Drill rigs for drilling bore holes generally comprise an upstanding mast supporting a drill head which is movable along the mast. The drill head is provided with means which can receive and engage the upper end of a drill rod forming part of a drill string to drive the drill string and drill bit mounted to the lower end of the drill string. In addition, the drill head may have means for applying a downward force to the drill string to facilitate penetration.
The drill string comprises a number of lengths of drill rod which are connected end to end, where the length of drill rod generally is at the most equal to the height of the mast. During a drilling operation when the drill head has reached the lower end of the mast, the drill string is retained to the mast and the drill head is disconnected from the drill string and raised to the upper end of the mast. A fresh length of drill rod is then raised and positioned in the chuck of the drill head and then the lower end becomes engaged with the upper end of the drill string. Once the fresh length of drill rod has been put in place, the drilling operation can recommence until the drill head again reaches the lower end of the mast. During drilling activities which may extend for hundreds of meters, it is necessary to locate fresh lengths of drill rod into a drill string at very regular intervals.
Throughout this specification the term “drill rod” should be construed as including all forms of elongate members used in the drilling, installation and maintenance of bore holes and wells in the ground, and will include rods, pipes, tubes and casings which are provided in lengths and are interconnected for use in the borehole.
In practice however, not all drill rods are the same, they differ significantly. For instance, rods for diamond core drilling (hereinafter diamond rods) are much lighter and more delicate than rods for reverse circulation drilling (hereinafter RC rods), particularly at the threads, so a means suitable for handing RC rods is generally unsuitable for handling diamond rods, and vice versa.
It is against this background and the problems and difficulties associated therewith that the present invention has been developed.
Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.