Process Benchmark

Process benchmarks refer to the standards used during the manufacturing process of parts. Depending on their purpose, process benchmarks can be categorized into process benchmarks, positioning benchmarks, measurement benchmarks, and assembly benchmarks.

Process Benchmark

In process drawings, the reference used to determine the dimensions, shape, and position of the processed surface in this operation is called the process datum.

2. Positioning Benchmark

During the machining process, the reference used to determine the correct position of the workpiece on the machine or fixture is known as the locating datum.

3. Measurement Standard

In the process or after processing, the reference used to measure the shape, position, and dimensional errors of workpieces is called the measurement datum.

4. Assembly Standard

During assembly, the reference point used to determine the relative position of parts or components on the product is called the assembly datum. For instance, the inner bore of a gear is the assembly datum for that gear. Generally, the design datum is specified on the part drawing, while the process datum is selected and determined by the process personnel based on the specific process.

When analyzing benchmark issues, be mindful of the following two points:

1) As the reference points, lines, and planes may not necessarily be physically present on the workpiece (such as the centerline of a hole, the axis line, etc.), they are instead represented by certain specific surfaces, which are known as datum surfaces. For example, the centerline of an inner hole is indicated through its surface, with the centerline of the inner hole serving as the datum and the inner hole surface as the datum surface. Therefore, the issue of selecting a datum is essentially about choosing the appropriate datum surface. Particularly, for the sake of convenience in description, the datum and datum surface can sometimes be collectively referred to as the datum.

2) As a reference, it can be a point or line without area or a very small surface, but the fundamental plane representing this reference always has a certain area. For example, when installing a long shaft on a lathe, the reference is the shaft centerline, which has no area; the fundamental plane is the conical surface, which has a very small but still certain area.