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In actual application, any product can only be arranged for sale and use after being processed and inspected in various series. According to the data, precision machining is the most frequently processed item in finished products. After all, mechanical equipment with excellent performance can produce better products. With the development of modern industries, the structure and configuration of machinery has become a focus. Only when the technology is continuously upgraded will the future development of various industries be played to a greater extent.

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

The design basis for precision machining is the reference used to determine the position of other points, lines, and areas on the part drawing, which is called the design basis. The process benchmark of precision machining refers to the benchmark used in the processing and assembly of parts, and is called the process benchmark. Process benchmarks are divided into assembly benchmarks, measurement benchmarks and positioning benchmarks according to different uses.

1. Assembly benchmark: The benchmark used to determine the position of a part in a component or product during assembly is called the assembly benchmark.

2. Measurement benchmark: The benchmark used to check the size and position of the processed surface is called the measurement benchmark.

3. Positioning datum: The datum used for positioning the workpiece during processing is called the positioning datum. As the positioning reference surface (or line, point), only the unprocessed rough surface can be selected in the first process. This positioning surface is called the rough reference. In the subsequent processes, the processed surface can be used as the positioning reference , This positioning surface is called fine datum.