The choice of measuring instruments when checking the accuracy of parts is one of the most important stages in the development of technological control processes.

The basic principles for choosing measuring instruments are as follows: the accuracy of the measuring instrument should be quite high compared to the specified accuracy of the measured size, and the labor intensity of measurements and their cost should be as low as possible, ensuring the highest labor productivity and efficiency.

Insufficient measurement accuracy leads to the fact that some suitable products are rejected (type I error); at the same time, for the same reason, another part of the actually unsuitable product is accepted as acceptable (error of the second type).

Excessive measurement accuracy, as a rule, is associated with an excessive increase in the labor intensity and cost of product quality control, and therefore leads to an increase in the cost of production.

When choosing measuring instruments and methods for monitoring products, take into account

• permissible error of the measuring instrument;
• scale division price;
• sensitivity threshold;
• measurement limits, weight, overall dimensions, workload, etc.

The determining factor is the permissible error of the measuring instrument, which follows from the standardized definition of the actual size as well as the size obtained as a result of measurement with a permissible error.

The simplest way to select measuring instruments is based on the fact that the accuracy of the measuring instrument must be several times higher than the manufacturing accuracy of the part being measured. When monitoring the accuracy of technological processes by measuring the dimensional accuracy of parts, it is recommended to use measuring instruments with a division value of no more than 1/6 of the manufacturing tolerance.

The value of the permissible measurement error depends on the tolerance, which is associated with the nominal size and with the quality of the size accuracy of the controlled product. The calculated values ​​of the permissible measurement error in microns are given in standard tables.

2. Instrumentation

Tools with a linear vernier include calipers, height gauges, and depth gauges. The basis of a vernier tool is a ruler - a rod with divisions marked on it; this is the main scale. A frame with a cutout moves along the rod, on the inclined edge of which there is a vernier (auxiliary) scale.

Calipers (Fig. 2) is intended for measuring linear dimensions (diameters, depths, widths, thicknesses, etc.). On a length of 9 mm of the frame (vernier), corresponding to 9 divisions of the bar, 10 equal divisions are applied. Thus, each vernier division is equal to 0.9 mm.

Rice. 2.

If you place the frame so that the sixth stroke of the vernier is opposite the sixth stroke of the rod, then the gap between the jaws will be equal to 0.6 mm (Fig. 3, A).

Rice. 3. A – for size 0.6 mm; B – for size 7 mm; B – for size 7.4 mm

If the zero stroke of the vernier coincides with any stroke on the rod, for example the seventh, then this division indicates the actual size in millimeters, i.e. 7 mm (Fig. 3, B).

If the zero line of the vernier does not coincide with any line on the rod, then the nearest line on the bar to the left of the zero line of the vernier shows an integer number of millimeters. Tenths of a millimeter are equal to the ordinal digit of the vernier stroke to the right, not counting the zero, which exactly coincided with the stroke of the rod - the main scale (for example, 7.4 mm in Fig. 3, B).

In addition to verniers with a reading value of 0.1 mm, verniers with a reading value of 0.05 and 0.02 mm are used.

are intended for precise marking and measuring heights from flat surfaces.

The height gauge (Fig. 4, a) consists of a base 8, in which a rod 1 with a scale is rigidly fixed; frames 2 with vernier 6 and locking screw 3; device for micrometric feed 4, including a slider, a screw, a nut and a locking screw; interchangeable legs for marking 7 with a point and for measuring heights 9 with two measuring surfaces, the bottom flat and the top in the form of a sharp edge no more than 0.2 mm wide (Fig. 4, b); clamp 5 for securing legs 7 and 9 and holder 10 on the protrusion of the frame (Fig. 4, c) for needles of various lengths.

Fig 4.

The scale and vernier are the same as those of other caliper tools.

Measuring or marking with a height gauge is carried out on a marking plate. Before measurement, the zero setting of the instrument is checked. To do this, the frame with the leg is lowered until it comes into contact with the slab or a special base surface (depending on the type of leg). In this position, the zero division of the vernier must coincide with the zero division of the rod scale.

After aligning the height gauge, you can begin measurements. When measuring the height of a part, the frame with the leg is lowered manually, slightly short of the part. Further movement of the leg until it comes into contact with the part is carried out using a micrometric feed nut. The degree of pressing of the leg to the part is determined by touch. In the installed position, the frame is secured.

When marking, the size is set according to the vernier and rod scales in advance. The mark on the part is drawn with the sharp end of the leg when moving the height gauge along the plate. When measuring with needles (Fig. 4, c), it is necessary to subtract the value m from the reading of the height gauge M, which corresponds to the position of frame 2 when the tip of the needle is in the same plane with the plane of the base.

Dial indicators . Due to the small measurement range, instruments of this group are intended mainly for relative (comparative) measurements by determining deviations from a given size. In combination with special devices, these devices can also be used for direct measurements. They are also used to control the correctness of the geometric shapes of machine parts and their relative position. The most widely used of the devices in this group are dial indicators (Fig. 5, a) with a division value of 0.01 mm; Indicators with a division value of 0.002 mm are also used.

When the measuring rod moves 1 mm, the indicator needle makes a full revolution. Indicators whose measurement limits are more than 3 mm have a revolution counter arrow.

Measurement practice. Dial indicators are used when measuring radial and axial runout, deviations from straightness, deviations in the position of one part relative to another, when checking the relative position of surfaces, etc.

Rice. 5. Dial type indicator (a) and installation of the indicator for measurement:b – on a universal tripod; c – various ways to mount the indicator head on a tripod

When taking measurements, use a universal tripod and other devices.

The indicator installed in a universal stand (Fig. 5, b) can occupy a variety of positions in relation to the product being tested. The design of universal tripods may be different, but their basic design remains the same. The options are shown in Fig. 5, c.

For any measurement with an indicator (absolute or relative), it must be set to a certain initial position. To do this, the measuring tip is brought into contact with the surface of the setting measure (or table). The indicator is adjusted so that the arrow makes 1-2 turns. In this way, tension is given to the indicator rod so that during the measurement process the indicator can show both negative and positive deviations from the initial position or setting standard. In this case, the indicator arrow is set against any scale division. Further readings should be made from this arrow reading, as from the initial one. To make readings easier, the initial reading is usually set to zero. The indicator is set to zero by turning the dial by the grooved rim.

When measuring indicator bore gauge it is pre-adjusted to the size being measured using a micrometer, a block of plane-parallel gauge blocks or a calibrated ring and then set to zero.

The adjusted bore gauge is carefully inserted into the hole being measured and with slight rocking (Fig. 6, a) the deviation of the needle from the zero position is determined. This will be the deviation of the measured size from the one for which it was configured. In cases where the measuring rod of the indicator head cannot touch the surface being measured, they resort to special lever devices connected to the indicator body. The structure of these devices is clear from the figure (Fig. 6, b).

Rice. 6. Indicator bore gauge (a) and lever devices for the indicator (b), used for measurements in hard-to-reach areas places

Micrometers for external measurements (Fig. 7), micrometer bore gauges and micrometer depth gauges are classified as micrometer instruments.

Rice. 7. 1 – heel; 2 – micrometric screw; 3 – lock nut; 4 – bushing; 5 – drum; 6 – ratchet; 7 – bracket

The reading device of micrometer instruments consists of a sleeve 1 (Fig. 8, a) and a drum 2. On the sleeve, on both sides of the longitudinal line, two scales are marked with divisions of 1 mm so that the upper scale is shifted relative to the lower one by 0.5 mm.

At the beveled end of the drum there is a circular scale with 50 divisions. When rotating, the drum moves along the bushing and covers a distance of 0.5 mm in one revolution. Therefore, the drum scale division price is 0.5:50 = 0.01 mm.

When measuring, a whole number of millimeters is counted on the lower scale, half a millimeter on the upper scale of the sleeve, and hundredths of a millimeter on the drum scale. The number of hundredths of a millimeter is counted according to the division of the drum scale, which coincides with the longitudinal mark on the sleeve.

Examples of readings on micrometer scales are shown in Fig. 8.

Rice. 8. a – 11.0 mm; b – 9.36 mm; c – 10.5 mm; g – 9.86 mm

In order to limit the tension force on the part being measured when measuring with a micrometer and ensure the constancy of this force, the micrometer is equipped with a ratchet.

Before reading the micrometer readings, the drum is secured using a special stopper.

In addition to conventional calipers and other instruments with a vernier scale and a dial scale, models of instruments with electronic digital indicators are also used, which display digital readings of the measurement values ​​on the screen.

When operating measuring instruments, it should be remembered that the measuring surfaces of the tips must be clean, and the measured surfaces of the parts must be clean and their temperature should not differ from the temperature of the measuring instruments. It is unacceptable to measure hot parts with precision measuring instruments. Measuring instruments should not be held in your hands for a long time, as this affects the accuracy of measurements. It is not allowed to measure moving parts, because this is dangerous, leads to rapid wear of the measuring surfaces of the instrument and a loss of accuracy of the measurement results.

For short-term and long-term storage, wipe the measuring instrument with a soft rag containing aviation gasoline and lubricate it with a thin layer of technical petroleum jelly. The measuring surfaces of the tips are separated from each other, and the stoppers are loosened. For long-term storage, instruments are wrapped in oiled paper.

Before starting measurements, it is recommended to check the zero readings of the measuring instruments. To do this, first adjust the instrument scale readings to the size being measured using measuring tiles (plane-parallel gauge blocks) or using a calibrated ring or roller and thus determine the zero position during measurements.

Probes serve to determine the size of the gaps with an accuracy of 0.01 mm (Fig. 9).

Rice. 9.

Probes are manufactured of 1st and 2nd accuracy classes with plate thicknesses from 0.03 to 1 mm and with intervals of 0.01 mm or more, depending on the set number.

(Fig. 10) are the main means of checking the flatness of the surface of a part using the paint method. The plates are made of cast iron with dimensions ranging from 100x200 to 1000x1500 mm.

There should be no corrosion spots or pits on the surface of the slabs.

Surface plates serve more than just checking flatness. They are widely used as a basis for various control operations using universal measuring instruments (thicknessers, indicator stands, etc.)

Rice. 10.

Steel straight edges . Deviations from flatness and straightness (deviations in the shape of flat surfaces) are controlled using straight edges (Fig. 11). Straight edges are produced in patterns with a double-sided bevel (Fig. 11, a); triangular (Fig. 11, b) and tetrahedral (Fig. 11, c); with a wide working surface (rectangular section (Fig. 11, d) and I-section (Fig. 11, e), “cast iron bridges” (Fig. 11, f).

Rice. eleven

Rulers are available in various sizes (LxHxB mm): a – up to 320x40x8; b – up to 320x30; c – up to 320x25; g – up to 1000x60x12; d – up to 4000x160x30.

Straight edges are made in length: pattern rulers – up to 500 mm, “cast iron bridges” – up to 2500 mm and more. Curve rulers are used to check the straightness of the surface of a part “by light”, and straight edges “cast iron bridges” are used to check straightness “by paint”, using a feeler gauge or tissue paper.

When checking for transmission (Fig. 12, a), the ruler is laid with a sharp bevel on the surface to be checked, and the light source is placed behind the ruler and the part. The minimum slit width that can be detected by the eye is 3...5 µm. To control the lumen gap, probes are usually used.

Rice. 12. Scheme for monitoring deviations from flatness using a pattern ruler “in the light”:a – visually; b – with a sample of gaps

Measuring deviations from straightness with straight lines “in the light” requires skill from the performer. To develop the skill of assessing by eye the magnitude of the deviation from straightness by the size of the lumen, a sample of lumens is used (Fig. 12, b), which consists of a pattern ruler 1, a set of four end length measures with a gradation of 1 micron, two identical end length measures (2) and glass plate 3. When measuring between the end measures of length and the edge of the ruler, “gaps” are formed, colored in different colors due to diffraction of visible light and from the size of the gap between the ruler and the end measure of length.

According to such a criterion as the number of parameters that need to be checked during one installation of a part, all measuring instruments are divided into one-dimensional tools and multidimensional ones.

According to the degree of automation of the process, measuring instruments are divided into manual, mechanized, semi-automatic, and automatic instruments.

Measuring instruments can be general-purpose or special-purpose, depending on the nature of the application.

In turn, depending on such criteria as the principle of operation and design, universal measuring instruments are divided into mechanical products, lever-mechanical, optical, optical-mechanical, pneumatic, electrified.

Mechanical measuring instruments are vernier tools, universal protractors (that is, instruments with a linear vernier), as well as micrometers, micrometric bore gauges and depth gauges (that is, various types of micrometric instruments).

Lever-mechanical measuring instruments include lever-geared, toothed, lever and spring (microcators, indicators) instruments. Optical are interferometers, projectors, universal and instrumental measuring microscopes. Optical-mechanical measuring instruments include length gauges and optimeters.

Using special-purpose measuring instruments, parameters such as deviations in the location and shape of surfaces, characteristics of thread parameters, characteristics of gears, and surface roughness are monitored.

Measurement concept

By measurement is meant a process during which, using technical means specially designed for this purpose, any physical quantity is compared with a homogeneous quantity, conventionally taken as a unit. As a result of the measurement, a certain number is obtained that expresses the ratio of the quantity being measured to the one taken as a unit. Measurements are widely used in engineering. These include linear measurements, as well as angular measurements. In the process of measurements, the determination of those geometric parameters that have parts of machines and mechanisms, products and assembly units is carried out. In addition, measurements make it possible to determine the roughness and waviness of various surfaces, deviations in shape and location.

Concept of control

In principle, control is a very broad concept that covers both qualitative and quantitative assessment of how well a product meets certain requirements. Product accuracy control refers to a procedure during which it is determined to what extent the actual values ​​of product quality parameters correspond to acceptable values, that is, those established by specified tolerances and technical conditions. In addition, accuracy control also involves determining whether technological processes are acceptable for manufacturing a part. Thanks to this, it becomes possible to carry out so-called defect prevention, that is, to technologically ensure the required accuracy.

Selection of measuring instruments

Certain measuring instruments are chosen depending on the design features of the parts, the volume of their production, and the required manufacturing accuracy. The economic characteristics of the measuring instruments are also taken into account. The main principle is that the error of the measuring instruments themselves should not be more than permissible, and the cost and labor intensity of measurements should be as low as possible.

Products produced by the engineering industry - machines, machines, instruments, tools and fixtures - consist of parts of various shapes and sizes. In the manufacture of these parts, control and measuring tools are used. The process of measurement consists of comparing the measured quantity with another homogeneous quantity, which is a generally accepted unit of measurement.

Inspection and measuring instruments can be divided into three main groups: length measures, universal instruments, gauges and indicators.

Measures are instruments that reproduce units of measurement or its multiples. Line length measures - scale rulers, folding meters, tape measures - reproduce linear dimensions within certain limits.

1.1. Plane-parallel gauge blocks

Plane-parallel gauge blocks are a set of precise steel gauges in the shape of a rectangular parallelepiped with two mutually parallel measuring surfaces, the distance between which determines their size (Figure 1, a).

The end blocks are made from high-quality chromium steel, undergo a complex heat treatment cycle with hardening to a hardness of HRC 62...64 and are carefully processed by grinding and finishing. The nominal size between the measuring surfaces of plane-parallel gauge blocks is maintained with an accuracy of 0.0001 mm, and the roughness of the working surfaces is maintained according to class 13. Thanks to this, the end blocks have the ability to rub against each other, which makes it possible to make non-scattering blocks from several end blocks (Figure 1, b).

Depending on the manufacturing accuracy, gauge blocks are divided into accuracy classes: 0, 1, 2 and 3. The most accurate is class 0. End measures are completed in sets No. 1 (of 87 measures), No. 2 (of 42 measures), No. 3 (of 116 measures) and other numbers consisting of end measures selected in such a way that any required size can be made with an interval of 0.001 mm. When compiling a block of the required size, first take a gauge measure, which has a size that includes thousandths of a millimeter. The size of this gauge block is subtracted from the required block size. Then take a gauge measure of size including the required hundredths of a millimeter, and its size is subtracted from the remainder obtained after the first subtraction; then the size of the next end blocks is determined in the same way. It is necessary to strive to ensure that the block consists of as few end measures as possible. Figure 1, c, d, e shows examples of various uses of a set of plane-parallel gauge blocks.

With the help of various devices, gauge blocks can be used to control the size of a precise part, template or gauge, to install various measuring tools and devices using the relative method of measuring size, for precise marking.

1.2 Probes

Probes (Figure 2) are a set of precisely machined steel plates with a thickness of 0.02 to 1 mm and a length of 100 or 200 mm. Feeler gauges are used to check the size of the gaps between mating parts.

Figure 2 – Probes

They produce four sets of probes, differing from each other in the number of plates and their thickness. The thickness of the plates in the set is indicated on each of them and alternates in set No. 1 every 0.01 mm; set No. 2 has 17 plates, first every 0.01 mm, and then every 0.05 mm; set No. 3 has 10 plates ranging in thickness from 0.55 to 1 mm, and set No. 4 has 10 plates ranging in size from 0.1 to 1 mm.

To determine the size of the gap, the plates are introduced into the gap alternately (one at a time or two or three at a time) without force until their total thickness corresponds to the gap.

1.3 Rulers

A ruler (Figure 3, a) is a measuring tool made of sheet tool steel. Divisions in the form of strokes are applied to the ruler. Metal rulers are made with scale lengths of 100, 150, 200, 300, 500, 750 and 1000 mm.

A folding meter is a ruler consisting of ten plates connected with rivets. The protrusions on the plates ensure a stable position of the meter when unfolded.

Roulette (Figure 3,b) is a long steel tape with divisions printed on it. Tape measures with a division value of 1 mm along the entire length of the measuring tape are made with a length of 1; 2 5; 10; 20; 30 and 50 m.

1.4 Vernier tools

For more accurate measurement of linear dimensions, calipers, height gauges, height gauges, etc. are used.

Vernier tools include measuring instruments with a linear vernier: calipers, height gauges and depth gauges.

These instruments are equipped with linear scales, the reading of which is carried out using an additional scale - a vernier.

The ShTs-1 caliper (Figure 4, a) is widely used for measuring external and internal dimensions. The reading value on the vernier is 0.1 mm.

Measurement limits from 0 to 125 mm. The caliper has a rod 1, on which there is a scale with a division value of 1 mm. The rod has two measuring jaws 2 and 9. A slide 7 with jaws 3 and 8 moves along the rod. The slide has a scale called a vernier (Figure 6), which allows you to determine tenths of a millimeter when measuring. The rod on the reverse side has a groove in which ruler 5 of the depth gauge is installed.

The ShTs-P caliper (Figure 4, b) with a vernier reading value (Figure 5) of 0.05 and 0.1 mm allows for more accurate measurements.

The height gauge (Figure 5) is a measuring and marking tool. The height gauge has a vertical ruler 2, fixed in a massive base 1. A slider with a vernier 4 moves along the ruler, secured to the ruler 2 with a screw 5. A replaceable leg is attached to the slider foot - a scriber 10 with a tip 11 made of a carbide plate.

The engine 6 is connected to the slide with a micrometric screw 8 and is installed on a vertical ruler with a locking screw 7.

Vernier is used to count the fractional part of the division interval of the main scale.

a - caliper type ШЦ-I: 1 – rod; 2, 9 – fixed measuring jaws; 3, 8 – movable measuring jaws; 4 – frame clamp, 5 – depth gauge ruler; 6 – vernier; 7- frame; B - caliper type ШЦ-П: 1 – jaws for measuring internal dimensions, 2 – jaws for measuring external dimensions. Figure 4 – Vernier tools	1 – base; 2 – vertical ruler; 3 – crawler; 4 – vernier; 5 – screw; 6 – engine; 7.9 – locking screws; 8 – micrometric screw; 10 – scriber; 11 – tip Figure 5 – Height gauge

Vernier (Figure 6) is characterized by the reading value A and module y, determining the length of the vernier relative to the main scale.

Quantities A And at can be determined by the formulas:

where – interval of division of the main scale – price of division of the scale (usually = 1mm); – number of divisions on the vernier; – vernier length.

Vernier tools are manufactured with a reading value A, equal to 0.05 and 0.1 mm, and with module y. equal to 1, 2 and less often 5.

1.5 Micrometers

Micrometers (Figure 7) are designed to measure the external dimensions of a part. The micrometer has a bracket, on one side of which a fixed heel 2 is installed. The second side of the bracket has a complex design. The main measuring mechanism of the micrometer consists of a nut 5 and a spindle 3 screwed into it. The spindle is pressed into drum 6. When drum 6 rotates, the spindle rotates. To determine the exact size, the ratchet 7, when rotating, transfers pressure to the micrometer screw and to the spindle 3. The spindle 3, resting against the surface of the part being measured, will stop the rotation of the drum 6. The micrometer allows you to measure dimensions with an accuracy of 10 microns. Micrometers are produced with measurement limits of 0...25, 25...50, 50...75, etc. up to 275...300 mm.

1.6 Straightness and flatness controls

The most common means of checking straightness are straight edges, which are available in several types.

Pattern rulers. Three types of pattern rulers are made: straight with a double-sided bevel (Figure 8, A), triangular (Figure 8, b) and tetrahedral (Figure 8, V). Straightness is checked using pattern rulers using the light slit method (through the light), while the pattern ruler is placed with its sharp edge on the surface being checked, and the light source is placed behind the ruler and the part being tested.

Rulers with a wide working surface are divided into four types: rectangular cross-section (Figure 8, G), I-section (Figure 8, d), bridge rulers (Figure 8, e) and triangular (Figure 8, and) with angles of 45, 55 and 60°

Checking straightness and flatness with rulers with a wide working surface is carried out by linear deviations (using a probe) and paint. When checking for paint, the surface of the ruler is covered with a thin layer of soot mixed with machine oil (Figure 8, h, And), placed on the test surface and the accuracy of the plane being tested is judged by the number of spots on a 25x25 mm square.

Quite accurate results are obtained by using strips of thin paper or metal foil, which are placed at certain intervals under the straight edge. By pulling the strips out from under the ruler, the amount of deviation from straightness is judged by the tension force of each of them. By measuring the thickness of the strips with a micrometer, you can establish the clearance value with an accuracy of 0.01 mm.

Verification plates (Figure 8, k, l) are the main means of checking surface flatness using the paint method. The plates are made from high-quality cast iron grade SCh 18-36, fine-grained structure, hardness HB 170-241.

The sizes of the slabs are 250x250, 400x400, 400x630, 630x1000 and 1000x1600 mm. The maximum deviations from the flatness of these plates depend on their size and accuracy class (classes 01; 0; 1 and 2) and are taken from 4 to 25 microns for a plate size of 400x400 mm.

The flatness of the slabs is checked with a straight edge against the light and using a set of plane-parallel end blocks, as shown in Figure 8. n . To do this, two gauge blocks 2 of the same size are placed on the surface of the plate 3 being checked, and a ruler 1 is placed on top of them, and a set of gauge gauges is inserted into the gap between the surface of the plate and the blade of the straight edge. 4. Difference between gauge blocks 2 and the set will show the amount of bending of the surface of the slab being tested.

Verification plates serve not only to control flatness, but they are widely used as a basis for various control operations using universal measuring instruments.

Corner plates (scraper squares), shown in Figure 8, m , They are used to check the mutual perpendicularity of planes using the paint method and are often used as auxiliary devices for various inspection, assembly and marking work.

1.7 Means of control and marking of corners

To check or mark angles, the following types of tools are used: squares, universal and optical protractors, flat corner tiles, sine rulers, optical dividing heads.

Test squares are designed for checking and marking right angles, to control the mutually perpendicular arrangement of surfaces of parts during their manufacture and assembly. The industry produces testing squares with angles of 90°. There are pattern squares - for precision work and metalwork squares - for ordinary use.

Pattern squares are made hardened, precisely ground and finished. They are used to control the transmission of precisely manufactured parts. Pattern marking squares have a wide base (shelf) with which the square is pressed against the edge of the part to be marked. According to the standard, the industry produces pattern squares of two accuracy classes: 0 and 1. For all squares, the height is made longer than the base. The standard provides for the following dimensions of the sides of pattern squares: 60x40, 100x60, 160x100 and 250x160 mm.

In Figure 9, a, b curved squares of the ULP and ULSh types are shown. In Figure 9, V a solid pattern square of the UL type is shown. It is used when checking precision parts of complex shapes on a surface plate and monitoring the assembly of small-sized precision dies, fixtures and molds.

In Figure 9, G a hollow cylinder-square of the ULC type is shown, which is used to check on the surface plate the correctness of the 90° angle for all other squares. Angles of the ULC type are produced in the following sizes (height x diameter in mm): 160x80, 250x100, 400x125 and 160x630.

Flat angle measures are intended for monitoring the angles of products, transferring angle values ​​during precise marking, for checking and calibrating angle measuring tools, templates and devices.

The measuring surfaces of corner gauges have the ability to rub against each other similarly to plane-parallel end gauges, which makes it possible to assemble blocks of several tiles. Checking corners using corner tiles is carried out against light.

Angle measures are produced in sets in the form of sets of three accuracy classes: 0, 1 and 2 with tolerances of ±3, ± 10 and ±30 s, respectively.

Each set of angle measures comes with a straight edge and a set of holders with holes and clamps for holding multiple tiles assembled into blocks. For this purpose, the corner tiles also have several holes (Figure 9, h, i, j).

Sine bars. Used for precise checking, marking or installation of corner parts of templates and gauges. Conventional sine bar (Figure 9, l) It is a precisely ground steel rectangular plate 7 with two prismatic cutouts in the side faces. Two steel rollers, precisely ground and finished, are attached to the cutouts. 8 certain diameter d(Figure 9, m). The rollers are located at a given distance L. Planks can be attached to the side edges using screws 5 And 6. On the upper plane of the ruler there are smooth threaded holes for fastening with screws additional mounting strips or the workpiece directly (for example, when marking).

To set the ruler at the required angle to the plane of the surface plate 9 under the roller 8 place a block of plane-parallel gauge blocks 10, the size of which H is determined by the formula

,

Where L- the distance between the centers of the rollers.

If the height of a block of tiles is known and it is necessary to find out the resulting angle a, then the calculation is carried out according to the formula

L .

Standard sine bars are produced in the 1st and 2nd accuracy classes and have the following gradation of main sizes:

The distance between the centers of the rollers is 100; 200; 300; 500.

Roller diameter 20; 20; thirty; thirty.

angles up to 45° are measured on sine rulers.

Goniometers. To measure the angles of parts, universal protractors with a vernier are widely used. The most widely used goniometers are the UM type (Fig. 30, A) and UN type (Fig. 30, b).

The UM type goniometer allows you to measure angles in the range from 0 to 180° with an accuracy of 5 minutes.

The UN instrumental protractor is more convenient. It is built on the principle of a circular scale and allows you to measure angles ranging from 0 to 320°. On the arc 4 protractor, at one end of which a measuring bar is fixed 5, The scale divisions are shown in degrees. A sector moves along an arc, on which a beveled arc bar 3 is mounted, having vernier divisions from 0 to 60. Squares are attached to the protractor 2 and a ruler 6 with a beveled measuring edge, as well as two clamps 1 for attaching the square and ruler to the protractor.

When assembled (with a square and ruler), the protractor makes it possible to measure angles from 0 to 50°. If you remove the ruler 6 and the clamp securing it, the angle measurement limit will change from 140 to 230°. If you install a measuring ruler in place of the square, then angles can be measured in the range from 50 to 140°. Finally, a protractor without a square or ruler allows you to measure angles from 230 to 320°. The vernier reading accuracy on this protractor is 2 minutes.

In Figure 10, V an optical inclinometer of the UO type is shown. Ruler 12, having a slot along the axis, rigidly connected to the body 16, inside which the limb is fixedly fixed 15, having a full angular scale with G divisions. The scale is divided into four quadrants, digitized from 0 to 90° every 2°. Ruler 8 can be moved off-axis and rotated around the center of the body 16 at a certain angle relative to the ruler 12.

In a longitudinal position the ruler 8 secure by turning the stopper 10. In the longitudinal groove of the ruler 8 includes a key connected to the upper disk, on which a magnifying glass 7 is installed with a magnification of x16 and glass 14 with scales having division values 5".

In the field of view of magnifying glass 7 two scales with division values ​​are visible 5" and an image of part of the dial 15, illuminated through glass 14. The angle between the rulers is set by turning the knurled ring clockwise 9 and secure with a stopper 10. Stand 13 with a flat surface and with a prismatic recess, it is used to install the protractor on a flat or cylindrical surface.

1.8 Indicators

Indicators are removable reading devices with a measuring mechanism that convert small measured deviations into large movements of the needle. For the purpose of measurement, indicators are installed on stands, tripods or mounted in special devices that ensure accuracy and convenience when performing work.

In the manufacture of technological equipment, dial indicators with scale divisions are most widely used.

0.01 mm. These devices (Figure 11) are used for relative or comparative measurements, checking deviations from a given shape, as well as the relative position of the surfaces of parts. They check the horizontal and vertical position of planes and individual elements of parts, ovality, taper of the outer surface of parts and holes, alignment of the hole with the surface of the part, runout of shafts, spindles, flywheels, gears and other rotating parts.

The operation of dial indicators is based on the use of a special gear transmission device, which converts minor linear movements of the measuring rod into enlarged and easy-to-read movements of the arrow on a circular scale.

Dial indicators come in two designs: type I - with the measuring rod moving parallel to the scale and type II - with the measuring rod moving perpendicular to the scale (end-mounted). Type I indicators have measurement limits from 0 to 5 mm and from 0 to 10 mm, type II indicators are manufactured with measurement limits from 0 to 2 mm and from 0 to 3 mm. For particularly accurate measurements, use multi-turn indicators with a division value of 0.001 mm and a measurement limit of
0 to 2 mm.

The indicators shown in Figure 11 are a, b, consist of a body 1, stopper 2, dial 3, rim 4, reference pointer 5, speed indicator 6, lug 7, sleeves 8, measuring rod 9 and tip 10. Setting the indicator scale to zero is done by rotating the scale by the rim 4. Mounting indicators in racks (Figure 11, V) produced by eye 7 or by sleeve 8.

1.9 Calibers

Calibers are scaleless measuring instruments. The gauges can measure one size. Calibers are divided into normal and limit.

Normal gauges have a nominal size indicated on the drawing. The accuracy of the measurement depends on the qualifications of the controller.

Limit gauges are used to check the size limits. One of the caliber sizes corresponds to the smallest permissible part size, the second to the largest. The first size is called pass-through and is designated by letters ETC, the second is impassable and is designated NOT(Figure 12).

1.10 Digital meters

The measuring instruments discussed above have one significant drawback: the measurement accuracy of these instruments significantly depends on the qualifications of the worker-controller.

Digital measuring instruments, built on the basis of the instruments discussed above, but equipped with microprocessor devices for converting measurement results and displaying the result on a digital display, do not have this drawback.

An example of such a device - a caliper with a digital display - is shown in Figure 13.

The use of caliper measuring surfaces is shown in Figure 14.

Figure 15 – Size measurement
absolute method

The relative method of measurement is a method based on comparison of the measured quantity with a previously known value of the measure.

To do this, using a block of tiles, we dial a denomination equal to the given size (Figure 16). The block size must be selected so that the number of tiles is minimal.

Then we reset the caliper readings to “0” (Figure 17).

Then we take measurements and find the deviation of the actual size from the required one (Figure 18).

Figure 16	Figure 17	Figure 18

2. Work order

1. Complete training on safety precautions and rules for working with measuring instruments.
2. Study the design and purpose of measuring instruments for measuring the geometric parameters of machine parts.
3. Obtain details from the teacher for testing. Draw a sketch of the part.
4. Obtain the necessary measuring instruments.
5. Perform measurements of each size using various instruments using absolute and relative methods.
6. Prepare a report on the work done.
7. Answer security questions.

3. Test questions

1. Purpose of control and measuring instruments. Types of test instruments.
2. What is a measure and how is it used in measurement?
3. Plane-parallel measures of length. Their purpose. Types. Use when measuring.
4. Probes. Purpose. Use in measurements.
5. Measuring rulers. Purpose. Application.
6. Vernier tools. Kinds. Purpose. Measurement accuracy. Method of application for measurements.
7. What is vernier? Purpose. Device. Use to improve the accuracy of measurement results.
8. Micrometers. Purpose. Use in measurements. Measurement accuracy.
9. Means for controlling the straightness of surfaces. Use for control.
10. Means and instruments for measuring angles.
11. Indicator heads. Device and purpose. Measurement technique using indicators.
12. Calibers. Purpose. Use in measurements.
13. Digital measuring instruments. Principle of measurement. Advantages and disadvantages.
14. Absolute measurement method. Measuring instruments built on this method.
15. Relative method of measurement. Measuring instruments built on this method.
16. Passameter. Device. Method of measuring with a passmeter. Setting the passmeter to a given size.
17. Setting up a digital caliper to measure using the relative method.

In any production that involves making something, it is impossible to do without measurements. Regardless of whether GOST requires this or you are creating a new product, you still have to measure it. We will now talk about how and with what to measure correctly. Discarding specialized geodetic instruments, without returning to ancient times to a rope with knots and a stick with notches, and without looking into the future with laser rangefinders, we will discuss simple, convenient, and most commonly used measuring tools.

Purpose and types

Speaking about their purpose, measuring instruments are classified according to their area of ​​application into:

• construction;
• carpentry;
• locksmiths.

A separate group can be identified as a universal measuring instrument that can be used in all or several industries.

By type, instruments are divided as follows:

This division into classes and types of measuring instruments is necessary for their professional use in work, compliance with storage and operation rules, purchase in stores and delivery from warehouses in factories.

Construction measuring tools

• Roulette. Used to measure linear dimensions of length, width, height. It is a housing made of solid material (plastic, metal), inside of which there is a metal or polymer tape. Available in different widths and lengths, but with the same scale, the graduations of which are 1 mm. Roulettes come with a manual or mechanical (spring) winding principle.
• Water level. Used for horizontal marking in height. Consists of a flexible polymer tube (length from 5 to 30 m) and two volumetric flasks at the ends. It works on the principle of communicating vessels.
• Level (spirit level). It is necessary to determine both horizontal and vertical indicators of structures. Made from various materials (wood, plastic, aluminum). The length ranges from 30 cm to 2.5 m. It mainly has three windows with glass tubes. The tubes are not completely filled with antifreeze liquid. The operating principle is vertical air lifting.
• Plumb. Used to set vertical values ​​during installation and construction. It has a simple design made of a cord on which a conical weight is suspended. Sometimes, in strong winds, to compensate for lateral vibrations, the load is placed in a container of water.
• Square. Made from wood or metal. It has a length of each side of up to 1 m. It is indispensable in the construction of buildings for checking right angles.
• Malka. Like a square, it can be metal or wood. The difference is that the two wings (clip and ruler) are hinged. Mainly used in the construction of roofs to install rafter pairs. Having set the desired angle, fix it with a wing nut and check the design.

Carpentry measuring tools

Considering the contiguity of some professions and the versatility of the measuring instrument, we will single out only the meter and the triangle separately. A tape measure is generally a universal tool, and we have already talked about a square and a small tool. They with shorter side lengths (up to 50 cm) are widely used by carpenters. A caliper is also used, for example, to select drills or check the diameter of holes, but we will talk about it later.

• Meter. The main material is wood and stainless steel. A plastic version was also produced, but due to its fragility it was not widely used. The name speaks for itself - meter, division value is 1 mm. Its main difference from a meter ruler is that it consists of separate sections that fold and unfold if necessary.
• Triangle. Everyone from school remembers this instrument and the size of its angles - 90, 60, 45 degrees. This is why it is widely used by all woodworkers. Usually the square also has a bevel of 45 degrees, but, firstly, not everyone does, and secondly, the dimensions do not always allow them to be used. This is where the triangle comes in handy. The main material is plastic, as well as wood or metal.

Locksmith measuring tools

Taking into account the specifics, scope of application, as well as the conditions when dimensions range from 0.1 mm to 0.005 mm, we can say that a locksmith is the most accurate measuring tool. And it's not just about accuracy. The work itself requires attentiveness, and the plumbing measuring tool requires knowledge and experience. Often the same device is used to measure different parameters.

Let's look at the indispensable assistant - calipers. Its upper lips are used to take internal dimensions of parts, and its lower lips are used to measure external parameters. In addition, the caliper has a depth gauge on a movable frame. But that's not all. On the main rod there is a scale for counting whole millimeters (division value - 0.5 mm), and in the cutout of the frame there is a Vernius scale for reading fractions of millimeters (division value 0.02 mm.). There is also a locking screw that secures the frame to the rod.

Yardstick It is a polished steel strip 20-30 cm long with marked divisions of 1 mm. It is used for linear measurements that do not require high accuracy.

For more accurate measurements, as well as angle measurements, measuring tools such as micrometer and protractor. They also have two scales - main and vernier. Often used calipers and bore gauge for measuring the external and internal dimensions of parts, respectively.

The specialist also has a variety of control and measuring instruments in his arsenal:

• straight edges of different configurations (double-sided, three-sided and tetrahedral);
• corner and reference tiles;
• measuring indicator;
• various probes.

Storage conditions

If we take into account the materials from which measuring instruments are made, it becomes clear that they cannot be stored under the same conditions. If plastic and plastic instruments are less susceptible to moisture, then wooden and especially metal instruments are afraid of water ingress. In this regard, they need to be stored in a dry, ventilated area. In addition, wooden instruments must be protected from direct sunlight to prevent them from drying out. Precision instruments are best stored in protective leather cases, and some instruments are best stored in hard wooden or plastic boxes.

Using the measuring tool

First of all, the measuring instrument you are working with must be in good working order, clean, and without traces of rust or oxidation. No mechanical impact is allowed (impacts, pressure, bending). Try to avoid dropping the instrument or getting water on it. Before operation, read the instructions, if any. Skillful and correct handling of the measuring tool is the key to quality work.

A measuring instrument is a broad concept that denotes a class of devices that allow one to establish quantitative relationships of any parameters in comparison with a standard. In scientific activities, measurements are associated with determining the numerical characteristics of a wide variety of quantities: mass, induction, spectral.

In production, measuring tools and instruments are used to compare the predominantly geometric characteristics of a manufactured product with a given sample.

Accuracy and error

The main characteristic of measuring instruments and devices is accuracy. This concept refers to the amount of deviation from the true values ​​that arises as a result of measurement error. Different industries have different accuracy requirements. In woodworking and the production of building metal structures, an error of 1 mm is allowed, in plumbing operations - 0.1-0.05 mm, in precision engineering, the deviation can be 0 microns.

The accuracy of measurements is affected by the physical condition of the instrument. To determine wear, the measuring tool is checked - an operation to identify the degree of non-compliance of the measuring instruments with the specified characteristics. The main verification methods that are used to assess the performance of a mechanical tool are methods of direct comparison and direct measurements. In these cases, control and measuring instruments for marking are used for verification. These are devices of similar design, the parameters of which have been verified.

The main requirement for accuracy is to use measurements to give the mating parts the shape that is needed for their constructive interaction. The accuracy of measuring the smoothness of races and balls in bearings must be at a level to ensure high rotation speeds. When assembling a frame, the wooden parts of which should not move relative to each other, it is enough to ensure that they fit tightly.

The physical properties of the processed materials and their ability to change parameters depending on climatic conditions are of great importance for accuracy. Hence the conclusion: carpenter's tools, the measuring devices of a turner, a mechanic and a carpenter have different accuracy.

Classes, types, types of measuring instruments

First of all, all meters are classified according to the nature of their use. The most extensive class is the universal tool. This includes all devices for general use - those that are used in all industries and fields of activity.

General purpose meters are interchangeable and are issued without restrictions. The devices are often in the personal use of the craftsmen. A special tool belongs to individual industries and technological complexes. This class includes instruments used to measure specific parameters: surface smoothness, its hardness. Can be used to determine the parameters of individual products, such as gears. The nature of the use and storage of such funds, as a rule, is of a sensitive nature. For example, in rocket science, measuring instruments are checked daily by metrologists before they are issued.

In addition, there are:

• measuring and marking tools;
• hand and mechanical tools;
• metal, plastic and wood.

There are types of measuring instruments based on technological characteristics, for example, metalworking tools. This type includes the following types: calipers, micrometer, probes, calibration and marking rulers. Another type is carpentry tools.

The most popular types here are represented by a square, a planer, a thickness planer, and a caliper. Construction tools are tape measures, spirit levels, folding meters. Many devices are universal: they are used by masters of all engineering professions.

Meters used in metalworking

The most common universal measuring instrument is a ruler. The marking ruler is used by all specialists, regardless of their profile. A more specific set of measuring devices include straight edges. They are used to identify deviations of products along the plane. The magnitude of deviations is determined using calibrated probes - metal plates, the thickness of which ranges from 0.01 mm to several mm. Using special rulers, modelers determine the shrinkage size of hot ingots.

In the metalworking industry, two main types of instruments are used to measure linear characteristics:

• line instrument with vernier;
• screw type micrometer instrument.

Line instruments with vernier scales

The most popular representative of this class is the caliper. Structurally, the device is a rod made of hard alloy, which ends at one end with a sponge. On the surface of the rod there is a metric scale with a division value of 1 mm. A carriage moves along the groove of the rod: one end ends with a sponge. There is a bar scale on the carriage. Several types of verniers are used in industry:

• by 9 or 19 divisions - with an accuracy of 0.1 mm;
• by 39 divisions - with an accuracy of 0.05 mm.

A variety of vernier tools are meters with a dial indicator and devices with digital electronic sensors. In the first case, translational motion is converted into rotational motion by a system of gears with a slider. The accuracy of such a caliper increases to 0.02 mm. Electronic devices provide measurements with an accuracy of 0.01 mm. Shtangelreismass is a subtype of caliper made on a stationary stand. This hand-held device is designed for measuring and marking.

A micrometer instrument is a pair of screws with a fine thread, to which a clamp with a precision heel is attached. The forward movement of the screw is communicated using two rotating mechanisms: a drum and a ratchet. Measurement procedure:

• the part to be measured is installed between the screw and the heel;
• the drum is turned until the part comes into contact with the screw and the heel on both sides;
• Use a ratchet to turn the mechanism until the part is completely secured.

Readings are taken from three scales. The first is located on the stem below: it shows the approximate size of the part in millimeters. On the scale above you can see whether the error of the first measurement is more or less than half a millimeter. The exact value of hundredths of a millimeter is marked on the drum scale. The final size of the part is equal to the sum of the data from all scales.