 Hello and welcome to the video lecture on Angular measuring instruments. Fifth part, at the end of this video lecture, students will be able to explain about various angle measuring instruments. The following topics will be discussed in this video lecture. Recap of fourth session, angle gauges. Sign center. Due to difficulty of mounting conical work easily on a conventional sign bar, sign centers are used. Two blocks as shown in figure are mounted on the top of the sign bar. These blocks accommodate centers and can be clamped at any position on the sign bar. The centers can also be adjusted depending on the length of the conical workplace to be held between centers. Sign centers are extremely useful for the testing of the conical work. Change the centers ensure correct alignment of the workpiece. The equipment consists of a self-contained sign bar hinged at one roller and mounted on its datum surface. The table is quite rigid one and the weight of the unit and the workpiece is given fuller and safer support. The table may be safely swing to any angle from 0 to 90 degree. By pivoting it about its hinged end. Due to the work being held axially between centers, the angle of inclination will be half the included angle of the work. It provides a convenient method of measuring the angle of a taper plug gauge. Angle gauges. This were developed by Dr. Tom Linsen in 1941 which enable any angle to be set to the nearest three seconds. These are pieces of hardened and stabilized steel. The measuring pieces are lapped and polished to a high degree of accuracy and flatness. They are 75 mm long and 16 mm wide and are available in two sets. One set consists of 12 pieces and a square block in three series of values of angle. So, here the square blocks means the 90 degree angle gauge, perpendicularity. So, these are the various series 1 degree, 3 degree, 9 degree, 27 degree and 41 degree. 1 minute, 3 minute, 9 minute, 27 minute and 6 seconds, 18 seconds and 30 seconds. Second set consists of 13 pieces and a square block in three series of values of angle. 1 degree, 3 degree, 9 degree, 27 degree and 41 degree. 1 minute, 3 minute, 9 minute, 27 minute and 3 seconds, 6 seconds, 18 seconds and 30 seconds. Addition and subtraction of angle gauges. Each angle gauge is accurate to within 1 second and is marked with engraved capital V. Which indicates the direction of the inclined angle. These gauges together with the square block can be so run that any angle between 0 degree to 360 degree can be set. Each angle gauge is a wedge. Thus two gauges with their narrow ends together provide an angle which is the sum of the angles of the individual gauges. Subtraction of angles is obtained when the narrow ends are opposed as shown in figure. Each angle gauge is marked with engraved V indicates the direction of included angle. When the angles of individual gauges are to be added then the V of all should be in line. When any angle is to be subtracted its engraved V should be in another direction. So, here this is the 30 degree block and 5 degree block. So, it is the 30 degree angle gauge. So, this is the V and this is another 5 degree block. This is the V I am getting here. So, addition of angle gauges when both the V are in same line. So, addition takes place. So, 30 degree plus 5 degree, 35 degree angle is formed. The same thing I take the 30 degree angle gauge and here V is there. So, both are in opposite direction. So, it will be 30 degree minus 5 degree that is 25 degree angle is formed. Numericals on angle gauges. An angle of 33 degree 9 minute 15 seconds is to be measured with the help of the following standard angle gauges. 1 degree, 3 degree, 9 degree, 27 degree, 41 degree, 1 minute, 3 minute, 9 minute, 27 minute, 3 seconds, 6 seconds, 18 seconds, 30 seconds. Show the arrangement of angle gauges with a neat sketch by selecting minimum number of gauges. So, this is the problem given. So, I want to form 33 degree. Is there the 33 degree angle gauges present? No. So, how it can be formed? Addition and subtraction concept of angle gauges I can use it. Here I will form 27 degree plus 9 degree. So, 27 plus 9 will form that is the 36 degree. Then 36 what should be subtracted? How many degrees should be subtracted? I have 3 degree angle gauge. So, 36 minus 3 33 degrees formed. So, the same thing 9 minutes 9 minutes angle gauges present. 15 seconds. So, 15 seconds is nothing but 18 seconds minus 3 seconds. It means engraved v should be in opposite direction here. So, minimum number of gauges required is 27 plus 9 both the engraved v are same direction. Then here opposite direction. So, 27 plus 9 36 minus 3 33 same thing. 9 minutes yes it is already there. Then 18 minus 3 15 seconds. This is always solved the problem using the angle gauges. Now pause this video for a few seconds and try to write answer to the following question. Straight true or false? For addition of angle the engraved v or the v of all the individual gauges should be in line. Probably you have wrote answer to the following question. Limitations of angle gauges. Block formed by combination of these gauges is bulky which cannot always be conveniently applied to work. The second is that errors are easily compounded when angle blocks are ranked in combination. Users of angle gauges. Angle gauges are widely used in industries for the quick measurement of angles between two surfaces. Second it is used to check whether the component is within its tolerance angle or not. These are the following references. A textbook. Metrology by E. M. Mahajan. Second IC Gupta. Engineering Metrology. Dhanpatrai Publications. Third R. K. Jain. Engineering Metrology. Khanna Publishers. Thank you.