SECTIONS OF SWORD-BLADES.
If we consider the sections of cutting weapons, we find them all modifications of that most ancient mechanical contrivance, the wedge, as shown by the following figures:
Fig. 118.—Sections of Sword-Blades.
The first form (fig. 118) is the wedge that would be produced by taking for base the dorsal thickness of an ordinary blade, and by continuing it in an even line to the apex of the triangle—the point. The two sides meet at an angle of nine degrees; consequently the edge lacks the thickness, weight, and strength necessary for every cutting tool. For soft substances it should range from ten to twenty degrees, as in the common dinner knife. An angle of twenty-five to thirty-five degrees, being the best for wood-working, is found in the carpenter’s plane and chisel. For cutting bone the obtuseness rises to forty degrees, and even to ninety; the latter being the fittest for shearing metals, and the former for Sword-blades, which must expect to meet with hard substances. But even an angle of forty degrees will be ineffectual upon a thick head, unless the cut be absolutely true. No. 2 illustrates the angle of resistance (forty degrees) and the entering angle (ninety degrees). No. 3 shows that the true wedge of forty degrees is too thick and heavy for use, requiring some contrivance for lightening the blade, while preserving the necessary angle of resistance. The remaining sections display the principal modes of effecting this object. In Nos. 4 and 6 the angle is carried in a curved and bulging line, thus giving the section a bi-convex form. When the back or base is flat this is the Persian and Khorásáni, vulgarly called the ‘Damascus blade.’ When baseless and two-edged it is the old ‘Toledo’ rapier—two shallow-crowned arches meeting (3a, fig. 124). In both cases the weapon is strong, but somewhat overweighted. In the next shapes (Nos. 5 and 7), the two sides are cut away to a flat surface and represent the ‘Talwár’ of India. When this flat surface is hollowed, as by the black lines of No. 5 (compare No. 8), we have the bi-concave section, as opposed to the bi-convex. This hollowing of the wedge into two broad grooves from the angle of resistance is one of the forms assumed by the English ‘regulation’ Sword: it was considered the lightest for a given breadth and thickness, but it is by no means the strongest, and there are sundry technical objections to it.
The remaining blades in the illustration are grooved in as many different ways. The function of the cannelure is to obviate over-flexibility; it also takes from the weight and adds to the strength. By channelling either side of a thin or ‘whippy’ blade it becomes stiffer, because any force applied to bend such a blade sideways meets with the greatest amount of resistance that form can supply. Mechanically speaking, it is to crush an arch inwards upon its crown, and the deeper the arch the greater the resistance. Hence the narrow groove is preferable to a broader channel of the same depth. No. 9, hollowed on each side near the base, is a good old form, superior to the ‘regulation’ (No. 8): its weak point, the space between the grooves where the metal is thinnest, lies in the best place—near the back, where strength and thickness are least required. No. 10, though somewhat lighter, doubles its weak points. No. 11 is better in this respect: it has three grooves which are far shallower, and consequently the metal between them is thicker. The same remark applies to Nos. 12 and 13, which are sections of claymores, single- and treble-grooved.
No. 14 shows an ingenious method of obviating the weakness caused by deep cannelures: it is the section of a blade made at Klingenthal (not ‘Klegenthal’), the Sword manufactory established by Napoleon Buonaparte in Elsass-Lothringen. Two very marked grooves are cut in the metal, but not directly opposite each other, and thus the channels can touch and even overlap the axial line. This disposition gives great stiffness, but, as testing shows, the edge is deficient in cutting power, probably from loss of force by vibration.
Nos. 15 and 16 are experimental blades. The former has the groove placed in the base, preserving the wedge-sides intact; but there is great difficulty about grinding this shape, and, the resistance of the arch-crown being wanting, there is a small increase of stiffening—the Sword, in fact, ‘springs’ almost as readily as the straight form. No. 16 has some good points, but, on the whole, the combination is a failure. Lastly, No. 17, the old ‘ramrod-back’ regulation blade, is perhaps the worst of all: the sudden change from the thick round base to the thin sharp edge makes an equal tempering very difficult, and the weapon cleverly undoes its own work, the base acting as check or stop to the cut.
Fig. 121.—Scymitar-Shape.