Vernier Calipers – Construction and Working
A Vernier Calipers is a precision measuring instrument used to measure internal, external, and depth dimensions accurately. It can measure up to 0.1 mm or 0.02 mm depending on the least count.
1. Construction of Vernier Calipers
A Vernier Calipers consists of the following main parts:
a. Main Scale
- It is a fixed scale engraved on the body of the calipers.
- It is graduated in millimetres or centimetres.
- It provides the main reading.
b. Vernier Scale
- It is a movable scale that slides over the main scale.
- It is used to read fractions of the smallest division on the main scale.
- It provides the extra precision.
c. Outside Jaws
- These are used to measure the external diameter or width of an object (e.g., a rod, pipe, coin).
d. Inside Jaws
- These smaller jaws are used to measure internal diameters, such as the diameter of a hole or pipe.
e. Depth Probe (or Depth Rod)
- It is a thin rod that extends from the end of the caliper when the movable jaw slides.
- It is used to measure depths of holes or steps.
f. Locking Screw
- This is used to lock the movable jaw in position after the object is measured.
g. Fine Adjustment Screw
- Some Vernier Calipers have this to allow fine movement of the sliding jaw for accurate measurement.
Diagram Description
To sketch in Word:
- Draw a horizontal main scale.
- Attach two jaws on the left – outer jaws (big) and inner jaws (small).
- Show a sliding vernier scale aligned with the main scale.
- Extend a depth rod from the right end.
- Label all the parts accordingly.
📝 Caption: Construction of Vernier Calipers
2. Working of Vernier Calipers
Steps to Measure:
Step 1: Clean and Prepare
- Ensure the object and calipers are clean.
- Set the calipers to zero before measuring.
Step 2: Take the Measurement
- Place the object between appropriate jaws:
- Use outer jaws for external measurements.
- Use inner jaws for internal measurements.
- Use depth rod for depth measurements.
- Slide the movable jaw until it fits the object snugly.
- Lock it using the locking screw.
Step 3: Read the Main Scale
- Note the reading on the main scale just before the zero of the vernier scale.
- Example: If it is 25 mm, then Main Scale Reading = 25 mm
Step 4: Read the Vernier Scale
- Find the line on the vernier scale that exactly coincides with a line on the main scale.
- Suppose the 7th line on vernier coincides.
- Then Vernier Scale Reading = 7 × Least Count
Step 5: Calculate Final Reading
- Total Reading = Main Scale Reading + Vernier Scale Reading
- If Least Count = 0.02 mm
- Then Total = 25 mm + (7 × 0.02 mm) = 25.14 mm
Least Count of Vernier Calipers
Least Count is the smallest value that can be measured using the instrument.
Formula:
Least Count = Value of 1 division on main scale – Value of 1 division on vernier scale
Or,
Least Count = (Smallest division on main scale) ÷ (Number of divisions on vernier scale)
Example:
If 1 main scale division = 1 mm and
10 vernier divisions = 9 mm
Then,
Least Count = 1 – (9 ÷ 10) = 1 – 0.9 = 0.1 mm
Or use directly:
Least Count = 1 mm ÷ 10 = 0.1 mm
(If 10 vernier divisions = 9 mm)
Applications of Vernier Calipers
- Measuring diameter of rods, wires, and balls
- Measuring depth of holes and steps
- Measuring internal diameter of pipes or cylinders
- Used in mechanical engineering workshops and labs
Advantages of Vernier Calipers
- High accuracy and precision
- Versatile – measures internal, external, and depth
- Portable and easy to use
- Cost-effective for precise work
Disadvantages
- Manual reading can lead to human error
- Requires careful handling
- Accuracy depends on skill of the user
Conclusion
Vernier Calipers is a widely used precision measuring tool in industries and laboratories. With proper usage and understanding of its parts and working, it allows measurements up to hundredths of a millimetre. Understanding its working not only improves accuracy but also helps in developing precise engineering practices.