# Z.2. Normal angles and tolerances of angles - Machine parts. Course design

## Z.2. Normal angles and tolerances of angles

GOST 8908-81 applies to angles (angular dimensions) and tolerances of the corners of cones, prismatic elements of parts with the length of the smaller side of the angle to 2500 mm.

The standard does not apply to the angles associated with the calculated dependencies with other accepted dimensions, to the cone angles in accordance with GOST 8593-81 and the tolerances of cones for which the diameter tolerance in each section is given on the length of the cone, and the cone angle deviations are allowed within the whole tolerance range of cone diameter.

GOST 8908-81 sets the normal angles (Table 11.57). When choosing angles, row 1 should be preferred to row 2, and row 2 to row 3.

For prismatic details (Figure 2.53), except for the angles shown in Table. Г1.57, it is allowed to apply slopes and corners corresponding to them, given in Table. A.58.

Fig. 2.53

GOST 8908-81 sets the following tolerances of angles:

b a is the angle tolerance expressed in angular units;

a is the tolerance of the cone angle equal to the tolerance of the diameter difference in two normal sections of the cone at a given distance/"between them (determined from the perpendicular to the axis of the cone).

In the designation of the tolerance of an angle of a given degree of accuracy, the number of the appropriate degree of accuracy is added to the notation of the angle tolerance, for example: 8 a 8, 5 a 10. GOST 8908-81 establishes 17 degrees of accuracy of the tolerances of angles'. 1; 2; 3; 17.

Tolerances for angular dimensions are given in Table. A.59.

The tolerances of the angles of cones with a conicity of not more than 1: 3 should be assigned depending on the nominal length of the cone b (Figure 2.54), but with a conicity of more than 1: 3 - depending on the length of the cone generator /, [(Figure 2.55) .

The tolerances of the angles of the prismatic elements of the parts are selected depending on the nominal length L of the smaller side of the angle (Table A.59). The values ​​of a, given in Table. P.59, are indicated for the extreme values ​​of the intervals of lengths i, and b.

In Table. 2.11 provides recommendations on the assignment of degrees of accuracy to the angular dimensions of parts.

Table 2.11

Recommendations for assigning degrees of accuracy to angular dimensions

 Degree Precision Details Processing Methods 3 Higher precision internal cones for sealed connections Rake grinding with subsequent debugging 4 High accuracy, requiring good centering; centering ends of shafts for gears and holes in gears of high degrees of accuracy High-precision grinding, deployment and turning 5.6 High accuracy, transmitting on the tapered connection large torques; friction cones and bushings; conical pins (1:50) and holes for them Grinding, unfolding and turning high precision; high precision machining 7.8 Normal accuracy: the cones of the friction parts with the subsequent adjustment of the bevel gears, the centering ends of the axles, the tapered conic pins (1:50) of normal accuracy, the carriage guides Turning on lathe and turret lathes of usual precision, high accuracy milling with the use of dividing mechanisms, grinding with installation on the table and in the device, deployment 9 Low precision, transmitting motion, stopping, etc .; angled grooves, sprocket sprockets, stopper locks to leashes, ratchet and friction stops, extruded parts Semi-pure turning, fine milling by marking, planing in adaptation, countersinking, grinding 10 Sizes, to the accuracy of which there are no high requirements (free dimensions) Rough machining on all kinds of machines, casting, bending in high precision bending dies

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