Mechanical processing factories emphasize that mechanical processing must meet a certain degree of precision, which refers to the level at which the main geometric parameters of steel parts after mechanical processing are consistent with the idealized values required by the part drawings. The level of inconsistency between them is called production and processing deviation.

The precision of production and processing in mechanical processing plants includes three levels: on the one hand, it is the precision of specifications, which limits the standard deviation between the production and processing surface layers to within the necessary range; On the other hand, the precision of geometric shapes limits the deviation of macroeconomic geometric shapes in the production and processing of surface layers, such as roundness, cylindricity, parallelism, and straightness.

On the other hand, it is the precision of each other's parts, which limits the deviation between the standards of the surface produced and processed by the mechanical processing plant, such as axis, flatness, and parallelism. Production and processing precision refers to the level of conformity between the actual specifications, appearance, and main geometric parameters of the surface layer of the parts after production and processing, and the idealized geometric parameters specified in the engineering drawings.

The main parameters of idealized geometric shapes, in terms of specifications, mean specifications; For the appearance of surface geometric shapes, it refers to circles, cylinders, planes, spheres, and parallel lines; For the mutual parts in the middle of the surface layer, it refers to parallel planes, vertical planes, coaxial outputs, symmetry, etc.

The deviation between the actual geometric parameters of the parts produced by the mechanical processing plant and the idealized geometric parameters is called the production and processing deviation. The precision and deviation of production and processing are all the main parameters for evaluating the surface geometric shapes of production and processing. The precision of production and processing is considered based on tolerance levels. The smaller the level value, the higher the precision; The deviation in production and processing is expressed as a scalar value, with the larger the scalar value.