418 
MINUTES OF PROCEEDINGS OF 
The rough jacket thus made weighs over 16 tons, but this weight is 
reduced to 9 tons by the turning, rough and fine boring, &c., which are 
necessary to bring it to the proper size and shape. 
The body is turned in a very powerful lathe, weighing, with its founda¬ 
tion, 100 tons, to the required shape. The operation takes sixty hours; 
consequently all the four big lathes, which are in a row, may be often seen 
at work together, and a fine mechanical spectacle it is. 
It being impracticable to turn down the trunnion ring in a lathe, it is 
slotted smoothly down by a self-acting vertical machine with a double motion, 
one of which moves the jacket round for a fresh cut at every stroke of the tool 
which the other works up and down accordingly. 
The trunnions themselves have yet to be turned down to shape ; so the 
jacket has to be moved for the purpose to another machine—a break lathe 
—in which it is made to revolve on the axis' of the trunnions while the 
sliding cutters act on their surface. 
The jacket is next rough and fine bored in a machine like that used for 
the B tube, but stronger, and the front of the G coil is recessed on the 
inside to a depth of 9 inches, and broad enough to overlap the B tube. 
Einally, the female thread for the cascable is cut by a machine in which 
the jacket revolves horizontally, while the cutter is fed forward by a copying 
screw—one pitch for every revolution of the jacket. 
Building up the Gun > or shrinking the parts together . 
The steel barrel and B tube being prepared for one another as described, 
are shrunk together in this manner:—The B tube is placed on a grating, 
and heated for about two hours by a wood fire, for which the tube itself 
forms a flue, until it is sufficiently expanded to drop easily over the muzzle 
end of the steel barrel, which is placed upright in a pit ready to receive it. 
The B tube is then raised, and the ashes, &c., being brushed from the 
interior, is dropped over the steel barrel by means of a travelling crane 
overhead. During the process of shrinking, a stream of cold water is 
poured into the steel barrel, to keep it as cool as possible, the water being 
supplied and withdrawn by a pipe and siphon at the muzzle. A ring of 
gas is placed at the muzzle or thin end of the B tube, to prevent its cooling 
prematurely, whilst jets of cold water play on the other end, and is 
gradually raised to the muzzle, for the purpose of cooling the whole tube 
consecutively from the breech end, which it is desirable should grip first, to 
ensure a tight fit at the shoulder. Moreover, were both ends allowed to 
contract simultaneously, the intermediate part of the tube would be drawn 
out to a state of longitudinal tension, and weakened accordingly. 
The A and B tubes shrunk up (see diagram), are placed in a lathe, and 
while one cutter fine turns the B tube to its proper shape and dimension, 
another cutter fine turns the breech end of the A tube according to the 
plan of the breech coil, -which has been made out on the principle already 
explained. 
The shrinkage on the steel tube being 0' /# 015 at the extreme breech 
end, 0"*0& at the shoulder round the end of the bore, and gradually 
diminishing to 0"*015 at the point where the jacket abuts against the 
B tube, the overlapped portion of the B tube is given a shrinkage of 0"*03. 
