Different Types of Micrometer and Outside Micrometer

In the ITI Turner trade, precision measurement is essential for maintaining accuracy and quality in machining operations. Micrometers are widely used precision instruments designed to measure dimensions with very high accuracy. This chapter explains the different types of micrometers and provides detailed information about the outside micrometer, its construction, principle, and uses.

Introduction to Micrometer

A micrometer is a precision measuring instrument based on the screw gauge principle. It is used to measure small dimensions such as thickness, diameter, and length with high accuracy, typically up to 0.01 mm or even 0.001 mm.

Principle of Micrometer

The micrometer works on the principle of a screw and nut mechanism. When the thimble is rotated, the spindle moves linearly. The distance moved by the spindle is proportional to the rotation of the screw.

This principle allows precise measurement of small dimensions.

Different Types of Micrometers

1. Outside Micrometer

Used for measuring external dimensions such as diameter and thickness.

2. Inside Micrometer

Used for measuring internal dimensions such as the diameter of holes.

3. Depth Micrometer

Used for measuring the depth of holes, slots, and recesses.

4. Digital Micrometer

Displays readings in digital form for easy and accurate measurement.

5. Thread Micrometer

Used for measuring the pitch diameter of threads.

6. Blade Micrometer

Used for measuring narrow grooves and slots.

7. Tubular Micrometer

Used for measuring thickness of tubes and hollow objects.

Outside Micrometer

Introduction

The outside micrometer is the most commonly used type of micrometer. It is used to measure external dimensions such as diameter, thickness, and length with high precision.

Construction of Outside Micrometer

The outside micrometer consists of a rigid U-shaped frame and a precision screw mechanism. The main parts include:

• Frame: Supports all components
• Anvil: Fixed measuring face
• Spindle: Movable measuring face
• Sleeve (Barrel): Contains main scale
• Thimble: Rotating part with circular scale
• Ratchet Stop: Ensures uniform pressure
• Lock Nut: Locks spindle position

Working Principle

When the thimble is rotated, the spindle moves towards or away from the anvil. The workpiece is placed between these two surfaces, and the measurement is taken based on the movement of the spindle.

Graduation

The outside micrometer has two scales:

• Main scale on the sleeve (mm or inch)
• Thimble scale divided into equal parts

Least Count

The least count is calculated as:

Least Count = Pitch / Number of divisions on thimble

Example:

• Pitch = 0.5 mm
• Divisions = 50

Least count = 0.01 mm

Reading of Outside Micrometer

Total reading = Main scale reading + (Thimble reading × Least count)

Uses of Outside Micrometer

• Measuring external diameter
• Measuring thickness of materials
• Precision measurement in machining

Advantages of Micrometer

• High accuracy and precision
• Reliable measurement
• Easy to handle

Limitations

• Limited measuring range
• Requires careful handling

Precautions While Using Micrometer

• Clean measuring surfaces
• Check zero error
• Use ratchet for proper pressure
• Avoid excessive force

Maintenance

• Keep clean and dry
• Store in protective case
• Lubricate lightly

Application in Turner Workshop

In the Turner trade, micrometers are used for accurate measurement of components. The outside micrometer is especially important for checking diameters and thickness of workpieces.

Proper use of micrometers ensures high-quality machining and adherence to specifications.

Conclusion

Micrometers are essential precision instruments in the ITI Turner trade. Understanding their types and working helps in selecting the right tool for measurement.

The outside micrometer is widely used for external measurements and provides high accuracy.

In conclusion, mastering micrometer usage is crucial for achieving precision and quality in engineering work.