Zero Runout

​I recently watched someone tapping their endmill with a brass hammer to reduce its runout. I didn’t ask how long he expected that to last.

To paraphrase Mike Tyson:
"Zero runout won't survive the first impact of the first tooth"

Don't mis-understand what I am saying here. Runout is bad. Concentricity is good. But, all milling tools are flexible (after tap-testing tens of thousands of tools have yet to see one with zero deflection). If you have a concentric and balanced tool running at the right speed and depth of cut for its frequency, you are the champ.