The Vibrations of Radial-Drilling Machines under Test and Working Conditions

Abstract

Machine-tool chatter is essentially a problem of dynamic instability. A drilling machine under working conditions can be regarded as a dynamic system which for certain values of its system parameters becomes unstable and bursts into oscillations. The system parameters are determined by the static and dynamic characteristics of the machine-tool structure, the geometric shape of the drill, certain features of the work-piece material and the working conditions, and it is the interrelation of these which results in chatter or chatter-free machining. The paper commences with a discussion of the dynamic characteristics of radial-drilling machines. This is followed by an experimental investigation of the behaviour of these machines under working conditions, and finally a theory of drilling chatter is developed. The results of this theory are presented in the form of a stability chart which shows those drill speeds at which, for given values of the system parameters, chatter-free drilling is ensured. Although the theory presented is based on an experimental investigation of radial-drilling machines drilling into solid material, it is directly applicable to drilling operations carried out on any other type of machine and yields also results concerning chatter occurring at drill break-through and when drilling up pre-drilled holes.