Some aspects of the design and classification of drill bits. Part 3: Design criteria and classification

Abstract

In general, developments in the design of rotary drill bits have proceeded in three main directions dictated largely by the properties of the materials that were being drilled and by the materials that were available for constructing the bits. Typical examples are firstly, screw point augers and centre bits for drilling relatively soft materials such as woods; secondly, spade bits and twist drill bits, which have more robust cutting edges, for drilling metals; thirdly, diamond bits, roller-cone and fish-tail bits for drilling relatively hard brittle materials such as rocks. New materials are being developed that cannot conveniently be classified under these headings, eg filled plastics, laminates, etc. Consequently production engineers are being called upon to drill such materials, often with drill bits that have not been specifically designed for the tasks they are being called upon to perform.As a consequence of specialization, drill bits and drilling techniques have been developed by engineers in different fields of engineering virtually unknown to each other. In attempting to adopt a completely fresh approach to drill bit design the author was led to consider the various ways in which holes are manufactured and the roles played by drill bits. A brief reference is made to the methods used by animals and plants. This could provide a useful field for research into new hole-making methods.The importance of considering the way in which a drill bit is to be used is emphasised, and some suggestions for definitions are given, in an attempt to clarify some of the confusing terminology found in some of the literature on drill bits. A classification system is described which originated from a collection of information on drill bits.