The arrow maker's conundrum
I know most readers are well aware that the static spine of an arrow is NOT the spine in flight. This is called the DYNAMIC spine of an arrow. Bamboo arrows are easy to manipulate safely. I call it the “arrow maker’s conundrum”. There are at least 4 (sometimes competing) priorities that need to be within a range of acceptability before you can have the confidence that these highly durable arrows will also group into a tea cup. One priority is the static spine. IT IS ONLY ONE OF 4 ISSUES WHICH NEED TO BE BROUGHT INTO HARMONY SO THAT ALL THE ARROWS OF A SET WILL BE HIGHLY PREDICTABLE AND GROUP TIGHTLY…IF YOUR FORM IS UP TO SCRATCH.
You may recall this photo from my last article.
These are 3 different bamboo shafts. They are below 30 pounds of deflection on the spine tester (very weak spines) because they just didn’t have the time to build a stronger wall. This also means the walls might be a bit uneven. You can imagine how a spine tester will give radically different readings depending on which part of the shaft the spine tester touches.
These arrows can be quite a problem. But, the shafts are straight, and the nodes and grain of the wood are clean. Of the 3 shafts shown above, the middle shaft is likely the most problematic. It just looks “suspect”, doesn’t it? The truth is, that it may be the most durable. I often find I simply can’t predict the durability of a shaft when compared to others until I flex them all several times. This is why it is often difficult to make a set of shafts with spines lighter than 30 pounds. Another reason I dislike working with shafts which have a spine lower than 30 pounds is because I can find some good, straight, strong, flexible shafts, but finding 12 which weigh the same and spine the same may take 12 months or longer.
A quick word about spine testers.
The spine testers I find which work well are the Ace Archery Tackle spine testers. The less expensive one is fine for an archer, but as a professional arrow maker, it isn’t good enough. The more expensive, spin-spine tester works very well for my purposes.
If you remember to reset the tester between each test, AND YOU TEST ALL 4 SIDES OF THE BAMBOO SHAFT, you can get a nice idea of exactly what the spine deflection of a shaft is…UNTIL YOU MEASURE IT A WEEK LATER AND FIND THE WEIGHT HAS CHANGED! For some reason, probably the nodes, bamboo can add or lose a pound or three of deflection over a year’s time. Just as often they will get a bit stiffer instead of weaker. This happens in arrows which I shoot very often, as well as the shafts which I have sorted to sell. I can find no pattern to this phenomenon.
I used to measure a shaft, find it was 42 pounds of deflection, and find 11 more of a similar weight, and set them aside for sale or use. It drove me crazy to find that 3 months later only half of them were now measuring 42 pounds. Some were 43 or 44…or even 45 pounds. Some were 40. I believe I now understand why this happens, and why it need not be a problem. I group them in 5 lb increments by static spine. Then I sort all the arrow shafts with a static spine which are within that 5 pound grouping and match them within 10 – 20 grains into 12 arrow bundles. This has worked very successfully when dealing with that “creeping spine” problem. Besides, static spine isn’t the end of matching arrow shafts. It is only the beginning of my job to make a full set of 12 with matching DYNAMIC spines...not STATIC spines.
I learned a profound truth about arrow making, which is that anyone can make an arrow that will hit the bulls eye, but can you make 12 which will group tightly? I suppose that in the end, this is what the art of arrow making is all about.
Fortunately, dynamic spine is quite easy to manipulate, AND THERE IS A WORLD OF DIFFERENCE BETWEEN THE STATIC SPINE OF AN ARROW AND THE DYNAMIC SPINE OF THAT ARROW. Dynamic spine is the art of manipulating the 4 main characteristics (plus other minor characteristics) which determine arrow flight. It is addressing this that is essentially what the arrow maker’s conundrum is all about.
Tonkin River Reed, the bamboo I use, is constantly moving and flexing as it grows. A cedar tree is too, but to a far less extent. If you can imagine all the activity which happens with the action of wind on bamboo, you can imagine that this might cause it to grow stronger and stiffen up. I suspect that this wind activity and plenty of sunlight may have to do with why some bamboo is stronger and straighter with good clean nodes and others are crooked. Growth causes stress. Stress causes growth, which is a universal truth.
Time may tell us more about why some bamboo grows straight, tough, and compact and other bamboo doesn’t. However, all this activity which I used to find puzzling and irritating doesn’t actually appear to mean anything with regard to making them group. Years of experience has taught me simply to ignore this slight creeping of static spine…It isn’t enough to cause a noticeable difference, if there is really any difference at all.
Matching dynamic spines into a group of arrows is what Roy Marlow defines as “DYNAMIC SPINE” in his excellent book, “Timeless Bowhunting; the Art, the Science, & the Spirit”.
The group above was a very good day for me on the range that day. Sadly not all days are this good. But on my website you will see many photos of groups similar to this one. Just so you know, I’m not a very good archer. I would consider myself a “fair” archer. So I cheat. I make arrows which I completely understand, can predict, and reproduce as many as I want, I go to the range two or three days per week, and work on my form.
When I started reading what Roy Marlow and others published about all the factors which enter into the manipulation of an arrow in flight so that they group tightly, it was as clear as mud. For instance, I knew that static spine was important, but I also learned how length was also important. I know that the balance point of an arrow is CRITICAL for tight groups in traditional archery, but of little or no value whatever for an archer shooting a compound bow. It took me a long time to fully appreciate the role that weight of the shaft plays on the dynamic spine of an arrow. But the information was out there in print, I just wasn’t paying attention. What I now understand is that arrow groups are a lot like a Chinese Puzzle Box. All the pieces have to be there, or you don’t have that perfectly tight fit. If one piece is missing, you have a collection of polished wood, BUT NO BOX.
It turns out that static spine is only one of 4 considerations in making arrows fly predictably. These 4 factors are what I call “The Arrow Maker’s Conundrum”. They are balance, length, static spine, and arrow weight.
? Balance
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 problem is straightforward.
In the example arrow above, the equation would be as follows:
? 20.875 - 16 = 4.875 inches (balance point minus the center of the arrow)
? 4.875 inches divided by 32 = 0.15234375 (this number divided by 100)
? 0.15234375 rounded down = 0.15
? 0.15 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 bamboo 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. Now keep in mind, that I consider a 13% balance point to be the lower limit of acceptability for my arrows. You may have another opinion.
? I did have two arrows in my mixed group, which had a 12.5% balance point. They were 100 grains apart in weight. However both were 34 pounds static spine and 32 inches long. Both arrows were unpredictable, but the heavier arrow with the light FOC was more so.
? Because I number each arrow, and keep data (as you will see in the data tables later in this article) I can begin to see patterns in the 4 arms of the Conundrum and learn. I invite you to consider doing the same. The results may surprise you.
? Another interesting point that this data revealed to me is how weight and balance point are intertwined closely. The data just below is worth looking into. Here is the important point to consider.
In this data table, arrows 0, 1, and 2 all have similar spines. They have exactly the same head weights. However, the total weights vary widely, with one arrow weighing 450 grains, while the one above it weights 60 grains more at 510 grains. Now ask yourself. Why does the lighter one have a greater balance point? Why isn’t the balance point of that arrow, arrow 1, not the same as arrow 2?
The reason is that with regard to weight and balance point; weight is not evenly distributed along all bamboo shafts the same way. Arrow number 2 may weigh closely to arrow number 1, but MORE of that weight is toward the FRONT OF THE SHAFT than the heavier arrow number 1.
Among other things, hopefully this demonstrates why grains per inch is not relevant to bamboo. They just don’t grow evenly like carbon does.
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.
? Length
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.
I can find no AMO (archery manufacturer’s organization) rule which places a standard on how to measure the length of a wooden arrow. I doubt I would follow it since that organization never used bamboo. However, they do have nice standardization for bows, bow strengths, string brace heights, and other information. The way I measure arrow length is a much older method that I suspect goes back several centuries, although I don’t know this for certain. If you have ever seen an advertisement where a company uses the acronym “AMO” in their advertising, this is what they are referring to. The website for AMO standards is https://www.outlab.it/doc/amostd.pdf. It is an excellent resource for many things other than bamboo arrows. I bring this up to make another point. Much as "grains per inch" has no relavence for bamboo arrows, neither does the term AMO have relavence.
AMO standards simply don't exist for bamboo arrows. When the grain runs lengthwise rather than crosswise on a shaft, the shaft itself is irregular in shape and weight isn't always evenly distributed ALONG the length of the shaft, bamboo arrows simply isn't a mass producable product. It takes craftsmanship, patience, and knowledge.
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 where the brass collar meets the point. There are several reasons for this) 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. Oddly enough, there may not be enough difference to notice. It just all depends on how good your form is. Have I made that point yet?
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, THEORETICALLY 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:
EXAMPLE 1
Static Spine
Shaft Weight
Shaft Length
Center of Length
Balance Point
FOC %
34
450
32
16
21
15.63
34
457
32
16
20
12.5
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?
EXAMPLE 2
Static Spine
Shaft Weight
Shaft Length
Center of Length
Balance Point
FOC %
34
450
32
16
21
15.63
34
457
31
15.5
20
14.52
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). So, shortening one arrow to match the FOC of the other arrows MAY 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 on the second arrow. 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 lighter, which typically will offset the strengthening 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 %
34
450
32
16
21
15.63
34
477
31
15.5
20.25
15.32
The first arrow will now have a 145 grain head, and the second arrow will have a 165 grain head.
By working through all 4 parts of the conundrum, I have two arrows which will theoretically group nice and tight…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 and head weights as necessary to be able to adjust the DYNAMIC SPINES of my bamboo arrows to “teacup” at 20 yards. It does work for me…. BUT, YOU MAY SEE ARROWS OF DIFFERING LENGTHS IN MY QUIVER. SOME MAY DIFFER BY AS MUCH AS 1 ? INCHES. I made the decision that if the performance is the goal for my arrows (rather than looks) then it would be inconsistent with that goal to worry about matching lengths.
My groups tend to look like this instead of the next photo below.
So, you can see that a “sweet spot” 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 put this another way. If shortening an arrow ? 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.
? Static 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 the arrow maker’s conundrum. With your permission, I’ll pass by this and move onto something probably more newsworthy.
? Arrow Weight
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 arrow shafts. Here is why.
If I make an extruded carbon tube which is homogenous in diameter and weight along its entire length, the weight will likely be evenly distributed along the entire length of the tube. But we have already seen in the photo at the beginning of this article that bamboo is ANYTHING but homogenous in width, OR WEIGHT DISTRIBUTION ALONG THE SHAFT. 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 strong of a 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! This would be inconsistent with my goal to sell the very best bamboo arrows to be found online. I know there are arrow makers who could do every bit as good of a job, but they simply can’t be found online.
These are nicely matched groups of shafts. But that isn’t enough! Do you want them to GROUP? Hopefully you know the answer by now. You have a conundrum to solve.
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 to replace the VICIOUS CYCLE of chasing your arrows around the face of the target trying to figure them out. When they become highly predictable, my arrows 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”.
Once again, I find that while writing this is not an easy task, it is nice to finally organize my thoughts. As always, I invite questions about bamboo arrows and shafts. I have been considering doing a Q & A section about my topics. If you have a specific question that you’d like me to give an opinion about, please send it to me at my website email: [email protected] My next article will be on several small topics, so if I can answer any questions, please feel free to send them.
You will find the data sheets for 13 of my arrows is attached just so you can see one way to approach the total problem of tracking weights, spines, balance FOC, and lengths in a set of arrows in order to find the “sweet spot” for you and your bow across an entire set of 12 high quality bamboo arrows This is a bit of research I did last year to find the relationship between shaft length, shaft weight, and teacup groups at 29 yards. This may help, or not. But I am a data nerd, and I love this kind of stuff!