Abstract: A fluid drilling head for drilling a bore hole through rock. The fluid drilling head has a rotatable nozzle assembly incorporating a plurality of nozzles arranged to form fluid jets when provided with a supply of drilling fluid under pressure. The fluid jets include pilot jets directed in the general direction of movement of the drilling head and reaming jets directed generally radially and arranged to enlarge the initial hole formed by the pilot jets. A gauging ring is located behind the cutting head and sized to the intended diameter of the bore hole. The gauging ring is arranged to slide axially relative to the rotating cutting head between a rearward position where the reaming jets are exposed, and a forward position where some or all of the reaming jets are shrouded by the gauging ring and inhibited from enlarging the diameter of the bore hole.

Abstract: A fluid drilling head for drilling a bore hole through rock. The fluid drilling head has a rotatable nozzle assembly incorporating a plurality of nozzles arranged to form fluid jets when provided with a supply of drilling fluid under pressure. The fluid jets include pilot jets directed in the general direction of movement of the drilling head and reaming jets directed generally radially and arranged to enlarge the initial hole formed by the pilot jets. A gauging ring is located behind the cutting head and sized to the intended diameter of the bore hole. The gauging ring is arranged to slide axially relative to the rotating cutting head between a rearward position where the reaming jets are exposed, and a forward position where some or all of the reaming jets are shrouded by the gauging ring and inhibited from enlarging the diameter of the bore hole.

Abstract: A fluid cutting head of the type having a plurality of nozzles in a rotatable nozzle assembly for cutting a bore hole in rock. The cutting head has nozzles arranged to be supplied with high pressure drilling fluid, forming jets positioned to cut adjacent rock. The nozzles include one or more generally axially facing pilot nozzles, and one or more generally radially facing reaming nozzles. At least the pilot nozzles include a non-tapering outlet section such that the jet issuing therefrom is of substantially constant cross-section in a zone immediately adjacent the outlet section. The pilot nozzles are located in a leading part of the rotatable nozzle assembly, and have a minimized diameter. The reaming nozzles are located in the following part of the rotatable nozzle assembly. The following part of the rotatable nozzle assembly is formed in a step-wise fashion to keep the reaming nozzles close to the rock face.

Abstract: A method of steering a fluid drilling head in an underground borehole drilling situation is provided by rotating the flexible hose through which high pressure is provided to the drilling head and providing a biasing force on the drilling head. The hose can be rotated from a remote surface mounted situation by rotating the entire surface rig (13) in a horizontal plane about a turntable (24) causing the vertically orientated portion of the hose (11) to rotate about its longitudinal axis. The biasing force can be provided in a number of different ways but typically results from the use of an asymmetrical gauging ring on the fluid drilling head.