Chatter can be caused by the cutter or the part depending upon frequencies. They could both be causing one to chatter more. One needs to determine the frequency of the vibration to eliminate the problem. The machine should only cause forced vibration by way of it's dynamic characteristics, which is usually far lower a frequency than the part or cutter. Yet a combination of frequency from the cutter could cause resonance of the machine tool in some situations, which I do not fully understand. You will need to see MLI on this condition, at my website. Forced vibration of the machine tool is usually due to high feed rates, to deep a cut that overloads the axis of a machine tool. Chatter and forced vibration are two different animals and they produce two different frequencies. Forced vibration occurs at spindle speed frequencies, chatter occurs at cutter or part natural frequencies. Unbalance also occurs at spindle speed frequency, which makes it not viable to chatter conditions. Spindle speed frequency is: RPM / 60. Compare. See:
http://members.cox.net/camminc/