The shaft and the hole are called the connected surfaces of the parts, and the shaft is the outer surface, and the hole is the inner surface of the parts. Hole system and shaft system. Features, differences, advantages What part in the shaft system is the main

14.07.2019

Tolerances and landings

The concept of interchangeability of parts

In modern factories, machine tools, automobiles, tractors and other machines are not manufactured in units, or even tens or hundreds, but in thousands. With these sizes of production, it is very important that every part of the machine during assembly fits precisely in its place without any additional fittings. It is equally important that any part arriving at the assembly allows its other one purpose to be replaced without any damage to the operation of the entire finished machine. Parts that satisfy these conditions are called interchangeably.

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

Mate parts

Two parts movably or motionlessly connected to each other are called mating. The size at which these parts are connected is called mating size. Dimensions that do not connect parts are called free the dimensions. An example of mating dimensions is the shaft diameter and the corresponding hole diameter in the pulley; An example of free dimensions is the outer diameter of a pulley.

To obtain interchangeability, the mating dimensions of the parts must be precisely made. However, such processing is complex and not always appropriate. Therefore, the technique has found a way to get interchangeable parts when working with approximate accuracy. This method consists in the fact that for various conditions of operation of the part, permissible deviations of its dimensions are established, at which faultless operation of the part in the machine is still possible. These deviations, calculated for different working conditions of the part, are built in a specific system called tolerance system.

Tolerance Concept

Size characteristic. The estimated part size, affixed to the drawing, from which the deviations are calculated, is called nominal size. Typically, nominal dimensions are expressed in whole millimeters.

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

Dimensions between which the actual part size may fluctuate are called marginal. Of these, the larger size is called largest size limitand the smaller one smallest size limit.

Deviation called the difference between the limit and nominal dimensions of the part. In the drawing, deviations are usually indicated by numerical values \u200b\u200bat a nominal size, with the upper deviation indicated above and the lower one 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 dimensions is called upper deviation, and the difference between the smallest limit and nominal sizes is lower deviation. For example, the shaft size is equal. In this case, the maximum size limit will be:

30 +0.15 \u003d 30.15 mm;

the upper deviation is

30.15 - 30.0 \u003d 0.15 mm;

smallest size limit will be:

30 + 0.1 \u003d 30.1 mm;

lower deviation is

30.1 - 30.0 \u003d 0.1 mm.

Manufacturing approval. The difference between the largest and smallest limit sizes is called admission. For example, for the size of the shaft, the tolerance will be equal to the difference in the limiting sizes, i.e.

30.15 - 29.9 \u003d 0.25 mm.

Clearances and interference

If you place a part with a hole on a shaft with a diameter, i.e., with a diameter under all conditions, less than the diameter of the hole, then in the connection of the shaft with the hole a gap will be obtained, as shown in Fig. 70. In this case, the landing is called mobileas the shaft will be able to rotate freely in the hole. If the shaft size is always larger than the hole size (Fig. 71), then when connecting the shaft will need to be pressed into the hole and then the connection will tightness.

Based on the foregoing, the following conclusion can be made:
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.

Landing and accuracy classes

Landing. Landings are divided into mobile and motionless. Below are the most used landings, and their abbreviations are given in brackets.

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

To know what class of accuracy you need to make a part in the drawings, next to the letter denoting the landing, put a number indicating the accuracy class. For example, C 4 means: a sliding landing of the 4th accuracy class; X 3 - landing landing 3rd accuracy class; P - tight fit 2nd accuracy class. For all landings of the 2nd class, the number 2 is not set, since this accuracy class is used especially widely.

Hole system and shaft system

There are two tolerance systems - the hole system and the shaft system.

The hole system (Fig. 72) is characterized by the fact that in it for all landings of the same degree of accuracy (of the same class), assigned to the same nominal diameter, the hole has constant limit deviations, and the variety of landings is obtained by changing the limit shaft deviations.

The shaft system (Fig. 73) is characterized by the fact that in it, for all landings of the same degree of accuracy (of the same class), assigned to the same nominal diameter, the shaft has constant limit deviations, while the variety of landings in this system is carried out beyond due to changes in the maximum deviations of the hole.

In the drawings, the hole system is denoted by the letter A, and the shaft system by the letter B. If the hole is made according to the hole system, then the letter A is put at the nominal size with a number corresponding to the accuracy class. For example, 30A 3 means that the hole must be machined 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 according to the shaft system, then the nominal size is marked with the fit and the corresponding accuracy class. For example, the hole 30C 4 means that the hole must be machined with extreme deviations along the shaft system, according to the sliding fit of the 4th accuracy class. In the case when the shaft is manufactured according to the shaft system, put the letter B and the corresponding accuracy class. For example, 30V 3 will mean shaft processing according to the shaft system of the 3rd accuracy class, and 30V - according to the shaft system of the 2nd accuracy class.

In mechanical engineering, the hole system is used more often than the shaft system, since this entails 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 the same class, only one reamer is required and to measure the hole one / limit plug, and with a shaft system for each fit within the same class, you need a separate reamer and separate limit plug.

Deviation tables

To determine and assign accuracy classes, landings and tolerance values, special reference tables are used. Since the permissible deviations are usually very small, then, in order not to write extra zeros, they are indicated in the tolerance tables 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 the hole system is given (Table 7).

In the first column of the table, nominal diameters are given, in the second column, deviations of the hole in microns. In the remaining columns, various landings with corresponding deviations are given. A plus sign indicates that the deviation is added to the nominal size, and a minus sign indicates that the deviation is subtracted from the nominal size.

As an example, let us define the fit of movement in the hole system of the 2nd accuracy class for connecting the shaft to the hole with a nominal diameter of 70 mm.

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

In the column "Landing movement" against the size from 50 to 80, the deviation for the shaft is indicated. Therefore, the largest limit size of the shaft is 70-0.012 \u003d 69.988 mm, and the smallest limit size is 70-0.032 \u003d 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 \u003d 0.001 mm)

GOST 8032-84. Basic norms of interchangeability. Normal linear dimensions
GOST 25346-89. Basic norms of interchangeability. Unified system of tolerances and landings. General provisions, series of tolerances and main deviations

saddleiness -

GOST 24642-81 establishes the following deviations surface shapes

Cone - deviation of the longitudinal section profile,

Tolerances of the shape and location of surfaces.
Tolerances of the shape and location of surfaces are governed by the following standards.
GOST 24642-81 . Tolerances of the shape and location of surfaces. Key terms and definitions.
GOST 24643-81 . Numerical values \u200b\u200bof deviations of form and relative position.
GOST 25069-81 . Unspecified tolerances on the shape and location of surfaces.
GOST 2.308-79 . An indication on the drawings of tolerances of the shape and location of the surfaces.

The influence of deviations in the shape and location of surfaces on the quality of products.

The accuracy of the geometric parameters of parts is characterized not only by the accuracy of the dimensions of its elements, but also by the accuracy of the shape and relative position of the surfaces. Deviations in the shape and location of surfaces occur during the processing of parts due to inaccuracies and deformations of the machine, tool and fixture; deformation of the workpiece; uneven machining allowance; heterogeneity of the workpiece material, etc.
In movable joints, these deviations lead to a decrease in the wear resistance of parts due to increased specific pressure on the protrusions of irregularities, to a violation of the smoothness of travel, noise, etc.
In fixed joints, deviations in the shape and arrangement of surfaces cause uneven interference, resulting in reduced joint strength, tightness and centering accuracy.
In assemblies, these errors lead to errors in the basing of parts relative to each other, deformations, uneven gaps, which causes disturbances in the normal operation of individual nodes and the mechanism as a whole; for example, rolling bearings are very sensitive to deviations in the shape and relative position of the seating surfaces.
Deviations in the shape and location of surfaces reduce the technological performance of products. So, they significantly affect the accuracy and laboriousness of the assembly and increase the volume of fitting operations, reduce the accuracy of dimensional measurements, and affect the accuracy of the base of the part during manufacture and control.

Geometrical parameters of parts. Basic concepts.

When analyzing the accuracy of the geometric parameters of parts, the following concepts are used.
Nominal surface - an ideal surface, the dimensions and shape of which correspond to the specified nominal dimensions and nominal shape.
A real surface is a surface that limits a part and separates it from the environment.
Profile - the line of intersection of a surface with a plane or with a given surface (there are concepts of real and nominal profiles, similar to the concepts of nominal and real surfaces).
The normalized section L is the section of the surface or line to which the tolerance of the form, the tolerance of the arrangement or the corresponding deviation refers. If the normalized section is not defined, then the tolerance or deviation refers to the entire surface under consideration or the length of the element under consideration. If the location of the normalized section is not specified, then it can occupy any location within the entire element.

Adjacent surface - a surface having the shape of a nominal surface in contact with the real surface and located outside the material of the part so that the deviation from it of the most distant point of the real surface within the normalized area has a minimum value. The adjacent surface is used as a base when determining deviations in shape and location. Instead of the adjacent element for assessing deviations in shape or location, it is allowed to use as a basic element a middle element having a nominal shape and carried out by the least squares method with respect to the real one.
Base - an element of a part or a combination of elements with respect to which the tolerance of the location of the element in question is specified, and the corresponding deviations are determined.

Deviations and tolerances of the form.

Deviation of the shape EF is the deviation of the shape of the real element from the nominal shape, estimated by the greatest distance from the points of the real element along the normal to the adjacent element. Roughnesses related to surface roughness are not included in shape deviations. When measuring the shape, the effect of roughness is usually eliminated through the use of a sufficiently large radius of the measuring tip.
TF tolerance is the largest tolerance for shape deviation.
Types of tolerances form.
Types of tolerances, their designation and image in the drawings are given in table. The numerical values \u200b\u200bof tolerances depending on the degree of accuracy are given in the appendix.
The selection of tolerances depends on the design and technological requirements and, in addition, is associated with
size tolerance. The size tolerance field for mating surfaces also limits any shape deviation along the length of the joint. None of the shape deviations can exceed the size tolerance. Tolerances of the form are prescribed only in those cases when they should be less than the size tolerance. Examples of assignment of tolerances of the form, the recommended degree of accuracy and the corresponding processing methods are shown in table.

Deviations and tolerances of the location of the surfaces.
Deviation EP location is called the deviation of the actual location of the element under consideration from its nominal location. Nominal refers to the location determined by the nominal linear and angular dimensions.
To assess the accuracy of the location of the surfaces, as a rule, appoint a base.
Base - a part element (or a combination of elements performing the same function), with respect to
which sets the tolerance for the location of the element in question, and also determines
deviation
Location tolerance is called the limit limiting the allowable value of the deviation of the location of the surfaces.
Location Tolerance Field TP - an area in space or a given plane, inside which
the swarm should be adjacent element or axis, center, plane of symmetry within the normal
an irreplaceable section, the width or diameter of which is determined by the tolerance value, and the location
relative to the bases - the nominal location of the element in question.
Types of Location Tolerances
Types of tolerances, their designation and the image on the drawings are tolerances that limit the deviation of the location between cylindrical and flat surfaces.
An estimate of the location deviation is made by the location of the adjacent surface drawn to the real surface; thus excluding form deviations from consideration.
In the column “Notes” (see table 3.4), tolerances are indicated that can be assigned in either radial or diametrical terms. When applying these tolerances, the drawings should indicate the appropriate sign in front of the numerical value of the tolerance.
The numerical values \u200b\u200bof tolerances depending on the degree of accuracy are given in the appendix

Total tolerances and deviations of the shape and location of surfaces.

The total deviation of the shape and location of the EU is called the deviation, which is the result of the joint manifestation of the deviation of the shape and deviation of the location of the surface or the profile under consideration relative to the bases.
The total tolerance field for the shape and location of TC is a region in space or on a given surface, inside which all points of the real surface or real profile should be located within the normalized area. This field has a specified nominal position relative to the bases.

Types of total tolerances.
Types of tolerances, their designation and image in the drawings are given in table. The numerical values \u200b\u200bof tolerances depending on the degree of accuracy are given in the appendix. Examples of assigning tolerances in the drawings and image deviations are given in table.

Dependent and independent tolerances.
Location or shape tolerances may be dependent or independent.
Dependent Tolerance - this is the tolerance of the arrangement or shape indicated on the drawing in the form of a value that can be exceeded by an amount depending on the deviation of the actual size of the element under consideration from the maximum of the material.
Dependent Tolerance - a variable tolerance, its minimum value is indicated in the drawing and is allowed to be exceeded by changing the dimensions of the elements in question, but so that their linear dimensions do not go beyond the prescribed tolerances.
Dependent location tolerances, as a rule, are prescribed in those cases when it is necessary to ensure the collectability of parts that mate simultaneously on several surfaces.
In some cases, with dependent tolerances, it is possible to transfer the part from the defective to fit by additional processing, for example, by expanding holes. As a rule, it is recommended to assign dependent tolerances for those elements of parts to which only collection requirements are imposed.
Dependent tolerances are usually controlled by complex gauges, which are prototypes of mating parts. These calibers are only walk-through, they guarantee non-fit assembly of products.
An example of assigning dependent tolerance is shown in Fig. 3.2. The letter “M” indicates that the tolerance is dependent, and the method of indicating that the value of the alignment tolerance can be exceeded by changing
sizes of both holes.

It can be seen from the figure that when making holes with minimum dimensions, the maximum deviation from alignment can be no more. When making holes with the maximum permissible dimensions, the value of the maximum deviation of the alignment can be increased. The largest marginal deviation is calculated by the formula:

ЕРСmax \u003d EPCmin + 0.5 D (T1 + T2); EPCmax \u003d 0.005 + 0.5 D (0.033 + 0.022) \u003d 0.0325 mm

For dependent tolerances, it is possible to assign their zero values \u200b\u200bin the drawings. This way
indication of tolerances means that deviations are permissible only through the use of part of the tolerance
on the size of the elements.
Independent tolerance is the tolerance of an arrangement or shape, the numerical value of which is constant for the entire set of parts and does not depend on the actual dimensions of the surfaces under consideration.

Indication of tolerances of the shape and location of surfaces in the drawings.

1. Tolerances of the shape and location of the surfaces indicated on the drawings by legend. Indication of tolerances of the form and arrangement with the text in the technical requirements is permissible only in cases where there is no sign of the type of tolerance.
2. With a symbol, data on tolerances of the shape and location of surfaces are indicated in a rectangular frame divided into parts:
in the first part - an admission mark;
in the second part - the numerical value of the tolerance, and, if necessary, the length of the normalized section;
in the third and subsequent parts - the letter designation of the bases

4. The frame is recommended to be horizontal. Crossing the tolerance frame with any lines is not allowed.
5. If the tolerance refers to the axis or plane of symmetry, then the connecting line must be
continuation of the dimension line (Fig. 3.4, a). If the deviation or base refers to the surface,
then the connecting line should not coincide with the dimension

6. If the size of the element has already been indicated, the dimension line should be without size, and it is considered as part of the tolerance symbol.
7. The numerical value of the tolerance is valid for the entire surface or length of the element, if a standardized area is not specified.
8. If for one element it is necessary to specify two different types of tolerance, then the tolerance frames can be combined and arranged as shown in Fig.

9. The bases are indicated by a blackened triangle, which is connected using a connecting line with a tolerance frame or a frame in which the letter designation of the base is indicated.
10. If there is no need to select as a base none of the surfaces, then the triangle is replaced by an arrow.
11. The linear and angular dimensions that determine the nominal location of the elements, limited by the tolerance of the location indicated on the drawings in rectangular frames.
12. If the tolerance of the arrangement or form is not indicated as dependent, then it is considered independent.
Dependent tolerances are designated as indicated in fig.
3.6. Sign “M” is placed:

after the numerical value of the tolerance, if the dependent tolerance is associated with the actual dimensions of the element in question;
after the base letter (see Fig. 3.6, b) or without the letter in the third
parts of the frame (see Fig. 3.6, c), if the dependent tolerance is associated with the actual dimensions of the base
item;
after the numerical value of the tolerance and the letter designation of the base (see Fig. 3.6, d) or without the letter designation (see Fig. 3.6, e), if the dependent tolerance is associated with the actual dimensions
considered and basic elements.

Surface roughness

[edit]

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Surface roughness - a set of surface irregularities with relatively small steps on the base length. Measured in micrometers (μm). Roughness refers to the microgeometry of a solid and determines its most important operational properties. First of all, wear resistance from abrasion, strength, density (tightness) of compounds, chemical resistance, appearance. Depending on the working conditions of the surface, a roughness parameter is assigned when designing machine parts, and there is also a relationship between the maximum size deviation and roughness. The initial roughness is the result of technological processing of the surface of the material, for example, abrasives. As a result of friction and wear, the parameters of the initial roughness, as a rule, change.

[edit] Roughness Parameters

The initial roughness is the result of technological processing of the surface of the material, for example, abrasives. For a wide class of surfaces, the horizontal pitch of irregularities is in the range from 1 to 1000 microns, and the height is from 0.01 to 10 microns. As a result of friction and wear, the parameters of the initial roughness, as a rule, change, and an operational roughness is formed. The operational roughness reproduced under stationary friction conditions is called equilibrium roughness.

Normal profile and surface roughness parameters.

The figure schematically shows the roughness parameters, where: - base length; - the middle line of the profile; - average step of profile irregularities; - deviation of the five largest profile maxima; - deviation of the five largest lows of the profile; - the distance from the highest points of the five largest maxima to the line parallel to the middle and not crossing the profile; - the distance from the lowest points of the five largest lows to a line parallel to the middle and not crossing the profile; - the highest profile height; - deviations of the profile from the line ; - profile section level; - the length of the segments cut off at the level .

Altitude parameters:

Ra - arithmetic mean deviation of the profile;

Rz - the height of the irregularities of the profile at ten points;

Rmax - the highest profile height;

Step parameters:

Sm - the average pitch of irregularities;

S - the average step of the local protrusions of the profile;

tp is the relative reference length of the profile, where p - the values \u200b\u200bof the profile cross-section from a row of 10 fifteen; twenty; thirty; 40; fifty; 60; 70; 80; 90%

Ra, Rz and Rmax determined at the base length l which can take values \u200b\u200bfrom a number of 0.01; 0.03; 0.08; 0.25; 0.80; 2.5; 8; 25 mm

The surface roughness is indicated in the drawing for all surfaces of the product performed according to this drawing, regardless of the methods of their formation, except for surfaces whose roughness is not caused by the design requirements.

The structure designation of surface roughness is shown in Fig. one.

When using a sign without specifying a parameter and processing method, it is depicted without a shelf.

In the designation of surface roughness, one of the signs shown in Figures 2-5 is used.

Height h should be approximately equal to the height of the digits of dimensional numbers used in the drawing. Height N equal to (1,5 ... 5) h . The thickness of the lines of signs should be approximately equal to half the thickness of the solid line used in the drawing.

In the designation of surface roughness, the method of processing of which is not established by the designer, a sign is used (Fig. 2).

In the designation of the surface roughness, which should be formed only by removing the layer of material, a sign is used (Fig. 3).

In the designation of the surface roughness, which must be formed without removing the material layer, a sign is used (Fig. 4) indicating the value of the roughness parameter.

The surfaces of the part made of material of a certain profile and size, not subject to additional processing according to this drawing, must be marked with a sign (Fig. 4) without specifying the roughness parameter.

The condition of the surface indicated by the sign (Fig. 4) must comply with the requirements established by the relevant standard or technical specifications, or another document. Moreover, this document should be referenced, for example, in the form of an indication of the range of materials in column 3 of the main inscription of the drawing according to GOST 2.104-68.

The value of the roughness parameter according to GOST 2789-73 is indicated in the roughness symbol after the corresponding symbol, for example: R a 0.4, R max 6.3; Sm 0.63; t 50 70; S 0,032; Rz 50.

Note. In the example t 50 70 relative reference length of the profile is indicated t p = 70 % at profile section level r = 50 %,

When specifying the range of values \u200b\u200bof the surface roughness parameter in the roughness designation, the limits of the parameter values \u200b\u200bare given, placing them in two lines, for example:

Ra	0,8	;	Rz	0,10	;	Rmax	0,80	;	t 50
	0,4		0,05		0,32			etc.

The upper line shows the parameter value corresponding to a rougher roughness.

When specifying the nominal value of the surface roughness parameter in the designation, this value is given with extreme deviations according to GOST 2789-73, for example:

Ra1 + 20 %; Rz 100 –10 % ;Sm 0,63 +20 % ; t 50 70 ± 40%, etc.

When two or more surface roughness parameters are indicated in the roughness designation, the parameter values \u200b\u200bare written from top to bottom in the following order (see Fig. 5):

When normalizing the requirements for surface roughness with parameters Ra , Rz , R max the basic length in the roughness designation is not given if it corresponds to that specified in Appendix 1 of GOST 2789-73 for the selected value of the roughness parameter.

Symbols of the direction of irregularities should correspond to those given in table 4. Symbols of the direction of irregularities are given in the drawing, if necessary.

The height of the sign of the symbol for the direction of the bumps should be approximately equal h. The thickness of the sign lines should be approximately equal to half the thickness of the solid main line.

Sketchy image	Designation

Landing system of the main hole or just hole system - this is a set of landings in which the maximum deviations of the holes are the same (with the same nominal size and quality), and different landings are achieved by changing the maximum deviations of the shafts.

Main hole Is the hole indicated by the letter H and whose lower deviation is zero (EI \u003d 0). When designating landings in the hole system, the numerator will always have the main hole “H”, and in the denominator the main shaft deflection intended to form one or another landing.

For example:

- landing in the system holes with a guaranteed clearance;

- landing in the hole system, transitional;

- landing in the system holes with a guaranteed interference fit.

Main shaft landing system or just shaft system - this is a set of landings in which the maximum deviations of the shafts are the same (with one nominal size and one quality), and different landings are achieved by changing the maximum deviations of the holes.

Main shaft - this is the shaft, which is indicated by the letter " h» and whose upper deviation is zero (es \u003d 0).

When designating landings in the shaft system, the denominator (where the shaft tolerance field is always written) will be the main shaft " h", And in the numerator the main deviation of the hole, designed to form a particular fit.

For example:

- landing in the shaft system with a guaranteed clearance;

- landing in the shaft system, transitional;

- landing in the shaft system with a guaranteed interference fit.

The standard allows any combination of tolerance fields for holes and shafts, for example:; and etc.

And at the same time, the recommended fittings are installed for all size ranges and for the sizes of 1 - 500 mm the preferred ones are selected, for example: H7 / f7; H7 / n6 etc. (see table. 1.2 and 1.3).

The unification of landings allows to ensure the uniformity of design requirements for connections and facilitate the work of designers on the appointment of landings. By combining various options of the preferred tolerance fields for shafts and holes, it is possible to significantly expand the system's ability to create different landings without increasing the set of tools, calibers and other technological equipment.

Tolerance and Landing System they call a set of tolerance and landing series, naturally built on the basis of experience, theoretical and experimental research and designed in the form of standards.

The system is designed to select the minimum necessary but practical options for tolerances and fittings of typical joints of machine parts, makes it possible to standardize cutting tools and calibers, facilitates the design, manufacture and achievement of the interchangeability of products and their parts, and also leads to an increase in their quality.

Currently, most countries of the world apply ISO tolerance and landing systems. ISO systems are designed to unify national tolerance and landing systems in order to facilitate international technical ties in the metal industry. The inclusion of ISO international recommendations in national standards creates the conditions for ensuring the interchangeability of similar parts, components and products manufactured in different countries. The Soviet Union joined ISO in 1977, and then switched to a unified tolerance and landing system (ESDP) and the main interchangeability feeds, which are based on ISO standards and recommendations.

Key interchangeability standards include tolerance and fit systems for cylindrical parts, cones, dowels, threads, gears, etc. ISO and ESDP tolerance and fit systems for typical machine parts are based on uniform principles of constructionincluding:

a system for the formation of landings and types of interfaces;
system of basic deviations;
accuracy levels;
tolerance unit;
preferred tolerance and landing fields;
ranges and intervals of nominal sizes;
normal temperature.

The system for the formation of landings and types of mates provides landing in the hole system (CA) and in the shaft system (CB).

Landing in the hole system - these are landings in which various gaps and interference are obtained by connecting different shafts with the main hole (Fig. 3.1, a).

Landing in the shaft system - these are landings in which various clearances and interference are obtained by connecting various holes to the main shaft (Fig. 3.1, b).

Key Terms and Definitions

& nbsp State standards (GOST 25346-89, GOST 25347-82, GOST 25348-89) replaced the OST tolerance and landing system, which was in effect until January 1980.

& nbsp Terms are given according GOST 25346-89 "The basic norms of interchangeability. A unified system of tolerances and landings."

Shaft - a term conventionally used to refer to the external elements of parts, including non-cylindrical elements;
Hole - a term conventionally used to refer to 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;
The size - the numerical value of a linear quantity (diameter, length, etc.) in the selected units of measurement;
Actual size - the element size established by measurement with an allowable accuracy;
Nominal size - size relative to which deviations are determined;
Deviation - the algebraic difference between the size (actual or limit size) and the corresponding nominal size;
Quality - a set of tolerances considered as corresponding to one level of accuracy for all nominal sizes;
Landing - the nature of the connection of the two parts, determined by the difference in their sizes prior to assembly.
Gap - this is the difference between the size of the hole and the shaft before assembly, if the hole is larger than the shaft size;
Preload - the difference between the dimensions of the shaft and the hole before assembly, if the shaft size is larger than the size of the hole;
Landing tolerance - the sum of the tolerances of the hole and shaft making up the joint;
Tolerance T - the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations;
Standard IT clearance - 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 size of the tolerance and its position relative to the nominal size;
Clearance landing - landing, at which a gap is always formed in the connection, i.e. the smallest limit hole size is greater than or equal to the largest shaft limit size;
Interference fit - landing, at which an interference is always formed in the joint, i.e. the largest hole limit size is less than or equal to the smallest shaft limit size;
Transition landing - landing, in which it is possible to obtain both clearance and interference in the connection, depending on the actual dimensions of the hole and shaft;
Landing in the hole system - Landings in which the required clearances and tightness are obtained by a combination of different fields of shaft tolerances with the tolerance field of the main hole;
Landing in the shaft system - Landings in which the required clearances and tightness are obtained by a combination of different tolerance fields of holes with the tolerance field of the main shaft.

& nbsp Tolerance fields and their corresponding limit deviations are set by different ranges of nominal sizes:
up to 1 mm - GOST 25347-82;
from 1 to 500 mm - GOST 25347-82;
over 500 to 3150 mm - GOST 25347-82;
over 3150 to 10.000 mm - GOST 25348-82.

& nbsp GOST 25346-89 sets 20 qualifications (01, 0, 1, 2, ... 18). Qualities from 01 to 5 are intended primarily for calibers.
& nbsp Tolerances and limit deviations established in the standard relate to the dimensions of parts at a temperature of +20 o C.
& nbsp Installed 27 main deviations of the shafts and 27 the main deviations of the holes. The main deviation is one of two limit deviations (upper or lower), which determines the position of the tolerance field relative to the zero line. The main one is the deviation closest to the zero line. The main deviations of the holes are indicated in capital letters of the Latin alphabet, shafts - lowercase. The layout of the main deviations with the qualifications in which it is recommended to apply them, for sizes up to 500 mm is given below. The shaded area refers to the holes. The diagram is shown in abbreviation.

Appointment of landings. Landings are selected depending on the purpose and operating conditions of equipment and mechanisms, their accuracy, and assembly conditions. In this case, it is necessary to take into account the possibility of achieving accuracy with various methods of product processing. First of all, preferred plantings should be applied. Mostly fit in the hole system. Landing of the shaft system is advisable when using some standard parts (for example, rolling bearings) and in cases where a shaft of constant diameter is used along the entire length to install several parts with different fits on it.

The tolerances of the hole and shaft in the landing should not differ by more than 1-2 quality. A larger tolerance is usually assigned to the hole. Clearances and interference should be calculated for most types of joints, especially for interference fit, friction bearings, and other fittings. In many cases, plantings can be assigned by analogy with previously designed products that are similar in working conditions.

Examples of fit applications, mainly related to preferred fittings in the hole system with sizes of 1-500 mm.

Clearance Landings. Hole combination N with shaft h (sliding landings) are mainly used in fixed joints when frequent disassembly is necessary (interchangeable parts), if it is necessary to easily move or rotate parts relative to one another when adjusting or adjusting, to center the fixedly fastened parts.

Landing H7 / h6 apply:

For interchangeable gears in machines;
- in connections with short working strokes, for example for shanks of spring valves in guide bushings (also fit H7 / g6 is applicable);
- to connect parts that should be easy to move when tightening;
- for precise direction during reciprocating movements (piston rod in the guide bushings of high pressure pumps);
- for centering housings under rolling bearings in equipment and various machines.

Landing H8 / h7 used for centering surfaces with reduced alignment requirements.

Landings H8 / h8, H9 / h8, H9 / h9 are used for fixed parts with low requirements for the accuracy of mechanisms, light loads and the need to ensure easy assembly (gears, couplings, pulleys and other parts connected to the shaft by a key; rolling bearing housings , centering of flange joints), as well as in moving joints during slow or rare translational and rotational movements.

Landing H11 / h11 used for relatively roughly centered fixed joints (centering flange covers, fixing overhead conductors), for non-responsible hinges.

Landing H7 / g6 characterized by a minimum compared with other values \u200b\u200bof the guaranteed clearance. They are used in movable joints to ensure tightness (for example, a spool in the sleeve of a pneumatic drilling machine), for precise direction or for short strokes (valves in a valve box), etc. Landings are used in particularly precise mechanisms H6 / g5 and even H5 / g4.

Landing H7 / f7 used in plain bearings at moderate and constant speeds and loads, including gearboxes; centrifugal pumps; for gears rotating freely on shafts, as well as wheels engaged by clutches; for guiding pushers in internal combustion engines. A more accurate fit of this type is H6 / f6 - used for precision bearings, hydraulic distributors of passenger cars.

Landing H7 / e7, H7 / e8, H8 / e8 and H8 / e9 used in bearings at a high speed (in electric motors, in the transmission mechanism of an internal combustion engine), with spaced bearings or a long mating length, for example, for a block of gears in machines.

Landing H8 / d9, H9 / d9 they are used, for example, for pistons in the cylinders of steam engines and compressors, in the connections of valve boxes with the compressor housing (for their dismantling, a large gap is necessary due to the formation of soot and significant temperature). More precise fits of this type - H7 / d8, H8 / d8 - are used for large bearings at high speed.

Landing H11 / d11 it is used for movable joints operating in dust and dirt (nodes of agricultural machines, railway cars), in articulated joints of rods, levers, etc., for centering the covers of steam cylinders with joint sealing ring gaskets.

Transitional landings. Designed for fixed joints of parts subjected to assembly and disassembly during repairs or operating conditions. Mutual immobility of parts is provided by dowels, pins, pressure screws, etc. Less tight fitings are prescribed, if necessary, in frequent disassembly of the connection, if inconvenience, high centering accuracy is required, under shock loads and vibrations.

Landing H7 / p6 (type deaf) gives the most durable compounds. Application examples:

For gears, couplings, cranks and other parts under heavy loads, impacts or vibrations in the joints, usually disassembled only during overhaul;
- landing installation rings on the shafts of small and medium-sized electric machines; c) landing of bushings, mounting fingers, pins.

Landing H7 / K6 (such as tense) on average gives a slight gap (1-5 microns) and provides good centering, without requiring significant effort for assembly and disassembly. It is used more often than other transitional landings: for landing pulleys, gears, couplings, flywheels (on dowels), bearing bushings.

Landing H7 / js6 (of dense type) has larger average gaps than the previous one, and is used instead to facilitate assembly if necessary.

An interference fit. The choice of fit is made on the condition that at the smallest tightness the joint strength and transmission, loads are ensured, and at the highest tightness the strength of the parts.

Landing H7 / p6 used for relatively small loads (for example, landing on the shaft of the o-ring, fixing the position of the inner ring of the bearing in crane and traction motors).

Landing H7 / g6, H7 / s6, H8 / s7 used in joints without fasteners for light loads (for example, a sleeve in the head of the connecting rod of a pneumatic engine) and with fasteners for heavy loads (landing on the key gears and couplings in rolling mills, oil drilling equipment, etc.).

Landing H7 / u7 and H8 / u8 used in joints without fasteners under significant loads, including alternating ones (for example, connecting a finger with an eccentric in a cutting apparatus of agricultural harvesting machines); with fasteners at very high loads (landing large couplings in the drives of rolling mills), at small loads, but a short mating length (valve seat in the cylinder head of a truck, a sleeve in the cleaning lever of a combine harvester).

High precision interference fit H6 / p5, H6 / g5, H6 / s5 they are used relatively rarely in joints that are particularly sensitive to interference oscillations, for example, landing a two-stage sleeve on the armature shaft of a traction motor.

Tolerances of non-mating dimensions. For non-matching dimensions, tolerances are assigned depending on functional requirements. Tolerance fields usually have:
- in the “plus” for the holes (indicated by the letter H and the number of qualifications, for example NZ, N9, N14);
- in the “minus” for the shafts (denoted by the letter h and the number of quality, for example h3, h9, h14);
- symmetrically with respect to the zero line ("plus - minus half tolerance" means, for example, ± IT3 / 2, ± IT9 / 2, ± IT14 / 2). Symmetric tolerance fields for holes can be indicated by the letters JS (for example, JS3, JS9, JS14), and for shafts by the letters js (for example, js3, js9, js14).

Tolerances for 12-18 - Qualities are characterized by non-mating or mating dimensions of relatively low accuracy. Repeatedly repeated limit deviations in these qualifications are allowed not to be indicated for the dimensions, but to be stipulated by a common record in the technical requirements.

With sizes from 1 to 500 mm

& nbsp Preferred landings are framed.

& nbsp Spreadsheet of tolerances of holes and shafts with fields according to the old OST system and ESDP.

& nbsp A complete table of tolerances and fits of smooth joints in bore and shaft systems, indicating tolerance fields for the old OST system and for ESDP:

section four

Tolerances and landings.
Measuring tool

Chapter IX

Tolerances and landings

1. The concept of interchangeability of parts

2. Pairing parts

3. The concept of tolerances

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

Dimensions between which the actual part size may fluctuate are called marginal. Of these, the larger size is called largest size limitand the smaller one smallest size limit.

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

30 +0.15 \u003d 30.15 mm;

the upper deviation is

30.15 - 30.0 \u003d 0.15 mm;

smallest size limit will be:

30 + 0.1 \u003d 30.1 mm;

lower deviation is

30.1 - 30.0 \u003d 0.1 mm.

4. Clearances and interference

5. Landing and accuracy classes

Landing. Landings are divided into mobile and motionless. Below are the most used landings, and their abbreviations are given in brackets.

6. Hole system and shaft system

There are two tolerance systems - the hole system and the shaft system.

7. Deviation tables

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

As an example, let us define the fit of movement in the hole system of the 2nd accuracy class for connecting the shaft to the hole with a nominal diameter of 70 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 \u003d 0.001 mm)

Control questions 1. What is called the interchangeability of parts in mechanical engineering?
2. What are the permissible deviations in the dimensions of parts for?
3. What are the nominal, limit and actual sizes?
4. Can the size limit be equal to the nominal?
5. What is called tolerance and how to determine tolerance?
6. What are the upper and lower deviations?
7. What is called clearance and interference? What is the gap and the interference fit for connecting the two parts?
8. What are the landings 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 the hole system and the shaft system?
12. Will the maximum deviation of the hole for different landings in the hole system change?
13. Will the limit deviations of the shaft be changed for different fits in the bore system?
14. Why is the bore system more commonly used in mechanical engineering than the shaft system?
15. How are the symbols for deviations in the hole dimensions affixed in the drawings, if the parts are made in the hole system?
16. In what units are the deviations in the tables indicated?
17. Determine using table. 7, deviations and tolerance for the manufacture of a shaft with a nominal diameter of 50 mm; 75 mm; 90 mm.

Chapter x

Measuring tool

To measure and verify the dimensions of parts, the turner has to use various measuring tools. For not very accurate measurements, use measuring rulers, calipers and calipers, and for more accurate measurements - calipers, micrometers, calibers, etc.

1. Measuring ruler. Calipers. Nutromer

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 measured part and then the stroke, which accounts for the second end of the part, is counted.

Possible measurement accuracy with a 0.25-0.5 mm ruler.

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

In fig. 75, 6, a spring caliper is shown. It is set to size using a screw and a fine-threaded nut.

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

Nutromer. For coarse measurements of internal dimensions, the caliper shown in Fig. 77, a, as well as a spring caliper (Fig. 77, b). The caliper device is similar to a caliper device; the measurement with these instruments is also similar. Instead of the caliper, you can use the caliper, turning its legs one after another, as shown in Fig. 77, c.

The accuracy of the calipers and caliper can be brought up to 0.25 mm.

2. Caliper with a reading accuracy of 0.1 mm

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

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 the frame 7 sliding along the ruler. Using screw 4, you can fix the frame on the ruler in any position.

To measure the outer surfaces, sponges 1 and 8 are used, to measure the inner surfaces of the sponge 2 and 3, and to measure the depth of the undercut, rod 6 is connected to the frame 7.

On frame 7 there is a scale with strokes for counting fractional fractions of a millimeter, called nonius. Nonius allows measurements with an accuracy of 0.1 mm (decimal nonius), and in more accurate calipers - with an accuracy of 0.05 and 0.02 mm.

Vernier device. Let us consider how the vernier caliper reading is performed 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 nonius 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 tightly, then the zero stroke of the vernier will exactly coincide with the zero stroke of the ruler. The remaining strokes of the nonius, except for the last, will not have such a coincidence: the first stroke of the nonius will not reach the first stroke of the line by 0.1 mm; the second stroke of the nonius does not reach the second stroke of the ruler by 0.2 mm; the third stroke of the nonius will not reach the third stroke of the ruler by 0.3 mm, etc. The tenth stroke of the nonius will exactly coincide with the ninth stroke of the ruler.

If you move the frame so that the first stroke of the nonius (not counting the zero) coincides with the first stroke of the ruler, then between the lips of the vernier caliper you get a gap of 0.1 mm. If the second vernier stroke coincides with the second stroke of the ruler, the gap between the lips is already 0.2 mm, when the third vernius stroke coincides with the third stroke of the ruler, the gap will be 0.3 mm, etc. Therefore, the nonius stroke that exactly matches which - either a stroke of the ruler, shows the number of tenths of a millimeter.

When measuring with a caliper, an integer number of millimeters is first counted, which is judged by the position occupied by the zero stroke of the vernier, and then they look at what stroke of the vernier the stroke of the measuring line coincided, and tenths of a millimeter are determined.

In fig. 79, b shows the position of the vernier when measuring a part with a diameter of 6.5 mm. Indeed, the zero stroke of the nonius lies between the sixth and seventh strokes of the measuring line, and therefore the diameter of the part is 6 mm plus the nonius reading. Further we see that one of the strokes of the line coincided with the fifth stroke of the nonius, which corresponds to 0.5 mm, so the diameter of the part will be 6 + 0.5 \u003d 6.5 mm.

3. Caliper

To measure the depth of grooves and grooves, as well as to determine the correct position of the ledges along the length of the roller, a special tool called depth gauge (Fig. 80). The device of the caliper is similar to the device of the 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, according to which using the vernier 3 on frame 2, the depth of the groove or groove is determined, as shown in Fig. 80. Counting by the vernier is carried out in the same way as when measured with a caliper.

4. Precision vernier caliper

For work performed with greater accuracy than hitherto considered, apply precision (i.e. accurate) calipers.

In fig. 81 shows the precision caliper of the plant named after Voskova having a measuring ruler 300 mm long and nonius.

The length of the nonius scale (Fig. 82, a) is equal to 49 divisions of the measuring line, which is 49 mm. These 49 mm are precisely divided into 50 parts, each of which is equal to 0.98 mm. Since one division of the measuring ruler is 1 mm, and one division of the nonius is 0.98 mm, it can be said that each division of the nonius is shorter than each division of the measuring ruler by 1.00-0.98 \u003d \u003d 0.02 mm. This value of 0.02 mm indicates that accuracywhich can be provided by the nonius of the considered precision caliper when measuring parts.

When measuring with a precision caliper, the number of whole millimeters that is traversed by the zero stroke of the vernier must be added as many hundredths of a millimeter as the vernier stroke coincides with the stroke of the measuring line. For example (see Fig. 82, b), along the vernier caliper line, the vernier stroke passed 12 mm, and its 12th stroke coincided with one of the strokes of the measuring line. Since the coincidence of the 12th stroke of the nonius means 0.02 x 12 \u003d 0.24 mm, the measured size is 12.0 + 0.24 \u003d 12.24 mm.

In fig. 83 shows the caliper of the Caliber 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 nonius is the number 25, against the tenth - 50, etc. The length of each division of the nonius is

From fig. 83 it is seen that with the jaws of the caliper closed tightly, only the zero and the last strokes of the vernier coincide with the strokes of the ruler; the remaining strokes of the nonius will not have such a coincidence.

If you move the frame 3 until the first stroke of the vernier coincides with the second stroke of the ruler, then between the measuring surfaces of the jaws of the vernier caliper, a gap of 2-1.95 \u003d 0.05 mm is obtained. If the second vernier stroke coincides with the fourth stroke of the ruler, the gap between the measuring surfaces of the jaws will be 4-2 X 1.95 \u003d 4 - 3.9 \u003d 0.1 mm. If the third stroke of the nonius coincides with the next stroke of the line, the gap will be 0.15 mm.

The countdown on this caliper is carried out similarly to the above.

The precision vernier caliper (Fig. 81 and 83) consists of a ruler 1 with jaws 6 and 7. The markings are marked on the ruler. In frame 1, frame 3 with jaws 5 and 8 can move. Vernier 4 is screwed to the frame. For rough measurements, frame 3 is moved along line 1 and, after fixing with screw 9, counts down. For accurate measurements, use the micrometric feed of the frame 3, consisting of a screw and nut 2 and a clamp 10. Tighten the screw 10, rotate the nut 2 and feed the frame 3 with a micrometer screw until the jaw 8 or 5 is in close contact with the measured part, after which they are counted.

5. Micrometer

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

In order that during rotation of the drum could not happen too strong pressing by the spindle on the measured part, there is a safety head 7 with a ratchet. Rotating the head 7, we will extend the spindle 3 and push the part to the heel 2. When this preload is sufficient, with a further rotation of the head its ratchet will slip and a rattle will be heard. After this, the rotation of the head is stopped, secured by turning the clamping ring (stopper) 4, the resulting opening of the micrometer and counting.

To produce readings on the stem 5, which is integral with the bracket of 1 micrometer, a scale with millimeter divisions, divided in half, is plotted. The drum 6 has a beveled chamfer, divided around the circumference into 50 equal parts. Dashes from 0 to 50 every five divisions are marked with numbers. In the zero position, i.e., when the heel touches 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, the spindle 3 will move by 0.5 mm. Therefore, if you rotate the drum not a full revolution, i.e., not 50 divisions, but one division, or part of a revolution, then the spindle will move to This is the accuracy of the micrometer. When counting, they first look at how many whole millimeters or integer and a half millimeters the drum on the stem opened, then the number of hundredths of a millimeter, which coincides with the line on the stem, is added to this.

In fig. 84 on the right shows the size taken by the micrometer when measuring the part; need to make a countdown. The drum opened 16 whole divisions (half not open) on the scale of the stem. The seventh stroke of the chamfer coincided with the line of the stem; therefore, we will have another 0.07 mm. The full count is 16 + 0.07 \u003d 16.07 mm.

In fig. 85 shows several micrometer measurements.

It should be remembered that a micrometer is an accurate tool that requires a careful attitude; therefore, when the spindle slightly touches the surface of the measured part, do not rotate the drum anymore, and to further move the spindle, rotate the head 7 (Fig. 84) until a rattle sounds.

6. Nutrometers

Nutrometers (shtikhmasy) are used for accurate measurements of the internal dimensions of parts. There are constant and sliding calipers.

Permanent or hard, caliper (Fig. 86) is a metal rod with measuring ends having a spherical surface. The distance between them is equal to the diameter of the measured hole. In order to exclude the influence of the heat of the hand holding the caliper on its actual size, the caliper is provided with a holder (handle).

To measure internal dimensions with an accuracy of 0.01 mm, micrometric calipers are used. Their device is similar to a micrometer device for outdoor measurements.

The head of the micrometer caliper (Fig. 87) consists of a sleeve 3 and a drum 4 connected to a micrometer screw; screw pitch 0.5 mm, stroke 13 mm. A stopper 2 and a heel / with a measuring surface are placed in the sleeve. Holding the sleeve and rotating the drum, you can change the distance between the measuring surfaces of the caliper. Counts are made, like a micrometer.

The measurement limits of the shtikhmas head are from 50 to 63 mm. To measure large diameters (up to 1500 mm), extensions 5 are screwed onto the head.

7. Ultimate measuring tools

In the serial production of parts according to tolerances, the use of universal measuring tools (vernier calipers, micrometer, micrometric caliper) is impractical, since measuring with these tools is a relatively complex and lengthy operation. Their accuracy is often insufficient, and, in addition, the measurement result depends on the skill of the employee.

To check whether the dimensions of the parts are within precisely defined limits, use a special tool extreme gauges. Gauges for checking shafts are called brackets, and for checking holes traffic jams.

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

The side of the smaller bracket is called impassable (branded “NOT”), the opposite side with a large size - checkpoint (branded "PR"). A shaft is deemed suitable if the bracket lowered on it by the passage side slides down under the influence of its weight (Fig. 88), and the impassable side cannot be found on the shaft.

To measure shafts of 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 check the largest permissible diameter of the part, and the rear the smallest one. These brackets are lighter and significantly speed up the control process, since for measurement it is enough to put a bracket once.

In fig. 90 shown adjustable limit bracket, which, when worn, can be restored to the correct dimensions by moving the measuring pins. In addition, such a bracket can be adjusted for a given size and thus a large number of sizes can be checked with a small set of brackets.

To change to a new size, loosen the locking screws 1 on the left leg, respectively move the measuring pins 2 and 3 and tighten the screws 1 again.

Widespread flat terminal brackets (Fig. 91) made of sheet steel.

Traffic jam measurement. Cylindrical limit gauge plug (Fig. 92) consists of the through plug 1, the through plug 3 and the handle 2. The through plug ("PR") has a diameter equal to the smallest allowable hole size, and the through plug ("NOT") is the largest. If the “PR” plug passes and the “NOT” plug does not pass, then the diameter of the hole is greater than the smallest limit and less than the largest, that is, lies within acceptable limits. The through plug is longer than the through plug.

In fig. 93 shows a hole measurement with a limit plug on a lathe. The passage side should easily pass through the hole. If the impassable 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, use two flat plug gauges (Fig. 94), one of which has a size equal to the largest, and the second to the smallest allowed. The passage side has a greater width than the passage passage.

In fig. 95 shown adjustable limit plug. It can be adjusted for several sizes in the same way as an adjustable limit bracket, or you can restore the correct size of worn measuring surfaces.

8. Rays and indicators

Reismas. To accurately verify the correct installation of the part in a four-jaw chuck, on a square, etc. thickness gage.

Using a thickness gauge, you can also mark the center holes in the ends of the part.

The simplest surface gage is shown in Fig. 96 a. It consists of a massive tile with a precisely machined bottom plane and a rod along which a crawler with a scriber needle moves.

Reismas more advanced design, shown in Fig. 96 b The reamer needle 3 with the help of the hinge 1 and the clamp 4 can be brought to the point with the tip to the surface being checked. Precise installation by screw 2.

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

The indicator (Fig. 97) has a metal case 6 in the form of a clock, in which the mechanism of the device is enclosed. Through the indicator housing passes the rod 3 with the protruding outward tip, always under the influence of a spring. If you press the bar from the bottom up, it will move in the axial direction and at the same time turn the hand 5, which will move on the dial having a scale of 100 divisions, each of which corresponds to the movement of the bar by 1/100 mm. When moving the rod 1 mm, hand 5 will make a complete revolution on the dial. To read whole revolutions, use arrow 4.

During measurements, the indicator should always be rigidly fixed relative to the original measuring surface. In fig. 97, and depicts a universal stand for mounting the indicator. The indicator 6 using the rods 2 and 1 of the couplings 7 and 8 is fixed on the vertical rod 9. The rod 9 is fixed in the groove 11 of the prism 12 with a knurled nut 10.

To measure the deviation of the part from a given size, the indicator tip is brought to it until it touches the measured surface and notice the initial indication of arrows 5 and 4 (see Fig. 97, b) on the dial. Then the indicator is moved relative to the measured surface or the measured surface relative to the indicator.

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

In fig. 98 shows an example of using an indicator to verify the alignment of the centers of the front and rear headstock of a lathe. For a more accurate check, you should install an accurate, polished roller between the centers, and an indicator in the tool holder. Having brought the indicator button to the surface of the roller on the right and noticing the indication of the arrow of the indicator, manually move the caliper with the indicator along the roller. The difference between the deviations of the arrow of the indicator in the extreme positions of the roller will show by what amount the tailstock housing should be moved in the transverse direction.

Using the indicator, you can also check the end surface of the part machined on the machine. The indicator is fixed in the tool holder instead of the tool and is moved together with the tool holder in the transverse direction so that the indicator button touches the surface to be checked. The deviation of the indicator arrow will show the amount of runout of the end plane.

Control questions 1. What parts does the caliper consist of with an accuracy of 0.1 mm?
2. How is the vernier caliper accurate to 0.1 mm?
3. Install on the vernier caliper dimensions: 25.6 mm; 30.8 mm; 45.9 mm.
4. How many divisions does the nonius of a precision vernier caliper have an accuracy of 0.05 mm? The same, with an accuracy of 0.02 mm? What is the length of one division of the nonius? How to read nonius testimony?
5. Set on a precision vernier caliper dimensions: 35.75 mm; 50.05 mm; 60.55 mm; 75 mm.
6. What parts does the micrometer consist of?
7. What is the pitch of the micrometer screw?
8. How is a micrometer measured?
9. Set by micrometer dimensions: 15.45 mm; 30.5 mm; 50.55 mm.
10. In what cases are calipers used?
11. Why are limit gauges used?
12. What is the purpose of the passage and non-passage sides of the limit gauges?
13. What constructions of limit brackets do you know?
14. How to check the correct size of the limit plug? Terminal bracket?
15. What is the indicator used for? How to use it?
16. How is the thickness gauge arranged and what is it used for?

Chapter 1. The bore system and shaft system. Features

differences, advantages ………………………………………………… .3

1.1. The concepts of “shaft” and “hole” …………………………………………… ... 3

1.2. Calculation of fit parameters and gauges for pairing in

hole and shaft systems ………………………………………………… .6

Chapter 2. Tolerances and fits of keyed joints ……………………… ... 10

2.1. Tolerance of the thread ………………………………………………………………… 15

2.2. Size tolerance. Tolerance field …………………………………………… ..18

2.3. Formation of tolerance and landing fields ……………………………… ..19

Chapter 3. Tolerance and landing systems ……………………………………… ..21

3.1. Layouts of tolerance fields of standard interfaces ……… .23

List of used literature …………………………………………… ..30

Chapter 1. The bore system and shaft system. Features, differences, advantages

1.1. The concepts of "shaft" and "hole"

Structurally, any part consists of elements (surfaces) of various geometric shapes, part of which interacts (forms landing-mates) with the surfaces of other parts, and the rest of the elements is free (non-conjugate). In the terminology on tolerances and fits, the sizes of all elements of parts, regardless of their shape, are conditionally divided into three groups: shaft sizes, hole sizes and dimensions not related to shafts and holes.

Shaft - a term conventionally used to refer to the external (covered) elements of parts, including non-cylindrical elements, and accordingly the mating dimensions.

Hole - a term conventionally used to refer to internal (covering) elements of parts, including non-cylindrical elements, and accordingly mating dimensions.

For mating elements of parts based on the analysis of working and assembly drawings, and, if necessary, product samples, set covering and covered surfaces of the mating parts and, thus, the belonging of the mating surfaces to the groups of "shaft" and "hole".

For non-mating elements of parts, the installation of this shaft or hole is performed using the technological principle that if the size of the element increases when processing from the base surface, then this hole, and if the size of the element decreases, then this is the shaft.

The composition of the group of sizes and elements of parts not related to either shafts or holes is relatively small (for example, chamfers, fillet radii, fillets, protrusions, depressions, axle distances (etc.).

When assembling, the parts to be joined are in contact with each other by separate surfaces, which are called mating surfaces. The dimensions of these surfaces are called mating dimensions (for example, the diameter of the bore of the sleeve and the diameter of the shaft on which the sleeve is fitted). Distinguish between covering and covered surfaces and, accordingly, covering and covered dimensions. The covering surface is usually called the hole, and the covered surface is called the shaft.

The interface has one nominal size for the hole and shaft, and the limit, as a rule, is different.

If the actual (measured) dimensions of the manufactured product do not go beyond the largest and smallest limit sizes, then the product meets the requirements of the drawing and is executed correctly.

The designs of technical devices and other products require different contacts of mating parts. Some parts must be movable relative to others, while others should form fixed joints.

The nature of the connection of parts, determined by the difference between the diameters of the hole and the shaft, creating more or less freedom of their relative movement or the degree of resistance to mutual displacement, is called landing.

There are three groups of landings: moving (with a gap), fixed (with an interference fit) and transitional (a gap or interference is possible).

The gap is formed as a result of a positive difference between the diameter of the hole and the shaft. If this difference is negative, then the landing will be an interference fit.

Distinguish the largest and smallest gaps and interference. The largest clearance is the positive difference between the largest limit hole size and the smallest shaft limit

The smallest clearance is the positive difference between the smallest limit hole size and the largest limit shaft size.

The largest interference is the positive difference between the largest limit shaft size and the smallest hole maximum size.

The smallest interference is the positive difference between the smallest limit shaft size and the largest limit hole size.

The combination of two tolerance fields (holes and shaft) determines the nature of the fit, i.e. the presence of a gap or interference in it.

The tolerance and landing system found that in each pair of one of the parts (main) any deviation is zero. Depending on which of the mating parts is taken as the main one, there are landings in the hole system and landings in the shaft system.

Landings in the hole system are landings in which various gaps and interference are obtained by connecting different shafts to the main hole.

Landings in the shaft system - landings in which various gaps and interference are obtained by connecting various holes to the main shaft.

The use of a hole system is preferred. The shaft system should be used in cases where it is justified by structural or economic considerations (for example, the installation of several bushings, flywheels or wheels with different fits on one smooth shaft).

1.2. Calculation of fit parameters and gauges for pairing in hole and shaft systems

1. Deviations of the hole and shaft according to GOST 25347-82:

ES \u003d +25 μm, es \u003d -80 μm

EI \u003d 0; ei \u003d -119 μm

Fig. 1. Arrangement of landing tolerance fields

2. Limit sizes:

3. Hole and shaft tolerances:

4. Clearances:

5. Average clearance:

6. Clearance tolerance (fit)

7. Designation of limit deviations of sizes on design drawings:

a) designation of tolerance fields

b) numerical values \u200b\u200bof limit deviations:

c) symbol of tolerance fields and numerical values \u200b\u200bof limit deviations:

8. Dimension designation in working drawings:

9. Calibration calculation for checking the hole and shaft.

Tolerances and deviations of calibers in accordance with GOST 24853-81:

a) for plug gauges

Z \u003d 3.5 μm, Y \u003d 3 μm, H \u003d 4 μm;

b) for caliber brackets

Z 1 \u003d 6 μm, Y 1 \u003d 5 μm, H 1 \u003d 7 μm;

Fig. 2 Layout of tolerance fields for calibers

Hole Test Gauges

Cork ol

Executive OL tube size:

Unlikely wear and tear
microns;

Wear cork workers allow up to size:

Wear plugs shop controller is permissible up to the size:

The cork is NOT

Executive plug size NOT:

Shaft Check Gauges

Executive clamp size OL:

Unlikely wear and tear
microns;

Wear staples workers allowable to size:

The wear of the bracket by the shop inspector is permissible up to the size:

Executive staple size is NOT

Chapter 2. Tolerances and fits of keyed joints

A key connection is one of the types of shaft connections with a sleeve using an additional structural element (keys), designed to prevent their mutual rotation. Most often, the key is used to transmit torque in the joints of a rotating shaft with a gear wheel or with a pulley, but other solutions are also possible, for example, protecting the shaft against rotation relative to a fixed housing. In contrast to tightened joints, which ensure mutual immobility of parts without additional structural elements, keyed connections are detachable. They allow disassembly and reassembly of the structure with the same effect as in the initial assembly.

The key connection includes at least three fittings: the shaft sleeve (centering coupling) the key-groove of the shaft and the key-groove of the sleeve. The accuracy of centering the parts in the keyway is ensured by the fit of the sleeve on the shaft. This is an ordinary smooth cylindrical mate, which can be assigned with very small gaps or interference, therefore transitional fit is preferred. In conjugation (dimensional chain) along the height of the keys, a clearance at face value is specially provided (the total depth of the grooves of the sleeve and shaft is greater than the height of the keys). Another pairing is possible - along the length of the key, if the prismatic key with rounded ends is laid in a blind groove on the shaft.

The key joints can be movable or fixed in the axial direction. In movable joints, directional keys are often used with screws attached to the shaft. A gear (a block of gears), a coupling half, or other part usually moves along a shaft with a guide key. The dowels mounted on the sleeve can also serve to transmit torque or to prevent the sleeve from turning during its movement along the fixed shaft, as was done at the bracket of the heavy rack for measuring heads such as microcovers. In this case, the guide is a shaft with a keyway.

In shape, the dowels are divided into prismatic, segment, wedge, and tangential. The standards provide for different designs of certain types of keys.

Prismatic dowels make it possible to obtain both movable and fixed joints. Segment keys and wedge keys, as a rule, serve for the formation of fixed joints. The shape and dimensions of the cross sections of the keys and grooves are standardized and are selected depending on the diameter of the shaft, and the type of key connection is determined by the operating conditions of the connection.

The maximum deviations of the depths of the grooves on the shaft t1 and in the sleeve t2 are shown in table No. 1:

Table number 1

Widths b - h9;

Heights h - h9, and with h over 6 mm - H21.

Depending on the nature (type) of the keyway, the standard sets the following tolerance fields for the width of the groove:

To ensure the quality of the keyway connection, which depends on the accuracy of the location of the symmetry planes of the grooves of the shaft and the sleeve, tolerances of symmetry and parallelism are assigned and indicated in accordance with GOST 2.308-79.

The numerical values \u200b\u200bof the location tolerances are determined by the formulas:

T \u003d 0.6 T sp

T \u003d 4.0 T sp

where T sp - the tolerance of the width of the keyway b.

The calculated values \u200b\u200bare rounded to standard in accordance with GOST 24643-81.

The surface roughness of the keyway is selected depending on the tolerance fields of the dimensions of the keyway (Ra 3.2 μm or 6.3 μm).

The symbol for the keys consists of:

The words "Key";

Designation of execution (execution 1 do not indicate);

Section dimensions b x h and key lengths l;

Designation of the standard.

An example of a symbol for a key of execution 2 with dimensions b \u003d 4 mm, h \u003d 4 mm, l \u003d 12 mm

Dowel 2 - 4 x 4 x 12 GOST 23360-78.

Prismatic guide keys are fixed in the grooves of the shaft with screws. A threaded hole serves to spin the keys during dismantling. An example of a symbol for a prismatic guide key, version 3 with dimensions b \u003d 12 mm, h \u003d 8 mm, l \u003d 100 mm, Key 3 - 12 x 8 x 100 GOST 8790-79.

Segment keys are used, as a rule, to transmit small torques. Sizes of segment keys and keyways (GOST 24071-80) are selected depending on the diameter of the shaft.

The dependence of the tolerance fields of the groove width of the segment keyway on the nature of the keyway:

For heat-treated parts, maximum deviations of the width of the groove of the shaft according to H11 are allowed, the width of the groove of the sleeve is D10.

The standard establishes the following key size tolerance fields:

Widths b - h9;

Heights h (H2) - H21;

Diameter D - H22.

The symbol for the segment keys consists of the word "Key"; designations of execution (execution 1 do not indicate); section dimensions b x h (H2); designations of the standard.

Wedge keys are used in fixed joints, when the requirements for alignment of the connected parts are low. The dimensions of the wedges and keyways are normalized by GOST 24068-80. The length of the groove on the shaft for the V-keys of execution 1 is equal to 2l, for other versions the length of the groove is equal to the length l of the key.

The maximum deviations of sizes b, h, l for wedge keys are the same as for prismatic (GOST 23360-78). For the key width b, the standard establishes connections for the width of the groove of the shaft and the sleeve using tolerance fields D10. The length of the groove of the shaft L is according to H15. The limiting deviations of the depths t1 and t2 correspond to deviations for the keys. Limit deviations of the angle of inclination of the upper face of the key and groove ± АТ10 / 2 according to GOST 8908-81. An example of the designation of a wedge key of execution 2 with dimensions b \u003d 8 mm, h \u003d 7 mm, l \u003d 25 mm: Key 2 - 8 x 7 x 25 GOST 24068-80.

The control of the keyed elements by universal measuring instruments is essentially difficult due to the smallness of their transverse dimensions. Therefore, to control them, calibers are widely used.

In accordance with the Taylor principle, the straight-through gauge for controlling an opening with a keyway is a shaft with a key equal to the length of the keyway or the length of the keyway. Such a caliber provides comprehensive control of all sizes, shapes and locations of surfaces. A set of pass-through gauges is designed for element-wise control and includes a pass-through gauge for control of the centering hole (smooth impassable stopper of a complete or incomplete profile) and templates for element-wise control of the width and depth of the keyway.

The straight-through gauge for controlling a shaft with a keyway is a prism (“rider”) with a key-protrusion equal to the length of the keyway or the length of the keyway. A set of pass-through gauges is designed for element-wise control and includes a pass-through gauge-bracket to control the dimensions of the centering surface of the shaft and templates for element-wise control of the width and depth of the keyway.

2.1 Thread tolerances

Screw and nut connection, depending on the accuracy of their threads. All threads accepted in mechanical engineering, except for pipe ones, have gaps along the tops and troughs, and if the threaded joint is correctly made, the screw and nut touch only on the sides (Fig. 167, a) For full contact of the sides of the profile of all threads involved in This connection, the main importance is the exact execution (to some extent) of the dimensions of the average diameter of the thread of the screw and nut, the pitch of this thread and the angle of its profile. The accuracy of the outer and inner diameters of the screw and nut is less important, since the contact of the thread surfaces along these diameters does not occur.

If the clearance is too large in the average diameter, the contact of the thread turns occurs on only one side (Fig. 167, b). If the average diameter gap is too small for screwing up threaded parts, one of which has a wrong thread pitch, it is necessary that the turns of one of the parts cut into the turns of the other. For example, if the screw pitch is more than due or, as they say, “stretched”, then to connect such a screw to a nut with the correct thread, the nut turns must cut into the screw turns (Fig. 167, at).This is obviously impossible, and the screwing of these parts can be achieved only by reducing the average diameter of the screw (Fig. 167, d) or by increasing the average diameter of the threaded parts, one of which has a wrong thread pitch, it is necessary that the turns of one of the parts cut into turns other. For example, if the screw pitch is more than due or, as they say, “stretched”, then to connect such a screw to a nut with the correct thread, the nut turns must cut into the screw turns (Fig. 167, at).This, obviously, is impossible, and the screwing of these parts can be achieved only by reducing the average diameter of the screw (Fig. 167, d) andwhether an increase in the average diameter of the nut. In this case, it may happen that only one extreme turn of the nut touches the corresponding turn of the screw and, not along its entire lateral surface.

In the same way, it is possible to ensure screwing of the thread of the parts if the angle of one of them or the position of this profile is incorrect. For example, if the profile angle of the screw is less than necessary, which excludes the possibility of screwing the screw with the correct nut (Fig. 167, d)then with a decrease in the average diameter of this screw, these parts can be screwed (Fig. 167, e).In this case, the screw and nut threads come into contact only in the upper portions of the side of the screw thread profile and in the lower portions of the nut thread profile.

By reducing the average diameter of the screw with the wrong position of the profile (Fig. 167, g)it is also possible to obtain screwing of this screw with a nut, however, even in this case, the contact surface of the screw and nut threads may not be sufficient for a high-quality threaded connection (Fig. 167, h).

Construction of tolerances of threads. Difficulties associated with checking the cut thread arise mainly when measuring its pitch and profile. Indeed, if all three diameters of the external thread can be checked with sufficient accuracy in most cases by means of micrometers, then for the corresponding (in accuracy) verification of the pitch and angle of the thread profile more complex measuring tools and even instruments are needed. Therefore, in the manufacture of threaded parts, tolerances are only set for thread diameters; permissible errors in the pitch and profile are taken into account in the tolerance on the average diameter, because, as was shown above, errors in the pitch and profile can always be eliminated by changing the average diameter of one of the threaded parts.

The tolerance on the average diameter is set so that, with small errors in the pitch or angle of the profile, the screw and nut are screwed without compromising the strength of the threaded joint.

Tolerances on the outer and inner diameters of the screw and nut are assigned so that a clearance is obtained between the top of the thread profile of the screw and the corresponding root of the thread of the nut.

The numerical values \u200b\u200bof these tolerances are taken to be large, exceeding approximately two times the tolerances on the average diameter.

Tolerances for metric and inch threads. For metric threads with large and small steps for diameters from 1 to 600 mm in accordance with GOST 9253-59, three accuracy classes are established: the first (cl./) second (Cl. 2)and third (Cl. 3),and for threads with small steps also class 2a (Cl. 2a).These designations were indicated on previously issued drawings. In the new GOST 16093-70 accuracy classes are replaced by accuracy qualifications, which are assigned the designations: h, g, eand d for bolts and Nand G for nuts.

For inch and pipe threads, two accuracy classes are installed - the second (Cl. 2)and third (Cl. 3).

Tolerances for trapezoidal threads. For trapezoidal threads, three accuracy classes are established, indicated: class 1, cl. 2, class 3, cl. ZX.

2.2. Size tolerance. Tolerance field

Size tolerance is the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations. The tolerance is indicated by IT (International Tolerance) or TD - hole tolerance and Td - shaft tolerance.

Size tolerance is always positive. The size tolerance expresses the scatter of the actual dimensions in the range from the largest to the smallest limit sizes, physically determines the size of the officially allowed error of the actual size of the part element during its manufacture.

The tolerance field is a field limited by upper and lower deviations. The tolerance field is determined by the tolerance value and its position relative to the nominal size. With the same tolerance for the same nominal size, there may be different tolerance fields.

The concept of a zero line is introduced for the graphic representation of tolerance fields, which allows one to understand the ratios of nominal and maximum dimensions, maximum deviations, and tolerances.

The zero line is the line corresponding to the nominal size, from which the limit deviations of the dimensions are plotted when the tolerance fields are graphically displayed. If the zero line is horizontal, then on a conditional scale, positive deviations are laid up, and negative deviations are laid down from it. If the zero line is vertical, then positive deviations are postponed to the right of the zero line.

The tolerance fields of the holes and shafts can occupy a different location relative to the zero line, which is necessary for the formation of various landings.

Distinguish between the beginning and end of the tolerance field. The beginning of the tolerance field is the border corresponding to the largest volume of the part and allowing to distinguish suitable parts from correctable unusable. The end of the tolerance field is the boundary corresponding to the smallest part volume and allowing to distinguish suitable parts from irreparable unusable parts.

For holes, the beginning of the tolerance field is determined by the line corresponding to the lower deviation, the end of the tolerance field is determined by the line corresponding to the upper deviation. For shafts, the beginning of the tolerance field is determined by the line corresponding to the upper deviation, the end of the tolerance field is determined by the line corresponding to the lower deviation.

2.3. Formation of tolerance and landing fields

The tolerance field is formed by a combination of one of the basic relationships with the tolerance in one of the qualifications, therefore the symbol of the tolerance field consists of the symbol of the main deviation (letter) and the number of the qualification.

Preferred tolerance fields are provided by cutting tools and calibers on a normal series of numbers, and recommended by only calibers. Additional tolerance fields are limited use fields and are used when the application of the main tolerance fields does not allow to fulfill the requirements for the product.

The ESDP provides for all landing groups: with clearance, interference and transitional. Landings have no names reflecting the structural, technological or operational properties, and are presented only in the symbols of the combined tolerance fields of the hole and shaft.

Landings are typically used in a bore system (preferably) or in a shaft system.

All landings in the hole system for given nominal sizes of mates and their qualifications are formed by tolerance fields of holes with unchanged basic deviations None of the main basic deviations of the shafts.

For landings with a gap in the system, holes are used according to shaft tolerances with basic deviations from a to h inclusive.

For transitional landings in the hole system, no shaft tolerances with basic deviations to, t, p, are used.

For interference fit in the hole system, the fields d of the shaft starts are selected with the main deviations from p to zc.

For landings in the shaft system for specified nominal sizes and coupling qualities, tolerance fields are used with constant basic shaft deviations h and various basic hole deviations.

For landings with a gap in the shaft system, select the tolerance fields of the holes with the main deviations from A to H inclusive.

For transitional landings in the shaft system, the fields are used before the start of the holes with the main deviations Js, K, M, N.

For the range from 1 to 500 mm, 69 recommended landings are allocated in the hole system, 17 of which are preferred, and 59 recommended landings in the shaft system, including 11 preferred.

Chapter 3. Tolerance and landing systems

Taking into account the experience of use and the requirements of national tolerance systems, the ESDP consists of two equal tolerance and landing systems: hole systems and shaft systems.

The allocation of these tolerance systems and landings caused by the difference in the methods of formation of landings.

The hole system is a tolerance and landing system in which the maximum hole sizes for all landings for a given nominal dimension dH of coupling and quality remain constant, and the required fit is achieved by changing the maximum shaft dimensions.

Shaft system - a system of tolerances and landings, in which the limit shaft sizes for all landings for a given nominal size of coupling and quality remain constant, and the required fits are achieved by changing the maximum size of the hole.

The hole system has wider application in comparison with the shaft system, which is associated with its advantages of a technical and economic nature at the design development stage. To process holes with different sizes, it is necessary to have different sets of cutting tools (drills, countersinks, reamers, broaches, etc.), and the shafts, regardless of their size, are treated with the same cutter or grinding wheel. Thus, the hole system requires significantly lower production costs both in the process of experimental processing of the interface, and in conditions of mass or large-scale production.

The shaft system is preferable in comparison with the hole system when the shafts do not require additional marking, but can go to the assembly after the so-called procurement processes.

The shaft system is also used in cases where the hole system does not allow the required connections to be made with these structural solutions.

When choosing a landing system, it is necessary to take into account the tolerances on standard parts and components of products: in ball and roller bearings, the fittings of the inner ring on the shaft are carried out in the hole system, and the fit of the outer ring in the body of the product is in the shaft system.

A part, the dimensions of which for all landings at the same nominal size and quality, do not change, it is customary to call the main part.

In accordance with the scheme of planting in the hole system, the main part is the hole, and in the shaft system, the shaft.

The main shaft is a shaft whose upper deflection is zero.

The main hole is the hole whose lower deviation is zero.

Thus, in the hole system, the shafts will be non-main parts, and holes in the shaft system.

The location of the tolerance fields of the main parts must be constant and independent of the location of the tolerance fields of the minor parts. Depending on the location of the tolerance field of the main part relative to the nominal interface size, extremely asymmetric and symmetric tolerance systems are distinguished.

ESDP is an extremely asymmetric tolerance system, while the Tolerance is set "into the body" of the part, i.e. in plus - in the direction of increasing the size from the nominal for the main hole and in minus - in the direction of decreasing the size of the nominal for the main shaft.

Extremely asymmetric tolerance and landing systems have some economic advantages over symmetric systems, which is associated with the provision of basic parts with limit gauges.

It should also be noted the use in some cases of unsystematic landings, i.e., the hole is made in the shaft system, and the shaft in the hole system. In particular, an unsystematic fit is used for the sides of a straight-line splined connection.

3.1. Layouts of tolerance fields of standard interfaces

1 Smooth cylindrical joint

Parameter	Value









Td \u003d dmax - dmin \u003d es - ei \u003d
TD \u003d Dmax - Dmin \u003d ES - EI \u003d
Smax \u003d Dmax - dmin \u003d
Smin \u003d Dmin - d max \u003d
Scp \u003d (Smax + Smin) / 2 \u003d
TS \u003d Smax - Smin \u003d
Pairing pattern
Landing job system	Main hole

Parameter	Value









Td \u003d dmax - dmin \u003d es - ei \u003d
TD \u003d Dmax - Dmin \u003d ES - EI \u003d
Nmin \u003d dmin - Dmax
Nmax \u003d dmax - Dmin
Ncp \u003d (Nmax + Nmin) / 2 \u003d
TN \u003d Nmax - Nmin \u003d
Pairing pattern
Landing job system	Main shaft

Parameter	Value









Td \u003d dmax - dmin \u003d es - ei \u003d
TD \u003d Dmax - Dmin \u003d ES - EI \u003d
Smax \u003d Dmax - dmin \u003d
Nmax \u003d dmax - Dmin \u003d
Scp \u003d (Smax + Smin) / 2 \u003d
TS \u003d Smax - Smin \u003d
Pairing pattern	Transitional
Landing job system	Main hole

For a combined landing, we determine the probability of formation of interference fit and fit clearance. The calculation is performed in the following sequence.

We calculate the mean square deviation of the gap (interference), microns

define the limit of integration

tabular value of the function f (z) \u003d 0.32894

The probability of interference in relative units

P N "\u003d 0.5 + F (z) \u003d 0.5 + 0.32894 \u003d 0.82894

The probability of interference in percent

P N \u003d P N "x 100% \u003d 0.82894 * 100% \u003d 82.894%

The probability of clearance in relative units

P Z "\u003d 1 - P N \u003d 1 - 0.82894 \u003d 0.17106

The probability of clearance in percent

P Z \u003d P Z "x 100% \u003d 0.17103 * 100% \u003d 17.103%

List of references

1. Korotkov V. P., Taits B. A. "Fundamentals of metrology and the theory of accuracy of measuring devices." M .: Publishing house of standards, 1978. 351 p.

2. A. I. Yakushev, L. N. Vorontsov, N. M. Fedotov. “Interchangeability, standardization and technical measurements”: - 6th ed., Revised. and add. - M.: Mechanical Engineering, 1986. - 352 p., Ill.

3. V. V. Boytsova "Fundamentals of standardization in mechanical engineering." M .: Publishing house of standards. 1983. 263 p.

4. Kozlovsky N.S., Vinogradov A.N. Fundamentals of standardization, tolerances, fit and technical measurements. M., "Engineering", 1979

5. Tolerances and landings. Directory. Ed. V.D. Myagkov. T.1 and 2.L., "Engineering", 1978

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