Deviations and tolerances of location - Applied Mechanics

Deviations and Location Tolerances

Deviation of the location Δ - deviation of the real location of the surface from its nominal location. When assessing the deviations in the location of the surfaces (profiles) considered relative to the basic elements (by which are meant surfaces, points) the deviations of the form are not considered. Therefore, real surfaces 2 and profiles are replaced by adjacent 1 , and axes, symmetry planes and centers of real surfaces are assumed to be axes, symmetry planes and centers of adjacent elements.

Deviation from parallelism of surfaces - difference Δ = a - b of the largest and smallest distances between planes within the normalizing section (Figure 3.7, a). Parallelism tolerance T is the largest deviation from parallelism.

Deviation from the perpendicularity of the planes - the deviation A of the angle between the planes from the right angle, expressed in linear units at the length of the normalized section (Figure 3.7, b). The greatest value of this deviation is the tolerance of the perpendicularity of T.

The deviation of the inclination of the plane relative to the plane or axis - the deviation A of the angle between the plane and the reference plane or the reference axis from the nominal angle, expressed in linear units along the length of the normed section. the allowable value of this deviation is the tolerance of the slope T.

Deviation from alignment relative to the axis of the reference surface 3 - the greatest distance A between the axis of the races

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of the rotational surface and the axis of the reference surface at the length of the normalized section L (Fig. 3.7, c). Deviation from alignment relative to the common axis 4 the greatest distance (Δ1, Δ2) between the axis of the rotating surface under consideration and the common axis of two or more surfaces of revolution at the length of the normalized section (Fig. 3.7), d). The alignment tolerance in the diametrical expression is twice the maximum allowable deviation from the coaxiality (with the sign 0 before the numerical value), and in radius - the nearest The greater the value of this deviation.

Fig. 3.7

Deviation from symmetry relative to the reference plane - the greatest distance A between the plane of symmetry of the surface in question and the base plane of symmetry 5 within the normalized section (Figure 3.7, ).

Deviation from the intersection of the axes - the smallest distance A between the axes that are nominally intersecting.

The intersection margin of the axes is the area in space bounded by two parallel planes spaced from each other at a distance equal to twice the intersection tolerance in the diametric expression (indicated with the sign T before the numeric value) or the intersection tolerance in the radius expression {is indicated with the sign T/2) and positioned symmetrically with respect to the reference axis 6 (Figure 3.7, e).

Positional deviation - the greatest deviation of the actual location of the element (its center, axis or symmetry plane) from its nominal location within the normalized section (Figure 3.7, g). Figure 7 - nominal axis location, 8 - nominal dimensions.

In addition to the above tolerances, the total deviations and tolerances of the shape and arrangement of the surfaces are normalized.

Radial runout - the difference A of the largest and smallest distances from the points of the real profile 1 of the surface of revolution to the base axis 2 in a section plane perpendicular to the reference axis (Figure 3.8, a). This beat is mainly the result of the deviation from the coaxiality of the surface under investigation with respect to the reference axis 2 and the deviation from the circularity of the profile of the section under consideration. If the difference of the greatest and smallest distances from all points of the real surface is determined within the normalized section L to the base axis 2, , then a total radial runout is found.

Fig. 3.8

End runout - difference Δ of the largest and smallest distances from the points of the entire end surface to a plane perpendicular to the reference axis 2 (Figure 3.8, b). It is the result of a joint manifestation of deviations from the flatness of the surface in question and a deviation from its perpendicularity relative to the reference axis.

The deviation of the shape of the specified profile (surface) - the greatest deviation of the points of the real profile 1 ( surfaces ) from the nominal profile 3 surfaces ), defined by the normal to the nominal profile ( of the surface) within the normalized section. The profile tolerance margin is the area bounded by two lines equidistant to the nominal profile 3 and obtained as envelopes of a family of circles whose diameter is equal to the tolerance of the shape of a given profile in the diametrical expression T, and the centers they are on the nominal profile 3 (Figure 3.8, in ). Here - the nominal values ​​of the coordinates.

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The rules for indicating the tolerances of the shape and location are established by GOST 2.308-79. The symbols for these tolerances are shown in Table. 3.3. The sign and the numerical designation of the tolerance, as well as the letter designation of the base, are inscribed in a rectangular frame divided into two or three fields (Figure 3.9). In the first place, the sign is indicated, on the second - the numerical value of the tolerance in millimeters, on the third, if necessary, the letter designation of the base (s) or the surface with which the tolerance of the location is related. The frame is placed horizontally, and the intersection of the ec with any lines is not allowed. A solid line with an arrow at the end connects the frame to the element to which the tolerance applies. If the tolerance refers to an axis or a plane of symmetry, then the connecting line is an extension of the dimensional one; if the tolerance refers to a common axis (the plane of symmetry), then the connecting

Fig. 3.9

The line is drawn to the common axis. The base is indicated by a blackened triangle and a letter. If the base is an axis or a plane of symmetry, the triangle is placed at the end of the dimension line. Sometimes the triangle of the base is connected by a line with the tolerance frame.

Table 3. 3

Tolerance group

Approval type

Sign

Numerical tolerance value

Forms

Straightness tolerance

Flatness tolerance

Limits the absolute deviation

Cylindrical tolerance

Round tolerance

Profile Section Tolerance

Limits the deviation in the radius expression

Locations

Parallelism tolerance

Tolerance of perpendicularity

Tilt tolerance

Limits the maximum deviation of the error from the base

Alignment tolerance

Tolerance of symmetry

Position tolerance

Axis intersection tolerance

Limits the deviation either in the diametrical (0 or T), or in the radial (0 or T/2) expression

Summary forms and locations

Radial runout tolerance

Face runout tolerance

Beating tolerance in the specified direction

Limits the total deviation displayed by the indicator when measured

Full radial Ί beat tolerance

Tolerance of total end runout

Then

Allowing a form of a given profile

Tolerance of the shape of the given surface

Limits the total deviation either in the form of T, or in the form of T/2

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