1. Process Benchmark

Process datum refers to the datum used in the process of the part. Depending on the purpose, the process datum can be sub-process datum, positioning datum, measurement datum and assembly datum.

1. Process benchmark

In the process diagram, the reference used to determine the size, shape and position of the processed surface of this process is called the process reference.

2. Positioning reference

In the processing, used to determine the workpiece in the machine tool or fixture in the correct position of the reference, known as the positioning reference.

3. Measurement reference

In the process or after processing, used to measure the workpiece shape, position and size error of the reference, known as the measurement reference.

4. Assembly benchmark

During assembly, the reference used to determine the relative position of parts or components on the product is called the assembly reference. For example, the inner hole of the gear is the assembly reference of the gear. In general, the design benchmark is given on the part drawing, and the process benchmark is determined by the process personnel according to the specific process selection.

In 2. analysis of the baseline problem, note the following two points:

1, as a reference point, line, surface in the workpiece does not necessarily exist specifically (such as hole center line, axis line, etc.), but by some specific surface to reflect, these surfaces are called the base surface. For example, the center line of the inner hole is reflected by the inner hole surface, the center line of the inner hole is the reference, and the inner hole surface is the base surface. Therefore, the problem of choosing the benchmark is the problem of choosing the appropriate base surface. In particular, sometimes for convenience of description, the datum and the base plane may be collectively referred to as a datum.

2. As a reference, it can be a point and line without area or a very small surface, but the base surface representing this reference always has a certain area. For example, to install a long shaft on a lathe, the reference is the axis line, it has no area; the base is a cone, it has a small area but does have a certain area.