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Bow technology
Part 3 of 3

Other Factors Affecting Cast.—It is to be remembered that the total mass put in motion by the force of recoil consists not only of the arrow but also of the limbs of the bow, the horn tips, and the string. The arrow, therefore, Only forms a fraction of the total of that which moves. The greater this mass for a given pull, the slower will be the bow, no matter if the added mass is found in the bigger arrow, or in the limbs, or in the horn tips forming the nocks. It is for this reason that the material forming the nocks, for instance, should be as light as possible. Many Of the horn tips on the ends of bows could be reduced in size and so improve the cast, though perhaps this might also reduce their decorative value somewhat. A bow with self-nocks should be a trifle faster than one with horn tips. Because it is the total mass set in motion which determines the speed of recoil, doubling the weight of the arrow adds only a minor fraction to this total. Therefore, a heavy arrow does not lag in flight behind the lighter one as much as one might suppose.

Mechanical Properties of Bow Woods.—The true archery enthusiast finds an endless fascination in studying woods out of which bows may be fashioned. He will never be fully satisfied with the reports of other investigators in regard to this or that wood, but must find out for himself the qualities inherent in different kinds or in combination of two or more woods in a single bow. Always there seems just ahead the miracle of a new discovery—of the bow supreme. And it is well that this is so; for, whether or not the miracle appears, he is happy in his efforts and gains knowledge of woods to a degree that he could never acquire in other ways. The amount of these efforts is merely a measure of his interest and enthusiasm.

Of course, if he is of a somewhat scientific turn of mind, he will study bow action from the standpoint of stresses and strains. He realizes that a bow is but a straightgrained stave tapered at both ends and connected by a taut string which, when pulled, bends the bow against the resisting forces. The string released, these forces restore the bow vigorously to its original shape and thereby drive the arrow, by means of the string, to its destination. With the bow at draw, the back fibers are in tension, the front or belly fibers in compression. That is, the back fibers tend to be torn apart while the belly fibers tend to be crushed. Somewhere between the back and belly of the bow is the so-called neutral layer, where the fibers are neither in tension nor compression. The farther a fiber is from this neutral layer the greater is its compression or tension. Therefore, the outer fibers of the back are under the greatest tensile strain, and the crown of the belly is under the greatest compressive strain. The total of the compressive forces is equal to the total forces of tension, there being a natural balancing action between them.

Woods in general are stronger in tension than in compression. Among our native woods this ratio of strength varies from double to as high as four times. So it is to be expected that, if the fibers give way at all, they will probably give way first in the compression or belly side, particularly at and near the surface. Eventually, however, if the bow breaks at all, it will be by tearing apart at the back. This is due to the fact that, as the crushing action or chrysaling proceeds at the front of the bow, the neutral layer is driven more and more toward the back. This leaves less and less area to carry the tension, until, by the sheer reduction of this tension area which must carry the full strain, the break comes. But—and this is lost sight of by some—if the chrysaling has proceeded to some depth, the bow has largely ceased to function even though it has not actually broken. The belly fibers are crushed and have ceased to be resilient. We should then be about as ready for a new bow as if the actual break had come.

The Backing of Soft Wood Bows.—It is for a reason connected with the above explanation that the writer finds it difficult to endorse the backing of a soft wood such as red cedar with a tough wood such as hickory. A drawn bow of this combination of woods naturally carries the neutral layer closer to the tough back. The chances of chrysaling or crushing of the belly fibers are therefore enhanced and the usefulness of the bow is likely to be destroyed quickly though the actual break is warded off. If the back tension fibers of a self red cedar bow can stand strains two or more times as intense as the front fibers can in compression, there should be ample strength there to balance against the front stresses of the bow, even though we recognize that the neutral layer is closer to the back than to the belly. If the bow fails, the belly fibers probably failed first, the actual break being merely the final episode of a bow already past real usefulness. The tough back of hickory merely deludes us into believing we still have a whole bow. A more reasonable procedure than backing this bow would be to make it of flatter section. Such a bow will lose some cast but it will last longer. Excessive stacking should be avoided anyhow in all bow making.