Wednesday, March 24, 2010

Arrow Shaft Sorting

As we all know (or should know), arrow shafts should be sorted before they turn into arrows.
The more uniform is the ammunition, the more uniform we can expect it to behave on the range or in the field.

Given that we're starting with quality shafts in the first place, we need to group shafts by their spine.
Not spline! I get all twitchy when I hear or see spline. It's spine!
Spine is a measurement of the flexure of the arrow shaft. The arrow flexes as it leaves the bow and an improper amount of flex can give poor results in arrow flight and on the target.
For wood arrows spine is measured by supporting the shaft on 26" centers, hanging a 2lb weight from the center of the shaft, and measuring the deflection.
While shafts used to be ordered by the deflection, today wood shafts are typically grouped into 5lb groups such as #40/44, or #55/59. These numbers are derived by dividing 26 by the deflection. For instance, 26 divided by .500 deflection = 52, usually called a #52 shaft. This number will give us a rough indication of what bow weight it should be used with but there are a myriad other factors to take into account:
Draw length, arrow length, bow type and design, bowstring material, arrow point weight, etc.
Oh, yeah, the shaft also has to be properly oriented on the tester. You can't just throw them on the tool and expect to get consistent and meaningful results.
Choosing the proper wood arrow can get rather complicated and it's not something I'm going to get into here lest I be typing until 6:00am. When you get arrows your arrow maker should ask you a series of questions that will enable him or her to determine the best shaft spine for you and your bow. There's no shame in asking how the decision has been reached and you'll probably learn something interesting about this aspect of archery.

While the shafts I order from the manufacturer are shipped in spine groups I feel I get the best results by going through them on my own and measuring their spine. There are a number of great tools for doing this, both purchased and home made.
I use an Ace Spine Master and have been really happy with it. While its design is a little different, this tool gives the same results as the 26" centers I mentioned earlier. Rather than mount it to a wall as intended I mounted mine to a piece of plywood and then made removable legs so I could take it anywhere. It's very convenient.


Here is a really good slow motion video showing the arrow flexing as it leaves the bow. The video's maker has even put in footage of what happens when using a dangerously underspined arrow. It's well worth watching.

In addition to measuring spine and grouping the shafts accordingly, we want to group our shafts by physical weight.
While some archers may not feel this is important I feel that it is, even for new archers.
Wood is a natural material and as such it can have some pretty wide variation, even in the same tree. Shafts that are the same spine can have wildly varying weights. If we don't match our shafts for physical weight we can easily get into a situation where our arrows have quite a bit of weight difference from one another. That is not generally good for accuracy.
Arrow weights are expressed by grains; there are 7000 grains in a pound. There have been a number of good inexpensive grain scales introduced to the market in recent years but I use one I got back when I reloaded all my firearm ammunition: a Dillon D-Terminator (the design has changed a little over the years since I got mine). While not the cheapest scale out there (although it was the best when I purchased it, and still is the best), Dillon is a great company and really stands behind their products.
Most arrow makers or shaft sellers who sort their shafts for weight go for +/- 10 grains. This means there could be a 20 grain variance from your heaviest to lightest shafts in a dozen. Believe me, 20 grains isn't very much so this standard works pretty well.


Here's the results of a day's worth of measuring shafts on the spine tool and the scale.


Now all I have to do is sort them by weight.

I'm going to bed.

1 comment:

Lady Arwen of the Silver Rose said...

I think even archers that have been shooting a long time will learn something new from this post. I know I did.