Tillering the Organic Bow
©Dean Torges/The Bowyer's Edge™
In Hunting the Osage Bow; A Chronicle of Craft, I defined a bow as "dry wood expertly tillered" and then spent 160 pages of directions and illustrations in explanation.
Ten years have passed since the book appeared (almost fourteen since the chapters began serialization in a magazine), and I continue to refine my own understanding of that simple proposition. The "dry wood" part no longer presents much problem for most of us. The proposal that osage could be quick-dried successfully, without checking, through the technique of stripping sapwood and shellacking the heartwood, went against common wisdom and the practice of air drying and natural aging. Bowyers may employ various sealers, but the quick-dry process is mainstream now, and few would argue a discernible difference between osage seasoned naturally, and osage brought to a low moisture content quickly.
It's the "expertly tillered" part of the equation that continues to give us fits, that still separates bowyers from one another, and that distinguishes bows from one another.
HOB brought the means for achieving expert tiller to the workbench, introducing our generation of bowyers to cabinet scrapers when broken glass, butcher knives and dull draw knives were the tools of choice, and to Nicholson patternmaker's rasps when farrier's rasps and 4-in-1 files were de rigueur. It introduced the Bowyer's Edge to a larger audience, too.
HOB brought a method to the means as well, introducing faceted tillering as a controlled approach to achieving tiller. That's its proudest and most important contribution to the methodology of bow building, I believe. It came at a time when we were enamored of Klopsteg's flat belly theory to the extent that we imposed it upon wide-limbed selfbow staves even when it interfered with results.
In summary, the means and the method to expert tiller no longer mystify most of us. It's the concept itself that we still struggle to understand.
"Whatchu talkin' 'bout, Willis?"
Tillering has several meanings, and it's not always easy to tell from context which way it's being used. It functions as both adjective, verb and noun, but it's the honorific use of the term, especially in a descriptive context, that causes the most confusion. To say that a bow is tillered may or may not say something of the quality of that tiller, but it usually implies that the tiller is expertly done. The term can be as nebulous as expert tiller is elusive.
I propose here to bring some understanding and illumination to the term. It is the linchpin to our craft, the key to all doors. Once we understand it and its components better, perhaps we can accomplish it more readily.
Building for a Purpose
HOB placed a premium on durability, predictability, noiselessness, and the ability to shoot a heavy hunting arrow, so it advocated a limb coming to compass at full draw, with stress distributed evenly along the length of both limbs. This is not the only way to correctly tiller a bow. It's a popular misconception that an ideal tiller exists. It does not. Indeed, there is no one right way. Different portions of a limb may be weighted or relieved, or various tapers may be employed to one purpose or another. That there is no right way hardly means that there are no wrong ways. Wrong ways abound.
Some right ways are more appropriate than others, determined exclusively by the purpose for which the bow is intended. For example, you could begin with several bow staves of equal profile and length, and tiller each one differently to its purpose—a different ideal for each one. You might tiller one for large game with lightning quick autonomic reflexes, one for flight competition, another for stump shooting and ethafoam targets at rendezvous, and yet another for English or York Rounds or for IFAA Classic competition.
You can make the limbs bend primarily after the dips and keep the tips very stiff, or you can make all of the limb bend evenly, or you can bend more of it toward the tips, or you can bend most of it midlimb, or you can whip-tiller it, etc. and so forth, the method determined by the result you wish to achieve, the purpose to which you intend the bow.
There's much latitude. You can begin with bow staves of various profiles and tiller each one the same. You can also begin with several similar staves and tiller each one differently. There are various ways to tiller a bow correctly, and various bows to tiller the same way correctly, but one constant to all of the possibilities is that if you are not mindful in each instance of tillering's fundamentals, the bow will reveal you.
The current bow-building climate tells us little about our abilities or our understanding of fundamentals. Many of us build one bow so hard upon the heels of another, moving from one to the next, that we lack accurate assessments of a bow's durability and our mastery of the bowyer's craft.
This is not to say that we lack pride in our bows. We pass them around at rendezvous for inspection, delighting in knot-hole bows from gnarly staves that demonstrate our ability to salvage something from the scrap heap. Yet how many times do we see the same character bow at next year's rendezvous with a year's worth of wear reflected upon its lines? How often do we see a straightforward selfbow with the reflection of thousands of arrows apparent in its hand-rubbed surface?
The Number is Up
By my count, there are five distinct goals that identify the tillered bow during the short measure of its draw and loose. The limbs should bend in the style you choose, to the weight you want, at the draw length you determine. Additionally, the bow should balance in the hand at full draw, and upon the loose the limbs should recover simultaneously.
Most of us are relieved to achieve the first three goals. If we talk about balance and timing, we aren't too sure how to approach them. Yet balance and timing are the components of tiller primarily responsible for providing sweetness in the hand (i.e., a lack of hand shock), optimum cast within its style, and quietness. They also contribute significantly to its accuracy and longevity.
Not only are we unsure how to effect these two goals of tiller, we also struggle to understand their relationship to each other. I base these observations upon the erroneous tillering advice prevalent on internet bulletin boards.
Consider the following tillering guidelines, intended for bowyers new to the craft, advocating bows of limbs measuring equal length outside the handle. Proponents of same-limb bows claim they are easier to build than bows with shorter lower limbs because we can switch them top for bottom anytime during the tillering process that one limb wishes to step forward and claim a role. Each of these guidelines came word for word from an internet bulletin board.
- A bow with a stiffer upper limb is upside down and is already out of tiller.
- No bow should ever have a stiffer upper limb.
- A bow with a stiffer upper limb will cause the upper limb to recoil faster than the lower limb and likely cause hand shock because it stops faster than the lower limb.
- When bow limbs are of equal length, to make both limbs synchronous, the bowyer MUST make the upper limb slightly weaker to match the longer lower limb so that they recoil at exactly the same speed.
- If your bow has equal length limbs outside the handle, and there is a greater gap between the string and limb in one limb [positive tiller], you should turn it so that that limb is the upper limb and shoot it that way.
I selected these statements because they represent the common truths which accompany the practice of building same-limb bows, the practice that most bowyers advocate, even experienced ones. They contain assumptions about tillering, specifically about balance and timing, that many of us would not think to question. We read them and their variations on internet bulletin boards and do not raise an eyebrow.
It's a generosity to provide bow-building help for hobbyists, even if the guidelines are flawed. Should their hobby turn into a passion, aspiring bowyers will find higher ground even if we stand in their way.
It's Not Archimedes
The path leads through balance and timing.
To illuminate the concept of balance, let's go to the playground, to the seesaw or, as it's sometimes called, the teeter-totter, and let's reason through its workings. It's simple stuff we're dealing with, common sense, and it applies directly to bows. Then we'll consider timing and add it to the balance.
Playground seesaws are constructed so that the fulcrum position is in the geographical center of the plank, equidistant from both ends. A 90 lb. boy placed on one end, and a 90 lb. boy in the same position on the other end will balance the board. Move the fulcrum toward either boy, and the longer section will overpower the shorter. To restore balance and share the workload, sufficient weight must be added to the shorter end or removed from the longer end.
For our purposes, let's distinguish between two fulcrums, the static fulcrum, which fixes the geographical center of the balanced board, and the dynamic fulcrum, which fixes the working center of the balanced board. With two boys of equal weight on each end of a board balanced at its midsection, the static (geographical) center and the working (dynamic) center are one and the same. They diverge when the fulcrum shifts or the weight changes.
Bring this simple principle to the wooden bow, where the term "balance" also has two applications. It's important not to confuse them. Static balance refers to the fulcrum position along the handle of the bow, braced or unbraced. It is the geographical center of the bow, the center between nocks as determined by a tape measure. Like the playground teeter-totter, it's the position where the bow balances in the hand as you carry it. Dynamic balance refers to the working fulcrum position when the bow reaches full draw, loaded with weight at the nock ends. It's achieved when the bow hand in the shooter's grip balances the loaded limbs perfectly at full draw. It may coincide with the static position, or the fulcrum may shift during the draw from the static to the dynamic, sometimes a little, sometimes a great deal. As with our seesaw comparison, any divergence between the two fulcrums has to do with unequal or shifting weights.
One limb bearing more weight than another will eventually work to destroy a bow of organic materials if the dynamic fulcrum does not balance the workload. For example, if our handhold of the bow at full draw is above or below the dynamic balance point, the bow will begin its steady decline. The decline may be slow, or it may be rapid, but it is certain. Fiberglassed bows risk no such hazard because fiberglass has no memory. They can be poorly tillered and miserably timed without jeopardy to the limbs. It's impossible to change the braced profile of a fiberglassed bow through repeated misuse. You can launch arrows time after time from the middle of the upper limb of one that is poorly balanced, for example, and not harm the bow.
Balancing weight on limbs to keep organic bows in equilibrium, thereby moving the dynamic fulcrum exactly under our bow hand, often requires weakening one limb over another. Positive or negative tiller is that simple, and required for that reason. There's no mystery to it, and this principle remains the same for bows regardless of which limb is longer, shorter or equal. We assign equal weight to limbs of equal length when the geographical and dynamic fulcrums coincide, and we remove weight when they don't from the longer limb sufficient to balance the "bow as seesaw", so that no kid has to work his nock end of the seesaw more vigorously than the other.
A bow with equal length limbs outside a four inch handle has a geographic fulcrum in the middle of the handle, but a dynamic fulcrum almost two inches above that, somewhere slightly below the arrow rest. This works out to a dynamic fulcrum on same-limb bows that is almost four inches further from the lower limb tip than from the upper limb tip. Its actual location varies only fractions of an inch depending upon how much the archer heels his bow in his bow hand or, to the other extreme, opens his palm in the high-wrist style. To successfully tiller such a bow, the bowyer must make the transition from static to dynamic fulcrum smooth, stable and complete.
The question is, How?
Who's On First, What's at Second
The answer for most of us is to assign positive tiller to the upper limb in same-limb bows, in deference to the five quotations excerpted from internet bulletin boards. However, since the lower limb works almost four inches further from the dynamic fulcrum than the upper limb, we are weakening exactly the wrong limb when we build such bows.
Let's turn to our seesaw for a clear illustration. Suppose we move the fulcrum away from the middle to approximate the dynamic fulcrum location of the same-limb bow. When that shorter end lifts skyward, we must add a heavier boy (or a lighter one to the longer end) to restore balance, right? And we should make certain that this shortened section is stiff enough to carry the extra weight, correct?
Why then with our same-limb bows do we head in the opposite direction? Why instead do we alter the limbs so the boy on the shorter end of the fulcrum can touch the ground with his feet (positive tiller), as though the ground rather than the fulcrum referenced working balance? We don't make it better, we make it worse. We are asking the upper limb to do heavier work than the lower limb by shifting the fulcrum toward it, but then we make it weaker. It makes no sense.
It's Simple
I stated earlier that there is no one right way to tiller a bow, though there are plenty of wrong ways. So, too, with combinations of limb lengths. You can make the upper or lower limb any length you prefer in any combination you wish as long as you account for the dynamic fulcrum and balance your weights. The Yumi bow is a case in point.
Since I began writing about selfbow construction, I've advocated making the lower limb shorter, by 1 ¼ to 2 inches, depending upon the total length of the bow. A sufficiently shorter lower limb makes the dynamic fulcrum and the geographic fulcrum nearly identical from the outset, locating them under the arrow at the handhold. It is simpler to build a bow with such limb combinations because you do not have to account for a sliding fulcrum.
"No," you may reply. "It is simpler to make same-limb bows and let the process help you decide which limb should be which." Such a sentiment ignores the distinction between simple and easy. It can be easier to make a same-limb bow, but only if you ignore the sliding fulcrum, if you already have your mind made up that you're upper limb should be the weaker one, if you don't mind keeping a relay of staves moving through the hotbox, one waiting to take the place of its failed predecessor, or if you suffer from BADD bad, unable to shoot a new bow long enough to reveal its flaws because there's another one that needs built and shot. Or if you flip the bow exactly the opposite from what you were told, making the slightly stiffer limb the upper one.
Simple means uncomplicated, but that hardly translates into easy. Simplicity forms the foundation of integrity and strength, and is achieved only with great difficulty. The root word for integrity, after all, is integer, which means indivisibility. Easy spawns dualities. Because of its unreflective nature, easy ushers us into confusion and a morass of complications. Simplicity is easily admired, but attained only with effort, dedication and discipline. Not without good cause did Thoreau urge us to "Simplify, simplify, simplify!" Simplicity attracts people to classical archery; easy herds them toward entanglements. Archery with the wooden bow is not supposed to be easy, it's supposed to be simple.
A Balancing Act
Hunting the Osage Bow advocated the use of the tillering tree and a view of the bow at full draw to determine tiller. Unlike fiberglassed bows, engineered and fairly predictable in their construction, it claimed that the popular method of prescribing a positive tiller to the upper limb, even in bows with shorter lower limbs, was irrelevant to the intrinsically unpredictable nature of the all-wood bow. Rather, HOB urged the bowyer to apply a critical eye to the bow at full draw, to feel it's fulcrum point in the bow hand, and then, when balance and tiller were satisfactory, to trace a fingerprint of the braced bow and keep it as a template for that particular bow.
If one follows this advice, he will quickly recognize the value of the seesaw comparison, especially if his tillering tree is constructed to reveal balance. The tillering tree illustrated in HOB serves this purpose poorly because it cradles the handle by spanning the four inches which represent the hand-hold. As such, it covers the static fulcrum but does little to reveal the dynamic fulcrum in bows with popular limb-length combinations.
Upon realizing this, my second generation tillering tree replaced the cradle with a radiused shoulder. It requires positioning the bow's handle on one contact point, specifically upon that contact point which most closely resembles your own handhold. Such a point would represent the dynamic fulcrum. For me, since I grip the bow by the side of the handle, that contact point is inside the thumb joint, about 5/8" below the arrow rest. By placing the bow on its dynamic fulcrum and then pulling it to full draw from the position of the middle finger on the bowstring, regardless of your finger style, you will learn what you need to know about balance and whether or not your bow achieves it. (You will better learn something of its stability, too, as rocking and twisting during the draw will reveal itself more readily with this set-up, especially from an end view.)
If you do this with a same-limb bow, you will discover that the bow only balances when the upper limb is a bit stronger than the lower limb, not weaker. How much stronger (negative tiller) depends upon the wood of the bow and the discrepancies in length between the upper and lower limb designed into the handle.
As an aside, this might be the place to mention that the reason sister billets were preferred by past masters over full-length staves is that the wood is nearly identical limb to limb. Its working properties therefore are nearly identical. By contrast, if you sift through a stack of full length osage staves you will discover in each one dramatic differences in the growth rings from one nock end to the other. Selfbows of ring porous wood seldom resemble each other not only when made from staves taken from the same tree, but even within themselves, from one end to the other in a full length stave. It may be easier to build a bow from a full length stave rather than having to join sister billets at the handle, but it is simpler not to.
There is a Time
Just as the bowyer must reach tiller at a desirable draw weight, so must he simultaneously bring balance and limb timing together. Once the bow is on its way toward balance, the best way I have found to time the limbs is to trace them, one superimposed upon another. The requirements are simple. A base line for the string, a large sheet of paper, such as butcher wrap, and a tillering stick. The bow limbs can be traced when registered along a string baseline both at brace height and at full draw, and corrections made to bring both limbs into a harmonious bend.
It's important to recognize that limb symmetry matters more than ideal tiller. In other words, if one limb approaches your intention more than another, your only recourse for preserving weight may be to make the ideal limb resemble the less than desirable one. The reason is that limb timing results from balanced symmetry at the full draw position, and that is the ultimate goal.
Once the limbs are synchronized and the bow balanced and shot in, it is time to take the bow's fingerprint. Trace the braced bow along its full length, inside the belly and along its taut string, record its ideal brace height and keep that paper as the key to the bow's identity. Periodic checks of your bow against its fingerprint will reveal the slightest departure from it. You'll be able to discover the reason and thereby become a better bowyer for it.
The Handle Wrap
There are guidelines but no formulas for tillering quality bows of organic materials. Formulas belong to engineered bows made up of laminations exclusively. However, commercially available engineered bows cannot approach the finessed precision of your own organic bow if you know what you're after and determine to get it. Each organic bow presents its own unique requirements and, once met, its own superlative rewards. I hope here that I've outlined a path respectful of those requirements.
In summary, it seems to me that a bowyer should be able to look at a stave that is not made of identical billets and discover several valid reasons why one limb could work harder than another, based upon problematic areas, and designate them top or bottom according to considered judgment. To leave that decision up to chance and circumstance (the flip of a bow) seems to me to shortchange the craft. Moreover, I would dispute that it's simpler to tiller same-limb bows with the dynamic and the static fulcrums in two separate locations because the conscientious bowyer must negotiate a truce between them. It may be easier to ignore this complication, but it's simpler to place them in essentially the same position to begin with. Balance and timing become the ripened fruits of such effort. And you'll have a bow you want to shoot next year, too.
