Bevel Protractor & Vernier Bevel Protractor – Function and Reading

In the ITI Turner trade, accurate measurement of angles is essential for machining operations such as taper turning, angular cutting, and inspection. Instruments like the bevel protractor and vernier bevel protractor are commonly used to measure and set angles with precision. This chapter explains their construction, functions, and methods of reading in detail.

Introduction to Angle Measurement

Angle measurement is important in engineering for producing components with correct geometry. Simple tools provide approximate values, but precision instruments like bevel protractors ensure accurate results.

Bevel Protractor

Introduction

A bevel protractor is a measuring instrument used to measure and mark angles. It consists of a circular scale and an adjustable blade.

Construction

• Stock (Base): Fixed part resting on the workpiece
• Blade: Adjustable arm for measuring angles
• Protractor Scale: Graduated in degrees
• Locking Screw: Fixes the blade position

Function

• Measures angles
• Sets required angles on workpiece
• Used in layout and inspection

Reading

The angle is read directly from the main scale where the blade indicates the value. It usually measures up to 360°.

Vernier Bevel Protractor

Introduction

A vernier bevel protractor is a precision instrument used to measure angles more accurately than a simple bevel protractor. It includes a vernier scale for fine measurement.

Construction

• Main Scale: Graduated in degrees
• Vernier Scale: Provides fine measurement
• Blade: Adjustable for angle measurement
• Stock: Base support
• Fine Adjustment Screw: For precise setting
• Locking Screw: Fixes the position

Least Count

The least count of a vernier bevel protractor is typically 5 minutes (1/12 of a degree).

Function

• Measures angles with high accuracy
• Used in precision machining
• Checks angular alignment

Reading of Vernier Bevel Protractor

Step 1: Main Scale Reading

Read the value on the main scale just before the zero of the vernier scale.

Step 2: Vernier Scale Reading

Find the vernier division that coincides with a division on the main scale.

Step 3: Calculate Total Reading

Total Reading = Main Scale Reading + (Vernier Reading × Least Count)

Example

Main scale reading = 30°
Vernier division = 6
Least count = 5 minutes

Total reading = 30° + (6 × 5') = 30° 30'

Advantages of Vernier Bevel Protractor

• High accuracy
• Precise angle measurement
• Easy adjustment

Limitations

• Requires careful handling
• Reading requires practice

Precautions While Using

• Ensure clean contact surfaces
• Check zero setting
• Lock the blade properly
• Avoid parallax error

Maintenance

• Keep clean and dry
• Store in protective case
• Avoid dropping

Application in Turner Workshop

In the Turner trade, bevel protractors are used to measure angles in taper turning, tool setting, and inspection work. Vernier bevel protractors are used for high-precision angular measurements.

They help in achieving accurate angular dimensions in machining.

Importance in Engineering

• Ensures correct angle measurement
• Improves machining accuracy
• Maintains quality standards

Conclusion

Bevel protractors and vernier bevel protractors are essential tools for measuring angles in engineering. Understanding their construction, function, and reading method is important for accurate measurement.

Proper use and maintenance ensure reliable performance.

In conclusion, mastering these instruments is essential for precision work in the ITI Turner trade.