The authors discuss application conditions of the casing-while-drilling method and present a layout of a compound rock-breaking tool. An advantage of such tool is the coupling of the central and annular bits by spring jaws, owing to which the inner passage section of a casing pipe experiences no reduction. Computer modeling assisted in the strength analysis of the components of the tool during transfer of the impact load from the central to annular bit via the spring jaws. The operational reliability of such components is evaluated, and a method is proposed for enhancing their strength by way of improving quality of their surface finish and optimizing geometry of the surface areas exposed to the highest load. On the basis of the implemented research, a developmental prototype of the compound rock-breaking tool is designed and manufactured.
Cheshchin et al. (Wed,) studied this question.