A rock drill feed shell is slidably mounted on a support bracket and is connected to a feed screw which is threaded through a feed nut mounted on an elongated supporting tube disposed telescopically within the feed shell. The supporting tube is displaceable with respect to the support bracket by a feed extension cylinder mounted on the support bracket. A rock drill is slidably mounted on the feed shell and engages a second feed screw supported by the feed shell. A feed motor is drivably connected to both screws.
The feed support of a rock drilling unit is adjusted to be a given distance from a rock surface wherein holes are to be drilled. A drill bit is moved into abutment with the rock surface. The feed support is moved relative to the bit toward the rock surface. Such movement is stopped when a depth measuring instrument determines that the feed support is at a position spaced the given distance from the rock surface.
