# Deviations and tolerances of the shape and arrangement...

## Deviations and tolerances of the shape and arrangement of surfaces

When manufacturing parts, errors can arise not only in linear and angular dimensions, but also in geometric shapes, as well as in the mutual arrangement of surfaces. Their values ​​should be limited to the maximum deviations in those cases when these errors violate the conditions of normal operation of the part.

If the limiting deviations of the shape and location of the surfaces are allowed within the entire margin of tolerance for the size, then in the drawing they should not be negotiated.

GOST 24643-81 applies to the tolerances of the shape and location of the surfaces of machine parts and devices and sets numerical values ​​of tolerances (Table P.60).

The terms and definitions of the tolerances of the shape and arrangement of surfaces are given in GOST 24642-81, indicating the tolerances of the shape and location on the drawings - in GOST 2.308-79.

The numerical values ​​of the shape tolerances, tolerances of location and total tolerances of the shape and arrangement of the surfaces should correspond to those indicated in Table. P.61-P.64.

The values ​​of the positional tolerances, the tolerances of the form of a given profit or the specified surface should be assigned according to Table. P.60; unspecified tolerances of the shape and arrangement of surfaces - according to GOST 25069-81.

The recommended relationship between the form and location tolerances and the size tolerance - according to the recommended annex 2 of GOST 24643-81.

Classification of the tolerances of the shape and arrangement of surfaces is given in Table. 2.12.

The tolerances of the shape and location, if necessary, determined by design or technological considerations, indicate in the drawings, according to GOST 2.308-79, in one of two ways:

• conventional symbols;

• the text in the technical requirements.

The use of conventions is preferable.

Table 2.12

Classification of the tolerances of the shape and arrangement of surfaces and their axes

The text part should include:

• the name of the tolerance;

• an indication of the surface or other element for which the tolerance is specified (for this use the surface designation or constructive name that defines the surface);

• numeric tolerance in millimeters;

• for the location tolerances and total tolerances of the shape and location, additionally specify the bases with respect to which the tolerance is specified and specify the dependent tolerances of the layout or shape.

The text should correspond to the terminology and definitions of GOST 24642-81, for example: "tolerance of the profile of the longitudinal section of the surface A 0.008 mm". The structure of the symbol is as follows (Figure 2.56).

Fig. 2.56

1 - frame;

2 - connecting line;

3 - the tolerance sign (Table 2.12);

4 - numeric tolerance value;

5 - the letter designation of the base (s)

The frame should be drawn with solid, thin lines.

The dimensions of the frame and its margins should provide the ability to clearly write all the data.

The height of the numbers and letters that fit into the frame should be equal to the font size of the size numbers.

Examples of designation in the drawings of the tolerances of the shape and arrangement of surfaces are given in Table. 2.13.

The tolerances of the shape and arrangement of surfaces should be assigned depending on the nominal size and degree of accuracy.

Examples of the assignment of degrees of accuracy and methods of processing to achieve them are given in Table. 2.14.

Table 2.13

Symbols in the drawings of the shape and surface tolerances (GOST 2.308-79)

Continuation of Table. 2.13

End of Table. 2.13

The location of the axes in detail can be specified in the drawings either by the interaxial distance or by the distance from any bases, for example, from one or two parts planes.

The tolerances of the holes are set in two ways:

• in the form of indicating the limiting deviations of the dimensions between the axes;

• in the form of indicating the limiting displacements of the axes of the holes from the nominal location (position tolerance).

Distinguish connections:

• Type A (for example, bolting);

• Type B (for example, hairpins).

In connection A, gaps are provided in both connected parts, in connection B - in one.

Table 2.14

Recommendations on the application of the degrees of accuracy (GOST 24643-81) and methods of processing to achieve them

 Degree Precision Scope of application Processing Methods Deviations of the shape of flat surfaces: flatness, straightness 3-4 Guides of high precision machines. Tables of milling, surface grinding and other high-precision machine tools Finishing, superfinishing, fine grinding, racing scraping 5-6 Guides of machines of normal accuracy, precision instruments and machines. Working surfaces of machine feet of normal and high precision Sanding, shabreniya, fine turning of increased accuracy 7-8 Basic surfaces of conductors and other technological devices. Guides of crank and hydraulic presses, sliders. Support surfaces of bearing housings. Joints for gearbox housings, oil pumps Sanding, fine milling and planing, broaching, fine turning

Continuation of Table. 2.14

 Degree Precision Scope of application Processing Methods 9-10 Support surfaces of machines installed on wedges and shock absorbers. Connecting surfaces of fittings and flanges. Brackets and bases of auxiliary and other mechanisms Clean milling, planing and chiselling, pulling, turning Deviation of cylindrical surfaces: roundness 3-4 Working surfaces of plunger and spool pairs at high pressures. Fitting surfaces of rolling bearings of accuracy classes 4 and 2 and holes in housings for these bearings. Neck spindles for bearings of high precision machines Rugged turning, grinding, diamond boring, honing, debugging 5-6 The bearing surfaces of rolling bearings of accuracy classes 0, 6, 5 on shafts and in housings. Pistons and cylinders of hydraulic devices, pumps and compressors at medium pressures. Cylinders of automobile engines. Surface of joints of bushings with cylinders and housings in hydraulic high-pressure systems Sanding, diamond boring, racing turning, thin deployment, honing, stretching 7-8 Sleeves, piston rings and pistons of tractor engines. Holes for bushings in the connecting rods of diesels, compressors, tractor engines Turning, drilling, boring, broaching, rough grinding 9-10 Pistons and cylinders of low-pressure pumps. Sliding bearings with light operating conditions Drafting, drilling, boring, reaming, cutting in stamps of usual accuracy Deviations from parallelism of planes 3-4 The main working surfaces of high and high precision machines. Sliding surfaces of pump parts Debugging, Thin Grinding, scraping 5-6 Working surfaces of machines of normal accuracy. Base surfaces of devices. Friction Surfaces Grinding, fine milling and planing, scraping 7-8 Nominally parallel surfaces of machine components of medium accuracy. Working surfaces of medium-precision conductors Grinding, milling, planing, filing, drawing, injection molding 9-10 Butt surfaces without mutual movement with low requirements for tightness and precision of joints. Non-working surfaces Milling, planing, chiselling 11-12 All rough ways of handling

Continuation of Table. 2.14

 Degree Precision Scope of application Processing Methods Deviations from parallelism of surfaces of revolution 4-5 (5-6) Working surfaces of machines of normal accuracy. Precise measuring instruments and precise conductors Grinding. Coordinate boring 6-7 (7-8) Accurate machine components and conductors of medium accuracy Grinding. Boring on a boring machine, broaching 8-9 (9 -10) Medium-precision machine components Boring, drilling and deployment by conductor 13-15 Cast parts of all sizes from non-ferrous alloys Boring, drilling Deviations from the perpendicularity of the planes 3-4 Basic guides and base surfaces of machines of normal and high accuracy. Precision instruments and measuring instruments Finishing, fine grinding, high precision scraping Responsible parts of precision machines, measuring tools and devices of medium accuracy Fine grinding, scraping 6-7 Responsible parts of medium precision machines, parts of pumps, internal combustion engines, precision conductors and devices Fine grinding, scraping, fine milling and planing 8 Responsible engineering components of conductors and devices Sanding, finishing, milling and chiselling 9-10 Medium-precision machine components Planing, milling, chiselling 11 All methods of processing Deviations from perpendicularity of the butt (face runout) 3-4 Supporting and rubbing surfaces of critical machine components, precision machines and turbines. Flanges of shafts of large turbines and generators Finishing, fine grinding, high precision scraping 5-6 Supporting and rubbing surfaces of critical machine components, precision machines and turbines. Flanges of shafts of large turbines and generators Grinding, scraping, fine grinding and boring 7 Supporting and friction surfaces of machine components Grinding, scraping, fine grinding and boring

End of Table. 2.14

 Degree Precision Scope of application Processing Methods 8-9 Low-level working surfaces of machine components Grinding, fine grinding and boring 10-12 Flat surfaces for the installation of gaskets, for reinforcement, etc. Free surfaces Grinding, grinding, boring Deviations from alignment (radial runout) 3-4 The working surfaces of spindles, tables and other details of machines of increased and normal accuracy. Details of hydraulic machines. Measuring instruments and devices Finishing, fine grinding, fine grinding, superfinishing, honing 5-6 Precision engineering components, manufactured according to 6-7 qualitites Fine grinding, fine grinding and boring 7 Machine-building parts, manufactured according to 8-9 qualitites Grinding, fine grinding and boring 8 Machine parts manufactured at 10-11 qualitites Turning, boring, countersinking, drawing in dies 9-10 Engineering details, manufactured by 12-13 qualitites Note. The degrees of accuracy indicated in parentheses are recommended for deviations from parallelism of the axis of one part with respect to the axis of the other (mating)

To determine the numerical values ​​of the tolerances for the location of the axes of the holes, the calculated displacement of the joint axes is determined.

The value of the limiting displacement of the axis from the nominal location D calculation is determined by the formulas:

a) for bolting:

b) for connecting with screws or pins:

Where - the calculated value of the displacement of the axes of the bolt (screw, hairpin) and the hole, mm; (1 тъ - diameter of the hole, mm; (I - diameter of the bolt (screw, hairpin), mm.

The calculated value of D calculation is rounded to the nearest lower standard value from the series:

The size of the limiting displacement determines the tolerance for linear dimensions of U (Table A.65).

The values ​​of tolerances for diameters O and radii R are also determined from the value of the limiting deviation A; the location of the centers of the holes, as well as the tolerances for the central angles a between the axes of any two holes and the angles between the axis of each hole and the axis of the base hole (φ) (Table A.66).

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