The use of high-pressure waterjets as a method for enhancing the performance of mechanical cutting tools has been well documented over the years. However, concurrent with this development for drag bit tools, there has been some evidence that the combination was not an effective one. By using sectioned samples of rock indented with a spherical indentor (of the type used in percussive drilling) the reason for the critical positioning of the jet at the rock, tool interface is shown to be due to the very limited gap through which access to the crushed material is available. Further, the gain to be achieved when the jet is played into the crushing zone as it develops, rather than later, is also evident from the experimental work. As with other forms of waterjet assist it is shown that even in rock as hard as basalt a jet pressure of 400 bar is sufficient for effective performance enhancement. In the second part of the paper tests are described in which the combination of a waterjet playing on a single indentor are extended into the behavior of the indentor as a component in a rotary percussive drill bit. The change in the performance levels of the separate components of the forces driving a rotary-percussive bit (i.e., cutting, thrust and impulse forces) is evaluated with the addition of a waterjet stream to the cutting process.
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