The top panel of the computer screen shown in this video shows the force of the tapping hammer's impact. The lower panel shows the tool's (or anvil's) response to that force as captured by an accelerometer attached to the opposite side of the hammer strike. It deflects, rebounds and then vibrates back to rest. After tap-testing tens of thousands of milling tools we have yet to see one with a response that was a flat line. They are all flexible and will deflect and vibrate from the forces of the tooth impacts.
No physical object can be perfectly rigid. It's physics.
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