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| Measuring tiller. |
Of course to get a valid result, we have to make this measurement in the correct way. Many traditional eastern bows have reflex handle, which means that the limbs bases are canted a little forward and then working parts of limbs are bending back toward the string - as a result bow handle is a bit closer to the string than limbs base. In such a case it is quite easy to measure top and bottom BH, we do it in the "deepest" parts of each limb, that means we pick a spot where belly side is farthest from the string, measuring at a right angle to it.
When a bow has neutral or deflex handle (when handle is actually the "deepest" part of the bow, being at the same or bigger BH than limbs bases) you often cannot see such obvious places for determining tiller, so you have to find them for example by measuring the same distance both sides from limbs bases or any similar method. Try to pick such symmetrical spots on both limbs, where the potential difference in brace height will be most significant.
We can take a special bow square, but it is also possible to use any straight stick or simply an arrow - taking care not to scratch bow surface with sharp arrowhead... Most convenient way is to measure BH at top limb first, mark the result with your finger and then move to the bottom limb and check the difference. Most often we will see, that now the string is not reaching up to the marked place, so top limb BH is bigger than lower limb's. This result we will call positive tiller (+). If top and bottom result is identical we have zero tiller, and if BH on top limb is smaller than at the bottom - that's negative tiller (-).
Now, what exactly is slightly positive tiller? Most often for a symmetrical design bow the correct value is about +0,5cm (let's say from +4 to +8mm). Then the archer holding bow at full draw feels the grip leaning firmly against his bow hand. If the tiller is too small (about zero or even negative, meaning bottom limb too weak) bow grip will lean too much against top part of archer's bow hand, he will feel that his whole bow "would like" to lean back. Too much positive tiller (more than +1cm, meaning top limb too weak) and bow grip will lean too much against bottom part of archer's hand and tip of the bow will lean forward. Of course it will depend also, to a certain extent, on archer's method of gripping his bow - with "high" or "low" wrist, or something in between. If in doubt about "feel" of the handle in the hand, we can try to actually SEE what exactly is happening during drawing, with a help of an extra arrow held together with the bow. Please see the enclosed photos for this method.In a modern sport equipment you usually have the possibility to adjust limbs angle, but in a traditional bow tiller is "build-in" by the manufacturer.
If properly made bow has incorrect tiller after bracing, most often it will be easy to fix - it "wants" to return to the proper shape and needs only a little help. In such a case we take its "weaker" limb in the hand in such a place, that we can reach the string with our fingertips and squeeze, pulling it closer to bow belly. This causes the limb to straighten and the opposite, "stronger" limb to bend more. After several seconds we release our grip and check geometry again.
In case of especially "stubborn" bow we can pull the string towards one limb and hold it there for as long as necessary by wrapping it with bow's own protective sleeve or some other strap, wide enough not to mark its surface. You can also try to shorten the string - with shorter string bow is more stabile and different problems will often disappear or at least decline (more about string length in the next part).What to do when tiller is still wrong, despite corrections? Assuming that limbs are not damaged, in case of natural composite bows it’s possible to carefully heat up stronger limb's horn layer and adjust it - by archer himself or skilled bowyer.
Modern materials bows "hold" their shape better, so it means that more often than not you can set a proper tiller easily. On the other hand, if something is wrong, our options are limited. Modifying fiberglass structure is a risky business. If a bow of this type is "keeping" tiller which is a bit incorrect, but only slightly - about 0 to +3mm or close to 1cm but stabile, not growing - I wouldn't mind, it's not perfect but also not a tragedy. Limbs are stable and we can adjust nocking height to compensate for slight imperfections, it's possible to shoot well.
If we have negative tiller, we can simply take the bow upside down. Many bows of eastern type are so symmetrically build, that you can tell top and bottom limb apart only by looking at poundage marks (most often found on bottom limb) or manufacturer logo - and, of course, by tiller. In many other models you have asymmetrical grip, but made as a separate element, completely independent of main construction. So, if tiller of limbs does not "agree" with markings or grip of the bow, often you can shift the grip. In fact, sometimes you can find mass-produced "plastic" bows tillered correctly, but by mistake finished and marked other way around.
Worst problem is too big tiller, significantly over +1cm. In such case limbs of equal length will be loaded much differently and not only the bow will feel wrong in the hand, but also very probably weaker limb will degrade further over time, making the bow completely useless. Assuming that the top limb is overloaded, but not yet damaged, we can try moving the grip a bit lower (something like 1-3cm lower), de facto converting our bow into asymmetric design. Tiller will remain the same, but we change the way the bow is drawn and we decrease load on upper limb. Possibility and the distance you can move the grip depend, of course, on a particular design.
Our considerations about tiller, thus far, concerned symmetrical designs, that means bows with limbs of equal or very similar length. Some eastern bows are more or less asymmetric, with different size limbs which HAVE to bent unevenly for the whole bow to work in balance. Infallibly the bottom limb is shorter and stiffer and top limb longer and more elastic, so the bow will have high, positive tiller. Size of those bows is typically from medium (about 1,5m length) to long (over 2m) and short bottom limb is convenient for an archer shooting from kneeling position or from horseback. Short bows are most often symmetrical, because they are handy in any case, and I have never seen any bow with significantly longer bottom limb; it’s quite hard to imagine situation, in which such design (theoretically possible) will bring any benefits.As we told, in asymmetrical bows big positive tiller is natural and something like +2 or +3cm result can be perfectly normal. It's difficult to give any specific directions, you have simply to decide when shape of a particular design is correct (in case of any doubts consulting with bow manufacturer), then measure tiller and from now on keep it the same when bracing this bow. There are bows with such different curvatures of limbs, that its real hard to tell where are sensible places to determine and compare top and bottom BH. Often in those cases their owners do not try to measure tiller, but relay solely on bow's shape and "feel" in the hand (this can be pretty accurate method, but of course requires experience), confirming this by additional check of nocking point height on the string.
Method for tiller visualization.
Please note, that instead of collecting several bows with different tiller settings, I "simulated" this on one bow, changing my grip up and down. Just imagine that on all photos my bow hand is in the same place...
Experienced archer will feel when his bow at full draw is leaning firmly against his bow hand, without tilting forward or backward. But if in any doubt, you can grip one end of an arrow or other straight stick in vertical position, together with bow handle (or even bind/tape them, with some padding if necessary to avoid contact with moving limbs), then place other end of our makeshift pointer over some marker and slowly draw your bow. If:
A) bottom end of the arrow remains over marker, bow is balanced (typically with slight positive tiller);
B) end of the arrow is drifting from marker towards you, top limb is too weak (too big positive tiller);
C) end of the arrow is drifting from marker away from you, bottom limb is too weak (zero or negative tiller);
D) and at the last photo, a comparison with "string walking" technique (used mostly on some longbows/recurves in barebow competitions) - bow drawn with string hand quite a long way below arrow nock. Top limb of normally balanced bow will bend too much. You need stronger top limb - the only case we WANT a negative tiller on our bow.
Getting the balance of limbs right is necessary before next step, which will be checking nockpoint height. If top limb is stronger, it will pull the string (together with center serving and nock point) up, just like stronger bottom limb will pull it down - so before we set correct tiller, the nock point will ALWAYS be in the wrong position.
In the next part we will proceed to the next point in checking the geometry: brace height and nockpoint height
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