Evaluating the use of a new type of impact damper for internal turning tool bar in deep holes

In internal turning operation of long holes, the tool is not rigid, since it must be out from the lathe turret in a length longer than the machined hole length. This problem is even more serious in the internal turning of hardened steels, where the requirements for surface quality are more restrict, due to the fact that this is a finishing operation, which aims to replace grinding. Therefore, some procedures have to be taken in order to minimize vibration and, consequently, to make the attainment of a good workpiece surface quality possible. One of these procedures is the use of a damped tool. In this work, we tried a simple and different kind of impact damped tool bar, using spheres placed in a cavity manufactured in the tool bar. The performance of this impact damper with three different sizes of spheres was compared to the performance of a solid steel bar, in terms of workpiece surface roughness, tool vibration, and tool life. The main conclusion of this work is that the use of the kind of impact damper tested in this work makes possible the increase of the tool overhang (tool length outside the machine turret) without damaging surface roughness and tool life and, consequently, it also makes possible the turning of longer holes than when a solid bar is used.