The drilling machine includes a frame that is supported for movement over the ground and a tower that is mounted on the frame. A rotary head is movable along the tower and engageable with a drill string for rotating the drill string. A pull down cable is connected to the rotary head for pulling the rotary head downward for pushing the drill string into the ground. A pull back cable is connected to the rotary head for pulling the rotary head upward for pulling the drill string out of the ground. The pull back cable is subject to a slack condition in response to elastic stretch of the pull down cable. A slack take-up device is connected to the pull back cable to remove the slack created in the pull back cable by the elastic stretch of the pull down cable.