Working principle of Vernier Bevel Protractor

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Working principle of Vernier Bevel Protractor

July 22, 2018 by Sundar Dannana 

In Metrology, The angular measurements are frequently necessary for manufacturing industries. Vernier Bevel protractor is one of the angular measuring instrument used for close tolerances. We are going to discuss the construction and the working principle of the Vernier Bevel protractor in this article.

Vernier Bevel Protractor

Bevel Protractors are the Angular measuring devices. Vernier Bevel protractor is the simplest angular measuring device which is having a Vernier Scale(Similar principle as the Vernier Calliper) along with the acute angle attachment.

(The meaning of bevel is which is not 90°)

Construction of Vernier Bevel Protractor

Vernier Bevel protractor consist of the following components.

1.    Main body

2.    Base plate stock

3.    Adjustable blade

4.    Circular Plate with graduated vernier scale divisions.

5.    Acute angle attachment

The following figure shows the vernier bevel protractor

·      The base plate(Stock) consisting of the Working edge will be mounted on the Main body.

·      And the Acute angle attachment is also mounted on the main body.

·      This acute angle attachment can be readily attachable/detachable with the Locking Nut.

·      A circular plate having a vernier scale in it, also mounted on the Main body frame.

·      This circular plate is carrying an adjustable blade which can travel along its length and locked at any position with the help of the blade locking nut.

·      The adjustable Blade one end is bevelled at angles 45° and the other end is bevelled at 60°.

·       This Main body frame itself having a graduated scale called the main scale.

·      The circular plate can rotate freely on the main body.

·      There is a slow-motion device which helps to control the rotation of the circular plate on the main body.

This is the construction of the Vernier Bevel Protractor

 

Working Principle of Vernier Bevel Protractor

1. As the Base Plate (Stock) acts as one of the working edges, and the other working edge will be the blade which is held on the circular plate. as you can see the some of the sample positions of the Vernier bevel protractor in action.

2. This Adjustment Blade can be rotated along with the circular plate on the main body.

3. Which means the vernier scale on the circular plate will be rotated on the Main scale which is graduated on the Main body as shown in below.

4. The Vernier scale has 12 divisions on each side of the centre zero. (It means there are 24 divisions on the vernier scale)

5. The 12 divisions are denoted as 60 min on the vernier scale (Like this 15, 30, 45, 60). That means 12 division = 60 minutes

6. One devision= 60/12 = 5 minutes.

7. On the Main scale, the same portion is represented as 23° (12 divisions on vernier scale = 23° on the main scale )

8. One division on the Vernier scale = 1.91666° = 1° 55′ (one degree 55 minutes).

9. As similar to the vernier calliper working principle as Zero on the vernier scale moves on the main scale.

10. While taking a measurement, The Zero line on the vernier scale shows the reading on the main scale, called main scale reading.

11. At somewhere The divisions on the vernier scale will coincide with the divisions on the Main scale. this reading is noted as the Vernier scale reading.

12. With these values along with the least count of the Vernier bevel protractor, we can calculate the Reading.

See the following example how to calculate the total reading

Measurements with Vernier Bevel Protractor

Consider the Following is a reading of an angular measurement.

The total reading =the main scale reading + the number of the division at which it exactly coincides with any division on the main scale × least count of the vernier scale.

In the above case

The main scale reading = 10°

Vernier scale reading (the number of the division at which it exactly coincides with any division on the main scale) = 3rd division

Least count of the vernier Bevel protractor = 5 Minutes

The total reading = 10°+15 minutes = 10 + (15/60) = 10.25°