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.