designed to cover a very wide range of work. The general form of limit gauge is of the fixed type. That is to say, the gauging contact elements remain fixed, during the gauging process. Gauging elements may, however, be provided with the means of size adjustment. Limit gauging is not confined to the use of simple gauges such as those normally designed to check the size of the shafts and holes. The progressive need for checking fine tolerances has led to the introduction of that form of limit gauging in which an instrument, e.g. a comparator, fitted with an indicator working between specified positions, is used without reference to the actual sizes of the features being examined. Objectives After performing this experiment, you should be able to • understand the fundamental of the gauges and their classifications, and • explain the working principles of various types of gauges and their application. 10.2 GO AND NO GO GAUGING Plug Gauges These gauges are “GO” and “NO GO” type, and used for gauging holes. This gauge is made from hardened steel cylinder, very accurately ground to the lower limit diameter of hole. If hole is near lower limit the gauge enters the hole smoothly under light push. This gauge is stamped “GO”. If hole diameter is close to upper limit it is stamped “NO GO”. A NO GO gauge is finished as GO gauge to be used in the hole and if it enters the hole, the hole is unacceptable. Hence NO GO should not pass through the hole. The GO gauge is longer in length because it is likely to wear as it rubs with inside of hole. The NO GO is made short in length since it does not pass through the hole hence no wear. Figure 10.1 : Go and No Go Gauge for Hole Figure 10.2 : Standard Ring and Plug Gauges
29. 29. 33 Measurement and Metrology Lab Figure 10.3 : Progressive and Double Ended Limit Plug Gauge In the renewable end plug gauge, the ‘GO’ end is renewable as it is subjected to wear. In order to increase considerably the wearing properties of plug gauges they are chrome plated. A further advantage of chromium plating is that when, finally, the surface wears it can readily be renewed by plating and brought to the original dimensions by grinding and lapping. Pilot Gauge The possibility of an operator to insert a plug gauge obliquely into the hole that is to be checked so that it jams across the hypotenuse of the triangle shown by the dotted line is avoided altogether in the ‘Pilot’ gauge by machining a groove behind the front of the gauge as in Figure 10.4. Figure 10.4 Figure 10.5 : Taper Plug and Ring Gauge It will be seen that there is first a small chamfer, then a narrow ring or pilot, the same diameter as the body of the gauge, after this the groove and finally the main body of the gauge. If the gauge is fitted, the pilot or leading portion is of the nature of an ellipse in respect to the hole so that on entering the hole it touches at two points across the major axis, which is the diameter of the plug. If the pilot can enter the hole, it is sufficiently large assuming the hole to be round-for the rest of the gauge to enter. Thus a ‘Pilot’ will enter a ‘size for size’ hole without jamming. Snap Gauges For checking external diameters a ring gauge having two limiting diameters could be employed in a similar manner, but this type had very largely been superseded by the snap gauge (Figure 10.6). This gauge is of flat shape and provided with two jaws of caliper form. One jaw is usually marked ‘GO’ and corresponds to the maximum allowable diameter or plus dimension, the other jaw is marked ‘NO GO’ and show the minimum allowable or minus dimension. This form of gauge and all other two unit gauges are often termed GO and NO GO or G and NG gauges.
31. 31. 35 Measurement and Metrology LabGO NO GO Figure 10.8 : Limit Taper Plug Gauge When the taper diameters vary within certain limits, two tolerance marks corresponding to the tolerance are engraved on the taper gauge. Before testing the taper surfaces of the workpiece, the testing instrument must be cleaned thoroughly. An equal contact of the tapers will be ascertained by means of the frictional contact method. The surface of the taper (taper plug or workpiece) will, in direction of the longitudinal axis, be provided with two pencil lines, which are staggered by 90o . After fitting workpiece and gauge together they are twisted somehow against each other with slight pressure. The lines must be evenly blurred out. If this is not the case, the taper has uneven contact and the two tapers are not identical.
32. 32. 36 Laboratory-IV EXPERIMENT NO. 11 :MEASUREMENT OF TAPERS (EXTERNALAND INTERNAL) Structure 11.1 Introduction Objectives 11.2 Instruments Used 11.3 Working Principle 11.4 Procedure 11.5 Precautions 11.6 Sources of Error 11.1 INTRODUCTION In this experiment, you will be introduced to the measurement of tapers – external and internal. Objectives After performing this experiment, you should be able to • calculate the taper angle both external and internal, and • understand the function of rollers for calculating the taper angle. 11.2 INSTRUMENTS USED (a) Micrometer, (b) Depth gauge/height gauge, (c) Surface plate, (d) Balls of known dimension 2 of each size, (e) Rollers of known dimension 2 of each size, (f) Gauge block set. Least Count/minimum reading of (a) Micrometer = 0.01 mm (b) Micrometer depth gauge = 0.01 mm (c) Vernier height gauge = 0.02 mm. 11.3 WORKING PRINCIPLE These methods make use of trigonometric functions. The required dimensions are computed by taking several readings with instruments.
33. 33. 37 Measurement and Metrology LabD d θ Figure 11.1 : Taper Angle 11.4 PROCEDURE Theory Taper angles of turned parts of standard taper plug can be checked by measuring the diameters at two sections and the distance between these sections. Referring to the Figure 11.1, if D and d are diameters at the section BB and AA respectively and H is the distance between these diameters, then from the triangle ABC it follows that Tan 2 D d H − θ = This method is applied for measuring the taper angle of a component such as a taper plug gauge. For External Taper (a) Stand the taper plug gauge (job) with its small end on the surface plate. (b) Select two piles of slip gauges (S1). (c) Place the roller of diameter (d) on the top of the block of slip gauges (S1). (d) Standardize the micrometer carefully on a slip gauge with a roller on each side. (e) Measure the size of the job or gauge over the rollers. (f) Select another value of slips (S2) and place the roller over it. (g) Measure the size over the rollers M2 by micrometer. For Internal Taper (a) Hold the ring gauge or job almost horizontal. (b) Roll the smaller ball gently inside the gauge or job until it rests. (c) Stand the gauge or job, small end down, on the surface plate. (d) If the ball protrudes, place the gauge on two equal piles of slips sufficient to keep the bottom of the ball clear of the surface plate. (e) Lower the depth attachment with the height gauge until it just touches the top of the ball. (f) The height gauge reading is noted and the procedure repeated about three times to get average value. (g) Next remove the smaller ball and insert the larger one. (h) Note the height with the larger ball. (i) Note the height of the top surface of the gauge (job).
34. 34. 38 Laboratory-IV 11.5 PRECAUTIONS (a) The taper gauge (or job) should be set up on its small end. (b) The roller should be of same diameter as small end. (c) Rollers must not swing under measuring pressure. (d) Check the zero error of the measuring instruments. (e) Check that the balls used for internal taper have true spherical surface. 11.6 SOURCES OF ERROR (a) Misalignment of rollers. (b) Uneven pressure while taking reading over the rollers. (c) Error due to improper wringing of slip gauges. (d) The height gauge may not be in contact with the highest point of the ball.
35. 35. 39 Measurement and Metrology LabEXPERIMENT NO. 12 :MEASUREMENT OF SPUR GEAR CHARACTERISTICS Structure 12.1 Introduction Objectives 12.2 Instruments Used 12.3 Working Principle 12.4 Procedure 12.5 Observations and Calculations 12.6 Precautions and Care of Instruments 12.7 Sources of Error 12.1 INTRODUCTION Spur gears are straight-toothed gears with radial teeth that transmit power and motion between parallel axes. They are widely used for speed reduction or increases, torque multiplication, resolution, and accuracy enhancement for positioning systems. In this experiment, you will be introduced to the measurement of spur gear characteristics. Objectives After performing this experiment, you should be able to • know and identify the principle characteristics of a spur gear, and • acquire the skill of measuring characteristics of a gear with gear tooth vernier. 12.2 INSTRUMENTS USED (a) Gear tooth vernier (b) Vernier caliper 12″ or 300 mm (c) Bench vice. Least count of (a) Gear tooth vernier, 0.02 mm (b) Vernier Caliper, 0.02 mm (c) Bench vice Figures 12.1 : Gear Tooth Nomenclature
36. 36. 40 (a) Diagram of gear tooth vernier (Figure 12.1).Laboratory-IV (b) Spur gear tooth profile for different nomenclature (Figure 12.2). Figure 12.2 : Approximate Representation of Involute Spur Gear Teeth Three sample spur gears in metric units for measurements of different characteristics may be used. 12.3 WORKING PRINCIPLE Brief description of measuring of tooth thickness by gear tooth vernier is given. It consists of a horizontal and a vertical vernier slide. It is based on the principle of vernier scale. An independent tongue which is adjusted independently by adjusting the slide screws on graduated beams measures the thickness of a tooth at pitch line and the addendum. Terminology of Gear Tooth (a) Pitch Circle Diameter (PCD) : It is the diameter of a circle, which by pure rolling action would produce the same motion as produced by the toothed gear wheel. D = pitch circle diameter OD = outside diameter or addendum circle diameter T = number of teeth (c) Module : It is defined as the length of the pitch circle diameter per tooth. Module, m = D/T and is expressed in mm. (d) Circular Pitch (CP) : It is the arc distance measured around the pitch circle from the flank of one tooth to a similar flank in the next tooth. D CP m T π = = π (e) Addendum : This is the radial distance from the pitch circle to the top of the tooth. It is equal to one module in standard depth of tooth. (f) Clearance : This is the radial distance from the tip of a tooth to the bottom of the mating tooth space when the teeth are symmetrically engaged. Its standard value is 0.157 m or 0.25 m. (g) Dedendum : This is the radial distance from the pitch circle to the bottom of tooth space.
37. 37. 41 Measurement and Metrology Lab Dedendum = Addendum + Clearance = m + 0.157 m = 1.157 m. or 1.25 m (metric gearing system) (h) Tooth Thickness : This is the arc distance measured along the pitch circle from the intercept with one flank to the intercepts with the other flank of the same tooth. For a correct gear t′ = D sin (90/T), D = PCD (chordal), T = No. of teeth Also chordal depth c = (D/2) (1 – cos (90/T)) 12.4 PROCEDURE For Finding PCD, Module, Addendum, Dedendum and Clearance (a) First find the blank diameter OD by a vernier caliper and also count the number of teeth T of the spur gear. (b) Next calculate pitch circle diameter 2 1 OD D T = ⎛ ⎞ +⎜ ⎟ ⎝ ⎠ . (c) Find addendum, clearance, pitch, module and dedendum as per formulae given in the theory. For Chordal Tooth Thickness (Using Gear Tooth Caliper) (Figure 12.3) (a) Set the chordal depth (addendum) on the vertical side of gear tooth vernier and then insert the jaws of the instrument on the tooth to be measured. (b) Adjust the horizontal vernier slide by the fine adjusting screw so that the jaws just touch the tooth. (c) Read the horizontal vernier slide and note the reading. It gives the chordal thickness of tooth. (d) Repeat the observations for different teeth. (e) Compare the values of different characteristics with the standard value and set the percentage error. Figure 12.3 : Measuring Gear-tooth Thickness and Profile with (a) A Gear-tooth Caliper and (b) Pins for Balls and a Micrometer (Source : American Gear Manufacturers Association)
38. 38. 42 Laboratory-IV 12.5 OBSERVATIONS AND CALCULATIONS Zero error horizontal vernier slide = Zero error of vertical vernier slide = No. of teeth on the spur gear Pitch circle diameter D = Module m = D/T mm Addendum = One module = m Dedendum = Addendum + Clearance = m + 0.157 m = 1.157 m (1.25 m) Clearance = 0.157 m (m is module of teeth) Circular Pitch P = π m Tooth thickness of gear tooth = t Standard value of tooth thickness (Chordal) t′ = D sin (90/T) % age error = 12.6 PRECAUTIONS AND CARE OF INSTRUMENTS (a) Gear surface should be cleaned properly before setting the instruments. (b) Zero error of the instruments should be taken into account. (c) Repeat the experiment by setting the instrument on different teeth. 12.7 SOURCES OF ERROR (a) The adjusting of jaws of gear tooth caliper may not be proper. (b) Zero error may be there. (c) Jaws may be worn out.
39. 39. 43 Measurement and Metrology LabEXPERIMENT NO. 13 :MEASUREMENT OF BORE WITH CYLINDER DIAL GAUGE FOR SIZE, TAPER AND OVALTY Structure 13.1 Introduction Objectives 13.2 Materials Required 13.3 Devices and Accessories Required 13.4 Experiment Sequence 13.5 Procedure 13.6 Precautions 13.1 INTRODUCTION The cylinder dial gauge has to have three contact points along the cylinder walls, such that spindle contact is at 90o to the centre line of the bore and the reading taken is correct. To ensure this position, the dial gauge is provided with a slider plate. In case dial gauge is not positioned correctly, this slider plate will go out of contact and will serve as a warning to the dial gauge user to position the dial gauge correctly in the bore. The cylinder bores, which are measured, are used in I.C Engines, hence we have to be very careful while taking reading for taper and ovalty especially. Objectives After performing this experiment, you should be able to • familiarise with the use of different accessories of the gauge, • know its dial reading + and – pre loading and zeroing of the dial, • measure the size of the bore, its taper and ovalty, and • decide suitability of the bore as per given specifications. 13.2 MATERIALS REQUIRED (a) Cylinder dial gauge, and (b) Cylinder bore. 13.3 DEVICES AND ACCESSORIES REQUIRED (a) A piece of muslin cloth or like. (b) A piece of paper and pencil.
40. 40. 44 Laboratory-IV Figure 13.1 : Ball-type Plug Gauge Figure 13.2 : A Simple Method of Bore Measurement 13.4 EXPERIMENT SEQUENCE (a) Look at the cylinder bore and roughly estimate its diameter. (b) With the help of dial gauge distance pieces, measure the bore approximately (the size of the distance pieces is stamped on them). (c) Fit a correct size spindle (size known at step (b) above) with the dial gauge. (d) See for general working of the dial gauge by pressing its spindle gently and seeing the needle. (e) See that dial needle goes both sides + and –. (f) Rotate dial, so as to ascertain that it can be brought to ‘0’ position, before actual measurement of the bore is taken. (g) With a piece of cloth, clean dial gauge spindle tips and the cylinder bore. 13.5 PROCEDURE (a) Hold dial gauge vertical and put it into the cylinder such that spindle and slider plate touch the cylinder walls. (b) Slightly move the gauge vertically to and fro and note for mean positions of the dial needle and the contact of slider plate and spindle.
41. 41. 45 Measurement and Metrology Lab (c) In this position rotate the dial and fix its ‘0’ position. (d) The portion of the bore at which the dial gauge is ‘0’ is the ridge portion, where piston has never worked; as such the size of the bore is the original size, standard size or zero size. Take out the dial gauge, and put in its, distance piece holder and fix only those distance pieces, such that needle reads ‘0’. Now this size indicated by distance pieces is the size of the bore. (e) Measure taper of the bore by taking one reading at the top of the bore, below ridge portion. (f) Put the gauge further down in the bore and take another reading. (g) The difference between the readings at (e) and (f) has a direct bearing on the taper of the bore. (h) For measuring ovalty of the bore, put dial gauge in the bore, just above its middle point on non-thrust side and take the reading. (i) Put dial gauge as at (h) at ‘0’ but on thrust side of the bore and take a reading. The difference between the readings at (g) and (i) is the ovalty of the bore. 13.6 PRECAUTIONS (a) Dial gauge tips and bore should be cleaned before reading is taken. (b) Make sure that slider plate always remains in contact with cylinder wall. (c) Do not tilt the dial gauge.
42. 42. 46 Laboratory-IV EXPERIMENT NO. 14 : MEASUREMENT OF ANGLE WITH SINE BAR AND HEIGHT GAUGE Structure 14.1 Introduction Objectives 14.2 Instruments Used 14.3 Working Principle 14.4 Procedure 14.5 Sources of Error 14.6 Precautions 14.1 INTRODUCTION The sine bar is one of the most widely used instruments for precision measurement of angles. It consists of a rectangular section bar of suitable grade steel having accurately ground pins of equal diameter, one at each end and lying on a line parallel to the axis of the bar. The distance between the centers of these pins is arranged to be a standard, either 5″, 10″ or 15″ or 125 mm, 200 mm, 500 mm etc. The sine bar is based on the principle that in a right angled triangle the length of hypotenuse is kept constant. The sine of different angles can be obtained simply by varying the length of the perpendicular as shown in Figure 14.1. sin h l θ = A sine bar is made up of a hardened steel beam having a flat upper surface. The bar is mounted on two cylindrical rollers. These rollers are located in cylindrical grooves specially provided for the purpose. The axes of the two rollers are parallel to each other. They are also parallel to the upper flat surface at an equal distance from its. In this experiment, you will be introduced to the measurement of angles with sine bar. Objectives After performing this experiment, you should be able to • develop skill to use sine bar for measuring the external taper angles accurately (by using a single trigonometrical parameter, i.e. sine of an angle), and • develop skill for setting the job and instruments and observing the readings correctly. 14.2 INSTRUMENTS USED A tapered surface of workpiece having good surface finish. Devices and Accessories Required (a) Sine bar, (b) Surface plate, (c) Height gauge, (d) Angle plate, and
43. 43. 47 Measurement and Metrology Lab (e) Square blocks. 14.3 WORKING PRINCIPLE It is based on trigonometric function sin = side opposite angle/hypotenuse. L Rolle d Steel Beam Top Flat Surface h Figure 14.1 : Sine Bar L h hθ Gauge Blocks Sine Bar Figure 14.2 : Use of Sine Bar for Angle Measurement 14.4 PROCEDURE (a) Clean the surface plate. (b) Clean the sine bar. (c) Clean the workpiece, and ensure that there are no damages and burrs on the surfaces of workpiece. (d) If there are any burrs remove them by means of oilstone. (e) Place the workpiece on surface plate with taper surface facing the surface plate. (f) Place the sine bar on tapered surface of workpiece with the rollers of sine bar in upward direction. (g) Clean the base of height gauge properly. (h) Mount the dial indicator on the height gauge. (i) Set the dial indicator on the highest point of one of the sine bar roller and put some pressure on dial indicator. (j) Note the reading of dial indicator and height gauge scale. (k) Set the dial indicator on second roller of sine bar. (l) Bring the same reading on dial indicator by adjusting the height gauge. (m) Note the reading of height gauge at the highest point of both the rollers of sine bar. (n) Calculate the difference of two height gauge readings, which will give the height (h) of one roller with respect to other. (o) The centre distance between the two rollers is known for a standard sine bar.
44. 44. 48 (p) Divide the height in step (n) by centre distance between two rollers. This will give the sine of taper angle sin h l θ = . Laboratory-IV (q) Using sine tables the value of taper angle can be calculated. 14.5 SOURCES OF ERROR (a) Improper cleaning of instruments or workpiece. (b) Damaged instruments and damaged workpiece surface. (c) Improper setting of instrument. (d) Initial error in measuring instrument. (e) Wrong observation of height gauge measuring head. (f) Uneven pressure at two points of reading may lead to error. 14.6 PRECAUTIONS (a) All the instruments should be cleaned properly. (b) Any burrs and damage on workpiece surfaces should be rectified. (c) Zero error in any instrument likely to be checked and if so correct it. (d) In case of circular workpiece sine bar should be clamped firmly with the angle plate. EXPERIMENT NO. 15 :CHECK THE ANGLES OF TEMPLATE GAUGE FOR
45. 45. 49 Measurement and Metrology LabLATHE TOOL/DRILL BIT ANGLES MADE IN FITTING SHOP Structure 15.1 Introduction Objectives 15.2 Instruments Used and Specifications 15.3 Procedure 15.4 Conclusion 15.5 Evaluation 15.6 Sources of Error 15.1 INTRODUCTION Tool angles are specified for machining of jobs. Tool angles depend on job material, operation, cutting tool material and volume of material removed/minute. The tool after grinding and regrinding is checked by a template, having angle grooves of standard profiles for accuracy of grinding. The tool angles are cut as V grooves in a sheet metal of 12-16 gauge steel as a fitting job and the angles are marked by punch marks. These templates are projected on a screen and the profile is compared with an accurately drawn profile on a transparency (or on a sheet on which the profile is projected). Thus, a template can be checked for accuracy so that it can be used in machine shop for checking the tool angles after grinding. In this experiment, you will be introduced to the measurement for checking the angles of template gauge for lathe tool/drill bit angles made in fitting shop. Objectives After performing this experiment, you should be able to • develop skill in finding accuracy of angles of template by comparison through magnification. 15.2 INSTRUMENTS USED AND SPECIFICATIONS Optical/Profile projector magnification 10 – 100. Screen 300 × 300 mm or overhead Projector vernier bevel protractor. Work/Jobs piece – Template gauge – lathe tool, angle gauge and drill angle gauge. Least Count/minimum reading of vernier bevel protractor 0o –5′. 15.3 PROCEDURE (a) Place the template in position. (b) Switch on the projector. (c) Adjust the position of template to a convenient position. (d) Focus the shadow on the screen. (e) Make sure that the shadow is not distorted. (f) Make the outlines with pencil taking due care.
46. 46. 50 Laboratory-IV (g) Remove the sheet and measure angles using vernier bevel protractor and check by using trigonometric functions. Reading Taken Drill point angle depends on material to be drilled. MS/CI 118o Aluminum 140o 15.4 CONCLUSION It is necessary for any template to be checked for accuracy, and the inaccuracies in grinding tool will result in an inefficient operation in production. 15.5 EVALUATION How accurate is the comparison of angle on drawing sheet with projected image of template. 15.6 SOURCES OF ERROR (a) V-grooves not having straight sides. (b) Error in measurement on transparency. (c) Screen of projector not aligned to reference screen. (d) Distortion of image on screen. (e) Error in marking on the drawing sheet. (f) Image not sharp due to the thickness of template.
47. 47. 51 Measurement and Metrology LabEXPERIMENT NO. 16 :MEASUREMENT OF WORN OUT IC ENGINE PISTONS Structure 16.1 Introduction Objectives 16.2 Instruments Used and Specifications 16.3 Devices and Accessories Required 16.4 Procedure 16.1 INTRODUCTION Piston in automobile engines are to seal the gases on top of cylinder and partition the cylinder in two portions for different functions in various strokes. It means that it has to work like a plug with a minimum running clearance between it and the cylinder, so that the expansion due to heat generated during firing stroke of the engine is accommodated in the clearance. Normally this clearance between piston and cylinder is 0.075 mm or 0.003″ for aluminum alloy pistons and cast iron pistons. It means that the piston has to be of the same size as that of cylinder. During the process of engine overhaul, we have to ascertain whether same old piston can work in the cylinder, that is why the worn out piston is to be measured for its serviceability. The simplest method of measuring a piston is with the help of an ottometer. The ottometer measures pistons, rings and gudgeon pins within a shortest possible time without much adjustment in it. Minimum reading in this gauge is 50 mm and it can be zeroed with a nut provided. In this experiment, you will be introduced to the measurement of worn out pistons. Objectives After performing this experiment, you should be able to • measure a worn out piston with the help of ottometer. 16.2 INSTRUMENTS USED AND SPECIFICATIONS Worn out pistons with standard specifications. 16.3 DEVICES AND ACCESSORIES REQUIRED (a) Ottometer, (b) Feeler gauge, 0.15 mm Minimum reading, 50 mm. 16.4 PROCEDURE (a) Place the ottometer in a suitable place and see that its knobs and measuring band is working. Also see that its scale has been perfectly zeroed. (b) Place worn out piston in the space within the measuring band. (c) Rotate band knob, such that measuring band tightens around piston. (d) Lock the band knob. (e) Peep through magnifying glass window and note the reading. This is the size of the piston. Compare with the specification given. (f) Insert 0.15 mm feeler gauge in the top rings land with a new ring. It should not go.
48. 48. 52 Laboratory-IV EXPERIMENT NO. 17 :MEASUREMENT OF CLEARANCE BETWEEN BORE AND SHAFT WITH THE HELP OF PLASTIGAUGE AND FLAT GAUGES Structure 17.1 Introduction Objectives 17.2 Instruments Used and Specifications 17.3 Devices and Accessories Required 17.4 Working Principle 17.5 Procedure 17.6 Precautions and Care of Instruments 17.1 INTRODUCTION In this experiment, you will be introduced to the measurement of clearance between bore and shaft with the help of plastigauge and flat gauges. Objectives After performing this experiment, you should be able to • measure clearance between two mating surfaces (crank shaft and main bearing), and • know precise use of plastigauge and flat gauge. 17.2 INSTRUMENTS USED AND SPECIFICATIONS (a) A packet of plastigauge. (b) Flat gauges in the sizes of 0.001″, 0.002″, 0.003″ and 0.005″ or 0.01 mm, 0.02 mm and 0.03 mm. (c) A piece of cloth. 17.3 DEVICES AND ACCESSORIES REQUIRED A shaft or a crankshaft of automobile engine fitted into bores or main bearing of automobile engine. 17.4 WORKING PRINCIPLE When the fit between shaft and hole is tight-fit, the shaft will not rotate easily but if it is loose fit so that, it will rotate easily. The working of these gauges depend upon this principle.
49. 49. 53 Measurement and Metrology Lab17.5 PROCEDURE Flat Gauge (a) Wipe and clean both the surfaces of crankshaft and main bearing. (b) If the specified clearance between crankshaft and main bearing is 0.002″ take a flat gauge of 0.002″. (c) Put this flat gauge between the crankshaft and main bearing. (d) Tighten the nuts of the bearing one after the other slowly and gradually, till these are tightened to the specified torque. (e) Try to rotate crankshaft either side. (f) If the crankshaft rotates with a slight drag and a normal manual force, the clearance is correct to 0.002″. If it does not rotate at all, the clearance is less than two thousandth of an inch. If it rotates more freely, the clearance is more than 0.002″. (g) If it is required to know the exact clearance try for other sizes of flat gauges and repeat the process as mentioned in (d), (e) and (f) above. Plastigauge (a) Put a suitable plastigauge in between crankshaft and main bearing. (b) The size of the plastigauge should be little less say 2 to 3 mm than the bearing width. (c) Tighten bearing nuts one after the other slowly and gradually till specified torque is reached in the nuts. (d) Now loosen the nuts, take out pressed plastigauge. (e) Measure the thickness of plastigauge on the markings given on plastigauge packet. (f) If the thickness coincides with the clearance specified, it is correct, if less or more, still the clearance can be known from the width of the plastigauge where it coincides. 17.6 PRECAUTIONS AND CARE OF INSTRUMENTS (a) Do not rotate crankshaft when using a plastigauge for measurement. (b) If the thickness of plastigauge is not regular throughout its length, crank pin is tapered. (c) When using flat gauge, do not turn crankshaft more than 2 rotations on either side, otherwise the shim strip will embed.
50. 50. 54 Laboratory-IV EXPERIMENT NO. 18 :ALIGNMENT TESTS OF LATHE Structure 18.1 Introduction Objectives 18.2 Instruments Used and Specifications 18.3 Procedure 18.1 INTRODUCTION For metrology purposes, the term alignment refers to two axes merging in each other or one axis extending beyond the other. Two lines of axes are said to be in alignment when their distance apart at several points over a given length is measured and this distance does not exceed a given standard tolerance. The dimensions of a gauge, its surface finish, geometry and accurate production of components/parts depend upon the inherent quality and accuracy of the machine tools used for its manufacture. Therefore for maintaining the accuracy of the components within prescribed limits, the machines should be properly aligned as the quality of workpieces depend upon : (a) Stiffness and rigidity of the machine tool and its component parts. (b) The alignment of various machine parts in relation to each other. This is very important because the geometry of various shapes is based on the relative motions between various machine parts and hence on alignment of various parts. (c) The quality and accuracy of the control devices and driving mechanism. In most cases the machining of a given geometric surface is achieved through a combination of work tool movements and the accuracy of the surfaces generated depends on the accuracy of the mating elements present in the machine tool. The various tests applied to any machine tool could be grouped below : (a) Tests for the level of installation of machine in horizontal and vertical planes. (b) Tests for flatness of machine bed and for straightness and parallelism of bed ways or bearing surfaces. (c) Tests for perpendicularity of guide ways to other guide ways or bearing surfaces, which support motion in cross direction. (d) Tests for true running of the main spindle and its axial movements. (e) Tests for parallelism of spindle axis to guideways or bearing surfaces. (f) Tests for the line of movement of various members, e.g. saddle and table cross slides etc. along their ways. (g) Practical tests in which some test pieces are machined and their accuracy and finish is checked.
51. 51. 55 Measurement and Metrology Lab Objectives After performing this experiment, you should be able to • develop skill for performing alignment tests on various machine tools, • impart an up-to-date knowledge of need of alignment in machine tools, • explain the relationship of controlled movement of any component with respect to some other component, and • understand the effects of misalignment of any component on the performance of the machine. 18.2 INSTRUMENTS USED AND SPECIFICATIONS A lathe in good working condition with all standard accessories, i.e. live and dead centres, sleeve etc. (a) Dial indicator, (b) Dial stand with magnetic base, (c) Flexible dial stand, (d) Parallel blocks, (e) Straight edge, (f) Straight bar, (g) Standard test mandrel, (h) Straight spirit level, (i) Box type spirit level, (j) Alignment microscope, (k) Taut wire, (l) Set of spanners, (m) Mandrel and centre draw bar. Figure 18.1 : Trucing Up of Work in Lathe
52. 52. 56 Laboratory-IV 18.3 PROCEDURE (a) Clean all surfaces perfectly on which alignment tests are to be performed. (b) Level the bed of lathe for longitudinal as well as cross directions. (c) Follow the test chart for performing different alignment tests. Figure 18.2 : The Test for Parallelism of Spindle with Bed, using a Mandrel Inserted in the Centre Hole Figure 18.3 : Testing for Capability of a Lathe to Turn Parallel; an Accurate Mandrel being Placed between Centres and a Dial Indicator Run Along by the Slide Rest Figure 18.4 : Indicator Held in Slide Rest to Ascertain Truth of Faceplate
53. 53. 57 Measurement and Metrology LabEXPERIMENT NO. 19 :STUDY AND USE OF COMPARATORS Structure 19.1 Introduction Objectives 19.2 Instruments Used and Specifications 19.3 Working Principle 19.4 Procedure 19.5 Conclusion 19.6 Precautions 19.7 Sources of Error 19.1 INTRODUCTION In various production and other situations for assembly, matching of parts etc., it is not necessary to know the exact absolute dimensions of a job. If it is known what deviation of measurement is there from a standard, we may decide whether the sample is acceptable for selective assembly or interchangeable assembly. The comparator is a device, which takes a dimension of standard job as reference dimension, and gives a reading through a pointer on a scale, which is the variation in such dimension of the job. Objectives After performing this experiment, you should be able to • use comparators and develop skill in using them. 19.2 INSTRUMENTS USED AND SPECIFICATIONS Mechanical comparator-Sigma Comparator 0-150 mm range for pointer, scale 0.25 mm from centre, div. of scale 10, permissible error 10, magnification 3000. Slip Gauge Set Work pieces-Any 10 jobs of size within the range of comparator and master jobs. 19.3 WORKING PRINCIPLE Figure 19.1 gives the constructional details of sigma mechanical type comparator. A vertical beam is mounted on flat steel spring A connected to fixed member which in turn is screwed to a back plate. The assembly provides a frictionless movement with a restraint from the springs. The shank B at the base of the vertical beam is arranged to take a measuring contact, selected from available range. The stop C is provided to restrict movement at the lower extremity of the scale. Mounted on the fixed member is the hinged assembly D carrying the forked arms E. This assembly incorporates a hardened fulcrum (provided with means for adjustment of controlling the ratio of transmitted motion) operative on the face of a jeweled insert on the flexible portion of the assembly. The metal ribbon F, attached to the forked arms passes round the spindle G causing it to rotate in especially designed miniature ball bearings. Damping action to the movement is effected by a metal disc, mounted on the spindle, rotating in a magnetic field between a permanent magnet and a steel plate. The indicating pointer H is secured to boss on the disc. The trigger J (opposite K) is used to protect the measuring contact. At the upper end of the vertical beam, an adjusting screw is provided for final zero setting of the scale. A new-patented feature is shown at K. This is a magnetic counter balance, which serves to neutralize the positive ‘rate’ of spring reaching on the measuring tip. In this way a constant pressure over the whole scale range is achieved. The instrument is available with
54. 54. 58 Laboratory-IV vertical capacities of 6″, 12″ and 24″ and magnification of 500, 1000, 1500, 3000 and 5000. The scales are graduated both in English and Metric systems. The least count is of the order of 10 to 100 thousandth of an inch. K A B F G E H D A C J Figure 19.1 : Sigma Comparator A worktable on the base of this comparator stand is used to keep the job on. Special attachments are used for typical jobs like screw thread effective/outside diameter. Figure 19.2 gives the pictorial view of dial indicator type of mechanical comparator. It consists of a sensitive dial indicator mounted on a horizontal arm on a stand. The arm is capable of coarse and fine adjustment movements in the vertical direction for initial setting of the instrument. The base is heavy so that stability and rigidity of the instrument is ensured. Different attachments are available depending upon the type of job. A B Reeds R2 Reeds R1 Fixed Member Movable Member x (Input Displacement) Component Output Displacement x Scale Figure 19.2 : Mechanical (Reed) Comparator
55. 55. 59 Measurement and Metrology Lab19.4 PROCEDURE (a) Clean the comparator with flannel cloth or chamoise leather. (b) Wipe the standard job clean of dust etc. (c) After lifting anvil by pressing the trigger, mount the standard jobs/slip gauges on the work table. (d) Adjust the screw at the top of vertical beam to zero pointer reading. (e) Replace the standard job with sample job and record the reading on scale. (f) Repeat the comparisons for rest of sample jobs. Classify the jobs into acceptable/not acceptable and give code number for selective assembly. 19.5 CONCLUSION Instead of making absolute measurement we can easily know whether job is within two limits to classify the sample and give code symbol for selective assembly or reject it. 19.6 PRECAUTIONS (a) Cleanliness of measuring instrument and job. (b) Zero error (w.r.t. std. job). (c) Friction in mechanism not permitting anvil in contact with job. (d) Calibrations of the comparator. 19.7 SOURCES OF ERROR (a) Foreign particles between anvil and job. (b) Zero adjustment out. (c) Error in master. (d) Wornout components due to friction in mechanism. (e) Anvil not exerting correct pressure on jobs.