Mechanical parts benchmark

Mechanical parts are made up of several surface, studies the relative relations on the surface of the parts, must determine a benchmark, the benchmark is used to determine other parts of dot, line, the position is based on dot, line, face.According to the different function of the benchmark, the benchmark can be divided into two categories, design datum and technology datum.
1. The design basis
On the part drawing is used to determine the benchmark of other point, line, face, referred to as the design reference.As shown in figure 32-2 [cc2] in the shaft sleeve parts, the outer circle and inner hole design datum is part of axis, the design of the end face is B, C datum, the axis of the bore is the benchmark external circular radial runout.
2. Process benchmark
Parts used in the process of processing and assembling of the benchmark, known as benchmark process.Process benchmarking is divided into different according to the use assembly datum, measurement datum and position datum.
Assembly benchmark assembly (1) when used to determine the components in the component or product in the location of the benchmark, known as assembly benchmark.
(2) the measurement datum for inspection has been processed on the surface of the size and position of the benchmark, referred to as the measuring datum.As shown in figure 32-2 parts, in the inner hole axis is cylindrical radial runout measurement benchmark;Check length L is A size L and the surface of the measuring datum.
(3) when the locating datum processing workpiece positioning the benchmark, known as the locating datum.As the surface of the locating datum (or line and point), only choice in the first step in the raw surface of the blank, the positioning surface of said crude benchmark. In each process has been machined surface can be adopted as a locating datum, the positioning surface of the said fine benchmark.