What are the fundamental processes for precision mechanical part machining?

(1) Process Benchmarks
Process benchmarks refer to the reference points adopted during a part's manufacturing process. Based on their function, these benchmarks can be categorized as operation benchmarks, locating benchmarks, measuring benchmarks, and assembly benchmarks.
1. Operation Benchmark
In an operation diagram, the reference used to determine the dimensions, shape, and position of the machined surface after processing is called the operation reference.

2. Positioning Reference
During machining, the reference used to determine the correct position of the workpiece on the machine tool or in the fixture is called the positioning reference.

3. Measurement Reference
The reference used during or after machining to measure the shape, position, and dimensional errors of a workpiece is called the measurement reference.

4. Assembly Reference
During assembly, the reference used to determine the relative position of parts or components within a product is called an assembly reference. For example, the bore of a gear serves as its assembly reference. Generally, design references are specified on part drawings, while process references are selected and determined by process engineers based on specific manufacturing procedures.

When analyzing reference issues, note the following two points:
1) Points, lines, or surfaces serving as benchmarks may not physically exist on the workpiece (e.g., hole centerlines, shaft centerlines), but are represented by specific surfaces called benchmark surfaces. For instance, the centerline of an internal bore is represented by the bore surface—the bore centerline is the benchmark, while the bore surface is the benchmark surface. Thus, selecting a benchmark involves choosing an appropriate benchmark surface. Specifically, for convenience in description, both the datum and the datum surface may sometimes be collectively referred to as the datum.
2) A datum can be a point, line, or very small surface with no area, but the datum surface representing such a datum always has a certain area. For example, when mounting a long shaft on a lathe, the datum is the shaft centerline, which has no area; the datum surface is the tapered surface, which has a very small but definite area.