The rotating accuracy of a machine tool spindle directly affects the roundness of machined parts. Commonly, a precision arbor and one or two probes are used to inspect the spindle axis error motion. When a reference precision arbor is notavailable or when the spindle error motion is in the same order of magnitude as the accuracy of the reference arbor, it is imperative to separate the roundness error of the reference arbor from the spindle error. One of the most widely used method is thethree-probe method. This paper presents an exact model and in-depth error analysis for the conventional three-probe method. The results show that contrary to conventional wisdom that a precise arbor is not needed with the three-probe method, the arboraccuracy should be at least ten times better than that of the axis motion. To reduce inaccuracy in the converted axis motion and arbor contour, it is also suggested that the mounting error of the probes should be less than on-fiftieth of the size of theaxis motion and the arbor size. The exact geometric model developed in this paper can also be extended to analyze the precision aspect of other methods.
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