Understanding Static vs. Dynamic Spine2020-07-02T13:31:22-05:00

To begin with, let’s get some definitions straight.  I often hear these terms used interchangeably, and they are not.  It is not accurate to call a car and a truck the same thing, but it is accurate to call them both automobiles.  With this in mind, let’s define “spline“, “spine“, and “dynamic spine”.

THE KEY TAKEAWAY FROM THIS PAGE…

I expect to learn and improve as an archer.

DYNAMIC SPINE ALLOWS FOR A GREAT DEAL OF FLEXIBILITY.

It took me quite a few years to understand that slightly underspining a bamboo arrow to the bow it will be shot off of is a good thing.  If an arrow doesn’t shoot straight out of the middle of the bow, such as a high speed compound bow, then it will flex more than you might suspect.  Since the arrow needs to flex, if you stiffen the dynamic spine, it will not flex as much and therefore it must “fishtail” as it flies downrange.

In simple terms, the arrow simply has to compensate in some manner due.  It is important to help the arrow accomplish this as quickly as possible in flight and not try to remove this.  The back of the arrow lauches slightly faster than the front end of the arrow and “smushes” into the bow.  Very quickly the arrow will then begin to flex around the bow as it begins to fly.  It is best to allow an arrow do this, and even better to help it do this as soon as possible.  The sooner the arrow starts flexing in the middle, the sooner it will straighten out and line up the entire weight of the arrow directly behind the tip of the arrow.  In my opinion, if an arrow hasn’t accomplished this by 10 yards of flight (at the greatest distance) it obviously will still be flexing.  Should a wooden arrow hit a target and embed into that target while still flexing, you just might hear it snap into 2 pieces.

However, if the arrow is lined up completely, with the full weight of the arrow directly lined up behind the tip, then a high quality bamboo arrow is quite unlikely to break.  I have arrived at a rule that works well for me and seems to work well for my customers.  My goal is to make the arrows so that this flexing is gone somewhere between 8 and 10 yards downrange.  This is important for an archer who is shooting 10 – 20 yard distances.  For the competition archer who shoots much longer distances, this is not an issue.

What is SPLINE?

  1. a rectangular key fitting into grooves in the hub and shaft of a wheel, especially one formed integrally with the shaft which allows movement of the wheel on the shaft.
    • a corresponding groove in a hub along which the key may slide.
  2. a slat.
    • a flexible wood or rubber strip used especially in drawing large curves.

How to measure the Static Spine of an arrow

Just so you know…accurately measuring the STATIC SPINE of an arrow doesn’t mean that this is where the process ends.  It is quite normal to manipulare a 36 spined arrow to fly like a 32 spined arrow.  However, an accurate static spine measurement allows us to further adjust some of our arrows to group well if necessary.

Manipulating the DYNAMIC SPINE of an arrow, how it performs in flight, is a whole “nother” topic which will be covered in the advanced section, in the ARROW MAKER’S CONUNDRUM” SECTION”.

AND JUST SO WE CAN ALL AGREE…NONE OF THIS INFORMATION MEANS A THING IF YOUR FORM IS NOT GOOD.  GET TO THE RANGE AND PRACTICE!

It is very important to know that not all spine testers accurately measure static spines of bamboo arrows.  I haven’t tried them all, but Ace Archery makes a very nice spine tester which is generally accurate for bamboo arrows if you take some time and learn to use it properly.

Of course, if you buy your shafts from Khan’s Arrows, they will come to matched and marked for you to use.

It is important to ACCURATELY measure the static spine of your bamboo shafts, and find where they match one another within the set of 12 arrows.  By finding this place, and placing the nock properly to allow you to place the cock feather on this spot, you will find your arrows fly more predictably.  However, this is NOT the end of the task.

Later it will probably be necessary to adjust some of your arrows so that they FLY THE SAME.  This is the dynamic spine which we will delve into in the ADVANCED SECTION.  For example, once the static spines are found and matched, we may find that some of the arrows will need to be shortened slightly, or a heavier or lighter head may need to be placed a specific arrow to match the balance of each arrow within the set as well.

There are 4 major specifications which will need to harmonize on an arrow, AND WITH EVERY OTHER ARROW WITHIN THAT SET to get those “teacup” groups.  These are arrow static spine, arrow weight, arrow length, and the balance point of each arrow FOC (forward of center).  Of these 4 specifications, withoug doubt, matching static spines and arrow weight are the two most important issues to harmonize if you are a traditional archer shooting at distances of 40 yards or less.  It is unknown how this might change at distances beyond 40 yards, but it is reasonable to think it might!

As you can see, prior to launching, the arrow on a traditional bow is NOT heading straight toward the target.  When the bowstring is drawn, the arrow DOES move into a straighter alignment with the target, BUT the moment the arrow is launched this all goes away.

Because the back of the arrow is moving faster than the front of the arrow, the arrow will flex INTO the bow initially.

Then the arrow will quickly leap off the bow rest and begin to flex in the other direction UNLESS YOU MONKEY THIS PROCESS UP.  This process is critical to properly spined arrows which regard to how they fly (DYNAMIC SPINE).

As you can see from this very nice video from YouTube, the arrow flexes even from a center shot bow.  Now imagine how much more an arrow will flex when shot from a primitive style bow with no shelf, or a center cut bow with a small shelf.  The arrow is going to flex.  Don’t fight it, just help it to straighten out as soon as possible.

The photos below are from a customer named Bruce.  He had exactly this experience with other wooden arrows made from SPRUCE.  The target backstop he uses is designed for archery ranges that use long distances.  Because his SPRUCE arrows broke when shot at 15 yards, he wanted to examine high quality bamboo arrows.

On the other hand, when he moved this very dense backstop to a greater distance, the outcome was different with high quality bamboo arrows, although he did have one break on this very dense backstop.  Hopefully this information will guide you to make good buying decisions and more successful with bamboo arrows.  Bruce sent me this information at my request to help me set realistic expectations for high quality bamboo arrows.  I certainly do owe him a beer.  Thanks Bruce.