In the actual production and application, any kind of product can only be sold and used after a variety of processing and inspection procedures. According to the data, precision machining is one of the most frequent processing methods in the finished products. After all, mechanical equipment with excellent performance can produce better products. With the development of modern industry, the structure and configuration of machinery has become a focus. Only by constantly improving the technology, can the future development of various industries have greater play.

Precision machining refers to the process of changing the overall dimension or performance of the workpiece through a kind of mechanical equipment. According to the difference in processing methods, it can be divided into cutting and pressure machining. A mechanical part is composed of several surfaces. To study the relative relationship of parts' surfaces, a datum must be determined. The datum is the point, line and plane on which the position of other points, lines and surfaces can be determined. According to the different functions of benchmarks, benchmarks can be divided into design basis and process basis.

The design datum of precision machining is the datum used to determine the position of other points, lines and planes on the part drawing, which is called design datum. The process datum of precision machining refers to the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, process datum can be divided into assembly datum, measuring datum and locating datum.

1、 Assembly datum

When assembling, the datum used to determine the position of parts in parts or products is called assembly datum.

2. Measurement datum

The datum used to check the size and position of machined surface is called measuring datum.

3. Positioning datum

The datum used for workpiece positioning in machining is called positioning datum. For the surface (or line, point) as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning datum in the following processes, and the positioning surface is called the precise datum.