THE GRAZE-FUSE
"A world of startling possibilities."
DOLE.
Graze-fuses (so called from the fact that the very slightest touch
or shock imparted to the fuse or foremost part of the shell by any
intervening object, and against which the fuse grazes whilst in flight,
is sufficient to cause the spark necessary for igniting the explosive
charge) were first taken in hand at Crewe in March, 1915.
It was at this time that the late Earl Kitchener, then Minister of War,
first drew attention in the House of Lords to the alarming position,
generally, in regard to munitions of war, "I can only say (cp. the
_Times_, March 15th, 1915) that the supply of war material at the
present moment, and for the next two or three months, is causing me
very serious anxiety." The persistent inconsistency of the "talking
men" may here well be exemplified by the fact that in the following
month of April, Mr. Asquith promptly retorted in the House of Commons
that he had "seen a statement the other day that the operations, not
only of our Army, but of our Allies, were being crippled or at any rate
hampered, by our failure to provide the necessary ammunition. There
is not a word of truth in that statement." However, as if to give an
irrefutable _démenti_ to this assertion, it was only a month later
that there came the sensational _exposé_ from the pen of the _Times_
military correspondent at the front, who wrote to the effect that
"the want of unlimited supply of high-explosive was a fatal bar to our
success" in the offensive operations round Ypres. _Per contra_ it was
pointed out from the same source that "by dint of expenditure of 276
rounds of high explosive per gun in one day, the French levelled all
the enemy defences to the ground."
Hence it came about that, emanating from a modest little
side-show claiming the energies of one or two apprentices and a
few highly-skilled and highly-paid mechanics, the manufacture of
graze-fuses developed into quite an industrial main-offensive (destined
within the space of a few weeks from its inception to be entrusted
to a bevy of local beauty, which became augmented as time went on
in proportion as the seriousness of the military situation became
apparent), pushed forward with a zeal and enthusiasm worthy of the
highest praise, as the supply of shells and consequently of fuses fell
hundreds per cent. short of the demand.
Trim in their neat attire of light twill cap and overall, with a
not infrequent hint of black silk "open-work" veiled beneath, the
ladies (God bless 'em), no sooner enlisted, lost no time in adapting
themselves in a remarkable manner to the exigencies of their new
surroundings. In some respects, certainly--
"Women's rum cattle to deal with, the first
man found that to his cost;
And I reckon it's just through a woman the
last man on earth'll be lost,"
but however that may be, in respect at least of the manufacture of
munitions of war the girls in Crewe Works showed themselves, not only
amenable to reason and discipline, but became regular enthusiasts in
the work on which they were engaged. Idling and indifference were
qualities unknown, patience and perseverance became personified, and
thanks to a highly efficient and praiseworthy organisation, coupled
with a system of three consecutive eight-hour shifts, the output of
fuses rapidly rose from a mere 150 per week to as many as 4000, or
a steady weekly average of 3000, finally reaching a grand total of
250,000 on the cessation of hostilities.
A portion of the locomotive stores department, comprising an upper
storey of the old works' fitting shop, familiarly known as the top
shop--that one-time nursery of juvenile and maybe aspiring apprentices,
many of whom have blossomed forth into full-blown engineers occupying
positions of prominence in the four corners of the globe--was speedily
transformed. Overhead shafting was fixed; lathes, drilling and tapping
machines, and benches were lined up in positions convenient for the
quick transition of the fuses, and their tiny components, passing
in regular sequence through the many operations necessary for their
fashioning.
[Illustration: GAUGES MADE AT CREWE AND USED FOR THE MANUFACTURE OF
GRAZE-FUSES.]
[Illustration: REVERSIBLE MECHANICAL TAPPING MACHINE FOR FUSE CAPS.
DESIGNED AT CREWE (_cp._ P. 81). [_To face p._ 78.]
The graze-fuse itself is an intricate and cleverly thought-out little
piece of mechanism, demanding a degree of accuracy in machining such as
one might reasonably have assumed would suffice to baffle even the most
knowing and perspicacious little minds attributable to the fair sex.
The requisite delicacy of touch may perhaps be exemplified by the fact
that the pellet plug flash-hole must be drilled dead-true to a depth of
almost an inch with a drill no bigger than ·062, or 1/16 of an inch.
Mr. Lloyd George, when addressing the House of Commons in June, 1915,
in his capacity of Minister of Munitions, held up a fuse for members
to see. "This," he said, "is one of the greatest difficulties of all
in the turning-out of shells. It is one of the most intricate and
beautiful pieces of machinery--before it explodes, (laughter). It
indeed is supposed to be simple, but it takes 100 different gauges to
turn it out."
It was not, however, quite so much a question of the number of gauges
required (considerable though the above-quoted figure may sound to
those uninitiated in the art of fuse-making) as of the minuteness of
the limits or tolerances allowed in the manufacture of these gauges.
Some reference to, or explanation of, gauge-making will be found on a
later page, so that it may perhaps here be sufficient to remark _en
passant_ that whereas in the case of shell-body gauging, tolerances
ran into fractions approximating 10/1000 parts of an inch, those of
fuse-gauging were of an infinitely more exacting nature, being measured
in fractions so minute as 3/1000 parts of an inch.
Since the ultimate success or failure of the entire shell depended to
a very great extent on the combined and unfailing action, or lightning
series of movements, of the tiny internal component parts of the fuse
(action which was initiated by the motion of the shell itself), the
_raison d'être_ of dimensions measured in infinitesimal fractions of an
inch becomes somewhat more apparent. The beauty of this little piece
of mechanism is illustrated to some extent by the fact that it can be
assembled or put together complete with its tiny internal components to
the number of 10 or 12 all told, in less than a minute.
Cast in bars of brass, sections of the length required for each fuse
body are cut off, and drop-forged, the probability of blow-holes being
by this method eliminated as far as possible.
For the various machining operations, such as turning, boring and
screwing, drilling, automatic and turret lathes played a prominent
part, whilst an eminently suitable machine known as a "Sipp
three-spindle drill" to which were fixed special jigs, designed for the
purpose, was extensively used for the numerous small holes required.
Grooves were turned on a turret lathe round the taper-nose, these
affording a grip for the fingers, when lifting the fuses out of the
boxes in which they were supplied.
[Illustration: THE GRAZE-FUSE, shewn in section. [_To face p._ 80.]
Briefly, the mechanical action of the graze-fuse is regulated on the
following lines: A central pellet which creates the igniting spark by
striking the percussion needle, is held in position by a tiny plug,
which in turn is secured by a ball-headed pin, called the detent, kept
in place by a spring. On the gun being fired the sudden forward impetus
of the shell causes the detent pin to exert a backward pressure of
8-1/2 lbs. on the spring, this being sufficient to enable the detent
pin to withdraw itself from the plug controlling the ignition pellet.
The motion of the shell once launched in flight is rotary or
centrifugal, with the result that the pellet-plug flies outward,
leaving the pellet itself free to strike the percussion needle the
moment the fuse-nose hits or grazes the first intervening object.
The fixing of the percussion needle securely in the fuse-cap was an
erstwhile stumbling-block in not a few machine shops, it being no
exaggeration to say that in numerous instances at least 50 per cent. of
the fuse-caps were rejected owing to the needle not being sufficiently
securely fixed in the seating.
At Crewe a simple method ensuring absolute rigidity was devised, the
fuse-cap being so turned in the lathe that a slightly outstanding lip
was formed, which after the needle had been inserted in the recess
was spun or pressed, whilst revolving in a turret lathe, round the
taper profile of the needle, the metal being in this way packed so
closely and tightly all round that the protruding end of the needle,
if subsequently gripped in a vice, would sooner break off than allow
itself to be extracted or even disturbed in the slightest degree
whatever within its metal bedding. "Solid as a rock" is the only
description applicable.
In spite of this, however, the Government either could not or would not
insist on the universal adoption of so sound and simple a practice,
preferring rather to standardise an entirely new method involving a
more complicated and so more costly fitting, both as regards the needle
itself and the fitting of it in the fuse-cap.
The cap was thenceforward drilled and tapped, and the needle which was
a longer one than hitherto was screwed into the hole and joined with
petman cement. Crewe, in compliance with Government specifications had
perforce to toe the line, but very quickly rose to the occasion by
devising an extremely neat and efficacious little tapping machine, belt
driven, and reversible through the medium of a couple of hand-actuated
friction clutches. The spindle of the machine ran through a guide-bush
bolted to the bed of the lathe, and screwed to the pitch of the needle
thread. The hole through the fuse-cap was by this means certain of
being tapped to the correct pitch, without any risk of stripped
or "drunken" threads ensuing. The tap itself was of a "floating"
disposition; that is to say, it was held in a socket which permitted a
slight amount of freedom in action, thereby ensuring perfect alignment
with the fuse-cap hole.
The final operation of lacquering (or varnishing with a mixture of
shellac and alcohol which imparted a saffron or orange colour to the
metal and acted as a preservative) was effected by mounting the fuse on
a metal disc, which, acting in conjunction with a second disc and an
intermediary ball-race, was kept spinning round by hand, the operator
applying the varnish with a brush the while the fuse was kept spinning.
It was noticed at one time that a fairly large percentage of shells
were "duds," that is to say they were failing to explode, and the
reason for this was attributed to the supposition that on being
released by the plug the pellet tended to creep towards the percussion
needle, thenceforward remaining closely adjacent to it, with the result
that it was no longer in a position to jerk forward and strike the
needle with sufficient impetus to cause a spark. An additional spring
called a "creep" spring was consequently inserted, of sufficient
tension to prevent the pellet from creeping forward, and yet not strong
enough to prevent the sudden contact of pellet and needle, on the shell
reaching its objective. This overcame the difficulty.