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Page 19
After the above experiments it was hoped that, if a pair of barrels
were put together parallel and soldered only for a space of 3 in. at
the breech end, and were then coupled by two encircling rings joined
together as in Fig. 4, the left-hand ring only being soldered to the
barrel, very accurate shooting would be obtained. For, it was argued,
that by these means the barrel under fire would be able to contract
without affecting or being affected by the other barrel; that on the
right-hand, it will be seen by the illustration, was the one to slide
in its ring.
A pair of able 0.500 bore express rifle barrels were accordingly
fitted in this way. Fig. 3 shows the arrangement with the rings in
position. Upon firing these barrels with ordinary express charges it
was found that the lines of fire from each barrel respectively crossed
each other, the bullet from the right-hand barrel striking the target
10 in. to the left of the bull's eye, while the left barrel placed its
projectile a similar distance in the opposite direction; or, as would
be technically said, the barrels crossed 20 in. at 100 yards, the
latter distance being the range at which the experiment was made.
These last results have been accounted for in the following manner:
The two barrels were rigidly joined for a space of 3 in., and for that
distance they would behave in a manner similar to that illustrated in
Fig. 2, and were they not coupled at the muzzles by the connecting
rings they would shoot very wide, the charges taking diverging
courses. When the connecting rings are fitted on, the barrel not being
fired will remain practically straight, and, as it is coupled to the
barrel being fired by the rings, the muzzle of the latter will be
restrained from pointing outward.
The result will be as shown in an exaggerated manner by the dotted
lines on the right barrel in Fig. 3.
It would appear from these experiments that when very accurate
shooting is required at long ranges with double-barreled rifles, they
should be mounted in a manner similar to that adopted in the
manufacture of the Nordenfelt machine gun, in which weapon the barrels
are fitted into a plate at the extreme breech end, the muzzles
projecting through holes bored to receive them in a metal plate. No
unequal expansion would then take place, and the barrels would be free
to become shorter independently of each other. We give the above
experiments on the authority of their author, who, we believe, has
taken great pains to render them as exhaustive as possible, so far as
they go.--_Engineering._
* * * * *
BALL TURNING MACHINE.
The distinguishing feature in the ball turning machine shown opposite
is that the tool is stationary, while the work revolves in two
directions simultaneously. In the case of an ordinary spherical
object, such as brass clack ball, the casting is made from a perfect
pattern having two small caps or shanks, in which the centers are also
marked to avoid centering by hand. It is fixed in the machine between
two centers carried on a face plate or chuck, with which they revolve.
One of these centers, when the machine is in motion, receives a
continuous rotary motion about its axis from a wormwheel, D. This is
driven by a worm, C, carried on a shaft at the back of the chuck, and
driven itself by a wormwheel, B, which gears with a screw which rides
loosely upon the mandrel, and is kept from rotating by a finger on the
headstock. This center, in its rotation, carries with it the ball,
which is thus slowly moved round an axis parallel to the face plate,
at the same time that it revolves about the axis of the mandrel, the
result being that the tool cuts upon the ball a scroll, of which each
convolution is approximately a circle, and lies in a plane parallel to
the line of centers.
When the chuck is set for one size of ball, which may be done in a few
minutes, any quantity of that diameter may be turned without further
adjustment. A roughing cut for a 2 in. ball may be done in one minute,
and a finishing cut leaving the ball quite bright in the same time.
The two paps are cut off within one-sixteenth of an inch and then
broken off, and the ball finished in the usual way. On account of the
work being geometrically true, the finishing by the ferrule tool is
done in one quarter of the time usually required.
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