A rotary actuator is pivotally mounted on the end of a drill boom and supports a rock drill feed bar for rotation about a longitudinal axis of the actuator. The rotary actuator includes a piston with a piston rod portion having external and internal helical splines engaged with cooperating splines on the actuator housing and a rotating shaft, respectively. The shaft is connected to the feed bar and is operable to rotate the feed bar in response to axial movement of the piston. The axis of rotation of the shaft may be coincident with the longitudinal axis of the drill boom. The drill boom is mounted on a rotary actuator for swinging movement about a vertical axis.
A drilling boom has an articulated arm 12 which carries a drill feed beam 28 on its outer end. Apart from the articulation 36, 38 provided by the joint at the outer end of the arm, the feed beam can rotate about two mutually perpendicular axes at the end of the arm. One of these axes is defined by the so-called rollover unit 44 and the other axis 92 is at right angles to the length of a drill rod on the feed beam and allows at least 180 degrees of rotation so that parallel holes can be drilled in all parts of the roof, floor and side walls of a heading.
