The designation of the deviation of the form and location of surfaces GOST. Location tolerances

GOST 24642-81 establishes terms and definitions related to the main types of deviations and tolerances of the shape and location of surfaces of machine parts and instruments. The terminology standard complies with the international standards ISO 1101-83 and ISO 5459-81.

Consists of four parts:

1 - general terms and definitions;

2 - deviations and tolerances of forms;

3 - deviations and tolerances of the location;

4 - total deviations and tolerances of shape and location.

1. General terms and definitions

1.1. Element- a generalized term, which, depending on the conditions, can be understood as a surface (a part of a surface, a plane of symmetry of several surfaces), a line (a surface profile, a line of intersection of two surfaces, an axis of a surface or section), a point (the point of intersection of a surface or lines, the center of a circle or spheres). In addition, generic terms may be used: nominal element, real element, base element, adjoining element, middle element, and the like.

1.2. Profile- line of intersection of a surface with a plane or a given surface.

Note. Unless otherwise specified in the technical documentation, the direction of the cutting plane is determined along the normal to the surface.

1.3. Nominal form- the ideal shape of the element, which is specified by the drawing or other technical documents

1.4. Nominal surface- an ideal surface, the dimensions and shape of which correspond to the given nominal dimensions and nominal shape

1.5. Nominal profile- according to GOST 25142-82 nominal surface profile

1.6. real surface- according to GOST 25142-82, the surface limiting the body and separating it from the environment

1.7. real profile- according to GOST 25142-82.

Note to paragraphs. 1.6 and 1.7. Real surface and real profile in the definitions of shape and position deviations in this International Standard are understood without regard to surface roughness.

1.8. Rated section- a section of a surface or line, to which the shape tolerance, location tolerance, total shape and location tolerance, or corresponding deviations belong.

The normalized area must be specified:

Dimensions that determine its area, length or angle of the sector, and, if necessary, the location of the site on the element;

For curved surfaces or profiles - the dimensions of the projection of the surface or profile.

Note: If the normalized area is not specified, then the shape tolerance, location tolerance, total shape and location tolerance or the corresponding deviations should refer to the entire surface under consideration or the length of the element under consideration.

1.9. Basic element for evaluating form deviations- an element of the nominal shape, which serves as the basis for assessing the deviations in the shape of a real surface or a real profile. The adjacent surface or adjacent profile should be taken as the basic element for evaluating form deviations.

Note: The basic element for evaluating form deviations is also used to eliminate the influence of form deviations when determining location deviations.

1.10. 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.

Note: The condition of the minimum deviation value does not apply to the adjacent cylinder (see paragraph 1.12).

1.11. adjacent plane- a plane 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

1.12. Adjacent Cylinder- a cylinder of minimum diameter circumscribed around a real outer surface, or a cylinder of maximum diameter inscribed in a real inner surface.

Note: In those cases where the location of the adjacent cylinder relative to the real surface is ambiguous, it is taken according to the condition of the minimum deviation value.

1.13. Adjacent profile- a profile having the shape of a nominal profile, in contact with the real profile and located outside the material of the part so that the deviation from it of the most distant point of the real profile within the normalized area has a minimum value.

Note: The condition of the minimum deviation value does not apply to the adjacent circle (see clause 1.15).

1.14. Adjacent line- a straight line in contact with the real profile and located outside the material of the part so that the deviation from it of the most distant point of the real profile within the normalized area has a minimum value.

E< E1; E < E2

E, E1, E2 - deviations of the most distant point of the real profile from the tangent line

1.15. Contiguous circle- a circle of minimum diameter, described around the real profile of the outer surface of revolution, or a circle of maximum diameter, inscribed in the real profile of the inner surface of revolution.

Note: In those cases where the location of the adjacent circle relative to the real profile is ambiguous, it is taken according to the condition of the minimum deviation value.

r, r 1 , r 2 - radii of circles described around a real profile or inscribed in it

1.16. Adjacent longitudinal profile - two parallel straight lines in contact with the real profile of the axial (longitudinal) section of the cylindrical surface and located outside the material of the part so that the largest deviation of the points of the real profile from the corresponding side of the adjacent profile of the longitudinal section within the normalized area has a minimum value

1 - real profile; 2 - adjacent profile of the longitudinal section

1.17. real axis- locus of centers of sections of the surface of revolution, perpendicular to the axis of the adjacent surface.

Note: The center of the adjacent circle is taken as the center of the section. The axis of the adjacent surface of revolution.

1.18. Geometric axis of a real surface of revolution- as the geometric axis of the real surface of revolution, it is allowed to take the axis of the cylinder of the smallest possible diameter, inside which the real axis is located within the normalized area

1.19. Form deviation- deviation of the form of the real element from the nominal form, estimated by the greatest distance from the points of the real element along the normal to the adjacent element. (Instead of the adjacent element, it is allowed to use the middle element as the base element).

Notes:

1. Surface roughness is not included in the shape deviation. In justified cases, it is allowed to normalize the deviation of the form, including surface roughness.

2. Waviness is included in the shape deviation. In justified cases, it is allowed to normalize separately the waviness of the surface or part of the shape deviation without taking waviness into account.

3. A special case of estimating shape deviation is axis straightness deviation (see 2.1.4 and 2.1.5).

1.20. Shape tolerance- the largest allowable value of the deviation of the form

1.21. Form tolerance field- an area in space or on a plane, inside which all points of the real element under consideration must be located within the normalized area, the width or diameter of which is determined by the tolerance value, and the location relative to the real element - by the adjacent element

1.22. Base- an element of a part (or a combination of elements performing the same function), in relation to which the location tolerance or the total tolerance of the shape and location of the element in question is specified, and the corresponding deviation is also determined

1.23. Base kit- a set of two or three bases that form a coordinate system, in relation to which the location tolerance or the total tolerance of the shape and location of the element in question is specified, and the corresponding deviation is also determined.

1. The bases that form a set of bases are distinguished in descending order of the number of degrees of freedom they deprive (for example, base A deprives the part of three degrees of freedom, base B - two, and base C - one degree of freedom).

2. If the bases are not specified or a set of bases is specified that deprives the part of less than six degrees of freedom, then the location of the coordinate system in which the location tolerance or the total tolerance of the shape and location of the element under consideration relative to other elements of the part is specified is limited in the remaining degrees of freedom only by the condition of compliance with the specified tolerance , and when measuring - the condition for obtaining the minimum value of the corresponding deviation

1.24. Base area- point, line or limited area on the base surface of the part, where the part must be brought into contact with the base elements of the processing or control equipment in order to establish the bases necessary to satisfy the functional requirements.

1. Base areas must be given dimensions that determine their length and location on the base.

2. In cases where the basing sites must be specified for a set of bases of three mutually perpendicular planes (see above), the first base (base A) must be specified by three basing sites, the second base (base B) - by two and the third base (base C) - one basing area

1.25. common axle- a straight line, relative to which the largest deviation of the axes of several considered surfaces of revolution within the length of these surfaces has a minimum value

1.26. General plane of symmetry- the plane, relative to which the largest deviation of the planes of symmetry of several considered elements within the length of these elements has a minimum value.

1.27. Rated Location- the location of the considered element (surface or profile), determined by the nominal linear and angular dimensions between it and the bases or between the considered elements, if the bases are not specified. The nominal location is determined directly by the image of the part on the drawing without the numerical value of the nominal size between the elements, when:

1) the nominal linear dimension is equal to zero (requirements for coaxiality, symmetry, alignment of elements in the same plane);

2) the nominal angular size is 0° or 180° (parallelism requirement);

3) the nominal angular dimension is 90° (perpendicularity requirement).

1.28. Real location- the location of the considered element (surface or profile), determined by the actual linear and angular dimensions between it and the bases or between the considered elements, if the bases are not specified.

1.29. Position deviation- deviation of the actual location of the element under consideration from its nominal location.

Notes:

1. Location deviations can be further subdivided into location deviations and orientation deviations.

Location deviation- deviation from the nominal location, determined by nominal linear or linear and angular dimensions (deviations from alignment, symmetry, intersection of axes, positional deviations).

Orientation deviation- deviation from the nominal location, determined by the nominal angular size (deviations from parallelism and perpendicularity, tilt deviation).

2. Quantitative location deviations are evaluated in accordance with the definitions given in paragraphs. 3.1 - 3.7.

3. When assessing deviations of the location deviations of the form of the elements under consideration and bases should be excluded from consideration. In this case, real surfaces (profiles) are replaced by adjacent ones, and axes, symmetry planes and centers of adjacent elements are taken as axes, symmetry planes and centers of real surfaces or profiles.

1.30. Location tolerance- a limit that limits the allowable value of the deviation of the location. (May be further subdivided into location tolerances and orientation tolerances).

1.31. Location tolerance field- an area in space or a given plane, inside which an adjacent element or axis, center, plane of symmetry must be located within the normalized area, the width or diameter of which is determined by the tolerance value, and the location relative to the bases - by the nominal location of the element in question.

1.32. Protruding Location Tolerance- tolerance field or part of it, limiting the deviation of the location of the element under consideration beyond the extent of this element (the normalized section protrudes beyond the length of the element)

L is the length of the normalized section; TRR - positional tolerance

1.33. Dependent Location Tolerance(dependent shape tolerance) - the location or shape tolerance indicated on the drawing or in other technical documents as a value that can be exceeded by an amount depending on the deviation of the actual size of the considered element and / or base from the limit of the maximum material (the largest limit size of the shaft or smallest hole size).

1.34. Independent Location Tolerance(independent shape tolerance) - the tolerance of the location or shape, the numerical value of which is constant for the entire set of parts and does not depend on the actual size of the considered element and / or base.

1.35. Total deviation of shape and location- deviation resulting from the combined manifestation of the form deviation and the deviation of the location of the considered surface or the considered profile relative to the bases.

1.36. Total shape and location tolerance- the limit limiting the allowable value of the total deviation of the shape and location.

1.37. Total Tolerance Field of Shape and Location- an area in space or on a given surface, inside which all points of the real surface (profile) must be located within the normalized area, the width of which is determined by the tolerance value, and the location relative to the bases - by the nominal location of the element under consideration.

Any technological operation can be performed with a certain accuracy, which means that the dimensions of the part obtained as a result of processing will not be ideal, they may fluctuate in a certain range. In order to fulfill the conditions of assembly and ensure reliable operation of the part under the given conditions, it is necessary to set the allowable interval in which the final size must fall. This interval can regulate not only linear or diametrical dimensions, but also the shape or relative position of the surfaces.

The shape and location tolerances are assigned by the designer based on the assembly conditions and the features of the part in the mechanism.

Types of form tolerances

Form tolerance called the maximum allowable value of the deviation of the form.

Form tolerance field- this is an area on a plane or in space, inside which all points of the element under consideration must be located within the normalized area, the width or diameter of which is determined by the tolerance value, and the location relative to the real element by the adjacent element.

Form deviations and tolerances

There are the following tolerances for shape deviations:

Deviation from straightness in the plane

convex
concavity

Deviation from flatness and flatness tolerance

Convex
Concavity

Roundness deviation and roundness tolerance

ovality
Cut

Cylindricity deviation and cylindricity tolerance
Deviation and tolerance of the profile of the longitudinal section of the cylindrical surface
Deviation of the profile of the longitudinal section

taper
barrel shape
saddle shape

Permissible deviations are indicated by special symbols.

Types of location tolerances

Location tolerance- a limit that limits the allowable value of the deviation of the location.

There are location tolerances and orientation tolerances.

Location tolerance field- an area on a plane or in space, inside which there must be an adjacent element or a plane of symmetry, an axis, a center within the normalized area, the diameter or width of which is determined by the tolerance value, and the relative position is determined by the nominal location of the element in question.

Deviations and location tolerances

There are the following types of location tolerances:

Parallelism Deviation and Parallelism Tolerance
Deviation and perpendicularity tolerance
Deviation and tilt tolerance
Deviation and alignment tolerance

Radius Tolerance

Deviation and symmetry tolerance
Positional deviation and positional tolerance

Tolerance in diametric terms
Radius Tolerance

Deviation from intersection and tolerance of intersection of axes

Tolerance in diametric terms
Radius Tolerance

Total tolerances

There are several types of total shape and location tolerances.

Radial runout
Full radial runout
Face runout
Full axial runout
Runout in a given direction
Deviation and tolerance of the shape of a given profile
Deviation and tolerance of the shape of a given surface

These tolerances are indicated by symbols.

Designation of tolerances of shape and location in the drawings

Tolerances of shape and location are depicted in the drawings in the form of a frame, which is divided into several parts. In the first part, a graphic designation of the tolerance is depicted, in the second part - the numerical value of the tolerance, in the third and subsequent - the letter designation of one or more bases.

In the absence of a tolerance base, the frame consists of only two parts. Examples of shape and location tolerance frames are shown in the figure.

The figure on the left shows a frame with a shape tolerance (permissible deviation from straightness), on the right with a location tolerance (permissible deviation from parallelism).

The frame is made with thin lines. The height of the text in the frame should be equal to the font size of the dimension numbers. A line ending with an arrow is drawn from the tolerance frame to the surface or to the leader.

Before the numerical value of the tolerance, signs can be indicated:

f - if a cylindrical or circular tolerance field is indicated by a diameter
R - if a cylindrical or circular field is indicated by a radius
T - if the tolerance field for the intersection of the axes, symmetry, is limited by two parallel lines or planes in diametric terms.
T / 2 - in the same case as T, only in radius expression
Sphere - for a spherical tolerance field.

If the tolerance should not be applied to the entire surface, but only to a certain area, then it is indicated by a dash with a dotted line.

For one element, several tolerances can be specified, in this case the frames are drawn one above the other.

Additional information may appear above or below the frame.

Information about shape and location tolerances can be specified in .

Unspecified alignment tolerances according to GOST 25069-81.

Dependent tolerances

Dependent location tolerances are indicated by the following symbol.

This symbol may be placed after the numerical value of the tolerance, if the dependent tolerance is related to the actual dimensions of the element in question. Also, the symbol can be placed after the letter designation (if it is absent, then in the third field of the frame) if the dependent tolerance is related to the actual dimensions of the base element.

Assign shape and location tolerances

The more precisely a part is made, the more precise tools will be required for its manufacture and dimensional control. This will automatically increase its value. It turns out that the cost of manufacturing a part largely depends on the required accuracy in its manufacture. This means that the designer must specify only those tolerances that are really necessary for the assembly and reliable operation of the movement. Permissible intervals should also be assigned based on the conditions of collection and performance.

Form Tolerance Numeric Values

Depending on the accuracy class, standard values of form tolerances are set.

Flatness and straightness tolerances

In this case, the nominal size is considered to be the nominal length of the normalized section.

Tolerances of roundness, cylindricity, longitudinal section profile

These tolerances are assigned in cases where they must be less than the size tolerance.

The nominal size is the nominal surface diameter.

Tolerances for perpendicularity, parallelism, inclination, axial runout

The nominal size when assigning tolerances for parallelism, perpendicularity, inclination is understood as the nominal normalized section or the nominal length of the entire controlled surface.

Tolerances of radial runout, symmetry, coaxiality of the intersection of the axes in diametric terms

When assigning radial runout tolerances, the nominal size is considered to be the nominal diameter of the surface in question.

In the case of assigning tolerances for symmetry, intersection of the axis of alignment, the nominal size is considered to be the nominal diameter of the surface or the nominal size between the surfaces that form the element in question.

GOST 2.308-2011

Group T52

INTERSTATE STANDARD

Unified system of design documentation

INSTRUCTIONS OF TOLERANCES FOR THE FORM AND LOCATION OF SURFACES

Unified system of design documentation. Representation of limits of forms and surface lay-out on drawings

Introduction date 2012-01-01

Foreword

The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST 1.0-92 "Interstate standardization system. Basic provisions" and GOST 1.2-2009 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for the development, adoption, application, renewal and cancellation

About the standard

1 DEVELOPED by the Federal State Unitary Enterprise "All-Russian Scientific Research Institute for Standardization and Certification in Mechanical Engineering" (FSUE "VNIINMASH"), Autonomous Non-Profit Organization "Research Center for CALS-Technologies "Applied Logistics" (ANO NRC CALS-Technologies "Applied Logistics" )

2 INTRODUCED by the Federal Agency for Technical Regulation and Metrology

3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Minutes of May 12, 2011 N 39)

Short title	Country code	Abbreviated name of the national
countries according to MK (ISO 3166)	according to MK (ISO 3166) 004 -	standardization body

the Russian Federation				Rosstandart

Tajikistan				Tajikstandart

Uzbekistan				Uzstandard

				Gospotrebstandart of Ukraine

4 Order of the Federal Agency for Technical Regulation and Metrology dated August 3, 2011 N 211-st interstate standard GOST 2.308-2011 entered into force asthe national standard of the Russian Federation since January 1, 2012

5 INSTEAD OF GOST 2.308-79

Information on the entry into force (termination) of this standard is published in the index of "National Standards".

Information about changes to this standard is published in the "National Standards" index, and the text of the changes is published in the "National Standards" information indexes. In case of revision or cancellation of this standard, the relevant information will be published in the information index "National Standards"

1 area of use

This standard establishes the rules for specifying the tolerances of the shape and location of surfaces in graphic documents for products of all industries.

This standard uses normative references to the following interstate standards:

GOST 2.052-2006 Unified system for design documentation. Electronic product model. General provisions

GOST 24642-81 Basic norms of interchangeability. Tolerances of the shape and location of surfaces. Basic terms and definitions

________________

* The document is not valid on the territory of the Russian Federation. GOST R 53442-2009 is valid, hereinafter in the text. - Database manufacturer's note.

GOST 24643-81 Basic norms of interchangeability. Tolerances of the shape and location of surfaces. Numeric values

GOST 30893.2-2002 (ISO 2768-2-89) Basic standards of interchangeability. General tolerances. Tolerances of the form and arrangement of surfaces, not specified individually

Note - When using this standard, it is advisable to check the effect of reference standards in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet or according to the annually published information index "National Standards", which

published as of January 1 of the current year, and according to the corresponding monthly published information indexes published in the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replacing (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected.

3 Terms and definitions

This standard uses the terms according to GOST 24642, as well as the following term with the corresponding definition:

plane of designations and indications: The plane in the model space, on which visually perceived information is displayed, containing the values of the model's attributes, technical requirements, designations and instructions.

[GOST 2.052-2006, article 3.1.8]

4 General provisions

4.1 The tolerances of the shape and location of surfaces in graphic documents are indicated using symbols (graphic symbols) or text in the technical requirements in the absence of such symbols.

4.2 Graphic symbols (signs) to indicate the tolerance of the shape and location of surfaces are given in table 1.

Table 1

Tolerance group		Tolerance type


Shape tolerance		Straightness tolerance


		Flatness tolerance


		roundness tolerance


		Cylindrical tolerance


		Longitudinal section profile tolerance


Location tolerance		Parallelism tolerance


		Perpendicularity tolerance

Tilt tolerance

Alignment tolerance

Symmetry tolerance

Position tolerance

Total shape and location tolerances

Axis crossing tolerance

Radial runout tolerance

Runout tolerance

Runout tolerance in a given direction

Total radial runout tolerance

Full axial runout tolerance

Tolerance of the shape of a given profile

Tolerance of the shape of a given surface

Note - The total tolerances of the shape and location of surfaces for which separate graphic signs are not established are denoted by composite tolerance signs in the following sequence: location tolerance sign, shape tolerance sign.

For example:

The sign of the total tolerance of parallelism and flatness;

The sign of the total tolerance of perpendicularity and flatness;

The sign of the total tolerance of inclination and flatness.

The shapes and sizes of signs are given in Appendix A.

Examples of specifying tolerances for the shape and location of surfaces are given in Appendix B and ISO 1101 *.

________________

* Access to international and foreign documents mentioned hereinafter in the text can be obtained by clicking on the link. - Database manufacturer's note.

4.3 Tolerances of the shape and location of surfaces and their values in electronic models of products are indicated in the planes of designations and indications in accordance with GOST 2.052.

4.4 Numerical values of tolerances of the shape and location of surfaces - according to GOST 24643.

4.5 Tolerances of the shape and location of surfaces may be indicated in the text in the technical requirements, as a rule, if there is no sign of the type of tolerance.

4.6 When specifying the tolerance of the shape and location of surfaces in the technical requirements, the text should contain:

Type of tolerance;

- an indication of the surface or other element for which the tolerance is set (for this, a letter designation or constructive name is used that defines the surface);

- numerical tolerance value in millimeters;

- an indication of the bases relative to which the tolerance is set (for location tolerances and total shape and location tolerances);

- an indication of dependent tolerances of form or location (if applicable).

4.7 If it is necessary to normalize the shape and location tolerances that are not indicated in the graphic document by numerical values and are not limited by other shape and location tolerances indicated in the graphic document, the technical requirements should contain a general record of the unspecified shape and location tolerances with reference to GOST 30893.2.

For example:

"General shape and location tolerances - according to GOST 30893.2 - K" or "GOST 30893.2 - K" (K - accuracy class of general shape and location tolerances according to GOST 30893.2).

5 Application of tolerance symbols

5.1 With a symbol, data on the tolerances of the shape and location of surfaces

indicate in a rectangular frame divided into two or more parts (see Figures 1, 2), in which are placed:

- in the first - a tolerance mark according to table 1;

- in the second - the numerical value of the tolerance in millimeters;

- in the third and subsequent - the letter designation of the base (bases) or the letter designation of the surface with which the location tolerance is associated (see 6.7; 6.9).

Picture 1

Figure 2

5.2 Frames should be made with solid thin lines. The height of the numbers, letters and signs that fit into the frames must be equal to the font size of the dimensional numbers.

A graphic representation of the frame is given in Appendix A.

5.3 The frame is placed horizontally. In necessary cases, a vertical arrangement of the frame is allowed.

It is not allowed to cross the frame with any lines.

5.4 The frame is connected to the element to which the tolerance applies, with a solid thin line ending with an arrow (see Figure 3).

Figure 3

The connecting line can be straight or broken, but the direction of the connecting line segment ending in an arrow must match the direction of the deviation measurement. The connecting line is taken away from the frame, as shown in Figure 4.

Figure 4

In necessary cases, it is allowed:

- draw a connecting line from the second (last) part of the frame (see Figure 5 a );

- end the connecting line with an arrow and on the material side of the part (see figure

5 B ).

Figure 5

5.5 If the tolerance refers to the surface or its profile, then the frame is connected to the contour line of the surface or its continuation, while the connecting line should not be a continuation of the dimension line (see Figures 6, 7).

Figure 6

Figure 7

5.6 If the tolerance refers to an axis or plane of symmetry, then the connecting line must be a continuation of the dimension line (see figures 8a and 8b). If there is not enough space, the arrow of the dimension line can be combined with the arrow of the connecting line (see figure 8c).

Figure 8

If the size of the element has already been specified once, then it is not indicated on the other dimension lines of this element used to symbolize the tolerance of the shape and location. A dimension line without a dimension should be considered as an integral part of the shape or location tolerance symbol (see Figure 9).

The real surfaces of parts obtained using any technological processes are always characterized by deviations from the nominal (geometrically correct) shape.

Maximum deviations in the shape and location of the surfaces of the workpiece cannot be greater than those that allow the limiting contours of the part. So, if we take as a basis the concentric arrangement of the limiting contours that bound the cylindrical surface (Figure 6.1 a), then the permissible deviation of the shape (in the limiting case, the shape tolerance of the T shape, determined through the tolerance of the corresponding size) will not exceed half the value of the size tolerance (T shape = IT / 2). Similar reasoning can be carried out for deviations from straightness and flatness (Figure 7.1 b), in this case we can take the form T = IT.

Analysis of deviations in the shape of typical surfaces allows us to draw two conclusions:

1. Since form deviations are automatically limited by the specified dimensional tolerance fields, form deviations should be specially normalized only in cases where they are necessary toughen up compared to those values that are already actually set when assigning a dimension tolerance.

2. The system of tolerances of the form must necessarily include tolerances for the most common typical cases. First of all, it is necessary to normalize the shape tolerances of nominally flat surfaces and surfaces such as bodies of revolution.

The standard nomenclature of shape tolerances (tolerances of straightness, flatness, roundness, profile of the longitudinal section and the cylindricity tolerance of a nominally cylindrical surface) allows you to normalize not only flat and cylindrical surfaces, but also elements of any surfaces of revolution (sphere, cone, torus, ellipsoid, hyperbolic paraboloid, etc.). .d.), as well as their axes.

should be distinguished shape tolerances - normative restrictions on form deviations by designated tolerance fields and shape deviations are the characteristics of any real surface.

Form deviations are usually counted from a geometrically correct element, in the direction normal to it(along the perpendicular to a straight line or plane, or along the radius of a circle or cylinder). Such a "basic" element is built as a geometrically correct tangent element or an element that intersects the real one.

The GOST 24642-81 standard establishes as the basis for counting form deviations adjoining element . The adjoining element has a nominal (geometrically correct) shape and extends outside the material of the part. The principle of constructing an adjacent element (a straight line, a plane, a pair of parallel lines for a profile of a longitudinal section) - minimax. The adjacent element is positioned relative to the real one in such a way that the largest deviation has acquired the smallest of all possible values (Figure 6.2 a, 6.3). The adjacent circle, the adjacent cylinder must have extreme dimensions: for internal elements it is an inscribed circle or cylinder of the largest diameter, for external elements it is a circumscribed circle (cylinder) of the smallest possible diameter (Figure 6.2 b).

P The adjacent element performs one more function - from it "to the body of the part" the form tolerance field is built.

Real shape deviations can be analytically subdivided into complex and elementary. The elementary types of shape errors of nominally flat and nominally straight surfaces include convexity and concavity. Convex nominally flat surface (or nominally rectilinear element) is characterized by the fact that the removal of points of the real surface (or real straight line) from the adjacent plane (straight line) increases from the middle to the edges; with the reverse nature of the deletion of points, we have concavity.

Figure 6.3 - Deviations from straightness (a) and flatness (b, c)

The complex shape errors of nominally round sections of parts such as bodies of revolution include the deviation from roundness. For nominally cylindrical surfaces, it is customary to consider deviations from cylindricity, from roundness, and from the regular shape of the longitudinal section.

Particular cases of nominally round sections of parts such as bodies of revolution include ovality and faceting (Figure 6.4), and for nominally cylindrical surfaces - conical, barrel-shaped, saddle-shaped, as well as deviation from the straightness of the axis or curvature of the axis (Figure 6.5).

Figure 6.4 - Particular cases of deviation from roundness: ovality ( a),

square cut ( b) and trihedral cut ( in)

Ovality is a deviation from roundness, in which the largest and smallest diameters of the real profile are in mutually perpendicular directions (Figure 6.3 a). Cut (Figure 6.3 b, c) is a specific deviation from roundness, in which the cross section has the shape of a quasi-polygon. The most unfavorable cut with three and five "facets". An even cut can be detected and measured with any two-contact measuring instrument, and an odd cut can be detected with a three-point measurement scheme, for example, when checking a part in a prism, as described in special literature.

Figure 6.5 - Particular cases of deviation of the profile of the longitudinal section:

taper ( a), barrel shape ( b) and saddle shape ( in)

taper cylindrical surface is characterized by the fact that the real profile of the longitudinal section has almost rectilinear, but not parallel generators (Figure 6.5 a), the diameters decrease or increase from one extreme section to another. barrel shape(Figure 6.5 b) is characterized by the presence of convex generators (diameters increase from the edges to the middle); at saddle(Figure 6.5 in) forming concave, and the diameters decrease from the edges to the middle.

A quantitative assessment of all types of deviations in the shape of cylindrical surfaces (except for the curvature of the axis) is the greatest distance from the real element to the adjacent element in the normal direction (along the radius of the adjacent element).

Straightness deviation axes(curvature of the axis) of the surface of revolution is characterized by an almost equidistant bending of the generators and the axis. This deviation is estimated by the smallest value of the diameter of the cylinder, inside which the real axis is located within the normalized area.

Location tolerances- these are the largest allowable deviations of the actual location of the surface (profile), axis, plane of symmetry from its nominal location.

When evaluating deviations shape deviation locations (considered surfaces and base ones) should be excluded from consideration (Fig. 12). In this case, real surfaces are replaced by adjacent ones, and axes, symmetry planes are taken as axes, symmetry planes and centers of adjacent elements.

Plane parallelism tolerances- this is the largest allowable difference between the largest and smallest distances between adjacent planes within the normalized area.

For standardization and measurement tolerances and location deviations, base surfaces, axes, planes, etc. are introduced. These are surfaces, planes, axes, etc., which determine the position of the part during assembly (product operation) and relative to which the position of the elements under consideration is set. Basic elements in the drawing are indicated by the sign; capital letters of the Russian alphabet are used. The designation of bases, sections (A-A) should not be duplicated. If the base is an axis or a plane of symmetry, the sign is placed on the continuation of the dimension line:

Parallelism tolerance 0.01mm relative to the base

surfaces A.

Surface alignment tolerance in

diametrically 0.02mm

relative to the base axis of the surface

In the event that the design, technological (determining the position of the part during manufacture) or measuring (determining the position of the part during measurement) do not match, recalculate the measurements performed.

Measurement of deviations from parallel planes.

(at two points on a given surface length)

The deviation is defined as the difference between the readings of the head at a given interval from each other (the heads are set to "0" according to the standard).

Tolerance of parallelism of the hole axis relative to the reference plane A on the length L.

Figure 14. (Measurement scheme)

Axis parallelism tolerance.

Deviation from parallelism of axes in space - the geometric sum of deviations from parallelism of the projections of the axes in two mutually perpendicular planes. One of these planes is a common plane of the axes (that is, it passes through one axis and a point on the other axis). Deviation from parallelism in the common plane- deviation from parallelism of the projections of the axes on their common plane. Axes misalignment- deviation from the projections of the axes onto a plane perpendicular to the common plane of the axes and passing through one of the axes.

Tolerance field- This rectangular parallelepiped with section sides -, side faces are parallel to the base axis. or cylinder

Fig 15. Measurement scheme

Tolerance of parallelism of the axis of the hole 20H7 relative to the axis of the hole 30H7.

Alignment tolerance.

Misalignment relative to a common axis is the greatest distance between the axis of the considered surface of revolution and the common axis of two or more surfaces.

Concentricity tolerance field is an area in space bounded by a cylinder whose diameter is equal to the alignment tolerance in diametric terms ( F = T) or twice the alignment tolerance in radial terms: R=T/2(Fig. 16)

Alignment tolerance in radial expression of surfaces and relative to the common axis of the holes A.

Figure 16. Alignment tolerance field and measurement scheme

(axis deviation relative to the base axis A-eccentricity); R-radius of the first hole (R+e) - distance to the base axis in the first measurement position; (R-e) - distance to the base axis in the second position after turning the part or indicator 180 degrees.

The indicator registers the difference in readings (R+e)-(R-e)=2e=2 - deviation from alignment in diametric terms.

Shaft journal alignment tolerance in diametric terms, 0.02 mm (20 µm) relative to the common axis of the AB. Shafts of this type are installed (based) on rolling or sliding bearings. The base is the axis passing through the middle of the shaft journals (hidden base).

Figure 17. Scheme of misalignment of the shaft journals.

The displacement of the axes of the shaft journals leads to a misalignment of the shaft and a violation of the performance of the entire product as a whole.

Figure 18. Scheme for measuring the misalignment of the shaft journals

The basing is made on knife supports, which are placed in the middle sections of the shaft necks. When measuring, the deviation is obtained in the diametric expression D Æ = 2e.

Misalignment relative to the base surface is usually determined by measuring the runout of the surface being checked in a given section or extreme sections - when the part rotates around the base surface. The result of the measurement depends on the non-circularity of the surface (which is about 4 times less than the misalignment).

Figure 19. Scheme for measuring the alignment of two holes

Accuracy depends on the accuracy of the fit of the mandrels to the hole.

Rice. 20.

Dependent tolerance can be measured using a gauge (Fig. 20).

Tolerance of surface alignment relative to the base axis of the surface in diametric terms 0.02 mm, dependent tolerance.

Symmetry tolerance

Symmetry tolerance relative to the reference plane- the largest allowable distance between the considered plane of symmetry of the surface and the base plane of symmetry.

Figure 21. Symmetry tolerances, measurement schemes

The tolerance of symmetry in the radius expression is 0.01 mm relative to the base plane of symmetry A (Fig. 21b).

Deviation DR(in radius expression) is equal to the half-difference of distances A and B.

In diametric terms DT \u003d 2e \u003d A-B.

Alignment and symmetry tolerances are assigned to those surfaces that are responsible for the precise assembly and functioning of the product, where significant displacements of the axes and symmetry planes are not allowed.

Axis intersection tolerance.

Axis crossing tolerance - the largest allowable distance between the considered and the reference axes. It is defined for axes that, in the nominal arrangement, must intersect. The tolerance is specified in a diametrical or radius expression (Fig. 22a).

Figure 22. a)

The tolerance of the intersection of the axes of the holes Æ40H7 and Æ50H7 in radius terms is 0.02mm (20µm).

in)

Fig. 22. b, c Scheme for measuring the deviation of the intersection of the axes

The mandrel is placed in 1 hole, measured R1- height (radius) above the axis.

The mandrel is placed in the 2nd hole, measured R2.

Measurement result DR = R1 - R2 is obtained in a radius expression, if the hole radii are different, to measure the deviation of the location, you need to subtract the actual dimensions and (or take into account the dimensions of the mandrels. The mandrel fits over the hole, contact by fit)

DR = R1 - R2- ( - ) - deviation is obtained in radius expression

Axes intersection tolerance is assigned to parts where failure to comply with this requirement leads to a violation of performance, for example: a bevel gear housing.

Perpendicularity tolerance

Perpendicularity tolerance for a surface relative to the base surface.

Tolerance of perpendicularity of the side surface is 0.02 mm relative to the reference plane A. Squareness deviation is the deviation of the angle between the planes from the right angle (90°), expressed in linear units D along the length of the normalized section L.

Figure 23. Scheme for measuring perpendicularity deviation

The measurement can be carried out with several indicators set to "0" according to the standard.

Tolerance of perpendicularity of the hole axis relative to the surface in diametric terms 0.01 mm at the measurement radius R = 40 mm.

Figure 24. Scheme for measuring the deviation of the perpendicularity of the axis

The perpendicularity tolerance is assigned on the surface that determines the function of the product. For example: to ensure a uniform gap or a snug fit along the ends of the product, the perpendicularity of the axes and the plane of technological devices, the perpendicularity of the guides, etc.

Tilt tolerance

Deviation of the slope of the plane - the deviation of the angle between the plane and the base from the nominal angle a, expressed in linear units D over the length of the normalized section L.

To measure the deviation, templates and fixtures are used.

Position tolerance

Position tolerance- this is the largest permissible deviation of the actual location of the element, axis, plane of symmetry from its nominal position

Control can be carried out through the control of its individual elements, with the help of measuring machines, with - calibers.

Positional tolerance is assigned to the location of the centers of holes for fasteners, spheres of connecting rods, etc.

Total shape and location tolerances

Total flatness and parallelism tolerance

Assigned to flat surfaces that determine the position of the part (based) and provide a snug fit (tightness).

Total flatness and perpendicularity tolerance.

Assigned to flat side surfaces that determine the position of the part (based) and provide a snug fit.

Radial runout tolerance

Radial runout tolerance is the largest allowable difference between the largest and smallest distances from all points of the real surface of revolution to the base axis in a section perpendicular to the base axis.

Full radial runout tolerance.

Figure 26.

Tolerance of full radial runout within the normalized area.

radial runout is the sum of deviations from roundness and coaxiality in diametric terms, - the sum of deviations from cylindricity and coaxiality.

The tolerance of radial and full radial runout is assigned to critical rotating surfaces, where the requirement for the alignment of parts dominates, separate control of shape tolerances is not required. .

Runout tolerance

End runout tolerance is the largest allowable difference between the largest and smallest distances from points on any circle of the end surface to a plane perpendicular to the base axis. The deviation is made up of

deviations from perpendicularity and straightness (fluctuations of the surface of the circle).

Full run-out tolerance

Full end runout tolerance - this is the largest allowable difference between the largest and smallest distances from points of the entire end surface to a plane perpendicular to the base axis.

End runout tolerances are set on the surfaces of rotating parts that require minimal runout and impact on the parts in contact with them; for example: thrust surfaces for rolling bearings, plain bearings, gear wheels.

Tolerance of the shape of a given profile, a given surface

Tolerance of the shape of a given profile, the tolerance of the shape of a given surface - these are the largest deviations of the profile or shape of the real surface from the adjacent profile and surface specified by the drawing.

Tolerances are set on parts that have curved surfaces such as cams, templates; barrel profiles, etc.

Normalization of shape and location tolerances

Can be carried out:

by levels of relative geometric accuracy;

Based on the worst conditions of assembly or operation;

Based on the results of the calculation of dimensional chains.

Levels of relative geometric accuracy.

According to GOST 24643-81, 16 degrees of accuracy are established for each type of shape and location tolerance. The numerical values of the tolerances in the transition from one degree of accuracy to another change with an increase factor of 1.6.

Depending on the ratio between the size tolerance and the shape and location tolerance, there are 3 levels of relative geometric accuracy:

A - normal: set to 60% of tolerance T

B - increased - set 40%

C - high - 25%

For cylindrical surfaces:

Level A » 30% of T

Level B » 20% of T

By level C » 12.5% of T

Since the tolerance of the shape of the cylindrical surface limits the deviation of the radius, not the entire diameter.

For example: Æ 45 +0.062 in A:

In the drawings, the shape and location tolerance is indicated when they should be less than the size tolerances.

If there is no indication, then they are limited to the tolerance of the size itself.

Designations on the drawings

Shape and location tolerances are indicated in rectangular boxes; in the first part of which - a conventional sign, in the second - numerical values in mm; for location tolerances, the base is indicated in the third part.

The direction of the arrow is normal to the surface. The length of the measurement is indicated through the fraction sign "/" . If it is not specified, control is carried out over the entire surface.

For location tolerances that determine the relative positions of surfaces, it is allowed not to specify the base surface:

It is allowed to indicate the base surface, axis, without designation with a letter:

Before the numerical value of the tolerance, the symbol T, Æ, R, sphere,

if the tolerance field is given in diametrical and radius terms, the sphere Æ, R will be used for ; (hole axis); .

If the sign is not specified, the tolerance is specified in the diametrical expression.

To allow symmetry, use the signs T (instead of Æ) or (instead of R).

Dependent tolerance, indicated by the sign.

After the tolerance value, a symbol can be indicated, and on the part this symbol indicates the area relative to which the deviation is determined.

Rationing of shape and location tolerances from the worst assembly conditions.

Consider a part that contacts simultaneously on several surfaces - a rod.

In that case, if there is a large misalignment between the axes of all three surfaces, the assembly of the product will be difficult. Let's take the worst option for assembly - the minimum gap in the connection .

Let's take for the base axis - the axis of the connection.

Then the axis offset .

In diametric terms, this is 0.025 mm.

If the base is the axis of the center holes, then proceeding from similar considerations.

Example 2

Let us consider a stepped shaft contacting on two surfaces, one of which is working, the second is subject only to the requirements of collection.

For worst part assembly conditions: and .

Assume that the sleeve and shaft parts are perfectly aligned: In the presence of gaps and perfectly aligned parts, the gaps are distributed evenly on both sides and .

The figure shows that the parts will be assembled even if the axes of the steps are displaced relative to each other by an amount .

For and , i.e. allowable displacement of the axes in radius terms. = e = 0.625mm, or = 2e = 0.125mm - in diametric terms.

Example 3

Consider the bolted connection of parts, when gaps are formed between each of the parts to be joined and the bolt (type A), while the gaps are located in opposite directions. The axis of the hole in part 1 is shifted from the axis of the bolt to the left, and the axis of part 2 is shifted to the right.

Holes for fasteners are performed with tolerance fields H12 or H14 in accordance with GOST 11284-75. For example, holes can be used under M10 (for precise connections) and mm (for non-critical connections). With a linear clearance Offset of the axes in diametric terms, the value of the positional tolerance = 0.5 mm, i.e. is equal to = .

Example 4

Consider a screw connection of parts, when a gap is formed only between one of the parts and the screw: (type B)

In practice, accuracy margin factors are introduced: k

Where k \u003d 0.8 ... 1, if the assembly is carried out without adjusting the position of the parts;

k \u003d 0.6 ... 0.8 (for studs k \u003d 0.4) - during adjustment.

Example 5

Two flat precision end surfaces are in contact, S=0.005mm. It is required to normalize the flatness tolerance. In the presence of end gaps due to non-flatness (the slopes of the parts are selected using springs), leakage of the working fluid or gas occurs, which reduces the volumetric efficiency of the machines.

The deviation value for each of the parts is defined as half = . Can be rounded up to integer values \u003d 0.003 mm, because the probability of worse combinations is rather negligible.

Rationing of location tolerances based on dimensional chains.

Example 6

It is required to normalize the alignment tolerance of the mounting axis 1 of the technological device, for which the tolerance of the entire device is set = 0.01.

Note: the tolerance of the entire fixture should not exceed 0.3 ... 0.5 of the tolerance of the product.

Consider the factors affecting the alignment of the entire device as a whole:

Misalignment of part surfaces 1;

Maximum clearance in the connection of parts 1 and 2;

Misalignment of the hole in 2 parts and the base (mounted in the machine) surface.

Because the chain of dimensions is low-link (3 links), the method of complete interchangeability is used for calculation; according to which the tolerance of the closing link is equal to the sum of the tolerances of the constituent links.

The alignment tolerance of the entire fixture is equal to

To eliminate the influence when connecting 1 and 2 parts, you should take a transitional fit or with an interference fit.

If accepted, then

Value achieved in fine grinding operations. If the fixture has small dimensions, then it can be provided with assembly processing.

Example 7

Dimensioning with a ladder and a chain for holes for fasteners.

If the dimensions are elongated under one line, a chain is made.

TL D 1 = TL 1 + TL 2

TL D 2 = TL 2 + TL 3

TL D 3 = TL 3 + TL 4, i.e.

The accuracy of the master link is always affected by only 2 links.

If a TL 1 = TL 2 =

For our example TL 1 = TL 2 = 0.5 (±0.25mm)

This setting allows you to increase the tolerances of the constituent links, reduce the complexity of processing.

Example 9

Calculation of the value of the dependent tolerance.

If for example 2 are indicated, then this means that the 0.125 mm alignment tolerance determined for the worst assembly conditions can be increased if the gaps formed in the connection are greater than the minimum.

For example, in the manufacture of the part, dimensions of -39.95 mm; - 59.85 mm were obtained, additional gaps arise S add1 = d 1max - d 1izg = 39.975 - 39.95 = 0.025mm, and S add2 = d 2max - d 2izg = 59, 9 - 59.85 \u003d 0.05 mm, the axes can additionally be shifted relative to each other by e add \u003d e 1 dop + e 2 dop \u003d (in diametric terms, by S 1 dop + S 2 dop \u003d 0.075 mm).

The misalignment in diametrical terms, taking into account additional clearances, will be: = 0.125 + S add1 + S add2 = 0.125 + 0.075 = 0.2 mm.

Example 10

You want to define a dependent alignment tolerance for a sleeve part.

Symbol: hole alignment tolerance Æ40H7 relative to the base axis Æ60p6, tolerance dependent only on hole dimensions.

Note: the dependence is indicated only on those surfaces where additional clearances are formed in the fits, for surfaces connected by fits with an interference fit or transition - additional axle slips are excluded.

During manufacture, the following dimensions were obtained: Æ40.02 and Æ60.04

T head \u003d 0.025 + S 1dop \u003d 0.025 + (D bend1 - D min1) \u003d 0.025 + (40.02 - 40) \u003d 0.045 mm(in diametric terms)

Example 11.

Determine the value of the center-to-center distance for the part, if the dimensions of the holes after manufacturing are equal: D 1izg \u003d 10.55 mm; D 2izg \u003d 10.6 mm.