Answer: D
Answer analysis: For CNC machine tools, one of the most characteristic indicators of machine tool accuracy is the geometric accuracy of the machine tool.
The geometric accuracy of CNC machine tools refers to the geometric accuracy of the key components of the machine tool, including the flatness of the work table, the straightness of each guide rail, the parallelism between the guide rails, the perpendicularity, the axial runout of the spindle, radial runout, etc. These precisely affect the geometric accuracy and quality of the machined parts, so it is one of the most characteristic indicators of the accuracy of CNC machine tools.
Machine tool motion accuracy, transmission accuracy and positioning accuracy are also important accuracy indicators of CNC machine tools, but they are not the most characteristic. Machine tool motion accuracy reflects the motion accuracy of each moving part of the machine tool in the processing process, including positioning accuracy, repeated positioning accuracy and micro feed accuracy.
The transmission accuracy of the machine tool reflects the working accuracy of the machine tool transmission system, including the transmission accuracy of gears, screw nut pairs, clutches and other components.
Machine tool positioning accuracy refers to the ability of machine tools to be accurately positioned when working, including reverse deviation, positioning time, positioning accuracy, etc.
Therefore, according to the meaning of the title, for CNC machine tools, one of the most characteristic indicators of machine tool accuracy is the geometric accuracy of the machine tool, and the answer is D.