1. "Benchmark first" principle
The datum surface shall be processed first to make reliable positioning for the subsequent process. For example, the initial process of shaft parts is generally milling the end face and drilling the center hole, and then positioning the center hole to process other surfaces.
2. "Face before hole" principle
When there is a large plane on the part that can be used as the positioning reference, always process the plane first, and then position the hole with the plane to ensure the position accuracy between the hole and the plane, so that the positioning is more stable, the clamping is also convenient, and can avoid the deflection caused by rough surface drilling.
3. The principle of "first, then second"
The main surface (datum surface and working surface with high position accuracy requirements) shall be processed first, and then the secondary surface (such as keyway, screw hole, fastening hole, etc.) shall be processed. The secondary surface is generally after the main surface reaches a certain accuracy and before finishing.
4. The principle of "rough before fine"
For parts with high accuracy requirements, the machining accuracy shall be gradually improved in the order from coarse to fine. This point cannot be ignored especially for parts with poor rigidity.
