Preparing the bow for shooting part 5 CHECKING THE GEOMETRY - brace height and nockpoint height.

In the last chapter we considered tiller, in other words checking the limbs balance by measuring difference in distance between the string and top and bottom limb. Now it's time to look at brace height, that is distance between the string and the grip of our bow. Measuring this distance is an easy way to check correct string length.

Measuring brace height (BH)

You can ask: what is a problem to measure a piece of rope with two loops at each end? In reality THERE ARE numerous difficulties. First of all, a string normally described as for e.g. 50" is in fact about 46 - 46,5" long. Fifty inches is in this case a length of the bow, and a string designed to keep it bend needs to be shorter than that. Nowadays it becomes more and more popular to use double imperial-and-metric descriptions like FF 50-117,0 which means Fast Flight string for 50" bow and actual length 117cm. What's more, for the same bow you can use several strings a bit different in length, depending of exact result you want (more about this later), hence you can find labels saying 50-116,5 or 50-117,0 and other similar.

To make things more interesting you have to measure length of our rope under proper tension, because different materials will stretch differently under load - a popular method is stretching the string under 100# (45 kg) weight. Two strings, one from Dacron and other from Fast Flight, identical when loose can easily be 1 cm different when measured that way, and the longer the bow is, the more significant that stretching-induced differences become. Oh, did I already mention that one more important thing is that you place your string loops on properly-sized hooks for measuring? (standard is to use 0,25" diameter rod).

To sum up: direct approach for measuring string is not the most practical way under field conditions.
Fortunately we can much easier measure what depend on string length: the distance between braced string and bow handle (so called brace height or BH). Longer string will be closer to the handle and vice versa.

Officially we should measure BH from the place an archer support his bowhand web on the handle, perpendicularly to the string. This is easy to identify on modern ergonomic grip, with deep "pivot point", but a lot of eastern type bows have convex belly of the grip, with archer's hand resting on a slanted surface, and exact point for measurement can be hard to find. In such a case you can skip the official definition and choose other characteristic point somewhere within the grip - like bow's back or belly edge in the arrow pass area. During normal bow check we are not exactly interested in BH value (this is important when comparing different bows), but rather in checking that our brace height is always the same. Therefore, is not so much important between what points you take measurements, as long as those are the same points every time.

It's a bit hard to give a simple answer to the question what is correct brace height. Eastern bows have many different shapes and sizes, and even if we are talking about one specific type, than most reflex bows have rather wide range of acceptable BH, definitely wider than for example a wooden longbow. Bow's manufacturer should supply you with suggested starting value or, more commonly, a set of values, like from 16 to 18 cm (2-3 cm range being typical) to choose from, according to our needs. The general rule is that longer string and smaller BH will give us faster and more elastic, pleasant to draw bow, but at the same time more difficult to shoot - it will be less “forgiving” for our mistakes, the string can easier hit our forearm or even wrist etc. Also most of the possible geometry problems will be more visible, and in extreme cases, with very low BH the reflex design can become unstable and “reverse”, throwing off the string.

It's just the opposite with shorter, higher string - our bow become stiffer but slower (power stroke is shorter, meaning that the string is propelling arrow over shorter distance); on the other hand, it will be easier to shoot, much more "forgiving". With too short string you can over stress the limbs, and also we gradually loosing virtues of reflex design - limb tips are drawn more to the back, effectively straightening reflexes. If the bow has string bridges, too short string can lost contact with them.

In practice a happy owner of a new bow will probably adjust its string according to manufacturer specification, let's say in the middle of suggested range, shoot like this for some time, to get used to bow behavior (I'll suggest as much as 2-3 months for a beginner; of course less time will be necessary for more experienced archer) and then he starts tinkering: shorten the string a bit, lengthen it a bit and observe, when it is shooting better. By this trial-and-error process he will slowly come to the optimum brace height for his method of shooting and the particular arrows he uses. From now on he will keep this BH and check it after each bracing.

You can remember (or better still - write down...) a particular number of centimeters or inches and use a special bow square, mark a stick or measure by your hand, using a fist with outstretched thumb, span of particular extended fingers or some similar way (although I prefer former, more "scientific" techniques).

Interesting idea is to paint rings on the arrows shafts, positioned in such a place, that it will be at the back or belly edge of your bow when arrow is nocked - the only drawback is you have to repaint your shafts when changing BH.

When talking about changing brace height, we have three ways to do it. First and most common method is twisting the string. Strings made of modern materials should be twisted, to work as a one rope and not a bunch of individual strands, which spread during shoot and slowing down due to increased air drag. Suggested number of twists is 1 full rotation every 5 cm (2 inches) of length, so you can roughly measure middle part of your string (not including loops) and make a simple arithmetic. But this is only a suggestion from fibers manufacturers (exact numbers varying a bit according to different sources), but in practice you can quite freely add more twists (more info under enclosed photos), as long as the string is nicely round, without kinks or bumps and watching the end loops proper alignment - if we over twist the middle section, loops can start to twist as well.

When you add twists to the string you make it shorter (BH increases) and when removing twists you make it longer (BH drops). The longer a particular bow is, the more twist “will fit in” it's string and the more we can influence brace height.

You can count or measure, but it's quite easy to estimate twist rate by simply looking at the string (for clarity we show two-color string; if you use one color it will be the same, only a bit harder to recognize):
First one from the left: definitely not enough twist, almost completely straight.
Second from the left: still on low side, but not so bad (about 1 full twist in 3 inches (7,5cm).
Middle one: just right, 1 twist in 2 inches (5 cm).
Fourth from the left: still OK, about 1 twist in 1 inch (2,5 cm)
Fifth from the left, the last one: too much twist, string starts to develop kinks (slight bulges along its length).

Of course we can twist a string in two opposite directions. Descriptions like "clockwise or counterclockwise rotation" are very easy to confuse, as they depend on the direction we look, so I prefer to remember twist of either S or Z type: it means that if we look at vertical string we see its individual strands going down like the middle line in one of those two letters: from left to right (S) or from right to left (Z). This method of description does not depend which end of the bow is upwards; it always looks the same. See corresponding picture. Direction of twist DOES NOT MATTER during shooting (despite what you can read in some books, claiming that one direction is more appropriate for right-handed and other for lefties). The only important thing is always to twist the string in the direction it was twisted during manufacture, because all the serving is (or at least should be...) made according to twist. So, if we start to twist the string in the opposite way than it's manufacturer did (for example I almost always make S-type strings, because this way is more handy for me) we will make serving loose.

If we get a completely untwisted string there is a simple experiment to determine it's proper twist direction: clutch a length of serving between fingers of one hand, grip it with your other hand 1-2cm further and try to twit this short piece first in one and then in opposite direction. We should notice, that in one case there is not a lot of resistance and serving start to swell - this is wrong direction. In opposite, proper direction you feel more resistance and serving is remaining nice and tight. Twist the whole string in this direction, take a look and remember the adequate letter S or Z.

If twisting or untwisting is not enough it is necessary to change the string for other of more appropriate length (method 2) unless you have a more traditional string,with separate loop pieces. Then we have the possibility to re-tie the knots (method 3) changing length of end loops - but we should be careful, often knots should be located in more or less specific points on the bow, especially when it has string bridges. Also, both loops should be of equal size.

If during unbracing the bow we left its string loops on the limbs or at least remember to connect both loops, then we should get the same brace height when bracing it again. Still, it's best to always check BH. Especially with new string it's sometimes necessary to add 1-2 twists.

The final measurement is checking the nockpoint height. For every archer - except complete beginners - it should be obvious, that the nockingpoint, meaning the point to place arrow nock on the string, should be little higher than arrow pass at bow's handle. In other words arrow should not be placed perpendicular to the string, put with its head end pointing slightly downwards (the only exception from this rule are some - not all - modern compound bows). When propelled by the string it will raise and fly just above our bowhand. If nockingpoint is too low, arrow will scratch our thumb and its flight become unstable. In case of too high nocking height our skin is safe, but arrow still wobble in flight.

A special bow square is invaluable in this case, because after clipping it to the string allow us to easily determine a perpendicular line from arrow pass, and then measure appropriate distance up the string. When we are lacking this tool, we can use an arrow, setting it perpendicularly to the string “by eye” or using any object with two walls joined at a right angle - for example corner of a notebook or a matchbox.

Nocking height meaning how far exactly we should move arrow nock above right angle depends on bow type, its tiller, the way we are holding the bow grip and also arrow shaft diameter, so it's an individual matter - it can be anything from 4-5 mm up to over 1,5 cm; for example popular Korean bows require very high nocking point.

Detailed description of different methods used to determine its location is beyond the scope of this text, lets just say that the archer keep shooting and changing nocking point as long as necessary to achieve correct arrow flight and then measure and write down most appropriate set - measured very accurately, because a single millimeter can be important in this case.

It's true that properly set nockpoint - a knot or sometimes metal ring - will stay in the proper place for long, but it's best to check it nevertheless. First of all “for a long time” does not mean “forever”, it can become loose itself or the serving under it can start to move. According to Mr. Murphy laws something like this will always occur just before some competition or show, not during training. Also, if our nockpoint is in the proper position, we have additional confirmation, that bow's tiller is also correct - change of tiller will always influence nockpoint position upwards or downwards.

The last action to perform before actual shooting is to pull the bow carefully to full draw and then slowly return the string (without dryfirnig, of course!). We listen to any suspicious creaks and other sounds, and we observe if the string comes back exactly to the limbs center line. Only then we can (finally!) be certain, that our bow is ready to kill somebody...

We needed five quite extensive posts to cover details of all necessary steps in preparing our bow for shooting, so you can have an impression that this procedure takes lot of time and work before each shooting session. In fact, this is not the case once you get used to the standard procedure.

To sum up shortly:

• take a string, place one loop on the appropriate bow end;
• string a bow with one of the methods described earlier;
• KEEP HOLDING THE BOW firmly under control, check both string ends and general shape of limbs;
• release grip on the bow, look along the string, correct limbs ends if out of center;
• take bow square or an arrow, check tiller;
• check brace height;
• take a look if nocking point is firmly set on a string. In case of any doubts check nocking height;
• bring the bow to full draw and slowly back (without dryfire!), hear and look for anything wrong;
• you have the bow ready.

In case of bows made from modern materials the whole procedure takes me typically under one minute, certainly less than two (of course if no significant problems emerge) and now I'm sure my equipment is ready - the result will depend only on my abilities to use it...

In the last part of this mini-series we will discuss - in contrast - one of more “battlefield” techniques for preparing the bow for shooting - bracing the string while on horseback