# Prediction Methods and Experimental Techniques for Chatter Avoidance in Turning Systems: A Review
## 1 Introduction  
The study of chatter is closely related to the history of metal removal processes at the beginning of the 20 th century. As early as 1907, [PERSON], one of the fathers of modern machining, gives the first definition of chatter presenting this phenomenon as 'perhaps the most obscure and difficult to ascertain' [1]. However, it was not until midcentury when its main causes were identified. Among the different types of vibrations, chatter vibrations are defined as self-excited vibrations. When the tool/workpiece contact is not stiff enough, an oscillation is generated between them causing a distortion in the chip thickness parameter between two successive periods, \(t\) and \(t\)-\(T\), where \(t\) is be the actual time and \(T\) the workpiece rotation period in the context of turning. In this way, the process itself produces feedback causing a vibration whose frequency is near, but not exactly, to the natural frequency of the system. As a result, waves between subsequent passes lead to unacceptable surface roughness or even out of tolerance workpieces [2, 3]. To avoid vibration problems, attention must be paid at the very early stage of process planning. Particularly, the authors identified the following items as possible sources of vibrations: (1) cutting tool (grain size, geometry, coating and wear and their effect on cutting forces) [4, 5]; (2) workpiece material (type of material, homogeneity, hard grains, porosity, defects) [6, 7]; (3) machine-tool (machine, spindle, toolholder, tool overhang, clamping) [8].  
In a pioneering study, [PERSON] [9] characterizes in a very complete way the origin and onset of vibrations in the cutting tool when machining steel. In this study, the origin of chatter is found at the forces sustained by the cutting process itself and not external forces. Together with [PERSON], pioneers in detecting and studying chatter mechanisms were [PERSON], [PERSON], and [PERSON] [10; 11], who determined the presence of vibrations in machine tools due to the modulation or regeneration of the chip thickness. In low stiffness conditions, a feedback phenomenon turns current vibrations into vibrations of greater amplitude for the following period. At this time, [PERSON] [12] and [PERSON] [13] developed the basic dynamic theory for vibrations in machining, distinguishing between the different types of chatter, A or B, depending on the direction of the mode with respect to the plane where chip is formed.  
Chatter emerged over the last 30 years as maybe the most challenging research topic in the machining of metallic components. This problem can be approached in many different ways. In References [14; 15], the authors identified the most remarkable techniques including chatter stability prediction, chatter detection, and chatter control techniques.  
Indeed, works from the literature for chatter suppression and control can be grouped into three approaches/strategies. The first technique consists of adequately selecting two cutting parameters from the stability lobe diagrams: (1) spindle speed, or more exactly cutting speed; (2) depth of cut. Regarding the feed parameter, this is often neglected during stability analysis and regenerative effect. The second method is to disrupt the regenerative effect by continuously varying machining parameters. Finally, the third method is to passively or actively alter the machine-tool dynamics to improve chatter-free available zones, usually by installing new devices, actuators, and sensors into the machine. These three methods are discussed separately within this work as follows.