LLC "KVADRO" For almost a quarter of a century now, it has been, among other things, bushing manufacturer, pulleys, shafts and other products obtained. In addition, we carry out a very wide range of work on manufacturing parts to order according to the Customer's drawings, sketches and samples. Just pick up the phone and call us! Or send a drawing on email or by filling out the form feedback In chapter .

Let's look at what tolerances are using an example production of bushings(their internal holes) or shafts.

The bushing manufacturer is not perfect

Obviously, the bushing manufacturer cannot absolutely accurately fulfill the size indicated on the drawing. Therefore, the designer, based on the requirements for the operation of the mechanism, sets the boundaries within which the dimensions must be made. On the drawing for bushing manufacturer the constructor specifies nominal size and 2 maximum deviations: top and bottom.

The size then looks like this:

This means that the actual size obtained during the manufacturing process of the part according to the drawing must be in the range from 25.160mm to 25.370mm (“within tolerance”).

If one of the maximum deviations is not specified, then it is taken equal to zero. In this example, the allowed sizes are 24,790-25,000.

The choice of manufacturing accuracy of a part largely determines the established requirements for the surfaces of the part. It is also worth mentioning that in addition to size tolerances, there are .

Making bushings on various equipment

The value (for the first example) 0.370-0.160=0.210 is called tolerance. Graphically, the tolerance is depicted as a rectangular shaded area, located as required relative to the line of the nominal size, and is called tolerance zone.

It is obvious that when bushing manufacturing achieving the same tolerance size (eg 0.210mm) with a nominal size of eg 100 times larger (2500mm) is much more difficult. Therefore, the concept is introduced quality(degrees of accuracy): sets of tolerances considered to correspond to the same level of accuracy for different nominal sizes.

Everything is relatively simple: the same quality includes dimensions that are achievable on the same equipment, under the same conditions (for example, cutting conditions). For example, when manufacturing on a lathe, 7-8th grade accuracy is usually achieved, and on a grinding machine – 5-6th.

There are formulas for calculating tolerances for various qualifications, but in practice, designers and technologists when designing and production of bushings, shafts and other parts use tables.

A total of 20 qualifications have been established. The most accurate (with very narrow tolerance fields) 01, 0, 1, 2, 3, 4 are usually prescribed in the manufacture of measuring instruments, grades 5-11 - for mating sizes (by which parts are assembled with each other), grades 12- 18 (with the widest tolerance margins) - for non-matching sizes.

Deviations from the nominal size in the production of bushings and shafts

The quality of a given nominal size uniquely determines the width of the tolerance field. But the position of this tolerance field (its deviation) relative to the nominal size during the manufacture of the bushing (its hole) or shaft is determined by one of 27 standardized deviations, designated by letters of the Latin alphabet.

Hole deviations are indicated in capital letters. When hole sizes deviate from A to H, the tolerance fields are above the line of the nominal size (the bushing will hang on the shaft exactly corresponding to the nominal diameter), from K to ZC - below the line, J s - symmetrically to this line.

Shaft deviations are indicated in lowercase letters. When hole sizes deviate from a to h, the tolerance fields are below the nominal size line (the shaft will hang in a sleeve made with a hole exactly corresponding to the nominal diameter), from k to zc - above the nominal diameter line, j s - symmetrically to this line.

The choice of deviations in the manufacture of bushings and shafts is determined by achieving the required shaft-hole pair.

It should be noted that in the system of tolerances and fits, the term shaft is conventionally used to designate any external (male) elements of parts, which may also be non-cylindrical (for example, the length of a part). A hole is the name given to the internal, enclosing elements of parts, incl. non-cylindrical (for example, groove width).

How to decipher the size of the bushing being manufactured?

This table contains only the most commonly used tolerances. In other cases, you need to refer to more complete reference books

What can we say about the size when we see “25H7” on the drawing? This entry can be deciphered as follows: this size is covering (“hole”) since the letter is capitalized, the nominal size is 25, the quality is 7, the deviation of the tolerance field relative to the nominal size is H. Looking at the table, we will find the area of ​​​​allowed sizes for this element at intersection of the line “St. 24 to 30” and column “H7”: 25,000-25,021.

Designations:

· IT tolerance = International tolerance;

· Upper and lower deviations, ES = Ecart Superieur, EI = Ecart Interieur,

· For holes, large letters (ES, D), for shafts, small letters (es, d).

Hole tolerance zone diagram. According to the drawing - 4 mm, maximum dimensions - 4.1-4.5. In this case, the tolerance field does not cross the zero line, since both limit sizes are higher than the nominal ones.

Basic terms and definitions GOST 25346-89.

· Shaft- a term conventionally used to designate the external elements of parts, including non-cylindrical elements.

· Hole- a term conventionally used to designate the internal elements of parts, including non-cylindrical elements.

· Main shaft- a shaft whose upper deviation is zero.

Main hole- a hole whose lower deviation is zero.

• Actual size- element size established by measurement.
• Limit dimensions- two maximum permissible sizes of an element, between which the actual size must be (or can be equal to).
• Nominal size- the size relative to which deviations are determined.
• Deviation- algebraic difference between the size (actual or maximum size) and the corresponding nominal size.
• Actual deviation- algebraic difference between the real and the corresponding nominal sizes.
• Maximum deviation- algebraic difference between the limit and the corresponding nominal sizes. There are upper and lower limit deviations.
• Upper deviation ES, es- algebraic difference between the largest limit and the corresponding nominal sizes.

Note. ES- upper deviation of the hole; es- upper shaft deflection.

• Lower deviation EI, ei- algebraic difference between the smallest limit and the corresponding nominal sizes.

Note. EI- lower deviation of the hole; ei- lower shaft deflection.

• Main deviation- one of two maximum deviations (upper or lower), which determines the position of the tolerance field relative to the zero line. In this system of tolerances and landings, the main one is the deviation closest to the zero line.
• Zero line- line corresponding to the nominal size, from which deviations of dimensions are plotted when graphic representation fields of tolerances and landings. If the zero line is located horizontally, then positive deviations are laid up from it, and negative deviations are laid down.

· Tolerance T- the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations.

Note. Tolerance is an absolute value without a sign.

· IT standard approval- any of the tolerances established by this system of tolerances and landings.

· Tolerance field- a field limited by the largest and smallest limit sizes and determined by the tolerance value and its position relative to the nominal size. In a graphical representation, the tolerance field is enclosed between two lines corresponding to the upper and lower deviations relative to the zero line.

· Quality (degree of accuracy)- a set of tolerances considered as corresponding to the same level of accuracy for all nominal sizes.

· Tolerance unit i, I- a multiplier in tolerance formulas, which is a function of the nominal size and serves to determine the numerical value of the tolerance.

Note. i- tolerance unit for nominal dimensions up to 500 mm, I- tolerance unit for nominal dimensions St. 500 mm.

Linear dimensions, angles, surface quality, material properties, specifications are indicated.

Tolerance

• Size- numeric value linear magnitude(diameter, length, etc.) in selected units of measurement.
• Actual size- element size established by measurement.
• Limit dimensions- two maximum permissible sizes of an element, between which the actual size must be (or can be equal to).
• Nominal size- the size relative to which deviations are determined.
• Deviation- algebraic difference between the size (actual or maximum size) and the corresponding nominal size.
• Actual deviation- algebraic difference between the real and the corresponding nominal sizes.
• Maximum deviation- algebraic difference between the limit and the corresponding nominal sizes. There are upper and lower limit deviations.
• Upper deviation ES, es- algebraic difference between the largest limit and the corresponding nominal sizes.

Note. ES- upper deviation of the hole; es- upper shaft deflection.

• Lower deviation EI, ei- algebraic difference between the smallest limit and the corresponding nominal sizes.

Note. EI- lower deviation of the hole; ei- lower shaft deflection.

• Main deviation- one of two maximum deviations (upper or lower), which determines the position of the tolerance field relative to the zero line. In this system of tolerances and landings, the main one is the deviation closest to the zero line.
• Zero line- a line corresponding to the nominal size, from which dimensional deviations are plotted when graphically depicting tolerance and fit fields. If the zero line is located horizontally, then positive deviations are laid up from it, and negative deviations are laid down.
• Tolerance T- the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations.

Note. Tolerance is an absolute value without a sign.

• IT standard approval- any of the tolerances established by this system of tolerances and landings.
• Tolerance field- a field limited by the largest and smallest limit sizes and determined by the tolerance value and its position relative to the nominal size. In a graphical representation, the tolerance field is enclosed between two lines corresponding to the upper and lower deviations relative to the zero line.
• Quality (degree of accuracy)- a set of tolerances considered as corresponding to the same level of accuracy for all nominal sizes.
• Tolerance unit i, I- a multiplier in tolerance formulas, which is a function of the nominal size and serves to determine the numerical value of the tolerance.

Note. i- tolerance unit for nominal dimensions up to 500 mm, I- tolerance unit for nominal dimensions St. 500 mm.

• Shaft- a term conventionally used to designate the external elements of parts, including non-cylindrical elements.
• Hole- a term conventionally used to designate the internal elements of parts, including non-cylindrical elements.
• Main shaft- a shaft whose upper deviation is zero.
• Main hole- a hole whose lower deviation is zero.
• Landing- the nature of the connection of two parts, determined by the difference in their sizes before assembly.
• Nominal fit size- the nominal size common to the hole and shaft making up the connection.
• Fit tolerance- the sum of the tolerances of the hole and shaft making up the connection.
• Gap- the difference between the dimensions of the hole and the shaft before assembly, if the hole size is larger than the shaft size

Linear dimensions, angles, surface quality, material properties, technical characteristics

Linear dimensions, angles, surface quality, material properties, technical characteristics are indicated:

To eliminate excessive diversity, it is recommended to bring numerical values ​​into conformity (for example, round calculated values) with preferred numbers. Based on the series of preferred numbers, developed rows of normal linear dimensions(GOST 6636-69) . Normal linear dimensions, mm:

3,2	3,4	3,6	3,8	4,0	4,2	4,5	4,8	5,0	5,3
5,6	6,0	6,3	6,7	7,1	7,5	8,0	8,5	9,0	9,5
10	10,5	11	11,5	12	13	14	15	16	17
18	19	20	21	22	24	25	26	28	30
32	34/35	36	38	40	42	45/47	48	50/52	53/55
56	60/62	63/65	67/70	71/72	75	80	85	90	95
100	105	110	120	125	130	140	150	160	170
180	190	200	210	220	240	250	260	280	300
320	340	360	380	400	420	450	480	500	530
560	600	630	670	710	750	800	850	900	950

Note: Below the slash are the dimensions of the seats for the rolling bearings.

Maximum cone angle deviation

The maximum deviation of the cone angle: 1) if the cone is specified by the taper, it is indicated by the symbols and numerical value degree of accuracy; 2) if the cone is specified by an angle, it is indicated by symbols and a numerical value of the degree of accuracy.

Shape tolerance and surface arrangement

The shape tolerance and location of surfaces are indicated in the form of symbols (graphically with a numerical tolerance value) or text.

Signs of types of tolerances of shapes and surface locations

Access group	Type of admission	Sign
Shape tolerance	Straightness tolerance
	Flatness tolerance
	Roundness tolerance
	Cylindricity tolerance
	Longitudinal profile tolerance
Location tolerance	Parallel tolerance
	Perpendicularity tolerance
	Tilt tolerance
	Alignment tolerance
	Symmetry tolerance
	Positional tolerance
	Axis intersection tolerance
Total shape tolerance and location	Radial runout tolerance, axial runout, beats in a given direction
	Total radial runout tolerance, full axial runout
	Shape tolerance of a given profile
	Shape tolerance of a given surface

Quality

Quality is a measure of accuracy. As quality increases, accuracy decreases (tolerance increases).

Tolerance values ​​for main hole sizes up to 500 mm:

Size, mm	Tolerance, µm for quality
	01	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17
Until 3	0,3	0,5	0,8	1,2	2	3	4	6	10	14	25	40	60	100	140	250	400	600	1000
3-6	0,4	0,6	1	1,5	2,5	4	5	8	12	18	30	48	75	120	180	300	480	750	1200
6-10	0,4	0,6	1	1,5	2,5	4	6	9	15	22	36	58	90	150	220	360	580	900	1500
10-18	0,5	0,8	1,2	2	3	5	8	11	18	27	43	70	110	180	270	430	700	1100	1800
18-30	0,6	1	1,5	2,5	4	6	9	12	21	33	52	84	130	210	330	520	840	1300	2100
30-50	0,6	1	1,5	2,5	4	7	11	16	25	39	62	100	160	250	390	620	1000	1600	2500
50-80	0,8	1,5	2	3	5	8	13	19	30	46	74	120	190	300	460	740	1200	1900	3000
80-120	1	1,5	2,5	4	6	10	15	22	35	54	87	140	220	350	540	870	1400	2200	3500
120-180	1,2	2	3,5	5	8	12	18	25	40	63	100	160	250	400	630	1000	1600	2500	4000
180-250	2	3	4,5	7	10	14	20	29	46	72	115	185	290	460	720	1150	1850	2900	4600
250-315	2,5	4	6	8	12	16	23	32	52	81	130	210	320	520	810	1300	2100	3200	5200
315-400	3	5	7	9	13	18	25	36	57	89	140	230	360	570	890	1400	2300	3600	5700
400-500	4	6	8	10	15	20	27	40	63	97	155	250	400	630	970	1550	2500	4000	6300

see also

Notes

Literature

• A. I. Yakushev, L. N. Vorontsov, N. M. Fedotov. Interchangeability, standardization and technical measurements. 6th ed., revised. and additional.. - M.: Mashinostroenie, 1986. - 352 p.

Links

• The quality and roughness of the surfaces of holes and shafts in the hole system depending on the accuracy class

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Synonyms:

See what “Tolerance” is in other dictionaries:

- (RECOGNITION) the fact of recognition of the company's shares on the stock exchange. Setting the stock price. From this moment the shares begin to be listed on the stock exchange. Dictionary of financial terms. Permission Permission is a user attribute that allows access to all sensitive information... Financial Dictionary

Permissible deviation, tolerance, maximum size, allowance; permission, admission, admission Dictionary of Russian synonyms. admission see admission Dictionary of synonyms of the Russian language. Practical guide. M.: Russian language. Z. E. Alexandrova ... Synonym dictionary

- (entry) Admission to the market of a new supplier. The new supplier may be a newly established firm or a firm that has previously operated in other markets. Sometimes it is possible to join new market, starting all over from scratch. However… … Economic dictionary

Interchangeability of smooth cylindrical joints.

Smooth cylindrical joints are divided into movable and fixed.

Movable joints must create a guaranteed minimum gap between the shaft and the hole, ensuring fluid friction, the specified load-bearing capacity of the bearing and maintaining the specified type of friction as the gap increases.

Fixed connections must ensure accurate centering of parts and transmission of a given torque or axial force during operation due to guaranteed tension or additional fastening of parts with keys, screws, etc. in case of using transitional landings.

Transitional landings– these are fits that can have both small gaps and slight interference. In transitional landings, fixed connections can only be achieved through the use of additional fastening.

Any type of connection (fit) can be obtained by using a system of tolerances formalized in the form of standards. This tolerance system allows for mass production of parts that ensure good assembleability and interchangeability.

Based on the fact that parts up to 500 mm in size are used in tractor, automotive and agricultural engineering, the standard provides for an appropriate system of tolerances and fits within this interval.

Regardless of the type of connection, it must be made in one of two systems: a hole system or a shaft system.

Qualities

Quality, in another way, accuracy class (from the French gualite - quality) is a set of tolerances that vary depending on the nominal size so that the level of accuracy for all nominal sizes remains the same.

In the ISO system, for sizes up to 3150 mm, 18 qualifications are established: 01;0;1;..16. The CMEA system provides 19 qualifications for sizes from 1 to 10,000 mm (17 have been added).

Quality is characterized by the size tolerance and the difficulty of obtaining the size regardless of the diameter.

The tolerance is established depending on the nominal size and quality. Qualifications are designated by the letters IT and the serial number 01, 0.1, 2..17. For example: IT 5; IT 9; IT 16. Qualifications applied:

IT 01; IT 0; IT 1 - for the production of gauge blocks;

IT 2; IT 3; IT 4 - for calibers;

IT 5…IT 13 - for the formation of landings;

IT 14…IT 17 - for non-critical non-mating surfaces;

Application of precision grades in connections (fittings)

Quality	Application
5–6	critical connections in machine tool and engine building (high-precision gear wheels, spindle and instrument bearings in housings and on shafts)
6-7	connections such as piston - sleeve, gears on shafts, rolling bearings on the shaft and in the housing
7, 8, 9	precision connections in tractor construction and critical components of agricultural machinery
	for reduced accuracy requirements, as well as in connections where calibrated shaft material is used
	movable joints of agricultural machines with large gaps and significant fluctuations (rough assembly), as well as covers, ring flanges...
12-13	motionless welded joints agricultural machinery (ploughs, seeders, etc.)

Correctly assigning quality is no less important than calculating the dimensions of the part. The purpose of the quality is related to the accuracy and operational purpose of the mechanism, as well as the nature of the required landings.

When choosing manufacturing accuracy (quality), it is also necessary to take into account economic feasibility. Manufacturing parts to extended tolerances does not require large costs and reduces the likelihood of defects, but this reduces the reliability of the design (there is a large variation in clearances and interference) and, as a consequence, the durability of the machine.

Machines generally fail not due to destruction, but due to loss of performance caused by a decrease in the accuracy of assembly of components and assemblies.

Relationship between accuracy and cost of manufacturing parts

For qualifications from 5 to 17, tolerance values ​​are determined based on the tolerance unit i µm, which characterizes the pattern of tolerance changes depending on the diameter. For sizes up to 500 mm

where d avg in mm, i in µm.

The tolerance is expressed by the formula

Where A- the number of tolerance units, constant for a given quality, independent of the nominal size.

The values ​​of the number of tolerance units for qualifications from 5 to 17 are presented in the table.

Table Values ​​of tolerance units for qualifications IT5…IT17

Quality is characterized by the size of the tolerance. When moving from one quality to another, tolerances increase geometrically with a denominator of 1.6.

Changing tolerances when quality changes

Every five qualifications, starting from IT 5, tolerances increase approximately 10 times.

Main deviations

To create fits with various clearances and interferences, CMEA standards establish 27 main deviations for holes and shafts. They are designated capital letter Latin alphabet for holes and lowercase for shafts. Let us consider in the diagram the position of the tolerance fields of holes and shafts relative to the zero line.

Basic deviations of holes and shafts in the JSO system.

Deviations from A to H (from a to h) are intended to form tolerance fields in fits with gaps; from Js to N (from js to n) - in transitional landings; from P to Zс (from p to z с) - in interference fits. For holes and shafts designated by the letters Js and js, the tolerance field is strictly symmetrical relative to the zero line, and the maximum deviations are equal in magnitude, but have the opposite sign.

Main deviation is the deviation closest to the zero line. For all tolerance fields located above the zero line, the main one is the lower deviation (EI or ei); for tolerance fields located below the zero line - upper deviation (ES or es). The tolerance fields of the same name for holes and shafts are located strictly symmetrically relative to the zero line and their maximum deviations are the same, but opposite in sign (with the exception of transitional fits).

For landings A to H, EIs are known

For landings from J to ZC ES are known

The main deviation of the hole must be symmetrical to the zero line of the main deviation of the shaft, indicated by the same letter. It does not depend on the quality, i.e. it is a constant value for tolerance fields of the same name.

The upper (if the tolerance field is located above the zero line) or lower (if the tolerance field is located below the zero line) deviation is determined by the value of the main deviation and the tolerance of the selected quality.

Concepts - “hole system” and “shaft system”

The standards establish two equal landing systems: the hole system (SA) and the shaft system (SV).

As can be seen from the figure, the main hole in the hole system has a lower deviation EJ equal to zero. This is distinctive feature hole systems.

Formation of landings in the hole system

In the hole system, the hole is the main part and, regardless of the fit, is processed to the nominal size (with tolerance to the body of the part), and different fits are obtained by changing the maximum dimensions of the shaft.

In the shaft system, the shaft is the main part and, regardless of the fit, is processed to the nominal size (with tolerance to the body of the part), and different fits are obtained by changing the limiting dimensions of the hole.

Formation of landings in the shaft system

As can be seen from the figure, the main shaft in the shaft system has an upper deviation es equal to zero. This is a distinctive feature of the shaft system.

In the ISO system of tolerances and fits, a one-sided maximum location of the tolerance field of the main part relative to the nominal mating size is accepted. Therefore, if the tolerances are specified in the hole system, then the lower hole deviation will always be zero (EI=0), and if the tolerances are specified in the shaft system, then the upper shaft deviation will always be zero (es=0) regardless of the fit.

In other words, fits in the CA hole system are fits in which various clearances and interferences are obtained by connecting different shafts to the main hole. These landings are usually designated by the letter “N”.

Fitments in the SV shaft system are fits in which various clearances and interferences are obtained by connecting various holes with the main shaft. These landings are usually designated by the letter “h”.

Selecting a planting system.

The fit is formed by a combination of the tolerance fields of the hole and the shaft. For economic reasons (reducing the unreasonable variety of fits, systematizing cutting and measuring tools for holes, etc.), it is recommended to use two standardized equal fit systems: the SA hole system and the SV shaft system. These systems are equivalent, but are used in industry to varying degrees. For work, it makes absolutely no difference in which system the fit is assigned (with clearance, interference, or transitional fit); its specific value is important. From a technical point of view, mounting holes in the system is preferable. Shaft, i.e. The outer surface is much easier to process and control than the inner surface - the hole. To make holes, a dimensional cutting tool: countersink, broach, reamer, etc. a certain standard size, a complex measuring instrument, which increases the cost of the part. Therefore, the hole system is mainly used.

The shaft system is generally used in three cases:

1) if the shafts are made of calibrated rod material without additional processing of the seats;

To main

section four

Tolerances and landings.
Measuring tool

Chapter IX

Tolerances and landings

1. The concept of interchangeability of parts

In modern factories, machine tools, cars, tractors and other machines are produced not in units or even in tens or hundreds, but in thousands. With such a production scale, it is very important that each part of the machine fits exactly into its place during assembly without any additional fitting. It is equally important that any part entering the assembly allows its replacement by another of the same purpose without any damage to the operation of the entire finished machine. Parts that satisfy such conditions are called interchangeable.

Interchangeability of parts- this is the property of parts to take their places in units and products without any preliminary selection or adjustment in place and perform their functions in accordance with the prescribed technical conditions.

2. Mating parts

Two parts that are movably or stationarily connected to each other are called mating. The size by which these parts are connected is called mating size. Dimensions for which parts are not connected are called free sizes. An example of mating dimensions is the diameter of the shaft and the corresponding diameter of the hole in the pulley; an example of free sizes would be outside diameter pulley

To obtain interchangeability, the mating dimensions of the parts must be accurately executed. However, such processing is complex and not always practical. Therefore, technology has found a way to obtain interchangeable parts while working with approximate accuracy. This method is for various conditions work parts install permissible deviations its dimensions, at which flawless operation of the part in the machine is still possible. These deviations, calculated for various operating conditions of the part, are built in a specific system called admission system.

3. Concept of tolerances

Size specifications. The calculated size of the part, indicated on the drawing, from which deviations are measured, is called nominal size. Typically, nominal dimensions are expressed in whole millimeters.

The size of the part actually obtained during processing is called actual size.

The dimensions between which the actual size of a part can fluctuate are called extreme. Of these, the larger size is called largest size limit, and the smaller one - smallest size limit.

Deviation is the difference between the maximum and nominal dimensions of a part. In the drawing, deviations are usually indicated by numerical values ​​at a nominal size, with the upper deviation indicated above and the lower deviation below.

For example, in size, the nominal size is 30, and the deviations will be +0.15 and -0.1.

The difference between the largest limit and nominal sizes is called upper deviation, and the difference between the smallest limit and nominal sizes is lower deviation. For example, the shaft size is . In this case, the largest limit size will be:

30 +0.15 = 30.15 mm;

the upper deviation will be

30.15 - 30.0 = 0.15 mm;

the smallest size limit will be:

30+0.1 = 30.1 mm;

the lower deviation will be

30.1 - 30.0 = 0.1 mm.

Manufacturing approval. The difference between the largest and smallest limit sizes is called admission. For example, for a shaft size, the tolerance will be equal to the difference in the maximum dimensions, i.e.
30.15 - 29.9 = 0.25 mm.

4. Clearances and interference

If a part with a hole is mounted on a shaft with a diameter , i.e., with a diameter under all conditions less than the diameter of the hole, then a gap will necessarily appear in the connection of the shaft with the hole, as shown in Fig. 70. In this case, landing is called mobile, since the shaft can rotate freely in the hole. If the size of the shaft is, that is, always larger than the size of the hole (Fig. 71), then when connecting the shaft will need to be pressed into the hole and then the connection will turn out preload

Based on the above, we can draw the following conclusion:
the gap is the difference between the actual dimensions of the hole and the shaft when the hole is larger than the shaft;
interference is the difference between the actual dimensions of the shaft and the hole when the shaft is larger than the hole.

5. Fit and accuracy classes

Landings. Plantings are divided into mobile and stationary. Below we present the most commonly used plantings, with their abbreviations given in parentheses.

Accuracy classes. It is known from practice that, for example, parts of agricultural and road machines can be manufactured less accurately than parts of lathes, cars, etc. without harming their operation. measuring instruments. In this regard, in mechanical engineering, parts of different machines are manufactured according to ten different accuracy classes. Five of them are more accurate: 1st, 2nd, 2a, 3rd, Za; two are less accurate: 4th and 5th; the other three are rough: 7th, 8th and 9th.

To know what accuracy class the part needs to be manufactured in, on the drawings next to the letter indicating the fit, a number indicating the accuracy class is placed. For example, C 4 means: sliding landing of the 4th accuracy class; X 3 - running landing of the 3rd accuracy class; P - tight fit of 2nd accuracy class. For all 2nd class landings, the number 2 is not used, since this accuracy class is used especially widely.

6. Hole system and shaft system

There are two systems for arranging tolerances - the hole system and the shaft system.

The hole system (Fig. 72) is characterized by the fact that for all fits of the same degree of accuracy (same class), assigned to the same nominal diameter, the hole has constant maximum deviations, while a variety of fits is obtained by changing the maximum shaft deviations.

The shaft system (Fig. 73) is characterized by the fact that for all fits of the same degree of accuracy (same class), referred to the same nominal diameter, the shaft has constant maximum deviations, while the variety of fits in this system is carried out within by changing the maximum deviations of the hole.

In the drawings, the hole system is designated by the letter A, and the shaft system by the letter B. If the hole is made according to the hole system, then the nominal size is marked with the letter A with a number corresponding to the accuracy class. For example, 30A 3 means that the hole must be processed according to the hole system of the 3rd accuracy class, and 30A - according to the hole system of the 2nd accuracy class. If the hole is machined using the shaft system, then the nominal size is marked with a fit and the corresponding accuracy class. For example, a hole 30С 4 means that the hole must be processed with maximum deviations according to the shaft system, according to a sliding fit of the 4th accuracy class. In the case when the shaft is manufactured according to the shaft system, the letter B and the corresponding accuracy class are indicated. For example, 30B 3 will mean processing a shaft using a 3rd accuracy class shaft system, and 30B - using a 2nd accuracy class shaft system.

In mechanical engineering, the hole system is used more often than the shaft system, since it is associated with lower costs for tools and equipment. For example, to process a hole of a given nominal diameter with a hole system for all fits of one class, only one reamer is required and to measure a hole - one / limit plug, and with a shaft system, for each fit within one class a separate reamer and a separate limit plug are needed.

7. Deviation tables

To determine and assign accuracy classes, fits and tolerance values, special reference tables are used. Since permissible deviations are usually very small values, in order not to write extra zeros, in tolerance tables they are indicated in thousandths of a millimeter, called microns; one micron is equal to 0.001 mm.

As an example, a table of the 2nd accuracy class for a hole system is given (Table 7).

The first column of the table gives the nominal diameters, the second column shows the hole deviations in microns. The remaining columns show various fits with their corresponding deviations. The plus sign indicates that the deviation is added to the nominal size, and the minus sign indicates that the deviation is subtracted from the nominal size.

As an example, we will determine the fit movement in a hole system of the 2nd accuracy class for connecting a shaft with a hole with a nominal diameter of 70 mm.

The nominal diameter 70 lies between the sizes 50-80 placed in the first column of the table. 7. In the second column we find the corresponding hole deviations. Therefore, the largest limit hole size will be 70.030 mm, and the smallest 70 mm, since the lower deviation is zero.

In the column “Motion fit” against the size from 50 to 80, the deviation for the shaft is indicated. Therefore, the largest maximum shaft size is 70-0.012 = 69.988 mm, and the smallest maximum size is 70-0.032 = 69.968 mm.

Table 7

Limit deviations of the hole and shaft for the hole system according to the 2nd accuracy class
(according to OST 1012). Dimensions in microns (1 micron = 0.001 mm)

Control questions 1. What is called the interchangeability of parts in mechanical engineering?
2. Why are permissible deviations in the dimensions of parts assigned?
3. What are nominal, maximum and actual sizes?
4. Can the maximum size be equal to the nominal size?
5. What is called tolerance and how to determine tolerance?
6. What are the upper and lower deviations called?
7. What is clearance and interference called? Why are clearance and interference provided in the connection of two parts?
8. What types of landings are there and how are they indicated on the drawings?
9. List the accuracy classes.
10. How many landings does the 2nd accuracy class have?
11. What is the difference between a bore system and a shaft system?
12. Will the hole tolerances change for different fits in the hole system?
13. Will the maximum shaft deviations change for different fits in the hole system?
14. Why is the hole system used more often in mechanical engineering than the shaft system?
15. How they are marked on the drawings symbols deviations in hole dimensions if parts are made in a hole system?
16. In what units are the deviations indicated in the tables?
17. Determine using the table. 7, deviations and tolerance for the manufacture of the shaft with nominal diameter 50 mm; 75 mm; 90 mm.

Chapter X

Measuring tool

To measure and check the dimensions of parts, a turner has to use various measuring tools. For not very accurate measurements, they use measuring rulers, calipers and bore gauges, and for more accurate ones - calipers, micrometers, gauges, etc.

1. Measuring ruler. Calipers. Bore gauge

Yardstick(Fig. 74) is used to measure the length of parts and ledges on them. The most common steel rulers are from 150 to 300 mm long with millimeter divisions.

The length is measured by directly applying a ruler to the workpiece. The beginning of the divisions or the zero stroke is combined with one of the ends of the part being measured and then the stroke on which the second end of the part falls is counted.

Possible measurement accuracy using a ruler is 0.25-0.5 mm.

Calipers (Fig. 75, a) are the simplest tool for rough measurements of the external dimensions of workpieces. A caliper consists of two curved legs that sit on the same axis and can rotate around it. By spreading the legs of the caliper slightly larger than the size being measured, lightly tapping it on the part being measured or some solid object move them so that they closely touch the outer surfaces of the part being measured. The method of transferring the size from the part being measured to the measuring ruler is shown in Fig. 76.

In Fig. 75, 6 shows a spring caliper. It is adjusted to size using a screw and nut with a fine thread.

A spring caliper is somewhat more convenient than a simple caliper, as it maintains the set size.

Bore gauge. For rough measurements internal dimensions The bore gauge shown in Fig. is used. 77, a, as well as a spring bore gauge (Fig. 77, b). The device of the bore gauge is similar to that of a caliper; Measurement with these instruments is also similar. Instead of a bore gauge, you can use calipers by moving its legs one after the other, as shown in Fig. 77, v.

The measurement accuracy with calipers and bore gauges can be increased to 0.25 mm.

2. Vernier caliper with reading accuracy 0.1 mm

The accuracy of measurement with a measuring ruler, calipers, or bore gauge, as already indicated, does not exceed 0.25 mm. A more accurate tool is a caliper (Fig. 78), which can be used to measure both the external and internal dimensions of the workpieces. When working on a lathe, calipers are also used to measure the depth of a recess or shoulder.

The caliper consists of a steel rod (ruler) 5 with divisions and jaws 1, 2, 3 and 8. Jaws 1 and 2 are integral with the ruler, and jaws 8 and 3 are integral with frame 7, sliding along the ruler. Using screw 4, you can secure the frame to the ruler in any position.

To measure the outer surfaces use jaws 1 and 8, to measure the internal surfaces use jaws 2 and 3, and to measure the depth of the recess use rod 6 connected to frame 7.

On frame 7 there is a scale with strokes for reading fractional fractions of a millimeter, called vernier. The vernier allows measurements to be made with an accuracy of 0.1 mm (decimal vernier), and in more accurate calipers - with an accuracy of 0.05 and 0.02 mm.

Vernier device. Let's consider how a vernier reading is made on a vernier caliper with an accuracy of 0.1 mm. The vernier scale (Fig. 79) is divided into ten equal parts and occupies a length equal to nine divisions of the ruler scale, or 9 mm. Therefore, one division of the vernier is 0.9 mm, i.e. it is shorter than each division of the ruler by 0.1 mm.

If you close the jaws of the caliper closely, the zero stroke of the vernier will exactly coincide with the zero stroke of the ruler. The remaining vernier strokes, except for the last one, will not have such a coincidence: the first vernier stroke will not reach the first stroke of the ruler by 0.1 mm; the second stroke of the vernier will not reach the second stroke of the ruler by 0.2 mm; the third stroke of the vernier will not reach the third stroke of the ruler by 0.3 mm, etc. The tenth stroke of the vernier will exactly coincide with the ninth stroke of the ruler.

If you move the frame so that the first stroke of the vernier (not counting the zero) coincides with the first stroke of the ruler, then between the jaws of the caliper you will get a gap of 0.1 mm. If the second stroke of the vernier coincides with the second stroke of the ruler, the gap between the jaws will already be 0.2 mm, if the third stroke of the vernier coincides with the third stroke of the ruler, the gap will be 0.3 mm, etc. Consequently, the vernier stroke that exactly coincides with which - using a ruler stroke, shows the number of tenths of a millimeter.

When measuring with a caliper, they first count a whole number of millimeters, which is judged by the position occupied by the zero stroke of the vernier, and then look at which vernier stroke coincides with the stroke of the measuring ruler, and determine tenths of a millimeter.

In Fig. 79, b shows the position of the vernier when measuring a part with a diameter of 6.5 mm. Indeed, the zero line of the vernier is between the sixth and seventh lines of the measuring ruler, and, therefore, the diameter of the part is 6 mm plus the reading of the vernier. Next, we see that the fifth stroke of the vernier coincides with one of the strokes of the ruler, which corresponds to 0.5 mm, so the diameter of the part will be 6 + 0.5 = 6.5 mm.

3. Vernier depth gauge

To measure the depth of recesses and grooves, as well as to determine the correct position of the ledges along the length of the roller, use a special tool called depth gauge(Fig. 80). The design of the depth gauge is similar to that of a caliper. Ruler 1 moves freely in frame 2 and is fixed in it in the desired position using screw 4. Ruler 1 has a millimeter scale, on which, using vernier 3, located on frame 2, the depth of the recess or groove is determined, as shown in Fig. 80. The reading on the vernier is carried out in the same way as when measuring with a caliper.

4. Precision caliper

For work performed with greater accuracy than those considered so far, use precision(i.e. accurate) calipers.

In Fig. 81 shows a precision caliper from the plant named after. Voskov, having a measuring ruler 300 mm long and a vernier.

The length of the vernier scale (Fig. 82, a) is equal to 49 divisions of the measuring ruler, which is 49 mm. This 49 mm is precisely divided into 50 parts, each equal to 0.98 mm. Since one division of the measuring ruler is equal to 1 mm, and one division of the vernier is equal to 0.98 mm, we can say that each division of the vernier is shorter than each division of the measuring ruler by 1.00-0.98 = 0.02 mm. This value of 0.02 mm indicates that accuracy, which can be provided by the vernier of the considered precision caliper when measuring parts.

When measuring with a precision caliper, to the number of whole millimeters passed by the zero stroke of the vernier, one must add as many hundredths of a millimeter as the vernier stroke that coincides with the stroke of the measuring ruler shows. For example (see Fig. 82, b), along the ruler of the caliper, the zero stroke of the vernier passed 12 mm, and its 12th stroke coincided with one of the strokes of the measuring ruler. Since matching the 12th line of the vernier means 0.02 x 12 = 0.24 mm, the measured size is 12.0 + 0.24 = 12.24 mm.

In Fig. 83 shows a precision caliper from the Kalibr plant with a reading accuracy of 0.05 mm.

The length of the vernier scale of this caliper, equal to 39 mm, is divided into 20 equal parts, each of which is taken as five. Therefore, against the fifth stroke of the vernier there is the number 25, against the tenth - 50, etc. The length of each division of the vernier is

From Fig. 83 it can be seen that with the jaws of the caliper closed tightly, only the zero and last strokes of the vernier coincide with the strokes of the ruler; the rest of the vernier strokes will not have such a coincidence.

If you move frame 3 until the first stroke of the vernier coincides with the second stroke of the ruler, then between the measuring surfaces of the caliper jaws you will get a gap equal to 2-1.95 = 0.05 mm. If the second stroke of the vernier coincides with the fourth stroke of the ruler, the gap between the measuring surfaces of the jaws will be equal to 4-2 X 1.95 = 4 - 3.9 = 0.1 mm. If the third stroke of the vernier coincides with the next stroke of the ruler, the gap will be 0.15 mm.

The counting on this caliper is similar to that described above.

A precision caliper (Fig. 81 and 83) consists of ruler 1 with jaws 6 and 7. Markings are marked on the ruler. Frame 3 with jaws 5 and 8 can be moved along ruler 1. A vernier 4 is screwed to the frame. For rough measurements, frame 3 is moved along ruler 1 and, after securing with screw 9, a count is taken. For accurate measurements, use the micrometric feed of the frame 3, consisting of a screw and nut 2 and a clamp 10. Having clamped the screw 10, by rotating the nut 2, feed the frame 3 with a micrometric screw until the jaw 8 or 5 comes into close contact with the part being measured, after which a reading is made.

5. Micrometer

The micrometer (Fig. 84) is used to accurately measure the diameter, length and thickness of the workpiece and gives an accuracy of 0.01 mm. The part to be measured is located between the fixed heel 2 and the micrometric screw (spindle) 3. By rotating the drum 6, the spindle moves away or approaches the heel.

To prevent the spindle from pressing too hard on the part being measured when the drum rotates, there is a safety head 7 with a ratchet. By rotating the head 7, we will extend the spindle 3 and press the part against the heel 2. When this pressure is sufficient, with further rotation of the head its ratchet will slip and a ratcheting sound will be heard. After this, the rotation of the head is stopped, the resulting opening of the micrometer is secured by turning the clamping ring (stopper) 4, and a count is taken.

To produce readings, a scale with millimeter divisions divided in half is applied on the stem 5, which is integral with the 1 micrometer bracket. Drum 6 has a beveled chamfer, divided along the circumference into 50 equal parts. The bars from 0 to 50 are marked with numbers every five divisions. At the zero position, i.e. when the heel is in contact with the spindle, the zero stroke on the chamfer of the drum 6 coincides with the zero stroke on the stem 5.

The micrometer mechanism is designed in such a way that with a full rotation of the drum, spindle 3 will move by 0.5 mm. Consequently, if you turn the drum not a full turn, that is, not by 50 divisions, but by one division, or part of a revolution, then the spindle will move by This is the precision of the micrometer. When counting, they first look at how many whole millimeters or whole and a half millimeters the drum on the stem has opened, then add to this the number of hundredths of a millimeter that coincides with the line on the stem.

In Fig. 84 on the right shows the size taken with a micrometer when measuring the part; countdown needs to be done. The drum opened 16 whole divisions (half not open) on the stem scale. The seventh stroke of the chamfer coincided with the line of the stem; therefore, we will have another 0.07 mm. The total reading is 16 + 0.07 = 16.07 mm.

In Fig. Figure 85 shows several micrometer measurements.

It should be remembered that a micrometer is a precision instrument that requires careful handling; therefore, when the spindle lightly touches the surface of the part being measured, you should no longer rotate the drum, but to further move the spindle, rotate head 7 (Fig. 84) until the sound of a ratchet follows.

6. Bore gauges

Bore gauges (shtihmas) are used for precise measurements of the internal dimensions of parts. There are permanent and sliding bore gauges.

Constant or hard, the bore gauge (Fig. 86) is a metal rod with measuring ends having a spherical surface. The distance between them is equal to the diameter of the hole being measured. To exclude the influence of the heat of the hand holding the bore gauge on its actual size, the bore gauge is equipped with a holder (handle).

Micrometric bore gauges are used to measure internal dimensions with an accuracy of 0.01 mm. Their design is similar to that of a micrometer for external measurements.

The head of the micrometric bore gauge (Fig. 87) consists of a sleeve 3 and a drum 4 connected to a micrometric screw; screw pitch 0.5 mm, stroke 13 mm. The sleeve contains a stopper 2 and a heel/with a measuring surface. By holding the sleeve and rotating the drum, you can change the distance between the measuring surfaces of the bore gauge. Readings are made like a micrometer.

The measurement limits of the shtihmas head are from 50 to 63 mm. For measuring large diameters(up to 1500 mm) extensions 5 are screwed onto the head.

7. Limit measuring instruments

In the serial production of parts according to tolerances, the use of universal measuring instruments(calipers, micrometer, micrometric bore gauge) is impractical, since measurement with these instruments is a relatively complex and time-consuming operation. Their accuracy is often insufficient, and, in addition, the measurement result depends on the skill of the worker.

To check whether the dimensions of the parts are within precisely established limits, use special tool - maximum calibers. The gauges for checking shafts are called staples, and those for checking holes are called traffic jams.

Measuring with limit clamps. Double-sided limit bracket(Fig. 88) has two pairs of measuring cheeks. The distance between the cheeks of one side is equal to the smallest maximum size, and the other - to the largest maximum size of the part. If the shaft being measured extends to the larger side of the bracket, then its size does not exceed the permissible limit, and if not, then its size is too large. If the shaft also passes to the smaller side of the bracket, then this means that its diameter is too small, i.e. less than permissible. Such a shaft is a defect.

The side of the staple with the smaller size is called impassable(stamped “NOT”), opposite side With large size - checkpoint(branded “PR”). The shaft is considered suitable if the bracket, lowered onto it by the go-through side, slides down under the influence of its weight (Fig. 88), and the non-go-through side does not rest on the shaft.

For measuring shafts large diameter instead of double-sided brackets, one-sided brackets are used (Fig. 89), in which both pairs of measuring surfaces lie one after the other. The front measuring surfaces of such a bracket are used to check the largest permissible diameter of the part, and the rear ones are used to check the smallest. These staples are lighter and significantly speed up the inspection process, since it is enough to apply the staple once to measure.

In Fig. 90 shown adjustable limit bracket, in which, if worn, the correct dimensions can be restored by rearranging the measuring pins. In addition, such a bracket can be adjusted to specified dimensions and thus checked with a small set of brackets a large number of sizes.

To change to a new size, you need to loosen the locking screws 1 on the left leg, move the measuring pins 2 and 3 accordingly and secure the screws 1 again.

They are widespread flat limit brackets(Fig. 91), made of sheet steel.

Measuring with limit plugs. Cylindrical limit plug gauge(Fig. 92) consists of a through plug 1, a non-go through plug 3 and a handle 2. The through plug (“PR”) has a diameter equal to the smallest permissible size holes, and the no-go plug (“NOT”) is the largest. If the “PR” plug passes, but the “NOT” plug does not pass, then the diameter of the hole is greater than the smallest limit and less than the largest, i.e., it is within the permissible limits. The pass-through plug is longer than the non-pass-through plug.

In Fig. Figure 93 shows the measurement of a hole with a limit plug on a lathe. The pass-through side should fit through the hole easily. If the non-passable side also enters the hole, then the part is rejected.

Cylindrical plug gauges for large diameters are inconvenient due to their large weight. In these cases, two flat plug gauges are used (Fig. 94), of which one has a size equal to the largest, and the second to the smallest permissible. The walk-through side is wider than the walk-through side.

In Fig. 95 shown adjustable limit plug. It can be adjusted to multiple sizes just like an adjustable limit bracket, or rebuilt right size worn measuring surfaces.

8. Resistance gauges and indicators

Reismas. To accurately check the correct installation of a part in a four-jaw chuck, on a square, etc., use Reismas.

Using a surface gauge, you can also mark the center holes at the ends of the part.

The simplest surface plan is shown in Fig. 96, a. It consists of a massive tile with a precisely machined bottom plane and a rod along which a slide with a scribe needle moves.

A gauge of a more advanced design is shown in Fig. 96, b. The gauge needle 3, using hinge 1 and clamp 4, can be brought with its tip to the surface being tested. Precise installation is carried out with screw 2.

Indicator. To control the accuracy of processing on metal-cutting machines, check the machined part for ovality, taper, and to check the accuracy of the machine itself, an indicator is used.

The indicator (Fig. 97) has a metal case 6 in the shape of a clock, which houses the mechanism of the device. A rod 3 with a tip protruding outward passes through the indicator body, always under the influence of a spring. If you press the rod from bottom to top, it will move in the axial direction and at the same time rotate the arrow 5, which will move along the dial, which has a scale of 100 divisions, each of which corresponds to the movement of the rod by 1/100 mm. When the rod moves 1 mm, hand 5 will make a full revolution around the dial. Arrow 4 is used to count whole revolutions.

When taking measurements, the indicator must always be rigidly fixed relative to the original measuring surface. In Fig. 97, and shows a universal stand for mounting the indicator. Indicator 6 is secured to vertical rod 9 using rods 2 and 1 of couplings 7 and 8. Rod 9 is secured in groove 11 of prism 12 with a knurled nut 10.

To measure the deviation of a part from a given size, bring the tip of the indicator to it until it comes into contact with the surface being measured and note the initial reading of arrows 5 and 4 (see Fig. 97, b) on the dial. Then the indicator is moved relative to the surface being measured or the surface being measured relative to the indicator.

The deviation of the arrow 5 from its initial position will show the size of the convexity (depression) in hundredths of a millimeter, and the deviation of the arrow 4 in whole millimeters.

In Fig. Figure 98 shows an example of using the indicator to check the alignment of the centers of the headstock and tailstock. lathe. For a more accurate check, install a precision ground roller between the centers and an indicator in the tool holder. By bringing the indicator button to the surface of the roller on the right and noticing the indication of the indicator arrow, manually move the caliper with the indicator along the roller. The difference in the deviations of the indicator arrow in the extreme positions of the roller will show how much the tailstock body should be moved in the transverse direction.

Using the indicator, you can also check the end surface of a machined part. The indicator is fixed in the tool holder instead of the cutter and is moved along with the tool holder in the transverse direction so that the indicator button touches the surface being tested. The deviation of the indicator arrow will show the amount of runout of the end plane.

Control questions 1. What parts does a caliper with an accuracy of 0.1 mm consist of?
2. How does the vernier of a caliper with an accuracy of 0.1 mm work?
3. Set the dimensions on the caliper: 25.6 mm; 30.8 mm; 45.9 mm.
4. How many divisions does the vernier of a precision caliper have with an accuracy of 0.05 mm? The same, with an accuracy of 0.02 mm? What is the length of one vernier division? How to read the vernier readings?
5. Set the dimensions using a precision caliper: 35.75 mm; 50.05 mm; 60.55 mm; 75 mm.
6. What parts does a micrometer consist of?
7. What is the micrometer screw pitch?
8. How are measurements taken using a micrometer?
9. Set the dimensions using a micrometer: 15.45 mm; 30.5 mm; 50.55 mm.
10. In what cases are bore gauges used?
11. What are limit gauges used for?
12. What is the purpose of the passing and non-passing sides of the limit gauges?
13. What designs of limit brackets do you know?
14. How to check the correct size with a limit stopper? Limit bracket?
15. What is the indicator used for? How to use it?
16. How does a surface gauge work and what is it used for?