Backings have been used in the crafting of wooden bows for hundreds of years. This topic is very broad based and covers many facets of the bowers craft. I will touch on the most common types of backings, their use, preparation and type of glues used for each. I am certainly no expert, however I can explain the results based on my personal experience.
Typically backings are used for specific reasons:
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To help tension weak wood bear the strain of bending so that a bow can be made. |
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Materials such as “lumberized” wood can be used that would normally not make a bow in combination |
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To induce and maintain a reflex into a wooden “core” wood such as a Reflex/Deflex design so that early |
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Staves that have a high crown that the bowyer has chosen to “de-crown” and back for performance reasons. |
Before a backing can be applied to a bow a number of choices must be made. The appropriate backing should be chosen based on the properties of the wood to be backed, the expectations of the bow,
the perceived environment the bow will exist in and the properties of the backing chosen. Many combinations will work, however choosing the RIGHT combination for the bow can mean the difference between a sluggish bow with undue set, a durable, fast, hard hitting bow with maintained reflex when unstrung or a broken bow. Any backing must somehow be glued to the back of the bow to be, with the exception of twisted cable backed bows. The correct glue choice is as important as the backing itself. The glue must be able to handle the stress of being bent without failure while keeping the backing intact. Certain combinations of glues and backings work together and bind as a matrix,
while others do not.
Sinew is the tendon out of animals such as Deer, Elk & Buffalo to name a few. These tendons are obtained from the front and real lower legs and also along the outer covering of muscles along the spine (backstrap sinew). These are collected, dried and pounded/shredded into small fibers. These fibers are then applied along the length of the bow in a glue matrix consisting of “hide glue” and sinew fibers. Once dried this matrix becomes very hard and elastic and is sometimes referred to as “nature’s fiberglass”. Sinew backings were used extensively by Native American tribes across North America. The properties of a sinew backing allow a short marginal piece of wood to bend to extremes without failure. These short bows emerged from the plains where the Native Americans developed them to shoot from horseback. It was also used in the Pacific Northwest with tension weak woods to make serviceable short bows from wood that would otherwise not be able to carry the strain. In modern times bowyers use sinew for basically the same reasons. A bowyer can take a short piece of wood and make a short hunting bow with high draw weight that is very advantageous for hunting in heavy brush.
The intended bow’s back must be prepared to accept the sinew backing. Typically this involves toothing the back with a hacksaw blade so the sinew can take and hold a better bond with the wood. The wood also needs to be cleaned and free of dirt, grit and oils, weather they be induced or the natural oils of the wood in the bow. I prefer to use Acetone to do this with as it flashes off very quickly and does a good job of cutting oils. Any grease cutting dish soap or even just plain old Very hot water will work in a pinch. Be sure to rinse very good with hot water if using soap.
Prepare the hide glue by warming with a double boiler or other heat source. I use a warming plate from an old coffee pot. Insure that the glue does not exceed 150 degrees. Knox gelatin can also be used as it is the same basic substance, only more refined. Take your glue granules (hide or Knox) put it into a heatable bowl and add just enough water to cover it. Leave it until it softens and begin to slowly heat it. It should be about the consistency of thin syrup and at a temperature of approx 110-120 deg before using.
Hopefully by now you have prepared your sinew of choice for the job at hand. From here you can go to the page entitled “Making a Sinew Static Recurve” for detailed instructions with pictures for laying the sinew on the bow.
The use of Bamboo or tension safe woods such as Hickory, Elm and even Osage for backings has been done for many years. The preparation of the bows back is essentially the same for all applications. The bows back must be cleaned, degreased and “toothed” in preparation of the backing strip. Most backing strips function well at approx 1/8” thickness. Thicker backings can be used but the risk of over compressing the “core” wood becomes a reality. Bamboo is very strong in tension and therefore easily over powers woods marginal in compression. That is why it must be THIN on these type woods. Hickory works well provided the grain is parallel with the bows length and is not violated such that there is run up’s in the side grain.
Prepare both surfaces as described and clean them. I prefer Urac 185 for wood to wood bonding but have had success with the Titebond brands of wood glues (TBII & TBIII). I mix the Urac by measuring amounts with the little white plastic spoons. I mix 3 ½ level spoons of hardener (powder) with 7 spoons of Resin (Liquid). This is enough to do one bow backing with a bit left over. Mix it well until there are no lumps and apply to both backing and bow’s back. Apply the backing and clamp using either split inner tubes or using “C” clamps space every 2” or so. Before all clams are applied the bow can be constrained to a form to induce reflex, reflex/deflex or any combination of both. Let the bow sit undisturbed for at least 24 hrs and longer if using Titebond products. (see the Bamboo backed Osage tutorial for details)
Silk can be applied to the bows back without “toothing” the surface of the back.
Take care.. Sparky
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