It is probably the simplest instrument for measuring the angle between two faces of component. It consists of a base plate attached to the main body, and an adjustable blade which is attached to a circular plate containing vernier scale. The adjustable blade is capable of rotating freely about the centre of the main scale engraved on the body of the instrument and can be locked in any position. An acute angle attachment is provided at the top ; as shown in Fig. The base of the base plate is made flat so that it could be laid flat upon the work and any type of angle measured.
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It is probably the simplest instrument for measuring the angle between two faces of component. It consists of a base plate attached to the main body, and an adjustable blade which is attached to a circular plate containing vernier scale. The adjustable blade is capable of rotating freely about the centre of the main scale engraved on the body of the instrument and can be locked in any position. An acute angle attachment is provided at the top ; as shown in Fig.
The base of the base plate is made flat so that it could be laid flat upon the work and any type of angle measured. The vernier scale has 24 divisions coinciding with 23 main scale divisions. This instrument is most commonly used in workshops for angular measurements till more precision is required. A recent development of the vernier bevel protractor is optical bevel protractor.
Vernier and optical Bevel Protractor. Fitted inside the mam body. A small microscope is fitted through which the circle graduations can be viewed. The adjustable blade is clamped to a rotating member which carries this microscope.
It is used for measuring and laying out of angles accurately and precisely within 5 minutes. The protractor dial is slotted to hold a blade which can be rotated with the dial to the required angle and also independently adjusted to any desired length.
The blade can be locked in any position. Refer Fig. The bevel protractors are of two types, viz. The mechanical bevel protractors are further classified into four types ;A,B,C and D. In types A and B, the vernier is graduated to read to 5 minutes of arc whereas in case of type C, the scale is graduated to read in degrees and the bevel protractor is without vernier or fine adjustment device or acute angle attachment. The difference between types A and B is that type A is provided with fine adjustment device or acute angle attachment whereas type B is not.
Type D is graduated in degrees and is not provided with either vernier or fine adjustment device or acute angle attachment. Universal Bevel Protractor. In the case of optical bevel protractor, it is possible to take readings upto approximately 2 minutes of arc. The provision is made for an internal circular scale which is graduated in divisions of 10 minutes of arc. Readings are taken against a fixed index line or vernier by means of an optical magnifying system which is internal with the instrument.
The scale is graduated as a full circle marked 0—90—0— The zero positions correspond to the condition when the blade is parallel to the stock.
Provision is also made for adjusting the focus of the system to Fig. Mechanical Bevel Protractor with Vernier and acute angle attachment. Mechanical Bevel Protractor without Vernier and acute anele attachment.
The scale and vernier are so arranged that they are always in focus in the optical system. The principle of optical scales has already been discussed in details in chapter 6. It is designed in such a way that its back is flat and there are no projections beyond its back so that when the bevel protractor is placed on its back on a surface plate there shall be no perceptible rock.
Optical Bevel Protractor. The working edge of the stock is about 90 mm in length and 7 mm thick. It is very essential that the working edge of the stock be perfectly straight and if at all departure is there, it should be in the form of concavity and of the order of 0.
It can be moved along the turret throughout its length and can also be reversed. Its working edge should be straight upto 0. It can be clamped in any position. Using bevel protractor for checking the inside bevelled face of a ground surface.
It can be readily fitted into body and clamped in any position. Its working edge should be flat to within 0. Use of bevel protractor for checking of vee block. Use of Vernier protractor for measuring acute angle. The bevel protractors are tested for flatness, squareness, parallelism, straightness and angular intervals by suitable methods. Next post: Divided Circles Metrology. Vernier and Optical Bevel Protractor Metrology.
Vernier and Optical Bevel Protractor (Metrology)
The vernier bevel protractor is a precision instrument meant for measuring angles to an accuracy of 5 minutes. Apart from being used for measuring angles a vernier bevel protractor is also used for setting work-holding devices on machine tools, work-tables etc. For purposes of taking angular measurements, the full circumference of the dial is graduated in degrees. Every tenth division is marked longer and numbered. Each division represents 1 degree. The graduations on the dial are known as the main scale divisions.
Vernier Bevel Protractor
The bevel protractor is used to establish and test angles to very close tolerances. A circle can be divided into equal angles. Each angle is called degree. So a circle is degrees o. For calculation a degree is divided into 60 parts called minutes and a minute is sub-divided into 60 parts called seconds. When the edges of the beam and blade are parallel, a small line on the swivel plate coincides with the zero line on the graduated dial, and when any measurement of an angle between the beam and the blade of 90 degrees or under is desired, the reading may be obtained direct from the position of the line on the swivel plate with regard to the graduation numbers on the dial. But remember this: To obtain the measurement of the angle between the beam and the blade of over 90 degrees subtract the number of degrees as indicated on the dial from degrees.
Universal Bevel Protractor Series 187
Bevel and Digital Protractor