Measuring ruler is not always possible to measure the linear size with the required accuracy. In these cases, and should use a more accurate measuring instrument - a micrometer.
Micrometer is a measuring instrument with high accuracy.
The principles on which the micrometer is based are such that it is easy to master them, but they allow for the continuous improvement of measurement accuracy.
Where does this name come from?
Valid micrometer values.
The fact is that the minimum size changes that this measuring device can confidently fix are millionths of a meter (micrometers). 1 micron (0.001 mm) - a value almost indistinguishable to the human eye. Measurements with a micrometer can be performed with an accuracy of several micrometers.
The need for very accurate measurements arose in the sixteenth century in the arms industry. From the point of view of mechanics, the micrometer is arranged quite simply - a screw and a nut. Later, this principle began to be applied in geodesy, but as we know it, the micrometer became by the middle of the nineteenth century. The fact is that the testimony in it is removed from the most carefully marked and thoroughly calibrated scales, the production of which is possible only with a sufficiently high level of technology development.Back to table of contents
Mechanical micrometer - device and principle of operation
Along with conventional micrometers, electronic ones are produced. The principle of operation is the same, but the electronic display and the possibility of an improved calibration make it possible to increase the convenience and increase the accuracy of measurements. But they are still quite rare and expensive, and mastering work with them, being able to work with mechanical ones, is easy. Therefore, the following are recommendations for using a mechanical micrometer.
Figure 1. Micrometer device.
The appearance of the device is shown in Figure 1. Designations in this figure:
- Measured item.
- Micrometer screw spindle.
- Micrometric screw stop.
- Horizontal scale.
- Drum with dial.
The operation of the device is based on the displacement of the screw, caused by its rotation in the fixed nut. This offset is directly proportional to the angle of rotation. The screw pitch is exactly half a millimeter. The drum connected with the screw passes 0.5 mm per 1 turn, closing or opening the strokes of the horizontal scale. The scale applied to the drum has 50 divisions, therefore, the price of its division is 0.01 mm / div.Back to table of contents
Mechanical Micrometer - recommendations for use
There are two basic ways to measure with a micrometer:
Micrometer (a) and examples of calculation according to its scale (b, c, d).
- Absolute, when the connector of the device is applied directly to the measured object, clamps are set in accordance with its geometry. Then the dimensions are read directly from the scales of the meter.
- Relative, when the dimensions of borders or objects near the measured part are measured, the sizes of which are then found using mathematical calculations.
Before measuring a part, it should be kept together with a micrometer in a single temperature regime for at least 3 hours.
Immediately after purchase, and then periodically and during operation, the tool must be checked. To check without detail, close the heel and spindle. This should be done carefully, just before closing the screw rotate with a ratchet. After three clicks the rotation stops.
The drum should almost completely close the horizontal scale, and its initial mark should coincide with the longitudinal risk of this scale. If the scale is knocked down, it can be adjusted using a special key.
It would seem that measuring with a micrometer is simple - clamp the measured part between the heel and the spindle and take readings of the scales. But this is a high precision device, and even a small force can deform the part and distort the result. It is even worse if the instrument is knocked down.
The device mkrometr with digital display.
In order for this not to happen, a ratchet was invented. When, due to the rotation of the drum, the spindle approached the surface of the part, it is switched to its rotation using a ratchet. As with the calibration, after three clicks the rotation stops.
The part is fixed reliably, but not deformed, which makes it possible to measure with a micrometer precisely and with a small error.
The electronic device will immediately show the final result on its indicator. But if the device is mechanical, then measuring with a micrometer is not so easy. This applies primarily to the removal of his testimony. It begins with reading the values of the largest digit of digits (millimeters), and ends with the smallest - hundredths of a millimeter.
Millimeters are read from the scale deposited on the fixed part of the instrument case. The horizontal scale consists of two parts. Bottom divisions mean millimeters. Both on the left and on the right figure this value is 5 mm. The divisions above show halves of millimeters.
The division corresponding to half a millimeter, after the value of 5 mm on the lower scale is closed by a drum, therefore, the total reading is made up of 5 and 0.35 mm (on the drum). Part size 5.35 mm. On the drum the same value is 0.35, but the division corresponding to half a millimeter, from the top after the value of 5 mm on the bottom scale is open. The total reading now consists of 5, 0.5 and 0.35 mm. The total size of the part in this figure is 5.85 mm.
This is the most common micrometer option. For other types of tools, stroke values may be different.
But the differences are small, therefore, it is not difficult to understand the markings on the scales and learn how to measure with a micrometer of any type.