What are the positioning benchmarks for machining shaft parts

Firstly, the central hole of the workpiece is used as the positioning reference for machining. In the processing of shaft parts, the coaxiality of the outer circular surfaces, conical holes, and threaded surfaces, as well as the perpendicularity of the end face to the rotating axis, are important manifestations of positional accuracy. These surfaces are generally designed based on the centerline of the axis, positioned with a central hole, in accordance with the principle of overlapping the reference lines.

The center hole is not only the positioning reference for turning machining, but also the positioning and inspection reference for other machining processes, in accordance with the principle of unified reference. When using two center holes for positioning, multiple outer circles and end faces can be machined to the maximum extent in one clamping process.

Secondly, the outer circle and center hole are used as positioning benchmarks for machining. This method effectively overcomes the disadvantage of poor rigidity in locating the center hole, especially when machining heavy workpieces, which can cause unstable clamping and the cutting amount cannot be too large.

By using the outer circle and center hole as the positioning reference, there is no need to worry about this issue. During rough machining, the method of using the outer circular surface of the shaft and a central hole as the positioning reference can withstand a large cutting torque during machining, and is the most common positioning method for shaft parts.

It uses two outer circular surfaces as the positioning reference for processing. When machining the inner hole of a hollow shaft, the central hole cannot be used as the positioning reference, so the two outer circular surfaces of the shaft should be used as the positioning reference. When machining machine tool spindles, two supporting journals are often used as positioning benchmarks, which can effectively ensure the coaxiality requirements of the taper hole relative to the supporting journal and eliminate errors caused by non overlapping benchmarks.

Finally, the conical plug with a central hole is used as the positioning reference for machining. This method is most commonly used in the machining of the outer surface of hollow shafts.