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Effect of Permanent Set and Reflexing on Static Strains and Stresses

Many bows take a permanent set after they have been used a great deal. This reduces the cast of the bow. Graph 6A shows the effect of permanent set on the string tension and drawing force. The curves marked 0 are for the new bow and the curve marked +10 are for the bow after it has taken a set. The figure 10 signifies that the angle A for the unbraced bow is 10°. It will be noted that the forces are all lower throughout the draw.

It is well known that the cast of a bow may be increased by constructing it so that it is reflexed back. On Graph 6A, the curves marked -10 show the string tension and drawing force for such a bow. In both of these conditions it is assumed that the cross section of the bow, its length etc., are the same as for the bow marked 0.

It is interesting to see what effect set and reflex has on a bow when the full draw force is the same for both conditions. The curves in Graph 6B show the drawing force, and the string tension for four bows which have identical drawing force at full draw. One bow is straight (0), one is reflexed 10 degrees (-10), one is reflexed 20° (-20) and the other has a set of 10 degrees (10). It is evident that reflexing a bow increases the amount of work that may be obtained from it and that a set reduces its cast.

Effect of Reflex and Set on String Tension and Drawing Force
Graph 6A
Effect of Reflex and Set on String Tension and Drawing Force

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Graph 6B Effect of Reflex and Set on String Tension and Drawing Force
Graph 6B
Effect of Reflex and Set on String Tension and Drawing Force

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