Indian Bow Making-Sinew
thin. Again I glued the horse sinew on the back with Elmer's carpenter's glue. What a disappointment! It looked very nice but didn't shoot worth a darn. After shooting a while and then unstringing the bow, I noticed that the bow followed the string (bent towards the archer) but after being unstrung a few hours it went back to its original shape. In general the bow was "flabby". My last experiment was a plains Indian style bow, made from a 48 inch black locust stave. This time I used hide glue to bond the horse sinew to the back. This bow was dynamite, powerful and fast. Did the hide glue make that much difference? The engineer in me took over. What are the material properties which will yield a superior bow and how can I measure them? The things which matter are the elastic modulus (how much it stretches with a given tension), the tensile strength (how much tension is needed to break it), and how much it shrinks when it dries. In addition, it helps to define some other useful terms: Potential energy: the ability to do work. When you pull the bowstring back you store potential energy in the bow limbs. The available potential energy is equal to the distance you pull the string back multiplied by the average force that it took to pull the string back to full draw. When you release the string the potential energy is transferred to the arrow, giving it. Kinetic energy: the energy of motion. A perfectly efficient bow would transfer all of the available potential energy stored in the bow limbs into kinetic energy of the arrow. Elastic modulus: a measure of how stiff a material is. Make a one inch cube out of the material and stretch it with a known force. The cube will get slightly longer. The elastic modulus is the force times the length of the block, divided by the area of the block times the distance the block stretched. Steel has an elastic modulus of 30 million psi (pounds per square inch), hickory has an elastic modulus of 2.2 million psi, black locust has 2.1 million psi, and the measurements I have made on yew wood give a figure of 1.2 million psi. Tensil strength: keep pulling on that one inch cube of material and eventually you will pull it apart. The force per square inch that it takes to pull something apart is the tensile strength. For tempered steel the number is 400,000 psi, for hickory it is 20,000 psi. For those of you who wonder: yes, it is very impractical to make these http://www.abotech.com/Articles/Baugh01.htm (3 of 5) [10/22/2003 5:06:28 PM]