English: Woodcut/drawing of a vertical boring machine. The boring mill was constructed for the purpose of boring the large cylinders, 10 ft. in diameter, for the Great Western steamship navigation company's vessel the Mammoth, at their works at Bristol. The motion is communicated by the driving pulley c to a bevel pinion working the bevel wheel d. The shaft on which this wheel is fixed has on its opposite end a worm for communicating motion to the upright shaft f and boring bar a. This boring bar has vertical grooves a', in which the cutter head b is movable, sliding up and down according to the progress of the work; k is a tool-carrier, fixed to the cutter head, by which the boring is effected. The foundation plate h forms a bearing for the upright shaft, the lower end of which rests in the step g, while the cylinder l is secured by the clamps j j to the supports i i, which are fixed to the foundation plate. Two strong pieces of masonry, m', support the entablature m, for carrying the self-acting apparatus for raising and lowering the cutter head b. The entablature is secured to the masonry by strong holding down bolts. This self-acting apparatus consists of a rack, n, worked by a pinion, the motion being transmitted by trunnion wheels through two spur wheels and pinions, o o. The whole of this upper machinery revolves with the boring bar, with the exception of the ring p, upon which the trunnion wheels rest and revolve. The motion thus produced is communicated to the rack, which is either raised or lowered according to the direction in which the boring bar revolves.