What is a benchmark? Benchmarking is a concept that is widely used in mechanical manufacturing. Mechanical products range from the marking of part dimensions during design, positioning of workpieces during manufacturing, measurement of dimensions during calibration, and determination of the assembly position of parts during assembly. The concept of benchmarks is used. The datum is used to determine the point, line or area on which the geometric relationship on the production object is based.
According to the different functions of the benchmark, precision machined parts are composed of several surfaces. Benchmarks can be divided into two types: design benchmarks and process benchmarks. The following are detailed explanations.
1. Precision design basis
The datum used to determine the position of other points, lines, and areas on the part drawing is called the design datum. For precision machined shaft sleeve parts, the design basis of each outer circle and inner hole is the axis of the part, the end face A is the design basis of the end faces B and C, and the axis of the inner hole is the basis for the radial runout of the outer circle.
2. Process benchmark
The benchmark used in the machining and assembly of precision machined parts is called the process benchmark
Process benchmarks are divided into assembly benchmarks, measurement benchmarks, and positioning benchmarks according to different uses.
Assembly datum: The datum used to determine the position of a part in a component or product during assembly is called an assembly datum.
Measurement datum: The datum used to check the size and position of the processed surface is called the measurement datum. As shown in the part in Figure 32-2, the axis of the inner hole is the measurement reference surface A for testing the radial runout of the outer circle.
Positioning datum: The datum used for workpiece positioning during processing is called positioning datum. As the positioning reference surface (or line, point), only the unprocessed rough surface can be selected in the first step. This positioning surface is called the rough reference. In the subsequent steps, the processed surface can be used as the positioning reference This positioning surface is called a fine datum.