Handle pulsation when quill is extended at low speeds

[Matanuska]

I've been thinking some more about this and now I'm leaning toward Ed's resonant frequency vibration explanation. Doing a bit more reading it appears gyroscopic precession forces are a response to a torque applied at right angles to the axis of rotation. Gravity might do this as the quill is moved in or out in the horizontal boring position but it wouldn't explain pulsation in the vertical drill press mode. Whatever the explanation, deburring and waxing the quill and tightening the setscrew have fixed the problem for me.