Popular wisdom says: “Measure twice, cut once,” and, despite the fact that this saying has long been perceived exclusively in an allegorical sense, it still does not lose relevance in the literal sense.
Man began to use various methods of measurement from ancient times, starting from elbows and knees, and then rulers and pointer measuring instruments, to modern control and measuring instruments.
It is used not only in various production and construction processes, but also at the household level: a ruler, tape measure, square, building level and is found in almost every home. After all, good measuring instruments allow you to make any measurement quickly and accurately.
The list of professional control and measuring instruments is quite wide, but a number of them are constantly used in ordinary homes where construction, repairs or improvement of home comfort are being carried out.
Ruler
The simplest measuring instrument is . It is a flat plate with marked divisions that are multiples of the length unit. The ruler is used for geometric constructions, linear measurements and calculations. For geometric constructions, straight, triangular and curly rulers are used. To check the straightness and flatness of surfaces, a straight edge is used, and a scale ruler is used to convert dimensions from one scale to another, and metal rulers are used to mark straight lines on products.
Yardstick
Used to measure large lengths and diameters. A measuring tape with a level will help not only measure the distance, but also determine the slope of the surface. The tape measure may have a magnetic tip, which will make your work much easier. When choosing, you should pay attention to the body of the tape measure and give preference to non-slip plastic or rubber. Such a tool will not slip out of your hands, and will not break if dropped. You also need to check the presence and quality of the stopper so that the tape measure does not curl up at an unnecessary moment. The measuring tape must also be carefully selected; it must have a suitable width (the longer, the wider).
There should be no gaps between the tip and the beginning of the applied divisions; the numbers themselves must be under a wear-resistant layer to avoid rapid wiping.
Compass
Compasses are used to mark and measure circles.
A compass with an adjustable screw can be used both for measuring and marking parts, especially when you need to divide a segment into several equal parts.
To measure external dimensions use calipers, for measuring internal dimensions – bore gauge, and for marking circles of large diameter – rod compass. These tools are also used to check the dimensions applied to the parts.
Vernier tools
Used to measure linear dimensions that do not require 100% accuracy. Measurement in vernier tools is based on the use of a vernier, which allows you to count fractional divisions of the main scale.
Special-purpose caliper tools are widely used for measuring grooves on external and internal surfaces, grooves, grooves, the distance between the axes of holes, small diameters, pipe wall thickness, etc. The design of different vernier tools differs in the shape of the measuring surfaces and their relative position. The vernier tool can be equipped with auxiliary measuring surfaces and devices to expand functionality (measurement of heights, ledges, etc.).
Calipers
A universal tool designed for high-precision measurements of external and internal dimensions, as well as hole depths. This is one of the most popular and sought after metric instruments due to its simple design, ease of use and ease of use. The service life, as a rule, is not limited, so you need to be very careful and picky when choosing this tool.
Vernier calipers are the main “measurement” in production. It has amazing versatility and is indispensable in every workplace. One tool for measuring the length of the part, the height of the ledge, the diameters of the hole and shaft, the width of the groove, the depth of the hole - all the capabilities of a caliper cannot be listed. Some main applications of ShTs-I type calipers are shown in the figures:
Shtangenreysmas
In fact, a vernier caliper mounted in a vertical plane on the base. It is used for marking parts, measuring the height, depth of holes and the location of surfaces of body parts.
Vernier depth gauge
Similar to a caliper, but does not have movable jaws on the rod. Designed to measure the depth of grooves and the height of ledges. The tool consists of a rod with markings, a frame with a vernier and a screw. The working part of the depth gauge rod is inserted into the groove to be measured, the frame is lowered all the way and fixed, and then readings are taken. The frame division price, like that of a caliper, is 0.5 mm, and - 0.02 mm. Micrometric, designed for measuring extremely small depths.
To obtain reliable measurements with any type of barbell tool, when measuring parts, do not allow strong clamping, as the slider may become skewed; in order to avoid skew of the legs, it is important to prevent loosening of the fit and movement of the slider on the barbell.
Micrometer
When the accuracy of measurements of caliper tools is not enough, they are used. Its operating principle is quite simple. The tube connected by a bracket to a fixed heel has an internal thread into which a screw is screwed, smooth on one side (spindle), and the other screw is connected to the drum. If you turn the drum one full turn of 50 divisions, the tube moves closer (removed) to the heel by one pitch of the screw thread (0.5 mm). When measuring, the part is clamped between the heel and the spindle, and turning the drum by one division leads to the spindle moving relative to the heel by 0.01 mm.
Goniometer
Designed for measuring the external and internal angles of parts by direct assessment; it is necessary, first of all, when carrying out carpentry and construction work. Using various types, you can measure the front and rear, outer and inner corners. A universal (adjustable) protractor can handle all types of angles. Protractors are either mechanical or digital. Mechanical ones can be equipped with bubble or spirit levels, as well as a tape counting device.
Test leads
Designed for measuring gaps. The principle of their use is simple - the possibility of the plate passing through the gap is checked. Based on thickness, they are divided into wedge and flat (when using the wedge variety, the feeler gauge is carefully inserted into the gap until it stops, then the resulting thickness value is verified on the body). When measuring gaps, it is preferable to use a set of feeler gauges.
Measurements are taken until the alignment plate barely enters, and the next one does not.
Thickness gauge – a device for determining the thickness of the applied coating. can measure not only the thickness of paint, but also determine the thickness of the film of liquid or dry powder mixture covering the surface.
Thickness gauges
Can be mechanical or electronic. Mechanical meters are practically no longer used, since measurements require destruction of the coating. Modern electronic thickness gauges are mainly divided into magnetic, digital and ultrasonic. All of them are easy to use, have a high degree of accuracy and a low error value.
Building level
A tool that no construction project can do without. It allows you to determine surface deviations from horizontal or vertical. The choice of this tool must be approached very carefully to eliminate the slightest deviations.
Verticality on high objects is established using an ordinary plumb line - a weight on a cord. And with the help of a plumb line - a spirit level (the weight is made in the shape of an isosceles triangle), you can check the horizontalness of the surface.
Test plates
Designed for checking the plane and for use as an auxiliary device for various control and marking work.
Also used as a mounting surface for assembly, measurements and verification.
To mark workpieces in carpentry practice, a scraper, a marking comb and a thicknesser are often used.
In addition to them, in practice various templates, patterns and other devices are used to speed up marking, but they are usually used in professional activities.
Otvoloka
Designed for applying marking lines to the edge of the workpiece. This is a large block with a bevel on one end and a protrusion with a nail driven in at the other. The lines are marked on the surface with the sharp end of this nail.
Marking comb (bracket)
Allows you to immediately make the required number of marks on several workpieces for subsequent selection of grooves.
To do this, make a wooden block with a selected quarter at the end and drive pins into it, according to the planned marks.
Reismus
Designed for marking parallel lines relative to the edge of the workpiece. In the thicknesser block, bars with sharp pins are moved and fixed in a certain position, with which markings are made. Thicknessers are made of both wood and metal with a metric scale applied to measure the extension of the marking pins.
In general, working with even the simplest measuring instruments requires great skill and special attention, not to mention particularly complex instruments. When taking measurements with any even high-precision equipment, no one is immune from errors.
Before taking measurements, you must make sure that all measuring surfaces are smooth, without potholes or bends. The main reasons leading to errors are the incorrect use of tools, the use of damaged or poor-quality devices, contamination of working surfaces and incorrectly selected temperature conditions for measurements (optimum 200C). In order for the tools to serve for a long time and properly, at the end of the work they are thoroughly wiped, if necessary, lubricated, the stoppers are loosened and the measuring surfaces are slightly moved apart. To avoid deformation, store any The measuring instrument needs to be kept in a dry and warm place.
The measuring tool is used to determine the parameters of parts. Experts distinguish between universal, scale, precision, and scaleless control and measuring instruments and instruments.
Ruler, meter, protractor - these are the main universal units designed to determine various parameters (length, width). If it is necessary to measure individual elements of a part, then additional construction tools are used (thicknesser, calipers, bore gauge). The choice of device depends on the type of work to be done. Experts distinguish the following types of measuring instruments:
- workers (used in workshops);
- control (check working devices).
When carrying out measuring work, you can get an inaccurate result. This is due to the imperfection of marking tools and the measuring method used. The deviation of the obtained value from the actual value is an accurate measurement, and the magnitude of the deviation is the degree of accuracy of the measurement.
To obtain reliable results, it is recommended to use high-quality testing and measuring instruments. A steel ruler can be used to determine very short lengths. This device allows you to obtain a measurement accuracy of 0.25-0.5 mm.
If it is necessary to measure a long distance, then use a steel or wooden hand-held measuring tool. Steel meters are presented in the form of tape measures. Unfortunately, the hinge joint of such devices quickly becomes loose. In this case, the measuring instrument will need to be repaired. Experts recommend measuring parts using a tape measure (length 1-2 m).
To accurately determine the length or diameter, use a caliper or caliper gauge. This measuring and marking tool consists of a rod, movable and fixed jaws, and a slider. If necessary, you can use a caliper with a depth gauge. The last part of the tool is located on the jaw frame.
Specifications
A micrometer is used to carry out measuring work with an accuracy of up to 0.01 mm. By rotating the sleeve, the spindle is set to the required value. A division scale is provided on the tube and sleeve. A micrometer gauge is used to determine the diameter of the hole. Experts include the following main parts of the device:
- sleeve;
- tip;
- tube with division scale.
Tools for marking and measuring angles include a protractor. Such a device is made with or without a vernier. The angle is measured with an accuracy of 2 degrees. A carpenter's tool for measuring angles consists of a half-disk with a ruler and a square. The devices of the Caliber plant are an arc with a degree scale along which a vernier and a plate move. The last part is equipped with a holder with which the square and ruler are fixed. The degree scale is designed for 130 degrees. Carpentry tools are used to mark angles from 0 to 320 degrees (while maintaining an accuracy of 2 degrees). To calculate the angle, take into account which divisions the zero is located between.
Bore gauge and caliper are auxiliary marking tools that are used to determine various quantities by transferring the size from the measuring device to the product, or vice versa. A caliper is a carpenter's marking tool. Its legs are connected to each other by hinges.
A surface thicknesser is a precision measuring device that is used when drawing parallel lines on a part or to mark and measure inaccessible parts of a part using other devices. The device stand is mounted on a special stand.
Additional devices
To determine the thread pitch, experts advise using a set of thread gauges. You will first need to select the comb profile to the angle of the thread profile. If necessary, additionally measure the outer diameter of the product. To do this, use a caliper. If the received data matches, then the number of threads or pitch is determined correctly. To make accurate measurements, an instrumental microscope is used.
- functionality (calculation of room area, built-in calculator, measurement memory);
- reliability;
- repair;
- high measurement accuracy (1.5-2 mm);
- long distance measurement (up to 200 m).
The laser tape measure is equipped with an optical or digital sight, level and inclinometer. For carrying out measuring work, experts recommend using only serviceable devices. If necessary, the controller of measuring instruments and special tools will calibrate and check the technological equipment of the measuring instruments. Experts identify the following methods for checking marking tools:
- without using comparison tools;
- comparison of the used unit with a model analogue using a comparator;
- direct and indirect measurement.
Initial verification is carried out after production and repair of the device.
Each instrument in use undergoes periodic verification.
To confirm the suitability of the product, an extraordinary verification is carried out.
To control the quality of the primary or periodic methodology, inspection verification is performed. This procedure is carried out by state supervision or departmental control.
If necessary, the measuring instrument is repaired. To control a measuring instrument for its suitability for use in world practice, calibration is used. In a special laboratory, measuring instruments are calibrated to determine and confirm their characteristics and functions. The result obtained is certified by the appropriate sign (it is applied to the measuring device) or by a certificate and an entry in the operational documentation.
The correctness of the required dimensions and shape of parts during their manufacture is checked using a line (scale) measuring instrument, as well as straight edges, plates, etc.
Therefore, in addition to a standard set of working tools, a mechanic must have control and measuring tools. These include: scale ruler, tape measure, calipers and bore gauges, calipers, square, measuring rod, protractor, protractor, straight edge, etc.
The scale bar has division lines located from each other at a distance of 1 mm, 0.5 mm and sometimes 0.25 mm. These divisions make up the measuring scale of the ruler. For the convenience of measuring dimensions, each half-centimeter scale division is marked with an elongated stroke, and each centimeter division with an even more elongated stroke, above which a number is placed indicating the number of centimeters from the beginning of the scale. A scale ruler is used to measure external and internal dimensions and distances with an accuracy of up to 0.5 mm, and with experience, up to 0.25 mm. Scale bars are made rigid or elastic with a scale length of 100, 150, 200, 300, 500, 750 and 1000 mm, a width of 10–25 mm and a thickness of 0.3–1.5 mm from carbon tool steel grades U7 or U8.
Measurement techniques using a scale bar are shown in Fig. 9.
Rice. 9. Scale metal rulers and methods of measuring them
The tape measure is a steel tape, on the surface of which there is a scale with a division value of 1 mm (Fig. 10). The tape is enclosed in a case and is pulled into it either by a spring (self-rolling tapes), or by rotating a handle (simple tapes), or pushed in manually (grooved tapes). Self-rolling and grooved tape measures are manufactured with scale lengths of 1 and 2 m, and simple ones with scale lengths of 2, 5, 10, 20, 30 and 50 m. Tapes are used to measure linear dimensions: length, width, height of parts and distances between their individual parts parts, as well as the lengths of arcs, circles and curves. When measuring the circumference of the cylinder, a steel tape measure is wrapped tightly around it. In this case, the scale division coinciding with the zero division indicates to us the length of the measured circumference. Such methods are usually used when it is necessary to determine the length of the sweep or the diameter of a large cylinder, if direct measurement is difficult.
Rice. 10. Roulettes:
a – push-button self-collapsing, b – simple, c – grooved, manually pushed in
To transfer dimensions to a scale bar and control the dimensions of parts during their manufacture, calipers and bore gauges are used.
Calipers are used to measure the external dimensions of parts: diameters, lengths, thicknesses of shoulders, walls, etc. It consists of two legs 150–200 mm long, curved along a large radius, connected by a hinge (Fig. 11, A). When measuring, take the caliper by the hinge with your right hand and spread its legs so that their ends touch the part being tested and move along it with little effort. The size of the part is determined by placing the legs of the calipers on the scale ruler.
A spring caliper is more convenient (Fig. 11, b); the legs of such a caliper tend to move apart under the pressure of the annular spring, but nut 2, screwed onto a clamping screw 3, mounted on one leg and freely passing through the other, prevents this. By rotating the nut 2 by screw 3 with fine threads, the legs are set to a size that cannot be changed arbitrarily. The measurement accuracy with calipers is 0.25 – 0.5 mm.
Rice. 11. Calipers and bore gauge. Measurement methods
It is made from carbon tool steel U7 or U8, and the measuring ends at a length of 15–20 mm are hardened.
The bore gauge is used to measure internal dimensions: diameter of holes, sizes of grooves, recesses, etc. In Fig. eleven, a, b ordinary and spring bore gauges are shown. Unlike calipers, it has straight legs with bent jaws. The device of the bore gauge is similar to that of a caliper.
When measuring the diameter of a hole, the legs of the bore gauge are spread until they lightly touch the walls of the part and then inserted vertically into the hole. The measured size of the hole will correspond to the actual size only if the bore gauge is not skewed, that is, the line passing through the ends of the legs will be perpendicular to the axis of the hole. The size is measured using a measuring ruler; in this case, one leg of the inside gauge is supported by the plane to which the end face of the measuring ruler is pressed at a right angle, and the size is measured along it (Fig. 11, V). In Fig. 11, d shows the measurement of the spread of the legs of the caliper using a caliper. This ensures greater accuracy (up to ±0.1 mm) than when reading using a ruler.
Bore gauges are made from carbon tool steel U7 or U8 with hardening of the measuring ends at a length of 15–20 mm.
The measurement accuracy that can be obtained using a scale ruler, folding meter or tape measure does not always satisfy the requirements of modern mechanical engineering. Therefore, in the manufacture of critical machine parts, more advanced scale tools are used, which make it possible to determine dimensions with increased accuracy. These tools primarily include calipers.
Vernier calipers are used to measure both external and internal dimensions of parts (Fig. 12, a). It consists of a rod 8 and two pairs of jaws: lower 1 And 2 and upper 3 and 4. Sponges 1 And 4 made integral with frame 6 sliding along the rod. Using screw 5, the frame can be fixed in the required position on the rod. The lower jaws are used for measuring external dimensions, and the upper jaws are for internal measurements. Depth gauge 7 connected to the movable frame 6, moves along the groove of the rod 8 and is used to measure the depth of holes, grooves, recesses, etc. Whole millimeters are counted on the rod scale, and fractions of a millimeter are counted on the vernier scale 9, placed in the frame cutout 6 caliper.
The vernier scale has ten equal divisions over a length of 9 mm; thus, each division of the vernier scale is less than a division of the scale (ruler) by 0.1 mm. When measuring a part with a caliper, first count a whole number of millimeters on the rod on a scale, looking for it under the first stroke of the vernier, and then use the vernier to determine tenths of a millimeter. In this case, mark the division of the vernier, coinciding with the division on the rod. The ordinal number of this division shows tenths of a millimeter, which are added to the whole number of millimeters. In Fig. 12, b three positions of the vernier relative to the rod scale are shown, corresponding to the dimensions: 0.1; 0.5 and 25.6 mm.
Rice. 12. Vernier caliper with measurement accuracy of 0.1 mm
It is often necessary to manufacture parts whose surfaces meet at different angles. To measure these angles, squares, angle gauges, protractors, etc. are used. Squares and angle gauges are the most common tools for checking right angles. 90° steel squares come in a variety of sizes, solid or multi-piece (Figure 13).
Squares are manufactured in four accuracy classes: 0, 1, 2 and 3. The most accurate squares are class 0. Accurate squares with chamfers are called patterned (Fig. 13, A, b). To check right angles, a square is placed on the part being tested and the correct processing of the angle being checked is determined in the light. When checking the outer corner, the square is placed on the part with its inner part (Fig. 13, V), and when checking the inner corner - with the outer part. Having placed one side of the square on the machined side of the part, pressing it lightly, combine the other side of the square with the machined side of the part and judge by the resulting gap the accuracy of the right angle (Fig. 13, d). Sometimes the size of the lumen is determined using probes. It is necessary to ensure that the square is installed in a plane perpendicular to the line of intersection of the planes forming a right angle (Fig. 13, d). In inclined positions of the square (Fig. 13, e, g) Measurement errors are possible.
Rice. 13. Squares with an angle of 90° and methods of their use
Simple fry (Fig. 14, A) consists of a clip 1 and rulers 2 , hingedly fixed between two strips of the cage. The hinged fastening of the holder allows the ruler to occupy a position in relation to the holder at any angle. The mold is installed at the required angle according to the sample of the part or along the corner tiles. The required angle is fixed with a screw 3 with wing nut.
A simple small scale is used to measure (transfer) only one angle at a time.
The universal tool is used to simultaneously transfer two or three corners.
To measure or mark angles, to adjust small tools or determine the magnitude of the angles transferred by them, goniometer tools with an independent angle are used. Such tools include protractors and protractors. Protractors are usually used to measure and mark angles on a plane. Goniometers are simple and universal.
Rice. 14. Simple malka and methods of its use
A simple protractor consists of a ruler 1 and protractor 2 (Fig. 15, a). When taking measurements, the goniometer is placed on the part so that the ruler 1 and bottom edge m protractor shelves 2 coincided with the sides of the measured part 3. The angle is determined by the pointer 4, moving along the protractor scale along with the ruler. A simple goniometer can measure angles with an accuracy of 0.5–1°.
Rice. 15. Goniometers: a – simple, b – optical
The optical protractor consists of a housing 1 (Fig. 15, b), in which a glass disk is fixed with a scale having divisions in degrees and minutes.
The price of small divisions is 10 ". The main (fixed) ruler 3 is rigidly attached to the body. On the disk 5 mounted magnifying glass 6, lever 4 and the movable ruler is strengthened 2 . Under the magnifying glass, parallel to the glass disk, there is a small glass plate on which is a pointer, clearly visible through the eyepiece of the magnifying glass. Ruler 2 can be moved longitudinally and using a lever 4 secure in the desired position. While turning the ruler 2 the disk will rotate in one direction or the other in the same direction 5 and magnifying glass 6. Thus, a certain position of the ruler will correspond to a very definite position of the disk and magnifying glass. Once they are secured with the clamping ring 7, observing through magnifying glass 6, read the inclinometer readings.
An optical inclinometer can measure angles from 0 to 180°. The permissible errors in the reading of the optical inclinometer are ±5".
Straight edges are used to check planes for straightness. In the process of processing planes, rulers are most often used. They are divided into pattern rulers with a double-sided bevel, triangular and tetrahedral (Fig. 16, a).
Rice. 16. Pattern rulers: a – structural forms of rulers: double-sided, triangular, tetrahedral, b – method of applying a ruler
Pattern rulers are manufactured with high precision and have thin ribs with a radius of curvature of 0.1–0.2 mm, thanks to which it is possible to very accurately determine the deviation from straightness using the light slit method (through transmission). To do this, the ruler is installed with its edge on the surface of the part being checked against the light (Fig. 16, b). Any deviations from straightness will be noticeable between the ruler and the surface of the part. In good lighting, deviations from straightness of up to 0.005-0.002 mm can be detected. Pattern rulers are made from 25 to 500 mm in length from carbon tool or alloy steel with subsequent hardening.
Storage and care of measuring instruments. The accuracy and durability of an instrument depend not only on the quality of workmanship and skillful handling, but also on proper storage and care.
The simplest measuring tool is usually stored in a workbench drawer, where it is arranged in a certain order by tool type and size. Calipers and measuring rulers are stored in special cases with lockable lids. To protect instruments from rust, lubricate them with a thin layer of pure technical petroleum jelly, after wiping them well with a dry cloth. Before using the tool, remove the lubricant with a clean cloth or by washing it in gasoline. If rust stains appear on the instrument, it must be placed in kerosene for a day, then washed with gasoline, wiped dry and lubricated again.
In any case, in every industry, in every sphere of human activity, there are measurements. Most often, this is required by drawings and state standards, sometimes by production or vital necessity. The modern market is filled with the latest control and measuring instruments and tools, including laser ones. But this does not mean that the old, convenient and most frequently used tools are a thing of the past. We’ll talk about it today, let’s try to figure out what types of measuring instruments exist and where they are used.
Classification
A measuring instrument can be classified according to several criteria.
- By type of work. It is impossible to distribute meters with great accuracy into construction, plumbing and carpentry. Many devices are used everywhere. So this classification will be conditional.
- Based on materials, it can be divided into: metal, wood, plastic and combined.
- By method of use: manual, mechanical, automatic.
- By design: simple and complex.
Such a distribution will help to use measuring instruments correctly and ensure their storage in accordance with the rules and regulations.
Construction measuring tool
First of all, this is roulette. The tool is a metal tape with divisions (1 mm pitch), enclosed in a plastic or metal case. Rewinding of the tape can be done manually or using a spring. They come in different lengths and widths. It is incorrect to classify a tape measure only in the construction category; a class called “universal measuring instrument” is more suitable for it.
You can view the varieties, descriptions, characteristics, prices or choose something for yourself by following the link - Construction tapes.
In addition, builders in their work must use:
Mechanic's measuring tool
A locksmith's work usually involves metal. Its tools are used in mechanical engineering and metalworking. It is believed that a mechanic's tool is the most accurate measuring tool. This fact is determined by the specifics and scope of its use, when tolerances range from 0.1 mm to 0.005 mm.
Besides a tape measure or ruler, the main measuring tool is a caliper. With its help, it is convenient to measure the internal and external diameters of holes and control the length of workpieces. It consists of a fixed rod with divisions and a mobile frame. The upper jaws are used to measure the inside of a workpiece or finished product, while the lower jaws measure external parameters.
The list of control and measuring instruments also includes height gauges. It is similar to a caliper, but has a special support. Equipped with measuring and marking stands. Used for marking workpieces, measuring the height, depth of holes, and the location of body elements of parts.
The micrometer is used where accuracy of up to 0.01 mm is required. The device consists of a tube with a scale, a sleeve and a tip. The specified value is set by rotating the sleeve. A type of micrometer is a micrometric depth gauge. Instead of a bracket, it is equipped with a special rod, with which the depth of the holes in the parts is measured.
Carpentry measuring tool
Most control and measurement instruments are universal in nature and are used by craftsmen of various professions. However, there are some that are used only in carpentry workshops. This:
A professional of any level always has measuring tools and devices in his arsenal, without which it is impossible to do a good job. It is important not only to be able to use them correctly, but also to provide decent storage conditions. Tools made of metal and wood should be protected from moisture, plastic tools - from direct sunlight and high temperatures. And it’s best when each item has a cover or a special box.
Any instrumentation requires periodic checks and verifications. Some meters need to be calibrated. The manufacturer indicates this need in the passport for the product or device. A competent attitude towards meters means high-quality work and a long service life of the instrument.
Video
Test instruments and measurement technology
The simplest measuring instruments include a scale ruler, calipers, and bore gauge.
The scale ruler is intended for measuring flat surfaces, as well as for determining dimensions measured with a bore gauge or calipers. Scale rulers are manufactured in different lengths from 100 to 1000 mm. The scale division value is 0.5 or 1 mm; to facilitate counting, every 5 and 10 mm are marked with elongated strokes. The zero division of most rulers is applied at the left end. When measuring, the ruler is applied to the part being measured so that the zero line exactly coincides with the beginning of the line being measured. In Fig. Figure 13 shows how to measure using a scale bar.
Rice. 13. Techniques for measuring with a scale ruler
Calipers are used to measure the external dimensions of parts. The value measured by the calipers is then determined by placing the calipers on the scale ruler. Calipers, like the simplest bore gauge, are rarely used.
A bore gauge is used to measure the internal dimensions of parts. The measured value is also determined using a scale bar.
Vernier calipers belong to multidimensional sliding measuring instruments (Fig. 14, a). It is intended for measuring external and internal dimensions and markings.
Rice. 14. Vernier calipers (a), examples of measuring the size and reading measurements with an accuracy of 0.1 mm (b, c, d)
A caliper consists of a rod with jaws rigidly attached to it, a frame with jaws moving along the rod, a device for micrometric feed, consisting of a slider, a locking screw, a nut and a screw.
The frame is moved as follows. The engine 6 is secured with a locking screw, and the frame locking screw is released. After this, by rotating the nut, the screw and the frame associated with it are slowly moved. The caliper has a vernier.
Calipers are produced with a measurement accuracy of 0.1; 0.05 and 0.02 mm. The last two have a micrometric feed, allowing you to install the caliper with high precision. The leftmost strokes of the vernier and the rod are called zero and when the jaws are closed they coincide. To determine the size to be measured, with the jaws of the caliper apart, count the whole number of millimeters that the left zero vernier stroke has passed along the rod, and then find the vernier stroke that exactly coincides with any division of the rod scale. The ordinal number of this division determines the fractions of a millimeter that should be added to the whole number of millimeters. When measuring internal dimensions, the thickness of the jaws, which is indicated on them, should be added to the reading made on the main scale and vernier. Examples of readings are shown in Fig. 14, b, c, d.
A depth gauge (Fig. 15, a) is used to measure the depth of holes, grooves on shafts, etc. Measurement with a depth gauge is carried out in the same way as with a caliper.
A vernier gauge (Fig. 15, b) is used to measure the thickness of wheel teeth. A vernier gauge is a combined measuring instrument consisting of two fixed rods that form a single unit and two movable verniers. The vertical vernier is designed to set the height at which the tooth thickness should be measured, and the horizontal vernier is designed to measure the tooth thickness at a given height. The measurement accuracy of the caliper is 0.02 mm.
The micrometer is used to measure the external dimensions of parts with an accuracy of 0.01 mm. The most common are micrometers with the following measurement limits: from 0 to 25 mm, from 25 to 50 mm, from 50 to 75 mm and from 75 to 100 mm.
The micrometer (Fig. 16) has a bracket into which a hardened and ground heel is pressed, a micrometer screw, a stopper, a stem, a drum and a ratchet.
Rice. 15. Vernier depth gauge (a), caliper gauge (b):
1 - locking screw, 2 - slider, 3 - micrometer screw, 4 - nut
Rice. 16. Micrometer
The ratchet is connected to the drum by a ratchet, pressed by a spring, and 50 divisions are marked on the left end of the drum, beveled along the circumference. The micrometer screw has a thread with a pitch of 0.5 mm, therefore, for one revolution of the screw, its end moves by 0.5 mm, and when the drum is turned by one division, the screw moves by 0.01 mm. On the surface of the stem there are divisions with an axial stroke.
Rice. 17. Micrometric bore gauge (a), extension to it (b)
To measure a part, it is placed between the micrometer screw and the heel, after which the drum is turned using a ratchet and the screw is pulled out until it comes into contact with the part. When the screw rests on the part being measured, the ratchet will turn freely, and the screw and drum will stop. To determine the measured size, you need to count the number of millimeters on the stem scale, including the half-millimeter division passed by the reference stroke (0.5), and then look at what number on the beveled part of the drum coincides with the axial stroke of the stem. This number will correspond to hundredths of a millimeter, which must be added to the previous data.
Rice. 18. Micrometric depth gauge
Rice. 19. Squares
A micrometric bore gauge (Fig. 17) is used to determine the internal dimensions of parts with an accuracy of 0.01 mm. A micrometric bore gauge consists of a micrometric screw (Fig. 17, a), a drum, a sleeve with a locking screw, and a tip with a spherical measuring surface. There is also a spherical measuring surface on the right side of the micrometer screw. Dimensions are measured in the same way as when measuring with a micrometer.
The micrometer bore gauge has a set of extensions that extend the measurement range. At one end of the extension there is an internal thread (Fig. 17, b), and at the other end there is an external thread. The end of the extension with internal threads is screwed onto the bore gauge stem, and the end of the extension with external threads is used to screw an additional extension onto it in order to increase the measurement limits.
Rice. 20. Universal protractor of the Semenov system
Rice. 21. Goniometer UG-2
The micrometric depth gauge (Fig. 18) is used to measure blind holes and recesses with an accuracy of 0.01 mm. It consists of a base, a drum, a ratchet, a vernier, a stopper, and a measuring rod. The principle of measuring with a depth gauge and a micrometer is the same.
To measure angles, as well as determine the accuracy of filing planes along the “clearance”, squares and universal protractors are used. Squares (Fig. 19) are usually made of steel.
The UG-1 goniometer (Fig. 20) of the Semenov system is universal, designed for measuring external angles. It consists of a base on which there is a scale from 0 to 120°, rigidly connected to a ruler, a movable ruler, a clamp, a removable square, a vernier and a micrometric feed device.
The UG-2 protractor (Fig. 21) consists of a base, a base ruler, a sector, a square, a removable ruler, clamps and a vernier. This protractor can measure external and internal angles.
On the main scale of protractors, degrees are counted, and on the vernier scale, minutes.
Limit gauges for measuring holes are made in the form of double-sided cylinders (Fig. 22) and are called plug gauges, and for measuring shafts - in the form of one-sided and double-sided staples, called gauge gauges (Fig. 23, a, b). Limit gauges can determine the largest and smallest permissible dimensions of parts.
In extreme gauges, one side is called passable and the other is called nonpassable. The go-through side of the plug gauge is used to measure the smallest hole, and the no-go side is used to measure the largest. With a clamp gauge, on the contrary, the largest shaft size is determined by the go-through side, and the smallest by the non-go-through side. When measuring, the pass side of the gauge must pass freely into the hole or along the shaft under the influence of the weight of the gauge. The non-go side of the gauge should not go into the hole or along the shaft at all. If the non-passing side of the gauge passes, the part is rejected.
Radius templates are used to measure the radii of curvatures of products.
Such templates are made in the form of thin steel plates with convex or concave curves. The templates are stamped with numbers showing the size of the radius of curvature in millimeters.
Probes. To measure the size of the gaps between parts, feelers are used (Fig. 24), which are steel plates of various thicknesses. Each plate indicates its thickness in millimeters.
Thread control is carried out using thread plug gauges, threaded rings and templates.
Thread plug gauges (Fig. 25, a) are used to check the threads of nuts. They are made from tool steel and look like a bolt with a precise thread profile. Checking the thread of the nut is done by screwing it onto the go-through or non-go-through side of the plug gauge.
Threaded rings (Fig. 25, b) are used to check the threads of bolts and represent a nut with an exact thread profile. The bolt thread is checked by screwing it into the threaded ring. One ring is a pass-through gauge and the other is a non-go-through gauge.
The thread gauge (Fig. 26) is designed to check and determine the thread pitch on bolts, nuts and other parts. It is a set of steel plates - threaded templates with tooth profiles corresponding to the profiles of standard metric or inch threads. Thread gauges usually have a set of templates with metric threads on one end and inch threads on the other. Each template is marked with thread dimensions.
Rice. 22. Size control with a double-sided plug gauge
Rice. 23. Double-sided (a) and single-sided (b) staple gauges
Rice. 25. Threaded plugs (a) threaded ring (b)
To check the threads on a bolt or nut, you need to apply the thread gauge templates successively until you find a template whose teeth exactly match the threads of the part without clearance. The measured thread will correspond to the size of this template.
The indicator is designed to measure deviations of dimensions from the specified ones, as well as to detect the ovality and taper of shafts and holes. In the repair business, the dial indicator is most widely used, the structure of which is shown in Fig. 27.
The indicator body contains a mechanism consisting of gears, a rack, a spiral spring, a sleeve, a measuring rod with a tip, a speed indicator, and a scale with an arrow. The large scale of the indicator has 100 divisions, each of which corresponds to 0.01 mm. When the measuring rod moves by 0.01 mm, the arrow will move around the circle by one division of the large scale, and when the rod moves by 1 mm, the arrow will make one revolution. The indicator scale is set to the zero position by rotating it by the rim.
Before measuring the product, the indicator is fixed in the bracket of the universal stand (Fig. 28) so that the tip of the measuring rod touches the surface of the product being measured. Next, behind the rim 5, set the zero division of the scale against the arrow (Fig. 27). After this, the product or indicator is slowly moved. The amount of deviation is determined by the arrow readings on the indicator scale.
Rice. 24. Probes
Rice. 26. Thread gauge
Rice. 27. Dial indicator:
1 - measuring rod, 2 - sleeve, 3, 10, 11, 13 - gears, 4 - scale, 5 - rim, 6 - body, 7 - arrow, 8 - speed indicator, 9 - spiral spring, 12 - spring, 14 - measuring tip
Rice. 28. Indicator with universal stand:
1 - the indicator itself, 2 - articulated lever, 3 - stand, 4 - base
Rice. 29 Indicator bore gauge
An indicator bore gauge (Fig. 29) is used to measure the diameters of engine cylinders. A full turn of the indicator needle corresponds to a change in dimension A by 1 mm. Since the scale has 100 divisions, the scale division value is 0.01 mm. The indicator arrow is set to zero by turning the rim. The indicator comes with a set of interchangeable tips that allow you to measure cylinders of various diameters.
Optical measuring instruments. Measuring instruments based on optical measurement principles include optimeters, instrumental microscopes, and various measuring machines.
Pneumatic instruments are used to measure the external and internal surfaces of precision parts, as well as to determine the cleanliness of surface treatment. Pneumatic devices operate on compressed air, which is supplied by a compressor. The advantage of such devices is the simplicity of their design and maintenance.
Electrical measuring instruments make it possible to make measurements with high accuracy. Such devices are based on electrical contact, capacitive and inductive measurement methods.
Measurement errors and their causes. When measuring parts, there is always some difference between the actual size of the part and the size obtained as a result of measurement. The difference between the measured value and the actual value is called error or measurement error.
The main causes of measurement errors are the following:
– inaccurate installation of the measured part or measuring tool;
– errors when taking instrument readings, which occur in cases where observation when taking readings is carried out from the wrong angle of view. It is always necessary to observe in a direction perpendicular to the plane of the scale;
– violation of the temperature conditions under which measurements must be made. The state standard for measurement provides a normal temperature of 20 °C. In practice, the part being measured often has a lower temperature than the temperature of the measuring instrument; this also leads to errors, since it is known that metals change their dimensions when the temperature changes. When cooled they contract and when heated they expand. When heated by 1 °C over a length of 1 m, metals elongate by the following values (mm): steel - 0.012, cast iron - 0.010, bronze - 0.018, brass - 0.019, aluminum - 0.024;
– the surface of the part being measured is dirty or dirty;
- measuring tool;
– errors of the measuring instrument;
violation of the constancy of the measuring force for which the measuring instrument is designed.
Storage and care of measuring instruments. Measuring instruments are stored in dry, warm rooms. Do not store instruments in damp areas or in areas with sudden temperature fluctuations, as this will lead to corrosion of the instruments. Each tool should have its place.
The simplest tools are stored in cabinets, on racks or hung on the walls. Complex instruments, such as micrometers, calipers, gauges, etc., are stored in special cases.
To protect against corrosion, measuring instruments are lubricated with acid-free petroleum jelly or bone oil. For long-term storage, the instrument is wrapped in oiled paper to protect it from contamination and exposure to humid air. Before work, the measuring surfaces of the instrument are washed with gasoline and wiped with a clean rag, and after finishing work they are wiped again, then lubricated and put in their place.
Measuring instruments must be checked regularly using precision test instruments.
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