A micrometer is used for measurements that require greater precision than a caliper. Though micrometers gives superior precision, it can only measure a very small length. It consists of a calibrated screw that which when rotates helps in giving an accurate measurement.
Reading measurements in a micrometer is not at all a difficult task. With a little care and precaution, one can learn to take the measurements easily. If you want a buy a good micrometer, Mitutoyo micrometers are really good.
Principle of Operation
The basic principle of operation of a micrometer is as follows:
- The amount of axial movement of a screw that is made accurately can be measured by the amount of rotational movement of it. This is because the pitch of the screw is constant.
- The measurement made due to the rotational movement is some amplified form of the actual axial movement of the screw.
A micrometer has the following parts:
- Frame: It is the C-shaped body that holds the anvil and the barrel together. This frame is heavy and thick which makes it difficult to strain under mechanical and thermal stresses.
- Anvil: It is the part that rests on one side of the frame. Spindle moves towards the anvil when in order to hold the object and take the measurement.
- Sleeves/barrel: The stationary cylindrical component that the frame holds on the other side of the anvil.
- Lock nut/thimble lock: The lever which is used to tighten the movement of the spindle so that it doesn’t move while taking the measurement.
- Screw: It is the main component on which the micrometer works and is hidden from the sight.
- Spindle: The cylindrical component which moves when you rotate the thimble. This touches the object which is to be measured and holds it tight.
- Thimble: It is the component which is turned by thumbs and which makes the spindle movement.
- Ratchet stop: The device which is at the end of the instrument and is responsible for exerting only allowable pressure to the object and not more than that.
Care and proper use of a micrometer
Before you rotate the thimble or the ratchet knob, unlock the locking lever. Make sure to clean the measuring faces with the help of a clean cloth before you begin taking measurements. As you begin measuring, start rotating the ratchet knob and not the thimble. The ratchet knob will ensure you do not over tighten the thimble as that will not only give an erroneous reading but can damage the instrument too.
It is also advisable that you do not keep the instrument in the Sun for long. The horizontal line on the sleeve should be aligned to zero when the when the micrometer is at minimum reading. In case it does not happen, the micrometer will be needed to calibrated. For calibration, each device comes with a half-moon adjusting wrench.
Remember to use the thimble lock while micrometer is still holding the object. If you do not do this, the spindle might move a little while taking the reading or taking the object off from the micrometer. Write the measurement when the lock is on and if you haven’t written it and taken the object out, redo the measurement.
Micrometer finds its use in almost all manufacturing industries. They can also be mounted on a bedways of the lathe or similar machine tools to make the measurements accurate and easy.