Machining plants emphasize that machining must meet certain precision requirements, which refers to the degree of consistency between the actual geometric parameters of a machined part and the ideal values specified in the part drawing. The degree of inconsistency between them is called machining deviation.
Machining precision in machining includes three aspects: First, dimensional precision, which limits the dimensional deviation between the machined surfaces to within a necessary range; second, geometric shape precision, which limits the macroscopic geometric shape deviation of the machined surface, such as roundness, cylindricity, parallelism, and straightness; and third, positional precision, which limits the positional deviation between the machined surfaces, such as coaxiality, flatness, and parallelism. Machining precision is the degree of conformity between the actual dimensions, shape, and positional geometric parameters of the machined part's surface and the ideal geometric parameters specified in the engineering drawings.
Idealized geometric parameters, in terms of specifications, refer to the mean specification; in terms of surface geometry, they refer to circles, cylinders, planes, spheres, and parallels, etc.; in terms of the relative positions within the surface, they refer to parallelism, verticality, coaxiality, symmetry, etc.
The deviation between the actual geometric parameters of machined parts and the idealized geometric parameters is called machining deviation. Machining precision and machining deviation are both technical terms used to evaluate the machining of surface geometric parameters. Machining precision is measured by tolerance grades; the smaller the grade value, the higher the precision. Machining deviation is expressed by numerical values; the larger the value, the greater the deviation.
