Chapter-4| Angular Measurement and Gauges used for angle check

The concept of Angle comes from the circle. Actually, Angle is a part of a circle. We measure an angle in Degree or Radian. Usually, the primary objective of angle measurement is not to measure angles but the assessment of the alignment of machine parts or products.

An Angle is defined as the opening between two lines which meet at a point.
In a current scenario, there is a wide range of angle measuring instruments available, from simple scaled instruments to complex types of techniques.


Some Basic Angle Measuring Instruments are

Gauges used for angle check

3.1 Protractor( Bevel & Digital )

A simple protractor is a basic device used for measuring angles with a least count of 1° or ½°. Bevel Protractor is an angular measuring instrument capable of measuring angles with a least count of  5’.

bevel scale

The protractor dial is graduated in degrees with every tenth degree numbered. The sliding blade is fitted into this dial I.e. it may be extended to either direction and set at an angle to the base.

vernier bevel protractor

Digital Protractor measures an angle over 360 degrees with high accuracy of 0.1 degrees. Digital Protractor is very simple and easy to measure the angle by just putting between levels or surface.

3.2 Sine Bar

Sine bar is a precision angle measuring instrument along with slip gauges. The name suggests that Sine bar work on sine principle. Slip gauge used to build up the height of sine bar.

The required angle is obtained when the difference in height between the two rollers is equal to the Sine of the angle multiplied by the distance between the centers of the rollers.

How to measure with Sine bar?

sine bar gh

Sine Bar is an indirect method of measurement. Sine Bar is working on Sine principle that is the ratio of length between two roller and height differences.

In the above picture, we are taking a very simple case. Height differences angle H1-H2 is zero, so, after calculation, our result is 180 degree.

3.3 Spirit Level

Spirit Level is a device which is used to check the level of surfaces especially surface tables.

A spirit level is a basic bubble instrument such as It is an angular measuring device in which the bubble always moves to the highest point of a glass vial mounted top surface on Spirit Level.

spirit level

Spirit Level is easy to measuring device, we just have to trace bubble movement. For example in our figure bubble cover two digits of a scale of one side, that means actual inclination is 0.02 per units.

Next, Chapter-5| Comparator gauges

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Preview, Chapter-3| Linear Measurement and Instruments used for Linear Measurement.

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