Thus it will be seen that by proper choice of the number of strips to be used and the thickness of each strip the limb may be designed to produce the best result for the type of service for which a particular bow is designed.
When it is said of these laminated limb structures that the fiber stresses are equal throughout the limb section at full draw position it will be understood that this condition can never be exactly obtained in practice. The variation in stress across a single lamination for a two lamination structure (or one with an infinite number of laminations) is, however, negligible as compared with the total stress but the approximation is not so close for structures with an intermediate number of laminations.
The relative cost of making a bow in accordance with the several methods described will often be an important factor in the choice of the construction to be used. By resorting to a slightly more expensive procedure, uniform fiber stress throughout a cross-section of the limb for any deflection at full draw can always be obtained with the two strip structure. For example, in the case discussed above where longer limbs are used to obtain the desired cast without pulling the limbs to the straight position, the two strips may be first steamed or otherwise formed to the shape desired a full draw. The strips are then further deflected the desired amount and glued in this position. A bow having limbs of this type may then be drawn until the limbs have the curvature of the original steamed strips and the stresses will then be uniform throughout the section.
It should also be noted that the general feature of the several limb constructions described, namely, a laminated structure built up in such a way as to have equal fiber stresses throughout its cross-section at full draw position, is not limited to the constructions described. For straight limb bows the strips would first be formed to the radius of curvature which the limbs are to have at full draw. Before glueing they would be bent back beyond the straight position far enough so that the glued limb would assume the straight position when released from the form. It will also be understood that this principle is not limited to limbs which are to be set forward according to the preferred construction and that reflexed limbs for ordinary bows may be made in accordance with the principles of this invention.
It should be particularly noted that the principle is not limited to bows with demountable limbs. The term "handle portion" as used above refers to a comparatively rigid section between the limbs but the limbs and handle may be made from a single continuous piece or a single unitary laminated structure formed to the desired shape and made rigid at the handle portion by the addition of a suitable stiffening member.
In making bow limbs it is common practice to form the limb to size by splitting so that the cleavage follows the grain of the material and results in a limb of maximum strength for a given limb thickness. Some of the best bow materials, including yew-wood and horn, usually have irregular grain so that laminations of these materials cannot be readily secured together in close relation without inducing undesirable stresses in them.
When such materials are to be used it may therefore sometimes be difficult to take full advantage of the novel methods of constructing laminated limbs which have been described. In such cases the belly of the bow may be made of one of these irregular grain materials and the back of a plurality of layers of some other material which will more readily conform to the irregular contour of the belly material. For example, if horn is used for the belly and silk ribbon or fibers for the back, the belly material may first be deflected to the maximum safe curvature, and a thin layer of the backing material secured to its concave side preferably under tension. The curvature of the member is then somewhat reduced and a second layer applied to the first under slightly less tension and this procedure is repeated until the desired thickness of backing has been obtained. As in the case of the limb composed entirely of many similar laminations, this limb may be built up so that all its fibers on the tension side will be equally stressed in the full draw position.