For angular measurements in mechanical engineering and instrument making they use different methods, implemented by a variety of measuring instruments that differ in design, accuracy, measurement limits, and performance.

Angle measurements can be divided into direct (carried out by measuring instruments graduated in angular units) and indirect, carried out using linear measuring instruments and requiring subsequent calculation of the desired angle values ​​using trigonometric functions. In some literature sources, direct measurements of angles are called “measurements by the goniometric method,” and indirect measurements are called “measurements trigonometric method" The term “goniometric” can be translated from Greek as “goniometer”; one of the instruments for measuring angles (goniometer) has the corresponding name.

The simplest means of measuring angles include angular gauge blocks. Angle measures (“rigid angle measures”) can be single-valued or multi-valued. They include squares (nominal angle 90°), prismatic angular gauges with one or more (three, four or more) working angles, as well as conical gauges. Angle gauge blocks, like length gauge blocks, are used for measuring control, as well as for setting up instruments when measuring by comparison with a measure.

Multivalued line angular measures (protractors) have a scale and all the metrological characteristics belonging to it (division value, upper and lower limits of the scale, scale range).

The second group of means for measuring angles is goniometric devices, with the help of which the measured angle is compared with the corresponding values ​​of the goniometric circular or sector scale built into the device. Such devices include protractor inclinometers with a vernier, optical inclinometers, dividing heads, and goniometers. Dividing heads (optical and mechanical) are used for angular measurements and for dividing work when marking and processing parts.

In addition, a number of universal measuring instruments have special goniometer devices, for example, OGU measuring heads, which are equipped with measuring microscopes, goniometers rotary tables on large measuring microscopes and large projectors, etc.

To measure the deviation of angles from the horizontal and/or vertical, various levels (bars, frames, with “cylindrical” and spherical ampoules), optical quadrants and other devices are used.

When measuring with a protractor, the flat or “knife” edges of the protractor rulers are placed “without clearance” on the sides of the measured angle of the part. One of the rulers is connected to a circular or sector goniometer scale, the other (rotary) is connected to a pointer or vernier. When measuring using a dividing head, goniometer or measuring microscope the edges of the corner are fixed using auxiliary optical or other devices.

The essence of indirect (“trigonometric”) measurements of angles is that the angle is obtained by measuring the linear dimensions of the controlled part, calculating its value through trigonometric functions. In this case, any universal means can be used for linear measurements, as well as aids, designed specifically to provide angle measurements on cones and prismatic parts.

Indirect measurements of angles are most often based on the use of sine or tangent schemes, and the object of measurement is the angle of a specially constructed right triangle. The two sides of this triangle are reproduced and/or measured by means of linear measurements. For example, you can measure two legs on a microscope or projector.

Of the tools intended for the implementation of “trigonometric measurements”, the most common are “sine bars” various types. The measured object is placed on a “sine ruler” with known value hypotenuse (base distance of the ruler) and measure the leg of the desired angle (Fig. 3.97).

Fig.3.97. Scheme of measuring control of the cone angle

There are also more complex implementations of sine and tangent measurement schemes (cone meters, devices for measuring internal cones using balls, etc.).

During production various parts machines use angular templates as measuring instruments with the angle that the product should have, and the product is adjusted according to the template without clearance. The contact of the measuring surfaces with the product must be linear, therefore, to control the corners of products formed by flat edges, templates are made with a pattern (rounded with a small radius) surface of one or both sides of the working angle.

The working angles of the limit templates differ from one another by the value of the entire tolerance field of the angle of the product.

Metal squares with a working angle of 90° are used to check the mutual perpendicularity of the planes (edges) of products, as well as to check the perpendicularity of the relative movements of machine parts. In addition, angles are used for installation work. Shapes, sizes and technical specifications for angles are standardized (GOST 3749 – 77).

When measuring the angle of a product by comparison with the angle of a square, the clearance between them is assessed. The deviation of the angle of the product from the angle of the square is determined by the ratio of the width of the opening to the length of the side of the square. Since the length of the angle is constant, clearance can serve as a measure of angle deviation. The gap can be observed both at the end of the side of the square (the angle of the product is less than the angle of the square) and at the top of the angle (the angle of the product is greater than the angle of the square). When checking for clearance, it is necessary to establish the absence of clearance between the measuring surfaces or its value. Under normal illumination of the order of (100...150) lux, the naked eye detects a gap between the flat surface and the edge of the pattern ruler of approximately (1.5...2) microns. The shorter the length of the contact line of the product and the square, the greater the error in estimating clearance.

The width of the surfaces in the direction perpendicular to the direction of the angle generatrix also plays an important role. With the width of the contacting surfaces (3...5) mm, invisible gaps can reach 4 microns. If, however, the contacting surfaces are not polished, but ground, the invisible gap can reach up to 6 microns.

For a more accurate assessment of lumens, a so-called lumen sample is used.

The gap, the width of which is to be assessed, is compared by eye with a set of certified gaps and its size is determined by the identity of the observed slits. With sufficient skill and the presence of a patterned surface on the ruler, such an assessment can be performed with an error of the order of (1...1.5) µm for gaps up to 5 µm, and for large gaps (up to 10 µm) - of the order of (2...3) µm. For a lumen greater than 10 µm, this method is not applicable. For gaps of 20 microns or more, probes can be used.

To control the dimensions of the outer and inner cones, conical gauges are used. Inspection of products by gauges is usually comprehensive, since not only the angle of the cone is checked, but also its diameter in the design section by the position of the gauge relative to the product along the axis. For this purpose, on the surface of the plug gauge there are either two limiting lines or a shoulder cut (the shoulder cut is also used on the bushing gauge).

The cone angle of the part is checked by the contact of the gauge surface with the surface of the part being tested. To do this, the caliber is thoroughly cleaned of dust and oil and a layer of paint (Prussian blue) is applied to its conical surface, evenly distributing it over the entire surface. Then the plug gauge is carefully inserted or the bushing gauge is put on the part being tested (also thoroughly wiped in advance) and turned 2/3 of a turn to the right and left.

If the taper of the gauge and the part being tested coincides, the paint will be evenly erased along the entire generatrix of the gauge. Based on the proportion of erased and remaining paint, the suitability of the part is judged by its taper. The errors of this measurement method are approximately 20". It is necessary that the working surfaces and surfaces of the parts being tested are free of nicks, scratches and other similar defects.

Certified balls or rollers are used to measure internal cones and wedge-shaped grooves. Sine and tangent schemes are used, based on the measurement or reproduction of the leg opposite to the measured angle (in both schemes), the hypotenuse (with a sine scheme) or the adjacent leg (with a tangent scheme). For small angles (up to approximately 15 o), both schemes are almost equivalent in accuracy, but for large angles the measurement error can be significant and the tangent scheme is preferable here.

Means for measuring angles and cones

The main parameter controlled when processing corners and cones is flat angle, the unit of which is taken to be a degree. A degree is 1/360 of a circle; it is divided into 60 minutes of arc, and minutes are divided into 60 seconds of arc.

Methods for measuring angles can be divided into 3 main types:

1. Comparison method with rigid angle measures or templates.

2. Absolute method, based on the use of measuring instruments with an angular scale.

3. Indirect method, which consists of measuring linear dimensions related to the cone angle by trigonometric relationships.

The simplest tools for checking angles are squares with an angle of 90 0, designed for marking and checking the mutual perpendicularity of individual surfaces of parts during equipment installation and for monitoring tools, instruments and machines. In accordance with the standard, there are 6 types of squares (Fig. 2.12.):

More universal tools for control and marking of angles - protractor inclinometers (simple, optical, universal). In mechanical engineering, inclinometers with a vernier type UN are widely used to measure external and internal corners and type UM for measuring only external angles (Fig. 2.13.).

For methods of measuring angles, see Fig. 2.14.

Calibers used to control the dimensions of holes and external surfaces of parts. In manufacturing, it is not always necessary to know the actual size. Sometimes it is enough to make sure that the actual size of the part is within the limits established tolerance, i.e. between the largest and smallest size limits. In accordance with these dimensions, limit gauges are used, which have two (or two pairs) measuring surfaces of the go-through and non-go-through parts. There are smooth, threaded, conical, etc. gauges. Plug gauges, staple gauges, depending on the size of the parts being controlled, the type of production and other factors, have different structural forms(Fig. 2.15, Fig. 2.16).

The pass side (PR) of the plug or staple has a size equal to the smallest limit size of the hole or shaft, and the non-pass side (NOT) has a size equal to the largest limit size of the shaft and, accordingly, the hole. Methods of measuring with plug gauges and clamp gauges are shown in Fig. 2.16.

Cone gauges tools are plug gauges and bushing gauges. Control of instrumental cones is carried out using a complex method, i.e. simultaneously check the cone angle, diameters and lengths (Fig. 2.17).

Templates used to check complex part profiles and linear dimensions. Templates are made from sheet steel. Inspection is carried out by mating the template with the surface being tested. The quality of processing is judged by the size and uniformity of the lumen (Fig. 2.18., Fig. 2.19.).

Thread control Depending on the type (profile) and accuracy, it is carried out using various control and measuring equipment.

Threaded templates to determine the thread pitch and profile, they are sets of steel plates fixed in a holder with precise profiles (teeth) of metric and inch threads. Each plate is labeled with pitch values, thread diameters, or threads per inch.

Radius templates are used to measure the deviation of the dimensions of convex and concave surfaces of parts (Fig. 2.18.). To measure the depth of the grooves, the height and length of the ledges, limit gauges-templates are used that work against the light. They also have two sides and are designated B (for bigger size) and M (for smaller sizes). In Fig. 2.19. templates for checking the length, width and height of tabs and grooves are shown various methods: “through the light”, “by pushing” and “by the scratch method”.

Thread gauges(plugs and rings) are used to control internal and external threads (Fig. 2.20.).

Thread micrometers with inserts are used to measure the average diameter of a triangular external thread.

Inserts are selected in accordance with the pitch of the thread being measured from the set available in the case for the micrometer (Fig. 2.21.). Reading the micrometer is done in the same way as when measuring smooth cylindrical surfaces.

Thread control can also be carried out with a micrometer using three measuring wires (Fig. 2.22.). With this method, the distance M is measured between the protruding points of three wires placed in the recesses of the thread, then the average diameter d 2 of the thread is determined through mathematical transformations.

The wire diameter dpr is selected from the table depending on the thread pitch. Two wires are installed in the depressions on one side, and the third - in the opposite cavity (Fig. 2.22.)

Average diameter metric thread d 2 = M – 3 d pr + 0.866 R

Average diameter of inch thread d 2 = M – 3.165 d pr + 0.9605 R

Plane-parallel gauge blocks are used to transfer the size of a unit of length onto a product (when marking), checking and adjusting measuring instruments (micrometers, staple caliber, etc. measuring instruments), direct measurement of the dimensions of products, fixtures, when setting up machines, etc.

One of the main properties of gauge blocks is adhesiveness, the ability to firmly connect to each other when one gauge is applied and pushed onto another with some pressure, which is achieved due to the very low roughness of the measuring surfaces. End gauges are supplied in a set with a quantity of 7…12 tiles (Fig. 2.23).

The most widely used sets are those consisting of 87 and 42 gauge blocks. Each tile reproduces only one size, which is marked on one of its sides. For ease of use of gauge blocks, sets of accessories are produced for them (Fig. 2.24.), which include: bases - 5, plane-parallel, radius - 2, scribers - 3, center sides - 4, holders - 1 for attaching blocks of gauge blocks with sides. The block of gauge blocks is compiled in accordance with the class or category of tiles and the sizes of the tiles available in this set.

Initially, a smaller tile is selected, the size of which includes the last decimal place, etc. Let's say you need to assemble a block of gauge blocks measuring 37.875 mm from a set consisting of 87 tiles:

1 tile 1.005 mm, remainder 36.87

2 tiles 1.37 mm, remainder 35.5

3 tiles 5.5 mm, balance 30.00

4 tiles 30 mm, remainder 0.

The block amount is 1.005+1.37+5.5+30 = 37.875.

In the same way, a block is assembled from a set of 42 tiles.

1,005+1,07+4,00+30 = 37,875.

Methods for measuring with plane-parallel gauge blocks of length and marking using accessories are shown in Fig. 2.25.

Angular prismatic measures (tiles) are intended for checking and adjusting measuring angle measuring instruments and tools, as well as for direct measurement of external and internal angles of parts with high density. Angle measures perform the same role when measuring angles,

same as gauge blocks when measuring length. The working sides of corner measures are subject to the same requirements as the end measures, i.e. ensuring adhesion (fitness).

Angle measures are produced in sets with a quantity of 7...93 tiles in each (Fig. 2.26.). Checking the corners with tiles is carried out “through the light”.

To increase the strength of a block assembled from corner tiles, they are supplied with a set of accessories, which include ties, screws, wedges and others (Fig. 2.27.). The block is strengthened through special holes in the tiles.

The rules for calculating angular measures for the formation of blocks, as well as the rules for preparing for assembly and assembling them into a block, are similar to the rules used in the preparation of end length measures.

Methods of measuring with angular measures are shown in Fig. 2.28.

The state standard GOST 10529-86 distinguishes three groups of theodolites: high-precision, precision and technical.

High-precision theodolites provide angle measurement with an error of no more than 1"; types T1, T05.

Accurate theodolites provide angle measurements with an error of 2" to 7"; types T2, T5.

Technical theodolites provide angle measurements with an error of 10" to 30"; types T15, T30.

An additional letter in the theodolite code indicates its modification or constructive solution: A - astronomical, M - mine surveyor, K - with a compensator in a vertical circle, P - direct image tube (terrestrial).

The state standard for theodolites also provides for the unification of individual components and parts of theodolites; the second modification has the number 2 in the first position of the code - 2T2, 2T5, etc., the third modification has the number 3 - 3T2, 3T5KP, etc.

Before measuring the angle, it is necessary to bring the theodolite into working position, that is, perform three operations: centering, leveling and installing the telescope.

Centering the theodolite is the installation of the axis of rotation of the alidade above the vertex of the angle being measured; the operation is performed using a plumb line suspended on the hook of a screw, or using an optical plummet.

Leveling a theodolite is setting the axis of rotation of the alidade in vertical position; the operation is performed using lifting screws and a level while alidating a horizontal circle.

Installing a pipe is installing a pipe according to the eye and the subject; the operation is performed using a movable eyepiece ring (installation according to the eye - focusing the reticle) and a screw for focusing the tube on the object (pos. 15 in Fig. 4.4).

Angle measurements are performed strictly according to the methodology corresponding to the measurement method; There are several ways to measure horizontal angles: this is the way separate angle(method of techniques), method of circular techniques, method in all combinations, etc.

Single angle method. The measurement of an individual angle consists of the following steps:

pointing the pipe at the point that fixes the direction of the first side of the angle (Fig. 4.16), with the circle to the left (CL), taking reference L1;

turning the alidade clockwise and pointing the pipe at the point that fixes the direction of the second side of the angle; taking L2 sample,

calculation of the angle for CL (Fig. 4.16):

moving the dial by 1o - 2o for theodolites with one-sided reading and by 90o - for theodolites with two-sided reading,

moving the pipe through the zenith and pointing it at the point that fixes the direction of the first side of the angle, with a circle to the right (KP); taking a reading R1,

turning the alidade clockwise and pointing the pipe at the point that fixes the direction of the second side of the angle; taking a reading R2,

calculation of the angle at CP:

when the condition |vl - vp|< 1.5 * t, где t - точность теодолита, вычисление среднего значения угла:

vsr = 0.5 * (vl + vp).

Measuring the angle at one position of the circle (CL or CP) is one half step; a full cycle of measuring an angle at two positions of the circle is one step.

Recording of readings on the limb and calculation of the angle are carried out in journals of the established form.

Method of circular techniques. If more than two directions are observed from one point, then the method of circular techniques is often used. To measure angles using this method, you must perform the following operations (Fig. 4.17):

with CL, set the reading on the dial close to zero and point the pipe at the first point; take a reading on the dial.

Rotating the alidade clockwise, point the pipe sequentially at the second, third, etc. points and then again to the first point; each time take readings along the limb.

move the pipe through the zenith and, at the control point, point it at the first point; take a reading on the dial.

rotating the alidade counterclockwise, point the pipe sequentially at (n-1), ..., third, second points and again at the first point; each time take readings along the limb.

Then, for each direction, the average of the readings at CL and CP is calculated, and after that - the values ​​of the angles relative to the first (initial) direction.

The method of circular techniques allows us to weaken the influence of errors acting proportionally to time, since the average readings for all directions refer to one physical moment in time.

The influence of theodolite eccentricity on readings along the limb. Let in Fig. 4.18 let the axis of rotation of the alidade intersect horizontal plane at point B", and point B is the projection of the vertex of the measured angle onto the same plane. The distance between points B and B" will be denoted by l, the distance between points B and A by S.

If the theodolite stood at point B, then when the pipe was pointed at point A, the reading on the limb would be equal to b. Let's move the theodolite to point B", maintaining the orientation of the limb; in this case, the reading along the limb when pointing the pipe at point A will change and become equal to b"; the difference between these readings is called the theodolite centering error and is designated by the letter c.

From triangle BB"A we have:

or by the smallness of the angle c

The quantity l is called the linear element of centering, and the angle Q is corner element alignment; angle Q is constructed by projecting the axis of rotation of the theodolite and is measured from the linear element clockwise to the direction to the observed point A.

The correct reading on the dial will be:

b = b" + c. (4.19)

The influence of the reduction of the sighting target on the readings along the limb.

If the projection of the sighting target A" onto the horizontal plane does not coincide with the projection of the center of the observed point A, then a reduction error of the sighting target occurs (Fig. 4.19). The segment AA" is called a linear reduction element and is designated l1; angle Q1 is called the angular element of reduction; it is constructed during the projection of the sighting target and is counted from the linear element clockwise to the direction to the theodolite installation point. Let's denote the correct reading on the limb - b, the actual one - b", the error in the direction BA is equal to r. From the triangle BAA" we can write:

or by the smallness of the angle r

The correct reading on the dial will be

b = b" + r. (4.21)

The largest correction values ​​c and r are reached at I = I1 = 90o (270o), when.

In this case

In the practice of measuring angles, two methods are used to take into account the eccentricity of the theodolite and the sighting target.

The first method is that centering is performed with such precision that the eccentricity error is not taken into account. For example, when working with technical theodolites, the permissible influence of centering errors of the theodolite and the sighting target can be taken as c = r = 10"; with an average distance between points S = 150 m, it turns out that l = l1 = 0.9 cm, that is, the theodolite or the sighting target it is enough to set the target above the center of the point with an error of about 1 cm. For centering with such accuracy, you can use a regular plumb line. Centering a theodolite or sighting target with an accuracy of 1-2 mm can only be done using an optical plummet. The second method is to directly measure the elements l and I, l1 and I1, calculating the corrections c and r using formulas (4.18) and (4.20) and correcting the measurement results with these corrections using formulas (4.19) and (4.21).The measurement technique for the theodolite centering elements and the sighting target is described in.

In the polygonometric course, abutment angles, rotation angles and notches of lateral points are measured.

There are two main ways to measure angles at polygonometry points: the method of circular techniques; single angle method.

Method of circular techniques

Measuring angles in this method begins with preparing a theodolite for measuring angles, consisting of:

Centering, which is performed using an optical plumb line with an accuracy of 1 mm;

Bringing the main axis into a plumb position using a level with an alidade of a horizontal circle and three lifting screws;

Installation of the observation tube, consisting of installation of the tube by the eye, installation of the tube by the subject and elimination of parallax of the reticle;

Work at the station is performed in the following sequence:

The sighting axis of the telescope during CL is aimed at the sighting mark, which is taken as the initial direction during measurement;

Set the dial and optical micrometer to a reading close to zero (preferably slightly more than zero); To do this, first, by rotating the handle of the micrometer, set the reading on the scale of the latter, close to zero, then by rotating the handle for rearranging the dial, carefully align the image of the strokes of the opposite edges of the dial, after which the reading is made and recorded in the journal;

Using the handle of a micrometer, spread the image of the combined strokes and connect them again (second combination), make a count and write it down in a journal; the difference between two readings should not exceed 2;

Unfasten the alidade and point the sighting axis of the pipe (rotating the alidade clockwise) to the second, and then the third, etc. brands; with two combinations, readings are made and recorded in a journal;

The observations are completed by re-sighting at the point of the initial direction and, based on the initial and final readings obtained, they are convinced of the stationary position of the limb.

The described actions constitute the first half of the technique.

Re-targeting the first mark is called horizon closure. The discrepancy between the observation results for the initial direction at the beginning and end of the reception half should not exceed 8.

Move the pipe through the zenith and take measurements of the second half of the reception in the following sequence:

Point the axis of the telescope to the initial direction and, with two alignments, make readings, which are recorded in the log in the line corresponding to the observation during CP: recording is done from bottom to top;

Unfasten the alidade and turn it counterclockwise to sight the pipe axis to the third (depending on the number of directions), the second and again to the first mark. Readings are made at two combinations and recorded in a journal.

This ends the second half-reception. Two half-meals make up a full reception.

The second and subsequent methods of measuring directions are carried out in the same sequence as the first, but to weaken the influence of systematic errors in the dial divisions, the dial is rotated by an angle

G = 180\ n +10", where n is the number of techniques.

Measuring angles using the single angle method

The order of observations when measuring an angle using the method of a separate angle between two directions remains the same as in the method of techniques.

The only difference is that they do not re-point to the starting point and rotate the alidade in both the first and second half-methods, either along the clockwise or only counterclockwise.

The angle values ​​in half techniques, as well as in individual techniques, should not differ by 8”.

The final angle value is calculated as the arithmetic mean of the angles measured in separate steps.

When measuring individual angles or directions with theodolites provided for by the "Instructions for topographic surveying on scales 1: 5000, 1: 2000, 1: 1000, 1: 500. Moscow, "Nedra", 1973", the measurement results must be within the established limits tolerances

In class 4 polygonometry for theodolites of types T2 and T1, the number of techniques is set to 4.

It is recommended to measure angles in the morning and evening hours. Times close to sunrise and sunset (about an hour before sunrise and an hour after sunset) should not be used, as these are the hours where image fluctuations are greatest. Before starting measurements, research, verification and adjustment of instruments are carried out. The angles to the left are usually measured, and observations are recorded in field journals.

In order to eliminate centering and reduction errors when laying polygonometric moves and to speed up angular measurements somewhat, it is recommended to use a three-post angle measurement system.

Currently, in the production of geodetic work, instruments for various purposes from leading foreign companies Leica, Sokia and other geodetic instrument making companies from Switzerland, Sweden, Germany, and Japan are widely used.

Angles and cones are measured using angular measures, templates, squares, cone gauges, balls, sine and tangent rulers, universal microscopes (coordinate method), optical dividing heads, vernier protractors, etc.

The most common method is to measure angles and cones angle measures and squares. Angle measures (tiles) are assembled in sets of 5, 19, 36 and 94 pieces, from which the appropriate tiles or blocks are selected for measuring specified angles (at least 10°). They are three- or tetrahedral prisms with one or four working angles.

Measurement using tiles is based on establishing the size of the largest gap between the sides of the corner being measured and angular measure or complete absence of clearance between them. The lumen is compared by eye with a set of lumens, the sizes of which are known (5... 10 µm), or is assessed using probes (over 30 µm). In terms of manufacturing accuracy, class 1 corner tiles have a working angle tolerance of ±10", class 2 ±30".

To measure right angles, depending on the required accuracy, squares of various types are used. The measurement method, like that of tiles, is based on measuring the clearance between the measuring and measured surfaces and the length of contact between these surfaces.

The angles of tapered shafts and bushings are measured goniometers. To improve the reading accuracy, protractors are equipped with verniers or optical devices.

To check the shaft taper angle, use conical bushing gauges(full and incomplete), and to check the angle of the tapered bushings - cone gauges - plugs. To check the taper angle of the shaft along the generatrix of the cone, draw a straight line with a pencil and carefully insert the shaft inside the conical gauge-bushing. Having applied some axial force to ensure a tight fit of the conical surfaces of the shaft and bushing, turn them relative to each other at a small angle. If the generatrix of the shaft cone is straight and the angle of the cone is made correctly, then the pencil graphite will be evenly distributed along the entire length of the cone, otherwise only individual spots will form. When checking internal conical surface details, a pencil line is applied to the plug gauge.

Thread control

The accuracy of the thread is determined by the accuracy of the main thread elements of the bolt and nut: outer diameter, average diameter, inner diameter, pitch, profile angle. Inspection of the threads of a bolt and nut can be carried out using a comprehensive method for all elements simultaneously or element by element using gauges or special devices. For precision threads and gauges, element-by-element thread checking on instruments is usually used.

The simplest is to control the outer diameter of the bolt and the inner diameter of the nut. These thread elements measure smooth staples and plugs, A. also with the help micrometer or caliper.

Measuring the internal diameters of bolt threads can be done thread micrometer, the design of which is similar to that of an ordinary micrometer, only instead of smooth tips it is equipped with special inserts that allow you to measure the internal and average diameters of the bolt. Threaded inserts are made replaceable depending on the pitch of the thread being tested. To measure the internal diameter of a bolt thread, two prismatic inserts are used so that their tops touch the thread recesses.

To measure the average diameter of a bolt thread, inserts are used that touch the sides of the thread profile with their side faces

close to the average diameter. These inserts are made with a shortened profile. The inserts can rotate in the supports of the measuring heels and self-align relative to the inclined part of the thread profile.

For a threaded micrometer with a measurement interval of 0...25 mm, the correctness of the reading is checked by bringing both inserts together until they stop; in this case, the reading on the micrometer scale should be equal to zero. When using a thread micrometer, it is necessary to install the bolt being tested between the threaded inserts and then carry out the measurement as with a regular micrometer; you just need to make sure that the axis of the measuring tips passes through the axis of the bolt. Figure 1.35

Use a thread micrometer to measure the average diameter of a bolt. direct method, i.e. the measurement results are read directly from the instrument scale. The scale division of the threaded micrometer drum is 0.01 mm. The average thread diameter can also be measured using an indirect method three wires. This method consists of placing three wires of the same known diameter into the recesses of the bolt thread on both sides, then using a micrometer with a flat tip to determine the distance M between external surfaces wires (Fig. 1.35). Subsequent calculations based on the value of this distance determine the value of the average thread diameter. Three wires are used to prevent distortion of the micrometer's measuring tips. Knowing the diameter of the wires d, thread pitch S and the distance between the outer surfaces of the embedded wires M, the average diameter of the metric thread d cp bolt is determined by the formula

d cp = M-3d+ 0.866S

This measurement method gives higher accuracy than measurement using a thread micrometer. Therefore, it is used to measure the average diameter of gauges and other precision threaded parts.

Thread pitch is measured using thread templates, which are sets of flat steel plates with a cut thread profile. different steps. The profile of the thread being tested (along the generatrix) is combined with one of the template plates. At correct production step, combining the thread profile and the template does not provide a light gap.