In a recent post I wrote about getting into traditional archery, typically with either a longbow or a one piece recurve bow. Today I had a student on my team struggling a little with his bow setup. When you shoot “off the point,” you line your arrow point up with something in your field of view that gets your bow in position to shoot your arrow into target center. I had made the point over and over that: if you have a “good tune” your “point of aim” will be on a 12 o’clock to 6 o’clock line through the center of the target. Unfortunately my student’s POA was to the right of that line. This means that, since he is right-handed (and everything else was okay), that his arrows were a bit too stiff. Either the arrows needed to be made weaker or the bow had to be made stronger. Since he was shooting a compound bow, we put one more turn on each limb bolt (thus making the bow’s draw weight 1-2 pounds higher) and, voila, problem solved.
This is one of the advantages of compound bows, that they have a draw weight that is adjustable typically over a range that is 25-33% of the maximum peak weight. (They are now making ultra-adjustable bows that have mammoth draw weight ranges, like 5-70#!) But then I thought “You can’t do this with a trad bow, so how do you tune up a trad bow?”
Good question: how do you tune a traditional bow?
To change the draw weight of a traditional bow is no small task, although at one time it was common practice. Back when most longbows were “self bows” that is made of a single thickness of wood or possibly with a backing made of linen or leather or a different wood, bows were often shot a while and if the bow started to take a “set,” that is go from being straight when unstrung to being curved (also called “following the string”) they were often reconfigured. Since the bow taking a curved shape when unstrung lowers its draw weight, it needed a draw weight boost and the way this was done was to cut an inch or two off of each limb tip and have new nock grooves filed in. A little filing and sanding and voila, a new bow, shorter by 2-4˝ and more powerful. (The shorter a piece of wood, the harder it is to bend.)
This is almost impossible to do with a recurve as it messes up the shapes of the curves of the limbs.
Another thing that was done was the limbs could be scraped or sanded to make them slimmer which would result in a bow with a lower draw weight (permanently). You can’t do this with a laminated longbow (or recurve), as it will reduce just the outside laminations only, so they sanded the dges only, creating a limb with less material and thus weaker.
So, let me just say that changing the draw weight of a traditional bow is not a first option and sometimes not even an option at all.
So, how does one tune a traditional bow?
You can adjust two things: the bowstring itself and/or the length of the bowstring.
Tuning with Your Bowstring
In general you can change the length of the string you have and it will change the power of the bow. This is how it works. By adding twists to the string (10, 20, 30, more) you can make it shorter. Placing it back on the bow you will see that the bow is now more bent at brace than it was before and that the string is farther from the handle (the “brace height” is greater). What this means is that when the arrow is shot, the string will stop more quickly and the arrow will come off the string sooner. Since the longer the arrow is on the string, the more energy it absorbs from the bow, so:
shortening the string, raises the brace height and makes the bow weaker
lengthen the string, lowers the brace height and makes the bow stronger.
The effects are not huge but they are significant.
The other thing you can do is switch to a different string of the same length but of different composition. A string can be made heavier (making the bow weaker) or lighter (making the bow stronger) by changing the number of strands. An 18-strand string is 50% heavier than a 12-strand string of the same length and materials. The bow’s energy gets wasted moving the heavier string rather than moving the arrow, so a heavier string makes the bow appear weaker, etc.
And string material changes can make substantial (but not huge) differences. Most older bows use Dacron strings. Dacron, as a bowstring material, is quite “springy” and some of the bow’s energy goes into stretching it rather than into the arrow. The stretchiness also protects the bow when the limbs are slammed to a stop when the string stops them at the end of a shot. More modern bowstring materials have very little stretch in them and transmit almost all of that shock to the bow and the archer. Modern bows have been designed to handle this, older bows not so much. (Do not put a modern material bowstring on an older trad bow, you could break the bow. The new materials are also more abrasive and have been known to cut into unreinforced limb tip notches.)
So, if you have a modern bow with a Dacron string, you can make it slightly stronger by putting in a bowstring made of a modern material, such as Fast Flight (a polyethylene material).
Tuning with Your Arrows
Most of bow tuning is really done my adjusting the weight, inherent stiffness, and length of your arrows. This is true for all bows and is the major source of tuning adjustments for traditional bows.
Once you have bought the bow, fiddling with the bowstring only buys you a little variability. The majority of making a good bow-arrow-archer system is going to be made with adjustments to the arrows. So, be very careful about the bow you buy. I have been known to buy bows with specifications that suit the arrow I want to shoot, not the other way around. Your arrows are more important than your bow to you or the students you coach becoming consistently accurate.
If you are interested I will address the processes used to tune a trad bow. Let me know.