The Vibrations of Vertical Milling Machines under Test and Working Conditions

Abstract

The investigation described in this paper consists of three parts. Part I is concerned with an experimental investigation of the vibration of vertical milling machines under test conditions. It is shown that in the frequency range investigated, 6-10 000 c/s, the machine structure has five modes of vibration which responded with large amplitudes. The dynamic deflections corresponding to these are discussed and attention is drawn to certain structural weaknesses frequently encountered in vertical milling machines. Part II of the paper reports various experiments concerned with face-milling chatter. It is shown that the severity of chatter depends on the relative position of cutter and work-piece and the depth of cut. When the depth of cut exceeds a certain minimum value, the machine chatters in definite speed bands which are separated by chatter-free speeds. As the depth of cut is increased, the chatter-free speed bands contract. From this and the variation of the chatter frequency, it is concluded that the chatter observed is of the regenerative type, similar to that arising in the case of drilling and other machining processes (1), (2)†. A theoretical interpretation of the experimental results is given in Part III. Chatter behaviour of the machine is discussed with the aid of a three-dimensional stability chart. The constants required for the construction of this chart are extracted from the experimental results given in Part II. Correspondence between theory and experiments is satisfactory.