Benchmark first principle. The surface used as a precision datum should be processed first, because the more accurate the surface of the positioning datum, the smaller the mounting and clamping error.

Roughing before finishing principle. The machining sequence of each surface in accordance with the roughing → semi-finishing → finishing → precision machining order in turn, and gradually improve the surface machining accuracy and reduce the surface roughness value.

The principle of first main and then secondary. The main working surface of the part, assembly datum surface should be processed first, so as to early detection of defects that may occur on the main surface of the blank. Secondary surfaces can be interspersed, placed in the main machining surface machining to a certain extent, before finishing.

First face after the hole principle. Box, bracket parts, plane contour size is large, generally the first processing plane, and then processing holes and other dimensions, so that the processing order, on the one hand, with the machined plane positioning, stable and reliable; on the other hand, in the machined plane on the processing of holes, easier, and can improve the accuracy of the hole machining, especially drilling holes, holes are not easy to deflection of the axis.