EXPERIMENT NO. 1 : MEASUREMENT WITH SCALE AND VERNIER CALIPERS

Transcription

1 EXPERIMENT NO. 1 : MEASUREMENT WITH SCALE AND VERNIER CALIPERS Measurement and Metrology Lab Structure 1.1 Introduction 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 ( ), a french mathematician. The vernier caliper essentially consists of two steel rules and these can slide along each other. After performing this experiment, you should be able to use the vernier caliper, and read the measurement with vernier caliper. 1.2 INSTRUMENTS USED (f) (g) Steel scale, 300 mm Steel scale, 150 mm Vernier caliper, size 150 mm, LC = 0.02 mm Vernier caliper, size 300 mm, LC =0.02 mm Surface plate, 450 mm 450 mm Magnetic base, 50 mm 50 mm Straight edge, 250 mm. 1.3 WORKING PRINCIPLE The principle of vernier was first introduced by Pierre Vernier in 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. 5

2 Laboratory-IV Then 1 VSD 49 = Division on main scale, 50 and LC 49 1 = 1 = of MSD Figure 1.1 shows the details of a vernier caliper. Figure 1.2 shows 25 divisions of vernier 24 1 coinciding with 24 divisions on main scale giving LC = 1 = divisions and since one division of main scale is hence LC = of main scale Reading of Dia Fine Adjustment Clamp Vernier Scale Not Shown Fine Adjustment Screw Dia Sliding Member Figure 1.1 : Vernier Caliper 1.4 PROCEDURE (f) 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. Measure sample piece, read and record the reading in the Proforma suggested. Study the vernier caliper and its constructional details; Figure 1.1 gives the important parts of the calipers. Understand the vernier principle and see how the least count is calculated. Calculate and check error if any. Read the instrument for at least three random vernier positions. Measure the samples at indicated places and record as per standard Proforma (Figure 1.2). Figure 1.2 6

3 Reading = (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 = Measurement and Metrology Lab Figure 1.3 : Some Details of Using Vernier Caliper 1.5 PRECAUTIONS AND CARE OF INSTRUMENTS (f) (g) 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. 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. Check if steel rule ends are worn round or unsquare before using. All instruments should be thoroughly cleaned, covered with mobil oil and put in dust free covers. When putting any instrument on table it should not be put violently or with a jerk. While measuring length standards by above instrument error of parallax or zero error should be avoided. In vernier calipers, there should be no play between sliding jaw and the fixed scale. 7

4 Laboratory-IV EXPERIMENT NO. 2 : MEASUREMENT WITH MICROMETERS INTERNAL AND EXTERNAL Structure 2.1 Introduction 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. 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, mm (vernier type) Measuring range as below : mm mm mm mm Internal Micrometres

5 Least count = 0.01 mm Calliper Type (5 mm-25 mm range) Internal micrometer with different extension rods. 25 mm upwards measuring range. Measurement and Metrology Lab 2.3 WORKING PRINCIPLE The limits of accuracy specified on certain component involves measuring to 0.01 mm or 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 1/2 mm pitch and 50 divisions on circular scale will be = = 0.01 mm Anvil B Measuring Range A to B A Measuring Faces Spindle Spindle Clamp Fiducial Line Barrel Thimble Friction or Ratchet Drive Frame Figure 2.1 : Micrometer Figure 2.2 : Inside Micrometer Caliper Figure 2.3 Read = 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 =

6 Laboratory-IV 2.4 PROCEDURE Study the main elements of external/internal micrometer : U-frame, barrel, thimble, locknut, and ratchet. Calculate the least count and note range of measurement of the instrument. Read off any three positions of the main and subsidiary scale. Measure the given piece and record as per standard Proforma. 2.5 PRECAUTIONS AND CARE OF INSTRUMENTS (f) (g) (h) 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. The micrometer should be wiped clean and free from oil, dirt, dust and grit. Clean the measuring surfaces of anvil and spindle for every measurement. Check for zero reading. If there is no ratchet, use the pressure on thimble for checking zero error. The anvil and spindle measuring surfaces should be flat and square to the anvil and spindles respectively. 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. 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. 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. 10

7 EXPERIMENT NO. 3 : MEASUREMENT WITH HEIGHT AND DEPTH GAUGE Measurement and Metrology Lab Structure 3.1 Introduction 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. 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 Height Gauge, 300 mm range, least count 0.02 mm Depth Gauge, 100 mm range, least count 0.02 mm Surface Plate, mm, Grade I V-Blocks, 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. 11

8 Laboratory-IV Figure 3.1 : Vernier Height Gauge Figure 3.2 : Vernier Depth Gauge 3.4 PROCEDURE Study the main elements of depth gauge, base, thimble, lock nut and depth gauge attachments. Study the main elements of height gauge, main scale, vernier scale, base, movable arm, scriber, adjusting scales. Calculate the least count and maximum range of measurement. Read off any three positions of the main and subsidiary scale and record the readings. Measure the given piece and record as per the standard proforma. 3.5 PRECAUTIONS AND CARE OF INSTRUMENT Height Gauge Do not allow the instrument to come in contact with dust and dirt. It is better kept in its case. 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. 12

9 Depth Gauge (f) 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. Check for rocking of base on surface plate at various points. 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. Make sure the reference surface, on which depth gauge is rested is true flat and square. Make sure the gauge itself is true and square. 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. 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. 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. 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. Measurement and Metrology Lab 13

10 Laboratory-IV EXPERIMENT NO. 4 : MEASUREMENT WITH DIAL INDICATOR USING SURFACE PLATE AND ACCESSORIES Structure 4.1 Introduction 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. 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 Dial indicator range 0 to 10 mm, LC = 0.01 mm, with stand. Surface plate, mm 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. 14 Figure 4.1

11 4.4 PROCEDURE Measurement and Metrology Lab For Checking Flatness 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. Place the flat piece on the surface plate. Mount the dial indicator on the stand and take at least four readings on the job at different positions. Record the readings in the table and note the deviations from flatness (if any). For Checking Concentricity of a Round Shaft Place the round job on the V-block. Mount the dial indicator on the stand and take different readings on the job by rotating it. Record the readings in the table of observations and note the deviations (if any) for checking the circularity. Note the maximum eccentricity. Circle Dial Indicator Part Part 4.5 PRECAUTIONS Figure 4.2 : Using Dial Indicator on Round Bar Some initial loading must be given at any given readings. The plunger should not be allowed to strike the work with force otherwise the teeth of the gears and rack will be damaged. The accuracy of the dial indicator may be checked with the help of slip gauges periodically. 15

12 Laboratory-IV 4.6 SOURCES OF ERROR Some variations may be there in the indicator when readings are being taken. This may be avoided if the pointer movement is damped properly. 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. 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. 16

13 EXPERIMENT NO. 5 : MEASUREMENT WITH COMBINATION SET Measurement and Metrology Lab Structure 5.1 Introduction 5.2 Instruments Used 5.3 Working Principle 5.4 Procedure 5.5 Precautions and Care of Instruments 5.6 Sources of Error 5.1 INTRODUCTION This is the most adaptable and commonly used non-precision instrument to be used in layout and inspection work. Combination set is used as a rule, a square, a depth gauge, a height gauge and a level. After performing this experiment, you should be able to understand the uses of combination set, measure angles by using combination set, and check the sequences by using combination set. 5.2 INSTURMENTS USED Combination set 450 mm with scale of 450 mm, square head, centre head, protractor head, levels and scribes. 5.3 WORKING PRINCIPLE The combination set is a non-precision instrument. Because of geometry involved the angles are usually more difficult to measure then linear dimension. This is most commonly used in layout and rough inspection work. The combination set consists of scale, square head, protractor head and centre head. Its usefulness lies in incorporation of such essential features as try square, mitre-square, protractor and centre-square. The protractor like any common protractor measures angle but has additional facility of being movable. It consists of a heavy scale, which is grooved in the center along its entire length. It is in this groove that square head, centre head or protractor head is fixed. The protractor head may be used in conjunction with the rule as a protractor for checking angles or scribing lines at angles to reference plane. The square head is used in conjunction with the rule as a try square. The square head is used for checking squareness and for marking purposes. It can also be used for measuring depth up to the accuracy of 0.5 mm. The centre head is used for finding the centre of bar stocks. The features of combination set are shown in Figure

14 Laboratory-IV Figure 5.1 : Combination Set 5.4 PROCEDURE For Measuring Angles Fix the protractor head on the scale. Place the scale on one side of the angle to be measured. Adjust the protractor by rotation, so that its working surface should touch the adjacent side of the angle to be measured. Lock the protractor. Read the angle on the scale. For Checking Squareness Fix the square head on the scale. Check the spirit level for parallelism. Check the surfaces for squareness by placing the job on the surface plate. For Marking Centre Fix the centre head on the scale. Hold the bar stock beneath the scale. See that the sides of centre head are touching the bar stock. Scribe a line along the scale in each position and rotate the bar stock for three positions. The centre of the triangle formed will be the centre of the job. 5.5 PRECAUTIONS AND CARE OF INSTRUMENTS (f) The job should be held in the left hand and the instrument in the right hand. The surfaces to be checked should be clean. The edge of the scale should be straight. Spirit level should be checked before taking reading. See that there are no nicks and scratches on the base of heads. 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 The edge of scale may not be straight. Zero error in the protractor scale may exist. Working surfaces of different heads may be worn. 18

15 EXPERIMENT NO. 6 : MEASUREMENT OF ANGLES WITH BEVEL PROTRACTOR Measurement and Metrology Lab Structure 6.1 Introduction 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. 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 360 o ) Least count = 5. Surface plate 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 1/12 o or 5. 19

16 40 Laboratory-IV Body Turret Slow Motion Device Scale Blade Locking Nut Blade Stock Working Edge Figure 6.1 : Bevel Protractor Figure 6.2 : Universal Bevel Protractor 6.4 PROCEDURE Figure 6.3 : Vernier Protractor Reading 20 o Study the bevel protractor and identify its main parts. Introduce the adjustable blade in the slot of body and clamp it with the help of knob in the convenient position. 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 Measure the angles of the sample pieces with the bevel protractor and record the reading in the proforma suggested. Measurement and Metrology Lab 6.5 PRECAUTIONS AND CARE OF INSTRUMENT Use the instrument with care. While readings are taken your eyes must be in front of the matching lines. Always check the tightness of clamping screws before taking reading. 6.6 SOURCES OF ERROR Base plate and adjustable settings. Blade and stock should be made parallel to the surfaces of the sample job otherwise the angles measured will be wrong. Instrument has marking errors. Parallax errors may occur. 21

18 Laboratory-IV EXPERIMENT NO. 7 : STUDY AND USE OF SLIP GAUGES Structure 7.1 Introduction 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. 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 Gauge block set (103 pcs) Surface plate, mm Magnetic base holder 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 mm slips of thickness 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 22 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 measurement. For wringing, the slips are first placed at right angle and then rotated through 90 o under pressure of about 5 N/mm 2. Slip gauges are classified according to their accuracy : C Grade : This generally used in workshop for checking dimensions of the products. B Grade : This grade is used in factories for checking the size of the articles. A Grade : This is used for reference purpose. 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 mm and 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 Measurement and Metrology Lab Range Steps Pieces mm mm mm Total : M 103 Set of 87 Pieces (Special Set) Range Steps Pieces mm mm mm mm 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). 23

20 Laboratory-IV Figure 7.1 : Gauge Blocks Figure 7.2 : A Set of Slip Gauges Reading Taken Building up size combination (sets of 103 pcs) mm mm 1st slip mm 1st slip gauge mm 2nd slip mm 2nd slip gauge mm Length mm 3rd slip gauge mm 4th slip gauge mm Length = mm 7.4 PRECAUTIONS AND CARE OF INSTRUMENTS (f) (g) (h) (i) The surface of the gauge must be protected against rust with neutral petroleum jelly or some other anticorrosive preparation. The gauges should be protected from dust and dirt. The gauges should be used under controlled conditions of temperature and maintained at constant temperature. Wipe the gauge clean with chamois leather everytime before use. The excessive pressure during wringing of gauges may cause damage to the surface. When building up size combination, see that you start with the minimum value of the right hand side of the decimal. Never drop a slip gauge. Never strike slip gauges with other metallic objects. Use minimum number of gauges for building up size combination. 24

21 7.5 SOURCES OF ERROR Measurement and Metrology Lab Improper wringing of the gauges. Noting the dimensions incorrectly from the gauge. The error may occur due to room not being maintained at proper temperature. 25

22 Laboratory-IV EXPERIMENT NO. 8 : MEASUREMENT OF THREAD CHARACTERISTICS Structure 8.1 Introduction 8.2 Material Required 8.3 Instruments Used and Specifications 8.4 Theory 8.5 Precautions 8.1 INTRODUCTION Thread can be defined as a raised, helical rib or ridge around the exterior of a cylindrical shaped object or the interior of a hole. Threads are found on screws, nuts and bolts. In this experiment, you will be introduced to the measurement of thread characteristics. After performing this experiment, you should be able to know and identify various kinds of threads, explain the important thread characteristics, acquire the skill of comparing the threads and finding the pitch, and acquire the skill of measuring effective thread diameter. 8.2 MATERIAL REQUIRED A standard size wooden box with about one dozen prepared samples, suitable for measurement, contains assortment of whitworth as well as metric threads. Maximum nominal diameter = 20 mm 5 metric threads, 5 whitworth threads. 8.3 INSTRUMENTS USED AND SPECIFICATIONS Screw pitch gauge (Metric and whitworth). Screw thread micrometer (Metric and whitworth). 8.4 THEORY 26 A few types of threads are (Figure 8.1) : Vee, Square, Buttress, Acme, and Knuckle. Common definitions involved in thread characteristics are shown in Figure 8.1 which show outline of a typical V-type screw thread and other threads. Different characteristics of threads are :

23 Full diameter (major) or diameter at top of the thread. Core diameter (minor) or diameter at bottom of thread. Effective Diameter (Pitch Diameter) : The length of a line perpendicular to, and intersecting the axis, between the points where it meets the sloping flanks of the threads on opposite sides. Pitch : The distance measured parallel to the axis of the screw, between corresponding point on consecutive thread contours. Thread Angle : The angle between thread flanks measured in an axial plane section. (f) Radius of crest. (g) Radius of root. Pitch, thread angle and effective diameter are some of important parameters to be measured. Full Diameter : With ordinary micrometer with anvils sufficient to span two threads, check first a standard cylinder and then the screw diameter. Core Diameter : An ordinary micrometer with a pair of special V-pieces check the diameter over the roots of threads. Effective Diameter. Three Wire Method Checking the effective diameter when a screw is measured over wires is given below for a general case. Distance over wires: where p L L De W cot = + 1 cosec d D e = effective diameter, d = diameter of wire, p = pitch, L = angle of thread, W = outer diameter of thread with wires, and D = nominal diameter or major diameter. Measurement and Metrology Lab L D W D e Figure 8.1 Whitworth Threads Depth of thread = 0.64 p, L = 55 o D e = W d p or D = W d p American Metric Thread Depth of thread = p, L = 60 o De = W 3 d p or D = W 3 d p [Note : Limiting wire size for thread measurement.] Thread Form Max. Wire Dia Min Wire Dia 27

24 Laboratory-IV Whitworth p p. Metric 1.01 p p. 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,,, and ). 1/6 D PITCH D /6 D P ½ P P P P ½ P P RAD ¼ P P 1/2 28 Figure 8.2 Thread Angle : Measured by Screw pitch gauge approximately and Toolroom microscope accurately.

25 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. Measurement and Metrology Lab 8.5 PRECAUTIONS When making a test, micrometer must be located at right angles to the axis of the screw being measured. Threads must be fixed on the table of the microscope, so that observation is not disturbed. Proper lighting of the object will assist in accurate recording of measurements. Screw pitch gauge with a stopper must be used especially in case of small nuts. 29

26 Laboratory-IV EXPERIMENT NO. 9 : MARKING AND MEASURING EXERCISE WITH ALL MEASURING DEVICES Structure 9.1 Introduction 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. 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 MS/Cl block or plate with three surfaces machined accurately and perpendicular to each other. Pieces of chalk or Prussian blue paste. 9.3 INSTRUMENTS USED (f) (g) (h) (i) (j) Marking table Height gauge with carbide tipped scriber Ordinary scriber with magnetic base stand Slip gauge set Angle plate Divider Scale Set of punches Dial indicator Set of parallel blocks. 30

27 9.4 WORKING PRINCIPLE Measurement and Metrology Lab Marking is based on the principle of transferring the dimensions from the measuring instruments to the job by means of scriber. 9.5 PROCEDURE (f) (g) (h) Clean the marking table and marking instruments. Check mutual perpendicularity of the three machined surfaces of workpiece with angle plate. Apply chalk or blue paste on the surfaces to be marked. Place the workpiece in xy-plane on marking table. 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. Scribe all the lines inclined with the marking table with the help of scale and scriber. Make punch marks on the scribed lines. Repeat marking steps of other reference planes, i.e. yz and xz. 9.6 PRECAUTIONS AND CARE OF INSTRUMENTS (f) (g) Scriber should be fixed firmly in the height gauge. Reference planes should not have any burrs and should be mutually perpendicular to each other. Marking table should be leveled. Scriber point should be sharp and scriber should be perpendicular to the marking surface. Movement of scriber on marking table should be smooth. All the dimensions should be marked carefully. All the dimensions should be verified before punch marking the scribed lines. 9.7 SOURCES OF ERROR Damaged base of height gauge. Loose holding of scriber in the height gauge. Tilting of height gauge during marking. Bluntness of scriber. Scribing wrong dimensions from wrong reference plane. 31

28 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. 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 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. No Go Gauge for Hole Figure 10.1 : Go and Figure 10.2 : Standard Ring and Plug Gauges 32

29 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 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. 33

30 Laboratory-IV Double Snap Gauge, the No Go Check is Made by the Inner Faces Figure 10.6 : Snap Gauge Adjustable Gauge A further improvement is to substitute two pairs of contact for the parallel faces of jaws as indicated. In this way, by making one of each pair of stops adjustable it is possible to set the gauge to any two limiting dimensions and also later on, to take up any wear effects on the contacts. Thread Gauges During mass production of threaded parts, it is uneconomical to measure each individual element, since measuring can eventually be more expensive than the workpiece. Instead, screw thread gauges, which permit a simultaneous testing of all thread dimensions, will be used. The external thread is tested with standard ring thread gauge and the inside thread with the standard plug thread gauge as shown in Figure The gauges must fit in such a way that they can be screwed in or out without any clearance in between. The smooth cylinder plug gauge is used for testing the core diameter of the internal thread. The testing depends on the sensitiveness. Moreover a thread, which can be screwed in with a snug fit, does not yet offer the guarantee that it fits properly. The flank diameter and the bearing of the flanks cannot be tested accurately with standard thread gauge, therefore these are seldom used. l l GO NO GO 34 Figure 10.7 : Thread Gauge Thread limit gauges are used for fast and accurate testing of all thread dimension. The same as with all other limit gauges, they have a GO and NO GO side. Internal thread is tested with limit screw plug. Taper Gauges If tapers and taper holes fit together, they must have the same conicity. Testing the serviceability of a taper consists mainly in the determination of proper conicity. It is well known that the dimensions determine conicity of a taper: big diameter D, small diameter d and length l. The measuring of these sizes is not a simple matter and it is generally tested at the same time with special taper gauges, which contain the prescribed dimensions. Standardized tapers (Morse tapers, Metric tapers) are tested with standard taper gauges. Thus, not only the individual dimensions are ascertained, but they are also determined. If the taper ring gauge corresponds with the taper or the taper hole with the taper plug gauge as shown in Figure 10.8, the diameters of the taper are correct.

31 GO NO GO Measurement and Metrology Lab 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 90 o. 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. 35

32 Laboratory-IV EXPERIMENT NO. 11 : MEASUREMENT OF TAPERS (EXTERNAL AND INTERNAL) Structure 11.1 Introduction 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. 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 INSTRUMENTS USED (f) Micrometer, Depth gauge/height gauge, Surface plate, Balls of known dimension 2 of each size, Rollers of known dimension 2 of each size, Gauge block set. Least Count/minimum reading of Micrometer = 0.01 mm Micrometer depth gauge = 0.01 mm Vernier height gauge = 0.02 mm WORKING PRINCIPLE 36 These methods make use of trigonometric functions. The required dimensions are computed by taking several readings with instruments.

33 D Measurement and Metrology Lab θ d 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 θ= D 2 d H This method is applied for measuring the taper angle of a component such as a taper plug gauge. For External Taper (f) (g) Stand the taper plug gauge (job) with its small end on the surface plate. Select two piles of slip gauges (S1). Place the roller of diameter on the top of the block of slip gauges (S1). Standardize the micrometer carefully on a slip gauge with a roller on each side. Measure the size of the job or gauge over the rollers. Select another value of slips (S2) and place the roller over it. Measure the size over the rollers M2 by micrometer. For Internal Taper (f) (g) (h) (i) Hold the ring gauge or job almost horizontal. Roll the smaller ball gently inside the gauge or job until it rests. Stand the gauge or job, small end down, on the surface plate. 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. Lower the depth attachment with the height gauge until it just touches the top of the ball. The height gauge reading is noted and the procedure repeated about three times to get average value. Next remove the smaller ball and insert the larger one. Note the height with the larger ball. Note the height of the top surface of the gauge (job). 37

34 Laboratory-IV 11.5 PRECAUTIONS The taper gauge (or job) should be set up on its small end. The roller should be of same diameter as small end. Rollers must not swing under measuring pressure. Check the zero error of the measuring instruments. Check that the balls used for internal taper have true spherical surface SOURCES OF ERROR Misalignment of rollers. Uneven pressure while taking reading over the rollers. Error due to improper wringing of slip gauges. The height gauge may not be in contact with the highest point of the ball. 38

35 EXPERIMENT NO. 12 : MEASUREMENT OF SPUR GEAR CHARACTERISTICS Measurement and Metrology Lab Structure 12.1 Introduction 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. 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 INSTRUMENTS USED Gear tooth vernier Vernier caliper 12 or 300 mm Bench vice. Least count of Gear tooth vernier, 0.02 mm Vernier Caliper, 0.02 mm Bench vice Figures 12.1 : Gear Tooth Nomenclature 39

36 Laboratory-IV Diagram of gear tooth vernier (Figure 12.1). 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 WORKING PRINCIPLE 40 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 (f) (g) 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 Module : It is defined as the length of the pitch circle diameter per tooth. Module, m = D/T and is expressed in mm. 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. π D CP = =π m T 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. 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 m or 0.25 m. Dedendum : This is the radial distance from the pitch circle to the bottom of tooth space.

37 (h) Dedendum = Addendum + Clearance or = m m = m m (metric gearing system) 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)) Measurement and Metrology Lab 12.4 PROCEDURE For Finding PCD, Module, Addendum, Dedendum and Clearance First find the blank diameter OD by a vernier caliper and also count the number of teeth T of the spur gear. Next calculate pitch circle diameter OD D = T 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) 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. Adjust the horizontal vernier slide by the fine adjusting screw so that the jaws just touch the tooth. Read the horizontal vernier slide and note the reading. It gives the chordal thickness of tooth. Repeat the observations for different teeth. 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 Gear-tooth Caliper and Pins for Balls and a Micrometer (Source : American Gear Manufacturers Association) 41

38 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 m = m (1.25 m) Clearance = 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 Gear surface should be cleaned properly before setting the instruments. Zero error of the instruments should be taken into account. Repeat the experiment by setting the instrument on different teeth SOURCES OF ERROR The adjusting of jaws of gear tooth caliper may not be proper. Zero error may be there. Jaws may be worn out. 42

39 EXPERIMENT NO. 13 : MEASUREMENT OF BORE WITH CYLINDER DIAL GAUGE FOR SIZE, TAPER AND OVALTY Measurement and Metrology Lab Structure 13.1 Introduction 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 90 o 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. 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 MATERIALS REQUIRED Cylinder dial gauge, and Cylinder bore DEVICES AND ACCESSORIES REQUIRED A piece of muslin cloth or like. A piece of paper and pencil. 43