What is Bevel Protractor: Uses, Types, Parts, Working & Advantages

Published: 4 Oct 2025

In engineering, construction, and machining, measuring angles with accuracy is very important. A bevel protractor is a special tool that helps in doing this job. It is widely used by engineers, toolmakers, and students. This article explains what a bevel protractor is, how it works, its types, uses, and advantages.

What is a Bevel Protractor?

A bevel protractor is a precision instrument used to measure and set angles. Unlike a simple protractor, it has a movable blade and a fine scale. This helps in getting very accurate angle measurements. It can measure angles from 0° to 360°.

Parts of Bevel Protractor

Base blade: Acts as the reference edge, placed against the object.

Movable blade (rule): rotates to align with the second surface of the angle.

Protractor dial (main scale): graduated in degrees for primary readings.

Vernier scale: provides fine readings in minutes (1/12 of a degree = 5’).

Locking device (clamp or nut): secures the blade in place once set.

Fine adjustment knob: helps in making small, precise movements.

Magnifying glass: available in some models for easier scale reading.

Working Principle of Bevel Protractor

Works on the principle of measuring the angle between two surfaces.
The base is placed on one surface, while the movable blade aligns with the other.
The angle formed between the base and the blade is measured using scales.
The main scale gives readings in degrees.
The vernier scale divides one degree into 12 parts (Least count = 5’).
Final measurement = main scale reading + vernier scale reading.

How to Use Bevel Protractor?

Place the base blade firmly against the reference surface.
Rotate and align the movable blade with the second surface forming the angle.
Tighten the locking screw to fix the blade in position.
Note the degree reading on the main scale where the Vernier zero coincides.
Find the vernier division that exactly aligns with the main scale division.
Multiply the aligned vernier division by 5’ (least count).
Add the main scale reading + vernier scale reading for the final angle.
Example: Main scale = 50°, Vernier = 3 divisions → 50° + (3 × 5’) = 50° 15’.

Types of Bevel Protractor

1. Vernier bevel protractor

The Vernier bevel protractor is one of the most common types. It has a vernier scale attached to the main scale which allows angles to be read with an accuracy of 5 minutes (5′). This makes it far more precise than a simple protractor. It is widely used in workshops and industries for tasks such as checking tool angles, measuring V-blocks, and inspecting beveled surfaces.

2. Universal Bevel Protractor

The Universal Bevel Protractor is a more advanced version. It features a detachable blade, fine adjustment knobs, and sometimes a magnifying glass for easy reading. This tool can measure angles up to 360°, including both acute and obtuse angles. It is especially popular among toolmakers and machinists because of its ability to set and verify angles with high accuracy in engineering components.

3. Optical Bevel Protractor

The optical bevel protractor offers the highest level of precision. Instead of relying only on a vernier scale, it uses an optical system such as a microscope or magnifier to read the graduated circle. With this setup, angles can be measured down to 1 arcminute, making it more accurate than both vernier and universal bevel protractors. However, due to its high cost and delicate construction, it is mainly used in laboratories, research, and specialized engineering applications rather than in regular workshops.

Use of a Bevel Protractor

Bevel protractors are useful in many ways:

Measuring the exact angles of workpieces.
Checking angles of cutting tools and dies.
Setting up machines for accurate cutting.
Measuring included angles in components.
Layout and inspection work in the workshops.

Advantages of Bevel Protractor

Very accurate in measuring angles.
It can measure a full 360° range.
Easy to use and read.
Useful for inspection and layout work.
Helps in tool making and quality control.

Disadvantages of Bevel Protractor

More costly than a simple protractor.
Needs careful handling to avoid damage.
Reading may be confusing for beginners.
Not as fast as digital angle measuring tools.

FAQs

What is the use of a bevel protractor?

It is used to measure, check, and set angles with high accuracy in engineering and machining.

The least count of a Vernier bevel protractor is?

It is 5 minutes (5’) of an angle.

What is a bevel protractor used for?

It is used for measuring angles between surfaces, checking tools, and inspection work.

What is the difference between an angle protractor and a bevel protractor?

A simple angle protractor measures only in degrees (1° or 0.5°), while a bevel protractor measures with much more accuracy (up to 5 minutes).

How accurate is a bevel protractor?

A Vernier bevel protractor is accurate for up to 5 minutes (5’). An optical bevel protractor could be even more accurate.

Is it standard for bevel protractors?

Yes, bevel protractors follow standards like IS 4239:1967 for their design and accuracy.