Principles for Arranging the Machining Sequence on CNC Lathes
1) Principle of Roughing First, Then Finishing: The machining sequence for each surface should follow the order of roughing → semi-finishing → finishing, progressively improving the surface machining accuracy and reducing the surface roughness value.
2) Principle of Datum Surface First: Surfaces used as the finishing datum should be machined first, because the more accurate the locating datum surface, the smaller the clamping error. Since the φ40 outer circle on the lathe is the datum for coaxiality, this surface should be machined first, followed by other surfaces.
3) Principle of Primary Surfaces Before Secondary Surfaces: The main working surfaces and assembly datums of the part should be machined first, so that any defects on the main surfaces of the blank can be detected early. Secondary surfaces can be machined intermittently, after the main surfaces have been machined to a certain degree, but before finishing.
4) Principle of Near-to-Far Machining: Generally, after the workpiece is clamped, the areas closer to the tool post should be machined first, and the areas farther from the tool post should be machined later, so as to shorten the tool travel distance, reduce idle travel time, and also help maintain the rigidity of the blank or semi-finished product, improving cutting conditions. For the internal holes of the lathe part, the tapered bore should be machined first, then the φ30mm bore, and finally the φ20mm bore.
