The Arrow Maker’s Conundrum
Why Arrows Scatter
The Arrow Maker’s Conundrum
How do we balance the competing issues of static spine, weight, balance, and length to get them to fly the same and group tightly? It can be a conundrum.
Finding the “Sweet spot” which will help you match your arrows to group tightly.
Part 1 – The Balance of the arrow starts with finding the BALANCE POINT of the arrow.
The balance of an arrow is determined by measuring how far forward the balance point of an arrow is from the center of an arrow. That seems easy, but not if I measure an arrow differently than you do. Below you can see how I was taught to measure the length of an arrow’s functional part, which is NOT the same as the overall length of an arrow. Happily, once the accurate length of an arrow is found, the mathematical calculation of the balance point, normally identified as the F.O.C, (forward of center) is not difficult. Since an arrow will fly poorly if the arrow is heavier at the back end, we always assume the balance point will be somewhere FORWARD OF THE CENTER OF THE ARROW…F.O.C is the usual abbreviation.
In the example of the 32 inch arrows above, the center of the arrow is 16 inches from the crotch of the nock. When placed across a straight edge, the arrow will not tip in either direction when this arrow rests on a point which is 20.875 inches from the crotch of the nock. Thus, the balance point of the arrow is FORWARD of the center…makes sense, right? The rest of the formula isn’t too difficult:
In the example arrow above, the equation would be as follows:
- 875 – 16 = 4.875 inches (balance point minus the center of the arrow)
- 875 inches 32 = 0.15234375 (this number divided by 100)
- 15234375 rounded down = 0.15
- 15 X 100 = 15
The FOC of this arrow shown above is 15%. In other words, THE BALANCE POINT OF THE ARROW BELOW IS 15% FORWARD OF THE CENTER OF THE ARROW.
Just a few notes about this which I have teased out of the data by experimenting on the range might be interesting to mention.
A heavier arrow with a low FOC balance point is going to scatter much more than a bamboo arrow of the same spine but lighter arrow with a low FOC.
The BIG TAKEAWAY POINT THAT I HOPE YOU KEEP IN MIND IS THIS: Bamboo arrows which may weigh the same, need to have more than just weight in common. They need to have more than just static spine in common. The weight distribution along the shafts need to be very similar too. You will know this by closely matching balance points!
This is important to match if you want tight groups. Each arrow needs to be remarkably similar to the others in the group to be dependable for the archer. The archer needs to have confidence about EXACTLY where they will ALL go if his/her form is up to scratch. Can I get an “AMEN”?
As you can imagine, this is very time consuming work. This is why my arrows cost more than “slap together” arrows of poor quality.
Part 2 – The Balance of the arrow is intertwined with the length of the arrow
I started out the previous section about weight, by showing you HOW TO MEASURE THE LENGTH OF AN ARROW. These two topics cannot be separated from one another when performance is the goal. By performance…I MEAN GROUPING AND PREDICTABILITY.
The way that I measure ALL of my wooden arrows, EXCEPT FOR THE BLACK ARROWS, is simple. I measure from the crotch of the nock to the place where wood meets metal. That is the length of an arrow in my workshop. (For my black arrows, I measure from the crotch of the nock to the beginning of the HEAD. It makes life easier for me.) When you look at the photo below, you can see that the length of an arrow might be shorter than the OVERALL LENGTH OF AN ARROW. Confusing, isn’t it? Since I can find no AMO standards for measuring the functional arrow length VS. the overall arrow length, the instruction below is what I was taught nearly 45 years ago, and it is what I still use today…
In the photo above, the center of the arrow is 16 inches because the MEASURED PART of the arrow (all of the arrow from the crotch of the nock to where the metal begins) is exactly 32 inches long. This allows us to then determine the balance point of each arrow individually to insure they fall within an acceptable range.
So, properly measured arrow length can help us determine an accurate balance point of an arrow. But it does more. Consider the following problem. Let’s say that I have two matching shafts by spine and weight, but one has a balance point which calculates to a 13% FOC, and the other has a 15% FOC. Clearly the two shafts weigh the same, but one weights more in the back half of the arrow than the other.
Why this information is important to me as a professional arrow maker? If you pay me to make a set of arrows which will “teacup” at 20 yards, the arrow which has a 13% FOC just might not group with the other eleven arrows which have an FOC of 15%…at least not as tightly. Perhaps your form isn’t good enough that you notice that…but you might notice if I shorten the arrow with the 13% FOC in order to match the balance points. It is a simple mathematics problem. If two arrows are the 32 inches long, 450 grains of weight, and each has a 145 grain head mounted, but the balance points are not the same, well the group isn’t going to be as good as possible. But this CAN BE CHANGED by shortening the arrow with the lower balance point. Please take a look at EXAMPLE 1 below:
|Static Spine||Shaft Weight||Shaft Length||Center of Length|
In this example, we have two identical arrows but arrow #2 has less weight forward than arrow #1. By using the formula which determines the FOC of an arrow already discussed previously, what happens if we cut on inch off arrow #2?
|Static Spine||Shaft Weight||Shaft Length||Center of Length||Balance Point||FOC %|
By shortening the arrow shaft by one inch, we move the balance points much closer to one another as you can see.
But since a shorter arrow has a stiffer dynamic spine (this arrow will tend to land to the left of the other arrows if you are a right handed archer shooting with his/her fingers) then to match the FOC will only create other problems. This is the point of the algorithm which I call the conundrum. How can I get them ALL in to group into that teacup?
One easy approach to this problem might simply be to put on a heavier head. By pulling off the 145 grain head, and replacing it with a 165 grain head, the arrow WILL BE 20 GRAINS HEAVIER. In theory this will cause the dynamic spine to become higher, which typically will offset the STIFFENING of the dynamic spine by removing an inch of length. Additionally, this will place more weight on the front of the shorter arrow shifting the FOC forward. The data on these two arrows might now look like this:
|Static Spine||Shaft Weight||Shaft Length||Center of Length||Balance Point||FOC %|
By working through all 4 parts of the conundrum, I have two arrows which will group nice and tight presumably…if my form is up to scratch.
If your form isn’t up to scratch, you may not notice…but then again, how can you improve your form if your arrows just aren’t up to scratch either? This is the viscous cycle that I suspect most of us go through in our search for great wooden arrows.
Solving this conundrum is the best way I know of replacing this vicious cycle and implementing the virtuous cycle of improvement and confidence.
As you can see, I made the choice a long time ago that I would adjust lengths if necessary to be able to adjust the DYNAMIC SPINES of my bamboo arrows to “teacup” at 20 yards. It does work for me….
My groups tend to look like the left photo instead of the photo on the right.
So, you can see that a balance between length and balance needs to be achieved for each arrow within a set because uniformity isn’t NEARLY as important as performance. At least it isn’t for me. Let me say this another way. If shortening an arrow ½ inch shorter than the others in your quiver is likely to make an arrow fly differently by raising the dynamic spine; AND by allowing yourself to be flexible with the weights of the arrow points you use in order to adjust them bothers you, there may be one or more arrows which just don’t group reliably where the others land in the target. I hope you don’t mind just a bit of frustration and disappointment on the range.
So, one can see that length is important for several issues, including dynamic spine adjustments, as well as determining the balance points of each arrow in order to manipulate them to “teacup” at 20 yards.
Part 3 – The Static Spine is NOT THE SAME as the Dynamic Spine
The Static spine of an arrow is usually easy to measure on a spine tester. One of the drawbacks of bamboo arrows is that they are not so easy to measure. Additionally, the high quality shafts which are more dense and thinner are more difficult still.
Over the years I have tried many different spine testers in order to speed up the laborious process of spine testing. The problem is that bamboo skin has slight irregularities in it which will make the readings unreliable. Additionally if one measures the static spine of an arrow, the static spine can change a bit on the spine tester for reasons not entirely clear.
Hopefully by now, you can see that the static spine of an arrow (as measured on an accurate spine tester such as the one I use from Ace Archery Tackle) is hardly as important as the entire picture of the four competing parts of what I call “the arrow maker’s conundrum”.
Part 4 – Why matching arrow weights is very important to grouping your arrows
Arrow weight is the last of the 4 major problems in matching a set of bamboo arrows, and it is an interesting problem. For instance, I often get asked questions about how many GRAINS PER INCH (GPI) my bamboo arrows are. Great question, but not appropriate to bamboo. Here is why.
If I make an extruded carbon tube which is homogenous in diameter and weight along its entire length, I can tell you that. I suppose if I made arrows of carbon I would use this data for making heavy vs. lighter arrows as needed. But we have already seen in the photo at the beginning of this article that bamboo is ANYTHING but homogenous in width. Another interesting note is that just because a bamboo shaft is smaller in diameter does NOT mean it is lighter. I see this all the time when sorting my shafts into closely matched groups.
As you can see in the photo below, this is a handful of fine high quality bamboo shafts which match elegantly between 65 – 70 lbs of static spine. The problem is that there are NOT 12 shafts in the bunch which will weigh within 25 grains of each other. I simply can’t YET form a set to sell. In time, more shafts of this spine will appear. Sometimes they get improperly spined in China. I have never in my life ordered shafts of this static spine, yet over time they do appear in a shipment. It may not be obvious from the photo below, but these shafts are different in their width, but they all have the same static spine values.
More to the point is the next photo which shows two matched sets of high quality bamboo shafts which have a static spine of 45 – 50 pounds of deflection. Some are chubbier than others, but one group weights 430 grains per shaft (+ or – 20 grains) while the other group weighs 350 grains per shaft (+ or – 20 grains). If didn’t match these groups by SPINE AND WEIGHT, they just won’t form tight groups, and they aren’t leaving my shop!
These are nicely matched groups of shafts. But that isn’t enough!
I hope now that you can understand why the question of grains per inch is appropriate for synthetic arrows, and possibly for cedar arrows. (I’m not qualified to say anything about cedar arrows other than they are nice arrows indeed.) The REAL QUESTION which I hope you ask is, “Do they match closely by static spine, weight, balance point, and length?” If so, then you have a wonderful opportunity to get to work on your archery shooting form!
When I have arrows which are this predictable, the VIRTUOUS CYCLE begins rather than the VICIOUS CYCLE of chasing your arrows around the face of the target trying to figure them out. When they become highly predictable, I make my shot and they either group or they don’t, but if they don’t, it was ME…not my arrows. Something was different with my form. Of this I can be certain. Now I know what I need to focus on to improve. My equipment is fine. It is the archer who needs to practice. It’s like the song says, “One thing leads to another”.
Let’s look at the data. This is the sweet spot for my 43 pound saluki horse bow which I shoot with a thumb ring.
I am now certain that this information is extrapolatable and transferable to any other traditional bow.
Both sets of arrows were shot at a 20 yard target. Both sets had the same static spine. All arrows were aimed directly at the center of the target. The white arrows were manipulated to have a slightly stiffer dynamic spine by using a lighter head and shortening the arrow length one inch. You can see the predictable outcome, if your form is good enough.
The Arrow Maker’s Conundrum is a term which I use which describes a problem:
We have already learned that an arrow can be manipulated in flight, but how do we take an ENTIRE set of bamboo (or any wooden shaft for that matter) which vary slightly in stiffness (spine), weight, and other unknown variables…HOW CAN WE MAKE ALL 12 OF THEM TO GROUP IN A TEACUP? Most archers are quite happy to group them all in a “pie plate” sized group. This is just fine, and represents a good day on the range. But since I CAN exceed this goal, why not shoot for a teacup sized group. It can be achieved…sometimes! But this will always be my goal on the range, and my arrows MUST be this consistent throughout the group. Unlike other wooden arrows, bamboo is a hollow tube with nodes that can grow inward as well as outward, or not much at all. So, if we have learned what we can do with one arrow in flight, how do we create a dozen of them? This is the Arrow Maker’s conundrum.
Why Bamboo (And Wooden Arrows) Scatter and How To Fix This Problem
When your arrows begin to scatter, there is a reason. Sometimes you are having a bad day on the range. Sometimes you are too fatigued to practice good form, but sometimes it isn’t that at all. Sometimes very small errors in making an arrow can really be magnified at 20 yards!
Regardless of what you hear, Brace height may make little difference on where arrows hit and how badly they scatter, or brace height can make a profound difference! I suspect that for high speed primitive bows with no shelf will be greatly affected by brace height changes much more than a recurve.
Let’s don’t bore ourselves with too much math here. The geometry behind this shot is simple and surprised me quite a bit. In the photo, you can see that the one arrow is out of the group. Not only is out of the group, but is over 5 inches away from the nearest other arrow in the group. Basically, if you have a triangle which is 20 yards long on one side, (720 inches) a second side which is also 720 inches, and a third side which is 51/2 inches long, we can run this problem, and discover that the arrow out of the group and either one or both ends which were a total of 1/16 inches off from the rest. So, while this seems painful to look at, small problems become highly magnified at 20 yards. When you can group a set of arrows tightly at 20 yards, YOU ARE LITERALLY SPLITTING HAIRS. All of your shots have been made with ALL of them having been launched with either end of the arrow within 1/16 of EVERY OTHER ARROW shot in that group…AND we haven’t discussed the effect of good follow through on a shot. Don’t dispair!! I pulled my arrows and reshot that miss. As you can see, the problem was not the arrow, it was the archer.
But, how can we know if it is the archer or the arrow? This is the same group of arrows a few weeks later on the same range and distance. As you can see, one arrow continually lands high, but it wasn’t doing so a few weeks ago. I reshot this arrow repeatedly, and got virtually the same result every time, as you can see. Suddenly, one arrow isn’t grouping. Since I am repeating the same result with this arrow, I can assume my form isn’t at fault. So, the question becomes “WHAT IS WRONG WITH ARROW #8”?
You may recall that in the section on the left, we just discussed how good archery is like splitting hairs. We have approximately an 8 inch variance, so how is it that this arrow consistently lands in such a way that it is launched 1/8 inch higher then every arrow, and only this arrow is, and it is doing so every time?
After considering, it came to me that I had split a nock in my arrows a few weeks before, and I began wondering about the nock. As you can see in the third image, a moment of inattention on my part two weeks ago when I replaced this nock led to an arrow that will never group.
I believe you can see my point. Sometimes arrows scatter because of the archer. But sometimes a very small (virtually unnoticeable flaw) can lead to an undesirable outcome. I now can generalize about my groups. When arrows are landing right or left, and the problem isn’t my form, then the problem has to be that the dynamic spine doesn’t match the rest of the group. When arrows land high or low, and the problem isn’t my form, then I need to start looking at my nocks. I also think this demonstrates a second point about nock placement. PAY ATTENTION!