Apparatus for tapping a wall of a metallurgical vessel wherein a drilling machine is carried by a mounting means for reversible displacement therealong on a track. The mounting means is suspended from a laterally extending boom which swings on a stationary support, and the boom is swung by a mechanism for selectively displacing the mounting means with its drill into an operative position for drilling a tap hole in a metallurgical vessel and an inoperative position. In one embodiment of the invention, the mounting means together with its guide track for carrying the drilling machine is pivotally connected to the boom and guide means are provided to guide the pivotal swinging of the mounting means relative to the boom to guide the mounting means over a predetermined path of movement when the boom is swinging. In a further embodiment, the boom is driven to swing in opposite directions with different motors respectively thereby permitting the boom to displace the mounting means to the inoperative position at a much more rapid rate than is desired for positioning the mounting means in the operative position. In yet a further embodiment, the mounting means together with its drilling machine is guided into and maintained in the proper operative position for tapping the vessel by an alignment strut which extends from the mounting means, the end of which is contactable with a stop which is prepositioned on the vessel to be tapped. Upon positioning in the operative position, the strut is continually driven into contact engagement with the stop without the requirement of additional mechanical locking mechanisms to maintain the drill in its proper prealigned operative position.