Benchmark refers to the points, lines, and surfaces used to confirm the connections between several elements of the production target. For a mechanical component, the reference is the point, line, or surface on which the orientation of other points, lines, or surfaces on the component is determined. In the planning and processing process of machine parts, selecting which points, lines, and surfaces to use as benchmarks according to different requirements is one of the main factors that directly affect the processing technology of parts and the accuracy of scale and orientation between surfaces. According to different functions and usage scenarios, benchmarks can be divided into two categories: planning benchmarks and process benchmarks.
1、 Benchmark
Benchmark refers to the points, lines, and surfaces used to confirm the connections between several elements of the production target. For a mechanical component, the reference is the point, line, or surface on which the orientation of other points, lines, or surfaces on the component is determined.
In the planning and processing process of machine parts, selecting which points, lines, and surfaces to use as benchmarks according to different requirements is one of the main factors that directly affect the processing technology of parts and the accuracy of scale and orientation between surfaces. According to different functions and usage scenarios, benchmarks can be divided into two categories: planning benchmarks and process benchmarks.
（1） Planning benchmark
Planning benchmark refers to the benchmark used to indicate the planning scale on the part drawing. On a machine part drawing, there can be one or multiple planning benchmarks. In Figure 1-1a, A and B are planning benchmarks for each other; In Figure 1-1b, the 40mm outer circle is the planning reference for the 60mm outer circle; In Figure 1-1c, Plane 1 is the planning reference for Plane 2 and Hole 3, and Hole 3 is the planning reference for Hole 4 and Hole 5; In Figure 1-1d, the centerline is the planning reference for an inner hole of 30mm, a gear indexing circle of 48mm, and a top circle of 50h8mm.
（2） Process benchmark
Process benchmark refers to the benchmark selected in the process of a part. According to different purposes, process standards can also be divided into process standards, positioning standards, measurement standards, and device standards.
1. Process benchmark
In the process diagram, the benchmark used to confirm the scale, shape, and orientation of the processed surface of this process is called the process benchmark., The surface of the machining is a D-hole, and the centerline is required to be perpendicular to the A-plane and maintain spacing dimensions L1 and L2 with the C-plane and B-plane. Therefore, A, B, and C are all the process benchmarks for this process.
2. Positioning reference
The reference used to confirm the correct orientation of the workpiece on the machine tool or fixture during processing is called the positioning reference.
3. Measurement benchmark
The benchmark used to measure the shape, orientation, and scale errors of the workpiece during or after processing is called the measurement benchmark. As shown in Figures 1-3, scale L1 can be measured using a depth caliper, and end face T is the measurement reference for end face A.
