The effects of tool vibration on hole-profile in deep drilling are examined by analysis of vibration with respect to frequency. Further, the mechanism and the causes of formation of multi-corner shape in holes with high length-to-diameter ratio are discussed. It is concluded that the frequency of the bending vibration of the boring bar during machining of the holes corresponds to the number of the corners of holes. From the fact that pentagonal shaped holes are produced frequently, the BTA system solid boring tool is supposed to behave like the equally spaced four-cutting edge tool. This behavior is clarified through measuring the movements of the axis of boring bar. The forming of multi-corner shaped holeitself may be due to one kind of self-excited vibration which is induced by the vibratory movements of the tool axis. Its movements occur at a rate of
Z times per one revolution of a workpiece in boring by the tool with
Z cutting edges, because of the unbalance of cutting forces. Multi-corner shaped hole tends to be oversized and the number of multi-corner become less as the hole is deeply machined.
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