1.     When selecting a reference surface prior to using a coordinate measuring machine (CMM), the principle of reference surface consistency must be followed

that is, the measurement reference surface, design reference surface, process reference surface, and assembly reference surface of the CMM must be consistent. If, for various reasons during the machining process, the process reference surface and the design reference surface cannot be aligned, then during in-process inspection, the measurement reference surface should align with the process reference surface; during final inspection prior to assembly, the measurement reference surface should align with the assembly reference surface.

2.      Selection of CMM Positioning Methods

The positioning method for a CMM is determined by many factors, but there are generally two scenarios: one where the measurement reference plane serves directly as the positioning reference plane, and another where the measurement reference plane cannot serve as the positioning reference plane.

The most typical positioning methods are surface positioning and line positioning. Surface positioning is further divided into plane positioning and outer cylindrical surface positioning. Line positioning primarily involves center point positioning.