Abstract: A swivelling arrangement for controlling relative angular movement between two components comprises a yoke pivotally mounted on one of the components and pivotally movable under the action of a ram. The yoke has two limbs to the radially outermost ends of which are fixedly secured the ends of a drive chain arranged drivably to engage a drive sprocket fixedly secured to other of the components.

Abstract: Drilling equipment comprises a single boom supporting a plurality of drilling masts each provided with a drilling machine, adjustment means being provided to simultaneously adjust the relative positions of the drilling masts.

Abstract: Rock drilling equipment includes a boom carrying an extensible beam arrangement supporting a drilling mast, the extensible beam arrangement comprising a support pivotally mounted on the boom, a first elongated element slidably mounted on the support for movement longitudinally of the first element, a second elongated element slidably mounted on the first element for movement longitudinally of the first element, and drive transmission means sensitive to movement of the first element and adapted to move the second element relative to the support upon sensing relative movement between the support and first element.