The morning news. [volume] (Savannah, Ga.) 1887-1900, 1898-03-27

OF contract. Every forging comes 10 the
government factory in the rough. They
are then placed in the big lathes. and
turned and bored to proper dimensions. in
Wnich work extreme care must be taken
Consider the construction Of the LARGEST
gun built for the navy-the thrteen-incn.
The central tube of this gun is 40 inches
long. Over length of about two hun
dred inches of the tube from the truck end
the Jacket fits in a Viselike grip, while
eleven hoops in Just as tight grasp encircle
both and a part of the tube beyond the
muzzle end of the jacket. The tube end
jacket each weigh many tons, and are all
worth many thousands of dollars.
The first preeaution against loss of any
part is system in working them down to
the proper dimensions; so, while the inte-
rior of the jacket is bored to accurate
dimensions, the exterior of the tube is
turned down to nearly accurate dimen-
sions, so that if, by any mistake, which
seldom or never happens, the interior of
the jacket should be made too large the
tube can still be fitted to it. The same
precaution is observed in boring the hoops,
and in turning the jacket to receive them.
The accuracy with which all this work is
done is hard for us to appreciate. 1t is
unusual 1t is unique. Every dimension
given on the mechanical drawing to guide
the workman operating the machine must
DE accurate to the one-thousandth part
of an inch. The measurements, of course,
cannot be gagged by the ordinary calibers
and foot rules and special calibers are
used, made of the best steel, which are set
not by a scale, but fundamentally. In the
master mechanics office a scientific ma
chine is kept for measuring distances TO
the ten-thousandth part of an inch.
cannot describe it, but it is there in a
padded case, which is always kept at the
same temperature, so there is no change
10 contraction or expansion of the parts
so the machine remains absolutely accu-
rate.
A set of steel rods, square in section,
and about one-third of an inch each way,
is cut, and one made for each dimension
given on the plans. By this accurate
measuring machine the length of each rod
is made to correspond to the dimension
which it is supposed to represent 60
within ne-ten-thousandth of an inch.
Each end is brought to a point, and the
mechanic sets his calipers by bringing
the points exactly tangent to the ends of
the rod. One can find no machine work.
as far as 1 know where such heavy masses
of material are operated on with such
exceeding accuracy. The tube alone of
thirteen-inch gun will weigh more than
thirty tons. From the time the fors-
ings go to the machines until they are as
sembled, the metal cannot undergo the
slightest change from contraction or ex-
pansion, for the building remains at a
constant temperature. The jacket and
tube being machined to the required di-
mansions, they are transported by the
giant crane to the shrinking pit where
some of the most interesting features OF
gun construction are carried out, and the
jacketing of a big gun invariably attracts
a large number of interested spectators.
The shrinking pit consists of a deep,
well-likc pit and a cylindrical furnace
about ten feet apart. The tube is placed
upright in the pit, muzzle down. A brass
pipe leads up through the center of the
tube to within a short distance Of the
Dreech end, and through il cold water is
kept constantly circulating that the tube
may not be affected in the slightest pos
sible degree from the heat of the furnace.
The furnace is double. consisting of an
iron cylinder surrounding one of fire
brick. The jacket is placed in the center
Of this furnace, the iron cover placed over
the top and the jacket expanded This
is because the assembling of the parts of
a modern built up gun is a Shrinking pro-
cess That is, the interior of the jacket is
smaller before ii it heated, than the eX-
terror of the tube over which it must fit.
The jacket is expanded so that it will go
over the tube and then allowed to cool.
The grip it has on the tube after 1t is set
can be calculated automatically but
everyone can see that this process adds
tremendously to the strength of the gun.
In general, such is the assembling of the
tube and jacket. But the operations are
themselves so interesting, so accurate, so
delicate, that 1 cannot pass lightly over
them. The jacket, as have said, is heated
and expanded, but not in the way in which
we usually heat a piece of metal There
is an air space between the outer and the
inner furnace, with a common floor for
the two. The packet is of course, in the
center of the inner furnace. The amount
of expansion necessary has been accurate
" calculated by the most abstruse mathe- |
matical calculations.
1t is imperative that the expansion |
should not continue beyond that point. and
that 1t should be absolutely equal, to avoid
the disturbance of the homogeniety of the
metals For these reason the temperature |
in the furnace is raised gradually, and does
not exceed six hundred degrees, and the |
products of combustion never come into |
contact with tine metal If one stands near |
the furnace while jacket or hoop is being |
expanded. he will note very rapid sue |
oession of light sharp explosions. This is
caused by q steady current of air being |
forced into the bottom of the outer fur
mace, which at that point comes into con- |
tact with the heat from burning petroleum |
underneath the floor. The heated gases CIV
en- off circulate around the furnace, ard |
thus gradually bring the jacket up to the |
required temperature. There is another |
reason why the products Of combination |
are not allowed to come into contact with |
the heated metal.
The calculated time required for the ex- |
pansion of a thirteen-inch jacket is thir- |
ty-six hours, and they are anxious hours |
for the master mechanic During that |
time the cover of the furnace is hoisted |
off at intervals, and the diameter of the |
Jacket calipered throughout its entire |
length, while the temperature is tested at
different points by the application of strips |
of fusible metal. The required degre of /
expansion Is now up. and the master me-
chanic and his gang stand by ready for |
the interesting operation of assembling, |
There is perfect quiet. That steady man |
in charge raise one finger, the giant crane |
moves forward, stops over the furnace, and |
in iiffy the cover is off and out of the |
way. Forward il moves again and stops |
over the furnace. The pulley block is
quickly hooked into an iron band at the |
top of the cylinder, the overseer gives he
sipnaI and il is hoisted out clear of the