A rock drill assembly which includes a drilling machine mounted within a sound-absorbing container. The container is longer than the length of the drilling machine so that the container acts as the guide for the drilling machine as the machine is advanced into the material being drilled. The drill is provided with bearings which engage the inside of the container for guiding the movement of the drill within the container. Apparatus is provided for advancing and retracting the drilling machine relative to the container. There may be apparatus for independently rotating the drill steel relative to the container.