What are the two types of chatter (vibration) in metal cutting operations?

Forced vibrations and self-generated vibrations

Explanation:

Forced vibration is caused due to the motion of the cutting operation itself it is common in operations that have interrupted cutting like milling.

The size of the chips are related to self-generated vibrations. If larger chips are formed this means higher depth of cut is given. If smaller chips are formed this means lower depth of cut is given. When we give excess depth of cut then self-generated vibrations are produced.