1) Red Cedarnote inlaid arrow plate with twisted chamois handle wrap. 2) Hickory Backwith 5 inch handle overlay/ resorcinol glue showing 3) Yew/Bamboo
|All Wood Composite:
Bow Building 101
by Murray Gaskins
This article is for bowyers who are looking for simplified instructions on building a durable all wooden bow which is economical and when properly constructed, will out perform all but the most meticulously crafted and best maintained self bows.
One of the most critical criteria for building a bow, any bow, is that the back be able to handle the stress of tension placed upon it during the draw. An interesting point to note here, is that bow backs can be made of many materials. For the purpose of this article we're going to deal only with backing one piece of wood with another piece of wood.
My experience shows that if a wood will make a good self bow, given that you can find a clear and straight enough piece of it, by properly orienting the grain when sawing a backing, you can generally back even a marginal wooden core with it. By backing it, a premium stave's performance can usually be improved, most specifically, when a reflex is introduced. A marginal or small piece of scrap wood can also be turned into a safe and durable bow instead of something to trip over in the shop or be wasted in some other fashion. We will explore the reasons why and methods how, as we go along.
For the backs of these bows I generally use hickory. The reason for using hickory is that it is available to me and I'm set up to deal with it. To date I have found nothing more consistent or durable. It is also a reasonable expectation for me to find stock clear and straight enough to not to have the grain running off the sides over short runs in the bow limbs. Other woods which have proven satisfactory for backing bows in my recent experience are various elms, swamp chestnut and several other oaks, maple, as well as bamboo, which is really a grass. Bamboo backing will be addressed here but only because the techniques in applying it are similar to using other woods. Bamboo is undisputably beautiful but it can often be very difficult to tiller because of the irregular thickness in and around the nodes. A consistent source of bow quality bamboo can be challenging to secure, I might add. Uniformly cut wood is much more available and easier to use. One means by which I am able to simplify this backing production process is that I generally use only the butt cut when selecting a tree for the purpose of producing backing. By using only the butt of the tree it's easier to have control over ring orientation and twist. The rings are at their thickest in the first cut, this is the point where the tree will be at its clearest, with the least knots and other flaws as well. A six foot piece of clear backing will go a long way toward insuring the performance, safety and longevity of our investment in time and other resources used in our bow. We will later discuss using three foot sections of backing.
Growth ring orientation is optimized by using edge or bias ring stock with the grains running the full length of the stock. If the grain runs off the backing, make sure it does not do so in the area of most stress. If it does so make sure it does not do so abruptly. If the grain runs off your backing at a point of high stress you are going to probably break the bow at that point. The same is not necessarily true on the belly, though continuous end to end rings, uninterrupted by knots are to be desired. Knots can cause compression fractures in the same fashion and for the same reasons they are generated in self bows. If a reflex is pulled into a bow by gluing a backing to it watch for compression fractures between knots as the knots deteriorate. The compression fractures, also known as chrysals and other names, are very dark demons indeed. The fact that we are are using flattened stock, created by sawing, planing, or rasping distributes the stresses of both tension and compression very evenly across the surface being stretched or compressed. This fact alone allows us infinitely more leeway in stock selection and tillering than when building a self bow with any sort of crown in it. Fill any loose belly knots with glue and sawdust or Loc-Tite and sawdust.
The core and handle of our bow can be made from a three foot 2x2 of almost any wood which is able to withstand the forces of compression during the draw. Good domestic choices are osage, yew, hickory, mulberry, hornbeam, walnut, maple, Eastern red cedar, and most of the oaks, just to name some of the options.
If you really get down to it, a core can be made from a three foot one by two from the wood of your choice. Split the 1x2 so that you have two 1/29x29x38 by two inch by three foot boards. Cut a fishtail or the simpler V splice in the two boards. I prefer to cross drill, then glue the splice creating in effect, one board, so it can't move when subjected to the pressure involved in the handle and backing glue-up process. All the gluing can be done at one time if a cross-pin is installed in the splice. If not, the belly pieces will try to separate every time pressure is applied. If you don't want to have to go through the exercise of splicing , use six foot pieces of whatever core and backing material desired. By using full length stock we will speed up construction by at least about 24 hours in most instances. Many of us will use two pieces of backing which are butted together in the middle of the handle, then overlaid in the center for about the length of the grip.
A word here about what backing wood to use with which belly wood. I have built more Hickory backed bows than any other kind except self bows (bows with no backing). My experience is that depending on the compression strength of the core wood, a backing of up to 3/16 inch is fine for a bow backing. Don't try such a thick backing on the conifers or a piece of any wood with many knots in it. Simply use a thinner backing. It can be thinned by sanding, after the glue-up. Hickory is so strong in tension that if a backing made of it is too thick, when the bow is drawn it can crush the belly stock and chrysal it. You can use lighter woods than hickory for backing such as maple, elm or some of the oaks, when backing less dense woods than osage and hickory. It is easy for me to simply use less hickory, sometimes I reduce it to less than 1/16 of an inch. Some of the woods which are less strong in tension tend to fragment and pull apart if thinned in this manner.
The belly can also be cut from a stave, by simply decrowning with a rasp, hand plane, power planer or saw. In this manner you can cut the belly to shape and have a self handle made of the belly wood, the only gluing involved would be to glue the backing to the belly. This is a good way to build a bow, from the start, if the wood is weak, or questionable in tension. By the decrowning technique it is also possible to save a bow which may have been over tillered, thus yielding a bow with too little draw weight. I've been there, have you?
Glue of some description is needed when building a backed bow to adhere the backing to the core. You can use hide glue, if you like but I use Franklin's Tite-Bond ll. I often will use Resorcinol, which incidently, Paul Comstock tells me is his preference. I've not used Urac-180 but I'm sure that it would work fine. The Resorcinol and Tite-Bond ll are both water proof when dry. Tite-Bond ll is available, inexpensive, one part, simple to use and I have not had a failure with it to date. Both clean up with water.
I always clean and degrease the gluing surfaces of my wood, generally using acetone, several times before glue up. You won't have to be reminded to do this if you omit degreasing and your bow's belly separates from its back.
To build a glued-up handle or riser do as follows. A ten inch long piece of the belly stock or other scraps can be used; stack, center and glue them over the handle splice until the apex of the handle is as high as you want it. Band saw or rasp the handle to the desired shape. I personally like bows to work through the handle slightly whenever possible. The simplest way to build is by not adding a handle and only gluing a backing to a single board. Then proceed as if you were building a standard "D" bow.
When gluing up the bow, you can build a form from a 2x6 by standing the board on edge and measuring out any length that is about two inches longer than your bow. Measure down and mark either end of the board 2 inches from the top. Starting at one end, draw a curve which crests about two inches from the center of the top of the 2x6, then repeat the sequence on the other end of the 2x6. Cut this curve out and you will be looking at a long, continuous curve that is slightly flattened at the top, where the handle will be. Remove enough bulk from the bottom of your form so that your "C" clamps can grip the bow and form together. Place the backing on a piece of Saran or wax paper, apply glue, then lay the core in the glue, handle up. Clamp the belly down with "C" clamps and you're in business. When the glue dries you will have a ready-to-work, roughed out bow with 2 inches of back set, or reflex in it.
In the absence of a form or the desire to build one, put two 4 inch blocks on your table and span them with the belly wood and backing. Place the core on the blocks first, apply the glue to the surfaces of the belly core, next place the backing on the top of the core. Now "C" clamp the middle of the bow grip to the work bench; you should pull about 2 inches reflex from center to the tips which are resting on the blocks. It is now a simple matter to tighten more "C" clamps along the length of the limbs, beginning with the inside near the fade outs then working toward the tips. Any time you use "C" clamps place small pieces of wood between the metal "C"clamps and the bow wood, both top and bottom. This will keep the clamps from crushing the back or belly of your bow and distribute the pressure more evenly. This is of particular importance when using conifers such as yew and cedar, which are very soft.
If the goal is not to introduce reflex into the bow, or if I don't want to bother with "C" clamps, sometimes I do this. Place a sheet of wax paper on the garage floor, board or other flat surface. Lay the backing down, apply the glue or epoxy, then set the belly core down, grip up, on top of the backing. Now set a 2x4 or other flat piece of wood on the belly of the bow, on either limb. Place bricks or other heavy objects evenly spaced, the length of the limbs and come back in the morning. You should find a glued up, perfectly straight core that is backed and ready to work. Cut and rasp away the excess backing, taking care not to push the rasp in such a manner that it might splinter, damage or separate from the core.
This part of the process is one not to be ignored. If you have a glued up handle on your bow belly and have not yet glued up a backing or reflexed the bow you may thin the belly (by about the thickness of a tablesaw blade,) up almost to the fade out on either side of the handle on a table saw. Stop an inch or so before hitting the fade out. Finish the last bit by rasping or scraping. By doing this you will perch the handle above the rest of the limb and it will be less likely to pop off. The fade out can be worked into this thicker piece of the limb then fade to the thinner section of the limb and look quite nice. A handle with non bending fade outs will also accomplish this. I repeat; the handle area must be more rigid than the working balance of the limb and should step down from above the limb or your handle will pop off. If you try to feather the fade outs to the limb you are courting problems unnecessarily. The limb should be tapered from the tip and rise to the fade out where the handle will be sitting on a thicker section, by about 1/8 of an inch. Thinning the limb to perch a handle can be done by any of several means. Reduction can include a sanding block, electric sander, rasp, hand electric planer, scraper and many more I'm sure. What ever means of belly reduction you choose, in the other hand should be a set of calipers . Use the calipers to insure the same thicknesses on both limbs at corresponding points.
Since the belly stock is a full 1 3/4 or 2 inches wide by 1/2 inch thick and if we have glued a wooden backing that's another 1/8 or 3/16 inch thickness added to it, and since we've possibly introduced a reflex into the equation, we are suddenly dealing with a fairly substantial stick. I go by the formula that states this; "Wood that is twice as wide is twice as strong, wood that is twice as thick is eight times as strong" If that formula isn't exact, it's close enough for me. Remember this fact when tillering, and the converse is true also. Pay particular attention when reducing limb thickness or you may create a hinge which will drive the whole process from that point forward, producing a bow of lower poundage than desired. Come to think of it, that may be why we're doing this exercise in the first place.
Moisture in your wood is not a problem when you want to glue the bow up. I actually prefer working wood a little wet since when gluing up the wood it is bent backward over the form, then clamped. It seems to me that if you begin clamping just past the fade outs and on toward the tips during the gluing process, the belly will stretch and the inside plane of the belly core will compress, where it will soon be glued up on the inside of the backing. It also seems to me that when the bow is dried the stretched fibers will compress less on the belly when the bow is strung, this should hopefully reduce string follow. The key here is what moisture content is correct for optimum performance in your region?
Use a drying box and moisture meter to find out. A glued up stave with a wooden backing will loose moisture through both back and belly. Don't over dry or your bow will explode.
I prefer bows which bend slightly in the handle when drawn. I also prefer about a 70 inch length, with very narrow tips for the last 9 or 10 inches. The less mass on the tips, the less hand shock you will feel. The bow we have just laid up can be tillered on the belly, back and sides, according to your taste. Tiller carefully, (it will be easy), most of these bows require very little actual tillering. Brace the bow to about 3 inches and let it sit strung several times for 4, then 6 hours. Break it in by drawing it about half way 20 or 30 times each session. Gradually increase brace height to about 5 or 5 1/2 inches. Don't pull the bow to full draw and hold it there, you will ruin it. If properly tillered and the moisture is correct the bow will tolerate a long stringing time and have very little string follow, if any at all, in fact if it was reflexed it should keep most of it. If the draw weight is too light when the bow is tillered and broken in, shorten it and cut in new nocks. If the draw weight is too heavy, sand it down to the desired weight, shoot it several hundred times, then steel wool it smooth and finally seal with three coats of polyurethane.
Several bows have been built of different woods before and during the composition of this article, specifically for the sake of comparison. I will briefly and generally relate the results and my experiences. (Please See Table) The bows were not identical, neither are the results. The Cedar bow that broke was a beautiful thing. We did everything right using two backings except we didn't reinforce the handle with an overlay. A piece of backing the size of a postage stamp would have probably held it together. It wouldn't hurt to have been tillering it at nearer the weight it was going to be shot at either. That way the wood wouldn't have been strained and putting set in the limbs, even if it didn't break. It broke right through the handle as the backing pulled up at about a 45° angle.