Checking large planes with a ruler and indicator.

A common way to check the straightness of planes is to check them using control rulers. This check can be carried out "on the paint" or using gauge blocks and an indicator. Checking "for paint" is usually carried out with the rulers of the "Caliber" plant of an I-section. However, for large surfaces, such a check cannot be recommended due to the deflection of long rulers from their own weight. This method can be successfully used to check planes up to 2500 mm long, having a straightness tolerance of up to 0.1 mm per 1 m of length. With tighter tolerances, for example 0.03 mm per 1 m, the length of the tested plane should not exceed 1500 mm.

A more objective way is to check large planes with a ruler and an indicator. In this case, a control ruler 3–5 m long is installed on the plane to be checked on two identical supports (for example, on two end measures) located at a distance from the ends of the ruler, equal to 0.22 of its total length. Surface deviations are measured according to the readings of an indicator that slides the measuring tip along the top of the ruler and is mounted on a stand that moves along the surface being checked. Sometimes deviations of the surface from straightness with this method of verification are measured with end measures, measuring the distance from the lower plane of the ruler to the surface of the product.

Use of rulers and others measuring tools large sizes is associated with the need to take special measures to eliminate their significant deflection from the influence of their own weight. So, for example, the deflection from the own weight of a control ruler of an I-section, having a length of 3000 mm, with the support located at the ends, can reach 0.3 mm, and for rulers with a length of 6000 mm - up to 1.5 mm.

When checking, for example, the guides of the machine bed, which have a concavity in the middle, a ruler installed directly on the plane, due to deflection, will significantly distort the results of the check. To obtain the smallest deviation from the straightness of the control rulers under the influence of its own weight, it is necessary to place the support points of the ruler from its ends at distances equal to 0.2232 of the total length of the ruler, or with sufficient approximation at distances of 0.22 of the length of the ruler.

The deflection arrow from the own weight of the ruler, lying on two supports located at its ends, is expressed by the formula

where P is the weight of one linear centimeter of the ruler in kg/cm; l is the length of the ruler in cm; E is the modulus of elasticity in kg / cm 2; I is the moment of inertia in cm 4. If this ruler is placed on two supports located from its ends at distances of 0.2232 of the length of the ruler, then the deflection arrow will be expressed by the formula

Comparing the values ​​f1 and f2 we get

Consequently, the specified optimal arrangement of supports reduces the effect of deflection compared to the location of supports at the ends of the ruler by approximately 48 times and, for the above case, can reduce the deflection of a ruler with a length of 6000 mm to 0.03 mm, and a ruler with a length of 3000 mm - up to 0.006 mm. A plane-parallel end measure with a length of 1000 mm and a cross section of 9X35 mm, supported in this way, decreases in length during deflection from its own weight by only 0.2 microns. By the way, its decrease from its own weight in a vertical position is also 0.2 microns. The same end measure with a length of 3000 mm, with the optimal arrangement of the supports, is reduced due to the deflection by only 2 microns. This value of measurement errors does not have practical value, and can be ignored. The limit of the use of long rulers is limited by their deflection from their own weight; usually in machine-building plants, control rulers are used only up to 5000 mm long.

To control the perpendicularity of the machined surfaces to the base surface, in some cases, on large parts, a boring machine spindle equipped with an indicator is used (see Fig. 219). However, with a significant extension of the spindle, its deflection from its own weight affects the accuracy of measurements, therefore, in this case, accurate levels are used, bearing in mind that the base and controlled surfaces have been checked in advance and are straight. If the base surface is separate, small in size and remote from each other sites (structural or technological), then its horizontalness is checked by an optical method using a telescope and target marks or by a hydrostatic device - the method of communicating vessels. The latter method is used to check the straightness and horizontality of surfaces.

Fig. 221. Checking with a hydrostatic device.

So, for example, for alignment on the machine and for further control of large beds on the base platforms in the horizontal plane, a hydrostatic device is used. On the base platforms 1, 5 and 7 of the bed of the working stand of the rolling mill (Fig. 221), located in the same plane and processed in one installation, three communicating measuring vessels 2, 4 and 8 are installed. A micrometer head is fixed in each vessel (node ​​M). 11 with pointed measuring tip. The heads in all three vessels are set to zero position from their scraped bearing surfaces. The vessels are connected by flexible hoses to the receiver 3; when the receiver is installed on the stand 9, located on the frame of the cage on the beam between the base platforms, water fills the hoses and measuring vessels. The moment of contact of the measuring tip with the water surface in the vessel is determined visually.

When the measuring tips touch the surface of the water in the vessels, the difference in the readings of all three micrometer heads is used to judge the correct location of the base platforms in the same horizontal plane. After checking the horizontality of the base plane, you can check the perpendicularity of the supporting surfaces 6 of the legs of the bed and the guide surfaces 10 to the base plane using a frame level or machine spindle.

The accuracy of the device, not exceeding 0.02 mm, is quite sufficient. When working, it is necessary to avoid the appearance of air bubbles in the hoses, which can lead to gross errors. Readings for all three micrometer heads should be carried out directly one after the other in order to avoid increasing errors.

The straightness of the planes during assembly and installation work ax is checked by methods that allow measuring directly linear or angular deviations. Linear methods include checking with a water mirror, using a string method, checking with a telescope and target marks, etc. Angular deviations from straightness are determined using a level, a telescope and a collimator.

4.1.1. Checking with a surface plate or ruler

Calibration rulers are carried out in two main types:

nye and rulers with wide working surfaces.

Checking the straightness of the surface of parts with curved rulers is usually carried out according to the “light gap” method (“through the light”). In this case, the curved ruler is applied with a sharp edge to the surface to be checked, and the light source is placed behind the part. The ruler is held strictly vertically at eye level. Observing the gap between the ruler and the surface of the part in different places along the length of the ruler, determine the degree of straightness of the surface\: the greater the gap, the greater the deviation from straightness.

Checking straightness and flatness with rulers with wide

mi working surfaces is usually performed by the method of "spots" -

"for paint". When checking “for paint”, the working surface of the ruler is covered with a thin layer of paint (red lead, soot), then the ruler is carefully placed on the surface being checked and moved smoothly, without pressure. After that, the ruler is also carefully removed and the flatness of the surface is judged by the location and number of paint spots on the surface being checked. With good flatness, paint spots are evenly distributed over the entire surface. The more spots on the surface of a 25-25 mm square, the better the flatness.

Surface plates are mainly used to check large surfaces of parts using the “paint” method, and are also used as auxiliary devices for checking parts.

lei. Checking the flatness of the surfaces of parts "for paint" when

the help of calibration plates is made in the same way as with rulers with shi-

rocky work surfaces.

Figure 4.1 shows the method of flatness control using a calibration plate 4 and a meter 3. The object of control 1 is installed on supports 2 of the same height and a meter 3 is placed in the gap between the plate and the object. after which they are statistically processed. The mass of the product must not exceed the limit at which an unacceptable deformation of the plate occurs.

All of the calibration tools considered have very finely machined working surfaces and therefore require careful and careful handling. It is necessary to protect the working surfaces of tools from corrosion and mechanical damage. During operation, place tools only on wooden or other non-rigid stands. At the end of work, wipe them with a clean rag or cotton and lubricate with acid-free Vaseline. Store these tools usually in special cases.

Rice. 4.1. Flatness check with surface plate and length gauge

As an example, let us consider the technology of testing asbestos friction linings for the purposes of certification for compliance with the requirements of technical specifications for deviation from flatness of the end surfaces of the linings.

Friction linings 2 are tested under pressure using pressure rings 3. The test method is based on measuring under pressure using a set of probes according to TU 2-034-225–87 the gap between the working (end) surface of the friction lining and the surface of the calibration plate 1 (Fig. 4.2), on which the overlay is placed.

The dimensions of the pressure ring are chosen in such a way that a pressure of (1.5 0.2) kPa is applied to the friction lining being tested. The overlay is placed on the calibration plate and a pressure ring or a set of rings is installed on top, providing pressure on the overlay (1.5 0.2) kPa. The control of the deviation from the flatness of the overlays is carried out using a set of probes with a maximum size that is 0.01 mm higher than that specified in technical documentation allowable deviation from flatness. The gap between the surface of the lining and the calibration plate is controlled along the entire circumference of the outer diameter of the lining.

The test result is taken as the maximum probe size,

which enters the gap between the end surface of the lining and the calibration plate without force to a depth of at least one third of the width of the lining field.

After checking the deviation from flatness for one end surface of the lining, it is turned over, placed on the other end surface, a pressure ring (or pressure rings) is installed on top and the deviation from flatness for the second end surface is controlled in the same way.

Rice. 4.2. Scheme for controlling the deviation from flatness of friction linings\:

1 - calibration plate according to GOST 10905 not lower than the 2nd accuracy class;

2 - friction lining \; 3 - pressure ring made of steel according to GOST 1050, hardness NRSe 57-63\; 4 - zone of control of deviations from flatness (along the entire circumference)

4.1.2. Control by hydrostatic level

One of the simplest and most reliable methods for checking the flatness of objects 1 (see Fig. 4.3) is using a hydrostatic level 2, which consists of two measuring vessels filled with liquid and connected by a hose. The difference in readings of the liquid levels in the vessels is a measure of the deviation from flatness. The mean square deviation of the reading difference at all control points can serve as a quality indicator that characterizes the flatness of the product surface.

The method is applicable for extended objects. However, the size of the object is limited by the curvature of the Earth's surface and the length of the hoses.

Rice. 4.3. Flatness control with hydrostatic level

4.1.3. Control with a spotting scope

Control is carried out with the help of spotting scope 3 (see Fig. 4.4), which has a center indicator, which is set at level 2 and aimed at the target - staff 4 with a length scale. The rail is installed at the specified control points of the object, and each time the readings are determined on the scale of the rail, after which they are statistically processed. The method is applicable for large horizontal objects up to 15,000 mm long, and when taking into account the influence environment and before

100,000 mm. Sometimes a narrow direction is used as a pointer.

ny beam of laser radiation.

Rice. 4.4. Flatness check with spotting scope

TO category:

measurements

Tools for flatness and straightness testing

Measurement is understood as a comparison of the same-name quantity (length with length, angle with angle, area with area, etc.) with a value taken as a unit.

All means of measurement and control used in plumbing, can be divided into control and measuring instruments and measuring instruments.

The first group includes:
– tools for flatness and straightness control;
- plane-parallel end measures of length (tiles);
- line instruments that reproduce any multiple or fractional value of a unit of measurement within the scale (meters, goniometers with vernier);
- micrometric instruments based on the action of a screw pair (micrometers, micrometric inside gauges and depth gauges).

The group of measuring instruments (second group) includes:
- lever-mechanical (indicators, indicator inside gauges, lever brackets, minimeters);
– optical-mechanical (optimeters, instrumental microscopes, projectors, interferometers);
– electrical (profilometers, etc.). The above measuring instruments are accurate, expensive instruments, therefore, when using them and storing them, it is necessary to follow the rules set forth in the relevant instructions.

Curved rulers are made of three types: with a double-sided bevel (YD) 80, 125, 200, 320 and (500) mm long; trihedral (LT) - 200, and 320 mm and tetrahedral (LCh) - 200, 320 and (500) mm (Fig. 365, a-c). Checking straightness with curved rulers is carried out according to the light gap method (through the light) or according to the trace method. When checking straightness using the light gap method, a curved ruler is applied with a sharp edge to the surface to be checked, and the light source is placed behind the ruler and the part. The ruler is held strictly vertically at eye level, observing the gap between the ruler and the surface in different places along the length of the ruler. The presence of a gap between the ruler and the part indicates a deviation from straightness. With sufficient skill, this method of control allows you to catch the gap from 0.003 to 0.005 mm (3 - 5 microns).

When checking by the trace method, the working edge of the ruler is drawn along a clean surface to be checked. If the surface is rectilinear, it will leave a continuous trace; if not, the trace will be discontinuous (spots).

Straightedges with a wide working surface are made of four types (sections): rectangular SHP, I-beam SD, bridges SHM, angular trihedral UT.

Depending on the permissible deviations from straightness, the SHP, ShD and SHM types of calibration rulers are divided into three classes: 0.1 and 2nd, and the UT type rulers are divided into 2 classes: 1st and 2nd. The rulers of the 0th and 1st classes are used for high-precision control work, and the rulers of the 2nd class are used for installation work of medium thickness.

Rice. 1. Curved rulers: a - LD with a double-sided bevel, b - J1T triangular, c - tetrahedral LCH

Rice. 2. Checking with a curved ruler according to the method of a light gap in the light: a - the position of the eye, b - setting the ruler, 1 - ruler, 2 - plate

Rice. 3. Rulers with a wide working surface: a - rectangular SHP, b - I-beam SD, c - CMM bridge, d - angular trihedral (wedges) UT

Rice. 4. Checking straightness with rulers: a - SD, b - with a CMM bridge using strips of tissue paper

Straightness and flatness are checked with these rulers by linear deviations and by paint (stain method). When measuring linear deviations from straightness, the ruler is placed on the surface to be checked or on two measuring tiles of the same size. The gaps between the ruler and the controlled surface are measured with a probe.

Accurate results are obtained by using strips of tissue paper, which are placed under the ruler at certain intervals. Pulling the strip from under the ruler, the pressing force of each of them is used to judge the magnitude of the deviation from straightness.

When checking for paint, the working surface of the ruler is covered with a thin layer of paint (soot, red lead), then the ruler is applied to the surface being checked and smoothly moved without pressure over the surface being checked. After that, the ruler is carefully removed and the location, number, size of spots on the surface is judged on the straightness of the surface. With good flatness, paint spots are evenly distributed over the entire surface. How more quantity spots on the tested surface of a 25x25 mm square, the higher the flatness. Triangular straightedges are made with angles of 45, 55 and 60°.

Surface plates are mainly used for checking wide surfaces for paint, and are also used as accessories for various control work in the workshop. Plates are made of gray fine-grained cast iron. According to the accuracy of the working surface of the plate, there are four classes: 0.1, 2 and 3rd; the first three classes are calibration plates, the fourth is marking. Checking for paint with surface plates is carried out as described above.

Plates are protected from impacts, scratches, dirt, after work they are thoroughly wiped, lubricated with mineral oil, turpentine or petroleum jelly and covered with a wooden shield (lid).

It is unacceptable to store the SD, SHM and UT rulers leaning against each other, against the wall at a certain angle: they bend and become unusable.

The performance of the surfaces of machine parts in contact with each other is largely determined not only by the given dimensions, but also by the deviation from straightness and flatness.

When measuring flatness, it is determined how much the surface of the machined part deviates from the ideal plane.

The most common straightness measuring instruments are test rulers (GOST 8026-64), which are divided into the following types:

1. Curved rulers: with double-sided bevel (LD), trihedral (LT), tetrahedral (LCh).
2. Rulers with a wide working surface: rectangular section (SHP), I-section (SHD), bridges (SHM).
3. Angular rulers: trihedral wedges (UT).

(Fig. 64, a) with a double-sided bevel (LD) are made of tool alloy steel with high precision and have thin working surfaces, called ribs or blades with a radius of curvature of not more than 0.1-0.2 mm, due to which it is possible to very accurately determine deviations from straightness.

Rice. 64. Lekal rulers:
a - with a double-sided bevel, b - with a wide working surface - a bridge (BM), c - trihedral corner - a wedge (UT)

GOST 8026-64 provides for two accuracy classes of rulers: 0 and 1st, with the 0th class being more accurate.

Checking with a curved ruler is carried out using the light gap method. A ruler is placed on the surface to be checked with a sharp edge and held vertically strictly at eye level, observing the gap between the ruler and the surface in different places along the length of the ruler. The presence of a gap between the ruler and the part indicates a deviation from straightness. With sufficient skill, this method of control allows you to catch the clearance from 0.003 to 0.005 mm.

Rulers with a wide working surface - CMM bridges (Fig. 64,b) according to GOST 8026-64 are made 400 long; 630; 1000; 1600; 2500; 4000 mm, 0, 1 and 2nd accuracy classes. They are used to check the flatness by the method of linear relations and "on the paint". The first method is to determine the gap between the working edge of the ruler and the tested plane. Using thin plates of a probe or tissue paper, the strips of which are not more than 0.02 mm thick are placed under the ruler evenly in several places, the gap is measured.

Greater accuracy gives a check for paint. The working surface of the ruler is evenly covered with a thin layer of paint (soot, red lead) and then it is smoothly moved without pressure with two or three circular movements over the surface to be checked, after which the ruler is carefully removed and the straightness of the product is judged by the location and number of spots on the surface. With ideal flatness, the surface of the part is covered with paint evenly. However, any surface has alternating protrusions and depressions, and therefore, the paint falls on the protruding parts.

Trihedral angular rulers - wedges (UT) are used to check for paint planes that are at an angle to each other, and are often used in the repair of machines.

Trihedral corner rulers (Fig. 64. c) according to GOST 8026-64 are made with working angles of 45; 55 and 60° and length 250; 500; 750; 1000 mm, tetrahedral - 630 and 1000 mm long. These rulers are checked for paint.

The verticality and horizontality of a surface are usually measured by a plumb or level. When measuring with a plumb line or level, it is necessary that the measured parts and measuring instruments are at rest.

Levels designed to check the horizontal and vertical position of the surfaces of machine elements during installation.

Bar levels(Fig. 65) is used to control deviations from the horizontal position of surfaces. The metal body of the level has a length of 100; 150; 200 (250) and 500 mm, inside it is placed a glass longitudinal tube - ampoule 2 and an installation (transverse) ampoule 3. Ethyl ether or ethyl alcohol is poured into the ampoules in such a way that a bubble forms. Ampoule 2 has a scale.

Rice. 65. Bar level:

At the scale division value of the main ampoule 2, the movement of the bubble by one division indicates the difference in the levels of these points, equal to 0.02 mm. The price of the division of the level is understood as its slope, corresponding to the displacement of the bubble of the main ampoule by one division of the scale, expressed in mm per 1 m.

In use, the level is applied to the surface to be checked and, moving it in the longitudinal and transverse directions, the amount of deviation from the horizontal position is determined on the scale of the ampoule 2.

Frame levels(Fig. 66) are designed to control the horizontal and vertical position of surfaces.

Rice. 66. Frame level:
1 - case, 2 - longitudinal ampoule, 3 - transverse ampoule

The length of the working surface of the frame levels 100; 150; 200 and 300 mm.

The frame level consists of body 1, main (longitudinal) 2 and mounting 3 (transverse) ampoules. The main scale determines the magnitude and direction of the deviation.

The accuracy of the level is determined on the test plate. The bubble of the main ampoule should show the same position when

The results of measuring the angles of the through cutter

LAB #6

1. Objective:

To study the devices and rules for using measuring instruments for straightness, flatness, horizontality and surface roughness.

2. Work schedule: 1 hour 20 minutes.

3. Workplace equipment:

3.1 Guidelines for this work

3.2 Posters

3.3 Rulers, levels, plates, block head, sleeves, fingers, paint, brush, samples.

4. Theoretical part:

The accuracy of the geometric parameters of parts is characterized not only by the accuracy of the dimensions of its elements, but also by the accuracy of the shape and relative position of the surfaces. Deviations (errors) of the shape and location of surfaces occur during the processing of parts due to inaccuracies and deformations of the machine, tool and fixture; deformation of the workpiece; uneven allowance for processing, etc.

The shape of flat surfaces is characterized by straightness and flatness.

mired area (Fig. 6.1. c.). Particular types of deviations from straightness and flatness are convexity (Fig. 6.1. a.), in which the deviations decrease from the edges to the middle, and concavity (Fig. 6.1 b.) - the nature of the deviations is reversed.

Surface roughness is a set of irregularities with relatively small steps that form the relief of the surface of the part and are considered within the base length.

Horizontal is understood as the position of the tested plane relative to the horizon.

By the value of deviations, flat surfaces are divided into 16 degrees of accuracy in accordance with the established tolerances for flatness and straightness within the normalized area. As the degree of accuracy increases, the size of the tolerance increases.

1) There are four types of curved rulers: with a one-sided bevel from 75 to 125 mm long, with a double-sided bevel from 175 to 225 mm, trihedral 300 and 400 mm long and tetrahedral 500 mm long. Curative lines

ki are divided into two classes 0 and 1.

2) Rulers with a wide working surface are divided into four types: steel rectangular sections from 500 to 2000 mm and cast-iron bridges from 500x4 to 4000x100 mm.

In the repair industry, rulers with a size of no more than 1000 mm are common. The rulers are divided into three classes: 1, 2 and 3.

Angular rulers are used to simultaneously control the flatness and angle between two intersecting surfaces (for example, when checking the "dovetail"). These rulers from 250 to 1000 mm are used for checking "for paint".

Corner rulers have a trihedral section and two scraped planes forming a working angle.

Plates. The surface plate is the main means of checking the flatness of the surface "on the paint". Plates are made of cast iron with dimensions from 100x200 to 1000x1500 mm of four classes: 0, 1, 2 and 3. 0, 1, 2 classes refer to calibration plates, and 3 classes to marking plates. The working surface of the surface plates intended for checking “for paint” must be scraped or cleanly ground, and the marking surface must be planed. Plates are also checked "for paint". Classes 0 and 1 include boards in which the number of spots with a side of 25 mm is at least 25, for boards of class 2 - at least 20, and for boards of class 3 - at least 12. Boards on their surface should not have corrosive spots or shells. Calibration plates are used as a base for various control operations using universal measuring instruments (thickness gauges, indicator racks, etc.).

To control the horizontal, vertical position of the planes of various parts, as well as to check the straightness and flatness of long surfaces, levels are used. They are also used in the installation of equipment and for checking the accuracy of machine tools.

In practice, measurements are most common levels bar (locksmith) and frame GOST 9392-60 (Fig. 6.3 a, b). Bar and frame levels have a body 1 with measuring surfaces 4, the main ampoule 2 and the mounting ampoule 3. The level is set on the surface to be checked using the ampoule 3 so that the ampoule 2 is in a horizontal plane. Ampoule 2 measures the deviation of the surface from horizontal and vertical (only frame level). The ampoule of levels (Fig. 6.4) is a cylindrical tube filled with ether so that an air bubble saturated with ether vapor remains inside the tube. The inner surface of the ampoule is barrel-shaped, so when the level is horizontal, the bubble occupies the upper position.

On the outer surface the ampoule is marked with a scale with a division interval of 2 mm. when tilted, the bubble moves relative to the neutral position (pulpunkta) proportional to the angle of inclination. Ampoule scales change

they give the slope of the level in millimeters, referred to a length equal to 1 m. The division value of the level ampoules is 0.02; 0.05; 0.10 and 0.15 mm-m and the error should not exceed ± 0.004, respectively; 0.0075; 0.015 and 0.02 mm. The slope of the level surface by 0.01 mm corresponds to an angle of 2 degrees.

You can use the formula: Eº = 200 Ƭ· n, where Ƭ is the division value in (mm-m), and n is the number of divisions by which the bubble will move.

The limit of permissible error of frame and bar levels when installed with their base on a horizontal plane or on a horizontally located cylinder, as well as when installing a frame level (any of its vertical working surfaces along a vertical plane or vertical cylinder) is equal to the deviation of the main ampoule from the middle (zero) position 1-4 divisions.

When installing the frame level with the upper side of the body on a horizontal surface or a horizontal cylinder, the margin of error is ½ of the division of the ampoule. The levels at the price of the main ampoule are classified (according to GOST 9392-60) as follows:

Optical quadrants are devices in which a goniometer is connected to a level. They are designed to measure the angles of inclination of flat and cylindrical surfaces of various products.

Surface roughness - a set of surface irregularities with relatively small steps forming a surface relief of the part, highlighted at the base length ℓ.

The surface roughness of the product is evaluated by comparing it with roughness samples.

For this purpose, flat or cylindrical specimens are usually used.

work surface. They are made of steel, cast iron, brass and other materials, processed with different surface roughness. Samples from the same material and the same type of processing are mounted in a special metal frame. The frames are completed in a set, and for each material and type of processing, samples of different accuracy classes are selected that can be obtained with this type of processing.

Comparison of the surfaces of the product and samples is usually made by inspection or by touch, running a fingernail across the traces of processing. Touch control has some advantage over eye inspection. Both methods are able to provide a reliable assessment within 3-5 roughness classes. Comparison accuracy can be increased up to 8 roughness class if a magnifying glass of 4-6 times magnification is used.

Contact measurements of roughness are carried out by continuous probing of the surface of the product - using a profilometer (due to the movement of the diamond needle).

5. The order of the work.

5.1 Checking straightness by the method of the light gap (through the light) or by the trace method.

To improve the accuracy of observations, it is necessary to create sufficiently bright and uniform illumination of the slit on the other side of the ruler. The lumen sample is made from a micron gauge block set, a finished bar with a wide working surface and a curved ruler. Two identical measures are installed on the bar (along the edges), and end measures of such dimensions are placed between them so that a gap is created with an increase in clearance 1, 2, 3, etc. microns to the required maximum clearance. Measurement error at-

measured 1-3 microns.

When checking by the trace method, the working edge of the ruler is carried out along a clean, finished surface of the product. After that, a thin light trace remains on the surface of the controlled product. If the surface has a non-flatness, then the trace will be discontinuous. When checking the plane, it is necessary to install the curved ruler sequentially in several positions and determine the deviations from straightness in each direction.

5.2 When measuring by the method of linear deviations, the ruler is placed on two identical supports located on the surface to be checked, and the distances from the ruler to the surface are determined using gauge gauge probes or a special device with a measuring head. The supports are placed at a distance of 0.21 of the length of the ruler from its ends.

When measuring by the “on the paint” method, the working surface of the ruler is covered with a thin layer of paint. Then the ruler is applied to the surface to be checked. The ruler is informed of the longitudinal movement and the flatness is determined by the location of the spots. Since the surface being checked practically consists of hills and depressions, paint also remains on the hills. With good flatness of the product, the spots are evenly distributed over the entire surface. Consequently, the number of spots on a given area will accurately characterize the flatness. For the calculated area, on which the nature of the distribution of spots is considered, a square with a side of 25 mm is taken.

For metalworking machines, at least 9 spots are allowed on the specified square, for plates and fixtures - 16, for control plates and precision machines - 25, for measuring instruments 30 spots.

The number of spots for various surfaces are given in table 6.1.