A micrometer is a device designed for measuring linear dimensions using the absolute contact method in the area of small dimensions with high accuracy (from 0.01 to 0.001 mm), the conversion mechanism of which is a screw-nut micropair.
It is necessary to keep the micrometer clean. Be careful not to drop the micrometer, as its clip may become deformed, resulting in inaccurate measurements.
The operation of the micrometer is based on the movement of the screw along the axis when it rotates in a fixed nut. The displacement is proportional to the angle of rotation of the screw around the axis. Full revolutions are counted on a scale printed on the stem of the micrometer, and fractions of a revolution are counted on a circular scale printed on the drum. The optimal movement of the screw in the nut is only a length of no more than 25 mm due to the difficulty of producing a screw with an accurate pitch over a greater length. Therefore, micrometers are manufactured in several standard sizes for measuring lengths from 0 to 25 mm, from 25 to 50 mm, etc. For micrometers with measurement limits from 0 to 25 mm, with the measuring planes of the heel and the micrometer screw closed, the zero mark of the drum scale must exactly coincide with the longitudinal mark on the stem, and the beveled edge of the drum - with the zero mark of the stem scale. For measuring lengths greater than 25 mm, a micrometer with replaceable anvils is used; setting such micrometers to zero is done using a setting measure applied to the micrometer or end measures. The product being measured is clamped between the measuring planes of the micrometer. Typically, the screw pitch is 0.5 or 1 mm, and the scale on the stem is marked with divisions of 0.5 or 1 mm, respectively. The drum is marked with divisions of 50 or 100 to obtain a reading of 0.01 mm. This reading is the most common, but micrometers with readings of 0.005, 0.002, and 0.001 mm are also available. A constant axial force during screw contact with the workpiece is ensured by a friction device called a ratchet. When the measuring surfaces of the micrometer are in close contact with the surface of the part being measured, the ratchet begins to rotate with a slight crackling sound, and the rotation of the microscrew should stop after three clicks.
When taking measurements, the object (2) is clamped between the anvil and the micrometer screw (3). On the surface of the stem are two line scales, offset from each other by 0.5 mm and with a division value of 1 mm. The drum (7) rotates around a circular scale, which is also located on the drum's bevel. The micrometer screw can be locked in any position. The screw is equipped with a ratchet mechanism to ensure constant measuring pressure.
1. Heel. 2. Object of measurement. 3. Spindle. 4. Wheel. 5. Measuring scale (in mm). 6. Ratchet. 7. Drum vernier. 8. Bracket.
- 1. The object is placed between the heel and the micrometer screw, while rotating the drum, the spindle is set to the approximate size of the object.
- 2. The spindle is carefully moved closer until it comes into contact with the object being measured.
- 3. The size in mm is determined using the drum vernier, which corresponds to the horizontal index line of the stem scale.
- 4. The overall size of the measured object is determined.
Note: When in contact with the object being measured, do not tighten the spindle by rotating the drum sleeve by hand, as this may damage the micrometer. To determine the dimensions more accurately, it is necessary to ensure that the item is well secured.
[Text obtained from the website Skodabook.ru]