It used to be that the re-sharpening of an endmill consisted of grinding just the primary and secondary land, as shown in figure 2 (Source: Gurhing), until the edge was restored. In addition to the dimensional change to the diameter of the endmill, this would also change the rake angle from positive to negative and reduce the space for chip evacuation. Dynamically, the tool's mass and length were changed enough to alter its frequency. To compensate, the performance of the reground endmill would have to be de-rated by as much as 50%.
With current CNC grinding equipment, the entire original geometry can be replicated. Diameter and length loss can be minimized if land wear is managed and chipping is avoided. Figure 3 shows a series of stability lobe diagrams; new in red, Regrind #1 in light blue (0.005” removed from diameter and length), Regrind #2 in purple (0.010”), Regrind #3 in green (0.015”) and Regrind #4 in burgundy (0.020” removed). As you can see picking a speed and depth of cut in the center of a robust lobe (yellow area) could maintain high performance through up to 4 regrinds.
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