VERNIER CALIPER & MICRO METER

INTRODUCTION OF VERNIER CALIPER

A calliper is a device used to measure the distance between two opposing sides of an object. It can be as simple as a compass with inward or outward-facing points. First the tips of the calliper are adjusted to fit across the points to be measured and the calliper is then removed and the distance between the tips is measured using a ruler. The modern Vernier calliper was invented by Joseph R. Brown in 1851. It was the first practical tool for exact measurements that could be sold at an affordable price to ordinary machinists.   The Vernier Calliper consists of a main scale fitted with a jaw at one end. Another jaw, containing the vernier scale, moves over the main scale. When the two jaws are in contact, the zero of the main scale and the zero of the Vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error.

Parts of a Vernier Caliper

1.Main Scale

The main scale consists of a steel metallic strip graduated in centimeters at one edge and in inches at the other edge . It carries the inner and outer measuring jaws. When the two jaws are in contact, the zero of the main scale and the zero of the Vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error.

2. Vernier Scale

A vernier scale  slides on the strip. It can be fixed in any position by the retainer. On the Vernier scale, 0.9 cm is divided into ten equal parts.

3. Outer Measuring Jaws

The outer measuring jaws helps to take the outer dimension of an object

4. Inner Measuring Jaws

The inner measuring jaws helps to take the inner dimension of an object.

5. Retainer

The retainer helps to retain the object within the jaws of the Vernier calipers.

6. Depth Measuring Prong

The depth measuring prong helps to measure the depth of an object.

Least Count

The least count or the smallest reading which you can get with the instrument can be calculated as;   First calculate the least count and only then place the object between the two jaws. Record the position of zero of the Vernier scale on the main scale.

Calculating the Reading

When a body is between the jaws of the Vernier Caliper; If the zero of the vernier scale lies ahead of the Nth division of the main scale, then the main scale reading (MSR) is;

 If nth division of Vernier scale coincides with any division of the main scale, then the Vernier scale reading (VSR) is;

 

Total reading, 

MICRO METER

A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers.

How is the Reading Taken?

In order to take the reading using a screw gauge, the object is placed between the jaws which are moved by the thimble. The ratchet knob is used to adjust the object firmly between the jaws. For accurate reading, the thimble should be moved until three clicks are heard from the ratchet. The ratchet ensures accuracy and also prevents the object from getting damaged. The main scale reading is taken by considering that marking on the sleeve which is visible just to the left of the thimble. It is also to note that the 0.5 mm divisions that are provided below the main scale should also be considered while taking the reading. The auxiliary scale reading is taken by observing the marking on the thimble that coincides with the main scale on the sleeve. The auxiliary reading figures will follow the main scale reading figures in the final reading. Let’s take an example to understand this.

Example :-

Let’s take one more example to understand it properly. Suppose the scales came to the positions shown in the figure. The main scale reading would be the marking that is fully visible immediately to the left of the thimble, i.e. 5.5 mm. For the auxiliary reading, the 30th division of the thimble matches with the main scale and thus its reading will be 0.30 mm. The final reading will be the addition of the readings of both the scale i.e. 5.5 + 0.30 = 5.80 mm.