Vernier Caliper – Construction, Principle, Graduation, Reading and Least Count
In the ITI Turner trade, accurate measurement is essential for producing quality components. One of the most commonly used precision measuring instruments is the Vernier caliper. It is used for measuring internal dimensions, external dimensions, and depths with high accuracy. This chapter explains the construction, working principle, graduation, reading method, and least count of the Vernier caliper.
Introduction to Vernier Caliper
A Vernier caliper is a precision instrument used to measure lengths with greater accuracy than a simple scale. It works on the principle of the Vernier scale, which allows readings up to fractions of a millimeter.
It is widely used in engineering workshops and manufacturing industries.
Construction of Vernier Caliper
A Vernier caliper consists of the following main parts:
- Main Scale: A fixed scale marked in millimeters or inches
- Vernier Scale: A sliding scale that provides fine measurement
- Fixed Jaw: Used for holding the workpiece
- Movable Jaw: Slides along the main scale
- Depth Rod: Used for measuring depth
- Locking Screw: Used to fix the position of the sliding jaw
The jaws are designed to measure both internal and external dimensions.
Principle of Vernier Caliper
The Vernier caliper works on the principle that two scales with slightly different divisions can be used to measure small differences in length.
The Vernier scale is designed such that a certain number of its divisions are equal to a slightly different number of main scale divisions.
This difference helps in measuring small lengths accurately.
Graduation of Vernier Caliper
The main scale is graduated in millimeters or inches, while the Vernier scale has divisions that correspond to a fraction of the main scale.
Example:
- 10 Vernier divisions = 9 main scale divisions
This difference allows measurement up to 0.1 mm accuracy.
Least Count of Vernier Caliper
The least count is the smallest measurement that can be read using the instrument.
Least Count = Value of one main scale division – Value of one Vernier scale division
Example:
- 1 main scale division = 1 mm
- 1 Vernier division = 0.9 mm
Least count = 1 – 0.9 = 0.1 mm
Reading of Vernier Caliper
The reading is taken in two steps:
1. Main Scale Reading (MSR)
Read the value on the main scale just before the zero of the Vernier scale.
2. Vernier Scale Reading (VSR)
Find the division on the Vernier scale that coincides with any division on the main scale. Multiply this value by the least count.
Total Reading
Total Reading = MSR + (VSR × Least Count)
Example
MSR = 10 mm
VSR = 5 divisions
Least count = 0.1 mm
Total reading = 10 + (5 × 0.1) = 10.5 mm
Types of Measurements
- External measurement (using outer jaws)
- Internal measurement (using inner jaws)
- Depth measurement (using depth rod)
Advantages of Vernier Caliper
- High accuracy
- Easy to use
- Versatile measuring tool
- Measures different dimensions
Limitations
- Requires skill for accurate reading
- Errors may occur due to parallax
Precautions While Using Vernier Caliper
- Clean the instrument before use
- Check zero error
- Do not apply excessive force
- Take reading carefully
Maintenance of Vernier Caliper
- Keep clean and dry
- Store in protective case
- Avoid dropping
- Lubricate lightly
Application in Turner Workshop
In the Turner trade, Vernier calipers are used to measure the diameter, length, and depth of workpieces. They help in ensuring accurate dimensions and maintaining quality standards.
Proper use of Vernier calipers improves machining accuracy and efficiency.
Conclusion
The Vernier caliper is an essential measuring instrument in the ITI Turner trade. Understanding its construction, principle, graduation, and reading method is important for accurate measurement.
By practicing proper techniques, trainees can achieve precise measurements and improve the quality of their work.
In conclusion, mastering the use of Vernier caliper is a fundamental skill for every Turner.