Positional Accuracy of Hole in Drilling : Effect of Rigidity and Point Geometry of Drill

Abstract

Hole positional accuracy, which is important in drilling operations with automated machine tools, e.g. NC machining-centers, is examined by a special runout device. Positional deviation of a drilled hole from the spindle rotating axis is mostly determined at the beginning of penetration. This deviation is caused by the deflection of tool rotating axis around a certain point on chisel edge. The experimental results indicate the drill overhang length has a significant influence on the hole positional accuracy. A fine feed in start of drilling and a spiral type of drill point grinding are effective to reduce such deviation. Stub tooling system, which gives a strong bending rigidity of tool, is a desirable technique to improve the positional accuracy in drilling operations.