On a Drilling System with a Retractable Bit

Abstract

For the purpose of saving time of the work to hoist up and down drill rods in each occasion exchanging drill bit, Sumitomo Metal Mining Co., Ltd. has manufactured trial equipments which enable to attach a drill bit to the top of an inner tube of a wire line core barrel. Exchange and examination of the bit can be done easily while operating the wire line. This is called the Retractable Drilling System (RDS), and has been tested for the drilling about 2000 m in total at 20 places.
A characteristic structure of the RDS is that a reaming bit attached to the lower part of the inner tube can be pulled into the inner tube when the inner tube is hoisted up in operating wire line.
Distinctive merits of the new system are to save working time substantially and to prevent the destruction of wall rock of a drill hole because it is not necessary to hoist up and down drill rods for exchanging a drill bit. A comparison with a conventional system has been made on drill holes up to 150 m in depth and the RDS has been proved to reduce the working time for drilling to the one-third of the conventional system.