MINUTE ACCURACY

79

gauging, tolerances ran into fractions approximating parts of an inch, those of fuze

10

1000

gauging were of an infinitely more exacting nature, being measured in fractions so minute as 1000 parts of an inch.

3 1

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.

Briefly, the mechanical action of the grazefuse 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 81 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

fingers, when lifting the fuses out of the boxes in which they were supplied.

Briefly, the mechanical action of the grazefuse 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 81 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