Micrometers are the ideal tool for the measurement of cylindrical and spherical shaped objects. In order to use a micrometer, you should follow these steps:
- Take time to acquaint yourself with the main technical terms
- Clean the micrometer, using a soft cloth to remove any marks and debris from between the anvil and spindle
- Begin by positioning the item being measured next to the anvil. It is important to keep the object stable and avoid any scratching. You may control the micrometer with your free hand, or alternatively, there is the option of using a stationary vise, leaving both of your hands free for control of the micrometer
- Spin the ratchet anti-clockwise, ensuring that the 0 mark on the thimble is positioned in accordance with the sleeve scale. Keep twisting until the spindle is within close contact of the object; three clicks is a good guide
- The thimble lock should be applied while the micrometer is within close proximity of the object. It should be possible to adjust the spindle as required. Once you are confident that the micrometer has fulfilled its function you can remove the object, taking care to avoid scratching the anvil and spindle surfaces
- Finally, record the reading, ensuring that the spindle is kept stable
The following sections will give you more information on how to read specific types of micrometers:
When using a metric micrometer, It is necessary to acquaint yourself with the number scales that are displayed on the micrometer thimbles. It is common for the top line of the sleeve to feature millimetres, with the line below that featuring half millimetres.
The reading of the metric micrometer should begin with recording the number of millimetres. An initial reading of 7 would correspond to 7mm. Each half mark on the thimble should be taken into account. This means carefully reading the lower bar and correctly identifying the corresponding number of 0.01mm.
Using a micrometer integrated with the vernier scale, the reading should be taken from the sleeve index line. This allows for precise readings, within 0.001mm. The initial reading should be taken from the sleeve. The measurements are likely to be featured in intervals of 0.25 millimetres or 0.025 inches.
The next step is to take the reading from the thimble. These measurements are likely to be featured in 0.1 millimetre or 0.01-inch intervals. The final reading should be taken from the vernier scale, which you will find on the sleeve, directly adjacent to the first set of graduations.
The vernier micrometer reading is displayed in the format of 0.001 mm or 0.0001 inches, establishing the size of the object with extreme accuracy.
You should be aware that fluctuations in temperature are likely to adversely affect the micrometer reading. Remember not to keep your micrometer in your pocket or within a working environment with excessive heat levels.
Customary or Imperial Micrometer
The spindle of an imperial micrometer features graduated levels of 40 threads per inch. Each turn results in movement of the spindle around an axis of 0.0025 inches, which equates to the area between adjacent graduations on the sleeve.
There are 25 graduations on the thimble, meaning that the measurements can be divided the corresponding number of times. The visible reading corresponds directly to the number of whole divisions that are featured on the sleeve scale, multiplied by 25. This means that the resulting diameter is displayed in thousandths of an inch.