The basic deviation of the Non-standard Precision nut refers to the upper or lower deviation of the tolerance zone relative to the zero line position, which generally refers to the deviation close to the zero line.

According to actual needs, the national standard stipulates 28 different basic deviations for holes and shafts respectively (as shown in the figure). The basic deviation values ​​of shaft and hole are shown in the attached table.

It can be seen from the figure that:

Basic deviations are represented in Latin letters, with upper case for holes and lower case for shafts.

The basic deviation of the axis is from a-h to the upper deviation, from j-zc to the lower deviation, and the upper and lower deviations of js are + and - respectively.

The basic deviation of the hole is from A-H to the lower deviation, and from J-ZC to the upper deviation. The upper and lower deviations of JS are + and - respectively.

Another deviation of the shaft and the hole can be calculated according to the following algebraic formula according to the basic deviation and standard tolerance of the shaft and the hole.
Non-standard Precision shaft

The upper deviation (or lower deviation) of the axis: es=ei+IT or ei=es-IT;

Another deviation (or lower deviation) of the hole: ES=EI+IT or EI=ES-IT.

If you only consider the drawings, the above points must be considered

The allowable amount of variation in the actual parameter value. Parameters include not only geometric parameters in machining, but also parameters of physics, chemistry, electricity and other disciplines. So tolerance is a widely used concept. For mechanical manufacturing, the purpose of formulating tolerances is to determine the geometric parameters of the product, so that the variation is within a certain range, so as to meet the requirements of interchange or coordination.

Tolerances of geometric parameters include dimensional tolerances, shape tolerances, and position tolerances. ①Dimensional tolerance. Refers to the variation of the allowable size, which is equal to the absolute value of the algebraic difference between the maximum limit size and the minimum limit size. ②Shape tolerance. Refers to the total amount of variation allowed by the shape of a single actual element, including 6 items of straightness, flatness, roundness, cylindricity, line profile and surface profile. ③Position tolerance. Refers to the total amount of change allowed by the position of the associated actual element to the datum, which limits the mutual positional relationship between two or more points, lines, and surfaces of a part, including parallelism, perpendicularity, inclination, and coaxiality. , symmetry, position, circular runout and full runout 8 items. Tolerance expresses the manufacturing accuracy requirements of the part and reflects its processing difficulty.

Tolerance grades are divided into 20 grades: IT01, IT0, IT1, …, IT18. The grades decrease in turn and the tolerance values ​​increase in turn. IT stands for International Tolerance. The basic principle of tolerance grade or tolerance value selection is: the comprehensive economic effect of the manufacturing cost and use value of machine parts should be the best. Generally, IT5~IT13 is used for matching dimensions, IT2~IT5 for special precision parts, and IT12 for non-matching dimensions. ~IT18, IT8~IT14 for raw materials.