The vernier bevel protractor is a precision instrument meant for measuring angles to an accuracy of 5 minutes.
Parts of a vernier bevel protractor
The following are the parts of a vernier bevel protractor.
- Locking Screws
- Stock : – This is one of the contacting surfaces during the measurement of an angle. Preferably it should be kept in contact with the datum surface from which the angle is measured.
- Dial :– The dial is an integrated part of the stock. It is circular in shape, and the edge is graduated in degrees.
- Blade:- This is the other surface of the instrument that contacts the work during measurement. It is fixed to the dial with the help of the clamping lever. A parallel groove is provided in the centre of the blade to enable it to be longitudinally positioned whenever necessary.
- Locking Screws :- Two knurled locking screws are provided, one to lock the dial to the disc, and the other to lock the blade to the dial..
Use of Vernier Bevel Protractor
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.
The vernier bevel protractor is used to measure acute angles than 90º obtuse angles more than 90º .
For setting work-holding devices to angles on machine
tools, work tables etc.
Graduations on Universal Bevel Protractor
The main scale graduations
For purposes of taking angular measurements, the full circumference of the dial is graduated in degrees. The 360° are equally divided and marked in four quadrants, from ‘0’ degree to 90 degrees, 90 degrees to ‘0’ degree. 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. On the disc, 23 divisions spacing of the main scale is equally divided into 12 equal parts on the vernier. Each 3rd line is marked longer and numbered as
0, 15, 30, 45, 60. This constitutes the vernier scale. Similar graduations are marked to the left of ‘0’ also.
One vernier scale division VSD
The least count of the vernier bevel protractor
When the zero of the vernier scale coincides with the zero of the main scale, the first division of the vernier scale will be very close to the 2nd main scale division.
For any setting of the blade and stock, the reading of the acute angle and the supplementary obtuse angle is possible, and the two sets of the vernier scale graduations on the disc assist to achieve this.