 Hello and welcome to the video lecture on Angular measuring instruments 2. 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 particular video lecture. The recap of first session, which was about Angular measuring instruments part one, it was about protectors, bevel protector, veneer bevel protector, optical bevel protector. Then we will be discussing about spirit level and afterwards we will be discussing about clinometer, introduction to angular measuring instruments. Precise measurement of angles is one of the important requirements in workshops and tool rooms. We need to measure angles of interchangeable parts, gears, jigs, fixtures, etc. So these are the devices that are used to measure the angle of the given specimens. Example bevel protector, sine bar, sine center, etc. Classification of Angular measuring instruments. Angular measuring instruments are classified based on various standards. Line standard Angular measuring devices. Line standard gives direct angular measurements from the engraved scales in the instruments. They are not very precise hence they are not used when high precision is required. However, they can be used in initial estimation of the angles in instrument. Example protractor bevel protector, phase standard Angular measuring devices. Phase standard Angular measuring devices include angle gauges and sine bars. The measurements are done with respect to two phases of the measuring instruments. Precision obtained in such instruments is more than the precision obtained in the standard Angular measuring devices. Example sine bar angle gauges. Measurement of inclines. Inclination of a surface generally represents its division from the horizontal or vertical planes. Standard principle can be used in construction of measurements of such inclinations. Spirits and clinometer are included in this particular category of measurement of inclines. Protractor. A simple protractor is the basic device for measuring angles. At best it can provide least count of one degree for smaller protractor and half degree for large protractors. Vernier bevel protector is the simplest angle measuring instrument. It consists of main body, base plate stock, adjustable blade, circular plate containing Vernier scale, then the acute angle attachment. The body of the Vernier bevel protector is designed in such a way that its black is flat and there are no projections beyond its back. The flatness of the body is tested by checking the squareness of blade with respect to base plate when the base plate is set at 90 degree. The base plate is attached to the main body and an adjustable blade is attached to a circular plate containing Vernier scale. The main scale graduated in degrees is provided on the main body. The adjustable blade is capable of rotating freely about the center of the main scale and graved on the body of the instrument can be locked in any position and acute angle attachment is provided at the top for measuring acute angles. The base of the base plate is made flat so that it could be laid flat upon the work and any type of angle can be measured. The blade can be moved along throughout its length and can also be reversed. Its ends are beveled at angles 45 degrees and 60 degrees respectively. The acute angle attachment can be readily fitted into the body and clamped in any position. The bevel protectors are tested for flatness, squareness, parallelism, straightness etc. The main scale is graduated in degrees of arc. The Vernier scale has 12 divisions each side of the center 0. These are marked 0 to 60 minutes of arc so that each division equals 1 by 12 of 60 that is equal to 5 minutes of arc. Base of Bevel Protector Bevel protector is used for checking inside beveled face of a ground surface. So here I have mounted this blade, here the blade is mounted and the stock is placed on this particular surface and I am measuring and my angle is measured. And Bevel Protector for checking V block. Here again blade is placed here and base plate stock is on the surface here, angle is being measured. Third workpiece is placed on the acute angle attachment and the angle is being measured. Optical Bevel Protector Optical Bevel Protector is recent development of Vernier Bevel Protector. By using this instrument it is possible to take reading up to approximately 2 minutes of an arc. The internal circular scale is graduated in divisions of 10 minutes of arc. These are taken against a fixed indexed line or Vernier by means of optical magnifying system which is integral with the instrument. The scale is graduated as a full circle marked 0 to 90, 0 to 90. The zero position corresponds to the condition when the blade is parallel to the stock. Covision is also made for adjusting the focus of the system to accommodate normal variation in the eyesight. The scale and Vernier are so arranged that they are always in focus in the optical system. Spirit Level A spirit level has a sealed glass tube ground on its inside surface to convex form with large radius of curvature r. The tube is almost completely filled with ether so that only a small volume remains at the top part of the blade which contains ether vapor in the form of a bubble. Cleanometer A cleanometer is a spirit level mounted on a rotary member. The angle of inclination of the rotary member relative to its base can be measured by a circular scale. There are various types of cleanometers, Vernier cleanometer. It consists of a spirit level mounted on a rotary member carried in a housing. One phase of the housing forms the base of the instrument, there is circular scale on the housing. The angle of inclination of the rotary member relative to the base can be measured by a circular scale. The scale may cover the whole circle or only part of arc generally used to determine the angle included between the two adjacent phases of a work piece. The base of the instrument is placed on one of the surfaces and rotary member is adjusted till zero reading of the bubble is obtained. The angle of rotation is then noted on the circular scale against an index. The instrument is then placed on the other surface and the reading is taken in the similar manner. If theta and phi are reading of the instrument then the included angle between the surface alpha is nothing but 180 degree minus theta plus phi. Micro cleanometer In this type spirit level is attached at one end of the barrel of a micrometer. The other end of the spirit level is hinged on the base. The base is placed on the surface whose inclination is to be measured. The micrometer is adjusted till the level is horizontal. This type of cleanometer is used for measuring small angles. Now pause this video for a few seconds and try to write answer to the following question. State true or false spirit level is mounted on a rotary member. Probably you have wrote answer to the following question. Users of cleanometer they are used for checking included angles, relief angles as well as angular faces on large cutting tools and milling cutter inserts. They can also be used for setting inclinable tables on jig boring machines and angular work on grinding machines. These are the following references. Thank you.