Positional Accuracy of Drilled Holes

Doctoral thesis, 1992

When selecting hole-making sequences, the positional accuracy mainly is determined during the first drilling operation. This dissertation consists of three papers which consider the influence of various factors on hole positional accuracy when drilling in inclined workpieces using high-speed steel twist drills with conventional point geometry. The chisel edge action, during the first few revolutions after contact with an inclined workpiece surface, causes the drill wandering phenomenon and thus the drill deflection. The influence of factors like drill length, rigidity, workpiece material, surface slope, and cutting resistance, as well as the machining data has been investigated in experiments, results of which have been presented and discussed. Mechanisms of chip formation at the chisel edge also have been investigated. A mathematical model for chip areas and corresponding cutting forces has been proposed and implemented in a computer program. If the flexibility of the drill also is implemented in it, as suggested in my equations, the program can be used to analyze the drill wandering.