Permissible micrometer errors

This measuring device is designed for accurate measurement, so you need to know the accuracy of the micrometer. It was invented by the scientist Laurent Palmer in the XIX century, was first called the circular caliper with a nonius. Americans became interested in seeing the Paris exhibition, after which its production and promotion began. Now it is a common, practical and popular tool for measuring the diameter outside the part, its thickness and width. The design is simple. The device quickly measures with very high accuracy.

The device mkrometr with digital display

The device mkrometr with digital display.

Indispensable for the production department, in linear measurements. Known to every machine operator, fitter, designer. Diverse in design. The universal range of surfaces measured by him is very wide.

Well-known companies specialize in the issue of MK: Swiss Tesa, Japanese Mitutoyo, German CarlMahr, domestic ChIZ and KRIN. For Chinese, they are careful.

Their quality is high, they have a grinding appearance, no gaps between the working parts, they are made of highly durable, hard metals. This ensures the advancement of the bolt without deforming the end plane. It is completely anti-corrosion, wear-resistant. The tool follows the Abbe rule, which improves accuracy.

There are two types of MK:

  • mechanical, have a dashed plane, nonius;
  • digital or electronic.

They are with analog or digital displays.

Devices with a dashed plane

Acceptable Micrometer Values

Valid micrometer values.

The main parts are screw, micrometric details. The movable measuring surface (end of the screw) is connected to the counting drum. Its turnover is equal to the bolt thread pitch. The standard step is 0.5 mm; the drum element has 50, 100 strokes. The price of the reference stroke is 0.01 mm, 0.05 mm. The more precisely the threaded element (made with maximum precision), the better the device works. The micrometer element is a separate measuring part - the head.

It is in the MK different devices and types: nutromer, depth gauge, stationary structures. This is the main measuring unit. In it, the bolt moves with the drum element of a relatively firmly fixed strip with a twist. The site is often equipped with two scales: circular (for fractional) and linear form (for counting complete bolt rotations).

Linear plane with strokes is outside on the stem. The price of the scale line is equal to the bolt pitch, if it is 0.5 mm, then two scale sections with a stroke of 1 mm are applied, they are moved together by 0.5 mm.

The screw range determines the length of the scale (usually it is 25 mm). The circular scale is on the bevel of the drum element, its end is a pointer for a linear plane. For a circular plane, the pointer is a longitudinal line on a linear one.

Micrometer device

Micrometer device

The drum has a diameter of 1 mm. Under fractional, the dimensional grid in a circle sometimes uses a nonius which is the same as in a vernier caliper with no parallax.

The nonius has a stroke size of 0.001 mm, its use is advisable for the grid fractions read when it is below the course error.

The special micrometer design (drum ratchet, friction clutch) stabilizes the efforts when measuring. The design has a device that locks the bolt. The planes for measurements are parallel end planes on a micrometer bolt with a heel (it is opposite the head), their standard width is 8 mm. There are devices with a size of 100 mm, and the diameter of the working planes is made smaller (6.5 mm). Devices with a bottom border of 25 mm have an installation measure.

In most cases, the stroke price is 0.01, 0.05 mm, the vernier is 0.001 mm. For diameters greater than 500 mm there is a type of micrometer with brackets of tubular parts made by welding. They are provided with thermal insulation. Staples are with a border measurements of 100 mm, they are equipped with interchangeable ends. The length can be increased by 25 mm, the boundaries of their measurements - up to 1500 mm. The error for them is calculated by the formula: U = ± (6 + L / 75) µm, where L is the maximum measurement limit in millimeters.

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Digital products: nuances

Measurements with a micrometer

Micrometer (a) and examples of calculation according to its scale (b, c, d).

Microscale counting is sometimes inconvenient. If the vision is poor or the lighting is not strong, this problem is solved by electronic MC. They differ little from mechanical ones; the planes with strokes are replaced by incremental capacitances, inductive conversion elements, and an electronic unit with a digital scoreboard. The converter is two disk plates with wires. One disk moves with a bolt, the other is rigidly fixed, held in place by a key. They move with a bolt for all its size.

The micrometer bracket has a processing unit, a scoreboard with indicators of 0.01 or 0.001 mm, a zero setting function, there are also possibilities for connecting to external computing devices. The device is powered by a battery with a life of one and a half years. Electrometers have a measurement limit of up to 300 mm. They make many different modifications, their parameters may vary. So, there are spherical planes for measuring tubular elements, with discs for measuring soft objects.

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Micrometric Depth Gauge

This device consists of a basic base, it contains a microbolt with measuring borders of 25 mm, there are also replaceable measuring inserts of various lengths. The measurement limit is 300 mm.

Such devices as the MK, are mechanical, digital devices.

Inaccuracy of measurements with a minimum insert - 5 mm.

Accuracy includes:

  1. Inaccuracy of the measuring unit.
  2. Inaccuracies of flatness, parallelism of the screw with the heel. They occur when turning corners, locking. This type of inaccuracy is different in various forms (round, flat). There are also inaccuracies of objects in the effort during the measurement.
  3. Change of staples due to effort.
  4. Incorrect installation measures.
  5. Inaccuracy due to the action of temperature, it is typical for large devices.
  6. In electronic devices, electrical components may malfunction.

The error is allowed for the head, if it acts as a separate device, within the limits established by GOST 6507-90. There are special systems with error limits for instruments. They have indicators depending on the measurement limits. The grid of inaccuracies indicates the allowable error G of the device at the point of measurement boundaries.

These boundary indicators consist of the inaccuracy of the micrometric node, the inaccuracy due to the deformation of the instrument brackets, the roughness, the non-parallelism of the measured planes.

Calibration, adjustment (verification) of the micrometer is performed using the end measures at several points of the measurement limits, respectively, ISO 3611: 2010, DIN 863, GOST 6207-90. They are taken to find out the value of G, that is, the extreme inaccuracy of the device at all points of the measurement range. Here are the standard, desirable parameters for measuring end measurements, for setting up the device: 3.1; 6.5; 9.7; 12.5; 15.8; 19.0; 21.9; 25 mm.

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Summarizing

Inaccuracies of flatness-parallelism of the butt of the bolt with the heel are checked with the help of three, four plane-parallel optical plates of glass, vertically graduated in 1/4 or 1/3 of the microbolt stroke (0.5 mm). So, 3 or 4 places will be checked with its full turn.

To carry out the micrometer calibration, the plane is fixed between the heel and the screw end. Shifting it between the measured planes, determine the minimum number of interference rings on one such plane.

The number of rings of the second measuring plane is added to the numerical result. If the light wave has 640 Nm, then the width of one strip will be about 32 μm. It is recommended to use certified measures for calibration.

It should be noted that MCs have good traceability when calibrating errors or calibrations using certified measures.

MK is a fairly versatile device. It is produced with advanced types of structures of work elements, thanks to which it is possible to measure parts of various non-standard sizes, for example, jagged surfaces.

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