The Durham daily globe. (Durham, N.C.) 1889-1894, 1894-10-04
SHRINKING a GUN JACKET.
A Process That Requires the Creates,

A Process That Requires the Greatest
Precision.
It is at the shrinking-pit that some
of the most striking of the details Of
manufacture of a gun are to be o2-
served, and the shrinking on of a thir-
teen-inch jacket is always the occasion
of a crowd of interested spectators. In
a corner of the pit is the tube, a cyiin-
der of steel two feet in diameter and
forty feet long. standing upright and
clamped in position. It's upper end for
a distance of some fifteen feet is bright
and smooth, having been turned to ex-
act dimensions. Inside of the tube cold
water is circulating. to prevent its eX-
p~ansion by the heat radiated from the
furnaces, and to keep it cool while the
jacket is going on. In the heating
furnace the jacket, another cylinder of
steel. seventeen feet in length and
weighing some twenty-three or twenty
four tons, has been slowly heating
since the day previous, carefully
watched both day and night by the at
PENDANTS. who SO regulate the supply
of air that no excessive temperature Is
obtained. From time to time the cover
of the furnace is lifted for a moment,
and the master-mechanic measures the
inside diameter Of the jacket at its up
per end. This must agree with the
calculated expansion of the cylinder
before the operation Of asse milling is
attempted. When all is ready the great
traveling-crane is brought over the
furnace, the cover is removed. and in a
moment the enormous mass OF steel is
suspended in the air. Now its interior
is carefully wiped out, in order that
the minutest particle Of foreign matter
shall be removed, and the inside diam
eter is measured throughout the
length of the jacket. Meantime,
by means of bars Of fusible metal,
the temperature is determined at
various points. The giant crane,
directed by a motion of the
hand of the master-mechanic, now
swings the suspended mass over the
tube, where it is accurately aligned
| and plumbed. When it is realized that
the inside diameter of the expanded
Jacket is less than One-tenth Of an inch
| greater than the exterior diameter Of
the tube, and therefore that the clear
| ance between the two is only about
four one-hundredths of an inch, and
hat the jacket must be lowered over
fifteen feet Of the tube without coming
in contact with it, or if it o come in
contact that the touch must be light
| and of the briefest duration, it is easy
to see that this adjustment is Of SUI
preme Importance. Finally the signal
is given. and, slowly at first, and then
more swiftly, the jacket is then low
| cred to it's place. The anxious express
sion which has marked the cOuntenance
| of the officer in charge gives place to
| one of content, the appreciation of the
spectators is manifested by smiles and
| applause, and the operation is over.
The jacketing Of a large gun is the
single process of the whole manufact-
ure which cause great concern to the
experimenting ordnance officer. The
lathe work, the boring and turning of
| guns, are questions of accurate meas
urement and careful workmanship, to
which as much time may be devoted as
is necessary. But from the moment
that the heated jacket is taken from
the furnace it is losing heat, and as a
consequence is contracting. The loss
of heat is, of course, very slow, but any
reduction in the diameter of the jacket,
where the allowed clearance is already
| small, is Of moment, and hence the
work must be done with celebrity. The
time required to put on a thirteen-inch
jacket, when all goes we'll, is less thar
fifteen minutes. Theodore F. Jewell,
U. S. N, in Harper's Magazine.