Boring and Turning

—A cannon is bored by giving it a rotary motion around its axis, and causing a rod armed with a cutter to pre against the metal in the proper direction. The piece, supported in a rack, is carefully adjusted, with its axis horizontal, and made to revolve on this axis by machinery attached to the square knob on the cascabel. After adjustment, the sprue-head is first to be cut off. This is effected by placing a cutter opposite the point at which the section is to be made, and pre ing it against the metal whilst the piece is turning. The head being cut off, and the cutter removed, the boring is commenced by placing the boring-rod, armed with the first cutter, called the piercer, in the prolongation of the axis of the piece, and pre ing it against the metal. The piercer is used till it penetrates to the bottom of the chamber, after which a second cutter, or reamer, is attached to the boring-rod, and with this the boring is made complete to the round part of the chamber. The reamer is then removed and its place supplied by the chamber-cutter, which gives the nece ary form and finish to that part of the bore. In hollow-cast cannon the piercer is dispensed with. Whilst the boring is taking place the workman contrives to finish the turning of all the exterior of the piece except the portion between the trunnions, which is afterwards planed off in another machine. These operations having been completed, the piece is placed in the trunnion-machine, and the trunnions are turned down to the proper size. Care is taken to make the trunnions of the same diameter, and perfectly cylindrical. Their axes should be in the same right line, perpendicular to the axis of the piece and intersecting it.