Measurement and EXPERIMENT NO. 1 : MEASUREMENT WITH Metrology Lab 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. 5 Laboratory-IV 49 Then 1 VSD = Division on main scale, 50 49 1 and LC =−1of = MSD 50 50 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 25 25 1 one division of main scale is 0.025 hence LC = of main scale. 1000 Reading of Dia Fine Adjustment Clamp 2 3 4 5 Vernier Scale Not Shown Fine Adjustment Screw Dia Sliding Member 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 6 Reading = 2 + 0.4 + 0.025 + 0.011 Measurement and Metrology Lab (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. 7 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 8 Least count = 0.01 mm Measurement and Metrology Lab (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 1/2 mm pitch and 50 divisions on circular scale will be ==0.01 mm . 250× Spindle Clamp Anvil B Measuring Range A to B Fiducial Line A 56 5 0 4.5 Measuring Faces Friction or Spindle Barrel Ratchet Drive Thimble Frame 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. 9 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. 10 Measurement and EXPERIMENT NO. 3 : MEASUREMENT WITH Metrology Lab 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.