1. Design benchmark for precision mechanical parts processing:
The datum used to determine the position of other points, lines and surfaces on the part drawing is called the design datum. For bushings processed by precision mechanical parts, the design reference for each outer circle and inner hole is the axis line of the part, end face A is the design reference for end faces B and C, and the axis of the inner hole is the reference for the radial runout of the outer circle.
2. Process benchmark:
The benchmark used in the processing and assembly of precision machining parts for hardware parts processing is called process benchmark. Process benchmarks are divided into assembly benchmarks, measurement benchmarks and positioning benchmarks according to different uses.
Assembly datum for hardware parts processing The datum used to determine the position of the part in the component or product during assembly is called the assembly datum; the measurement datum is the datum used to check the size and position of the machined surface, called the measurement datum; positioning datum processing The datum used for positioning the workpiece is called the positioning datum. As the surface of the positioning reference, in the first process, only the unprocessed blank surface can be selected. This positioning surface is called rough reference. In the subsequent processes, the machined surface can be used as the positioning reference. This positioning surface is called Fine benchmarks.