Micrometer is a measuring device that allows measurements with low error small items.
The most important components of the micrometer are the screw and nut, which are the conversion mechanism. The screw-nut pair is called micro pair or screw pair .
The principle of operation of the micrometer is based on the rotation of a screw in a fixed nut. Rotating, the screw moves along its axis, and this happens in proportion to the angle of rotation of the screw in the nut. Integer values are seen on the scale applied to the stationary stem of the micrometer - the division value of this scale corresponds to the pitch of the screw thread, and is usually equal to 0.5 or 1 mm. There is a second scale on the drum - a circular one, according to which the fractions of a turnover are determined, the division value of such a scale is usually 0.01 mm, less often - 0, 001, 0.002 or 0, 005 mm.
To measure an object (part), it is inserted between the micrometric screw and the fixed heel of the bracket. The constant contact of the screw with the measured object is ensured by a friction or ratchet. With proper, tight fit of the part, rotation of the screw causes the ratchet to turn with a slight click. Stop spinning after three clicks.
All parts of the micrometer that are prone to wear are hard-alloyed. To avoid measurement errors due to hand heat, the side pads are usually thermally insulated.
To measure workpieces larger than 300 mm, a micrometer with a movable or replaceable anvil is required to increase the measuring range.
Micrometers differ in design, scope, purpose, etc. Common types of micrometers and their designations are described in GOST 6507-90. So the measurement of the vernier drum and the stem is indicated by the letter H, digital indication - by the letter C.
Micrometer classification:
1) Smooth micrometer (MK ) - the most common type of micrometers, designed to measure the outer linear dimensions of products;
2) Sheet micrometer (ML) - allows you to measure the thickness of metal sheets, films and tapes;
Fig. 1. Sheet micrometer ML
3) Tube micrometer (MT ) - using this type of micrometer determines the wall thickness of the pipes.
4) Gear measuring micrometer (MZ) - designed to measure the length of the common normal of gears with a module of 1 mm;
5) Micrometer head (MG) - this type of micrometer is used to measure displacement;
6) Wire micrometer MKD (MP) - with it you can determine the thickness of the wire and the diameter of the balls of the bearings.
7) Lever micrometer MR - equipped with a built-in lever a gear indicator device that makes measurements by the evaluation and comparison method. Lever micrometer with measuring head is designated MRI.
8) Prismatic micrometers - equipped with a prism-shaped bracket heel. MTI - designed to measure the diameter of a three-edged cutting tool, MPI and MSI - for a five- and seven-edged cutting tool, respectively.
Fig. 2. Prismatic micrometers
It should be noted that imported micrometers are labeled differently.
The types of micrometers described above carry out measurements by a contact method. Optical micrometers measure objects in a non-contact way.
