Have you ever considered making your own arrows? Having considered that, you probably looked into how to do it and came across such arcane terms as front of center (foc) or Matched shafts? Well we are here today to explain such as this to you. Believe it or not your ability to get better as an archer depends on such arcanery as this.
We who use wooden arrows are faced with a number of technical handicaps, wood is not consistent and therefore each and every shaft is different. Weight varies, spine varies, this you can do little to fix but strive to combine arrows that all rest with in certain set standards for accuracy. By minimizing variance in these and other factors such as foc and having properly matched arrows we can minimize the mechanical side of our handicaps and move on to the mental and physical ones that impede our dream of being a ludicrous Bowman.
I suppose I should start out by defining "foc" and "Matched set" hunh?
Basically as you release the arrow, the force of the bow is transmitted into the arrow as forward motion or Kinetic energy which changes to potential energy when arrow and string come apart. This "energy" for the lack of a more descriptive word, is assumed ( for the sake of theoretical physicists) to be contained in the front end of the arrow and infact the arrow is sort of pulled along behind the point.
Of course this is assuming that the balance point is infact in front of the center point of the arrow by about 10-15 % for heavy or hunting arrows and closer to 10% for light weight arrows . More than this and the arrow is nose heavy and becomes unstable quickly as the fletching cannot stabilize the flight and any breeze will throw the tail about. Less than this and the arrow becomes tail heavy and as it slows down will start to stall and destabilize just like a plane will if it slides backwards.
You may hear some folks talk about the foc being at the 2/5ths. They mean that the foc should be 2/5ths of the total length behind the point. This works out to about 10% so either way they are right and you have nothing to worry about.
To Calculate foc you simply follow some simple steps.
As I said before, wood is variable and not consistent, this forces us to adopt standards of precision that are, well they are "close enough". Most fletching suppliers will provide arrow shafts in 5 lb spine groups, where all the arrows will be spined at between say 45-50 lbs. For most newbies, this is a sufficiently precise group that beginners will not see much of a difference if we spined them any closer.
The reason the suppliers do that is so that they can get more use of their stock, if they had to separate them into +/- 1 lb or half a pound or whatever then there would be 13- 49 lb arrows and 7- 46's and 23- 44's and so on. you can see the problem with that from a suppliers side can't you?
However for a skilled archer that will not be enough, as spine weight varies, the location of the arrow on the target will vary left and right. For my own arrows I spine then to within +/- 1/2 lb. My 47 lb arrows all sit within 46 1/2 and 47 1/2 for accuracy.
The other thing is to match them for weight, +\- 10 grains from the supplier is normal. This gives a 20 grain range. Trying to go for closer weight is possible and maybe even worth it as you get better but again for most newbies it won't make much difference.
If you want to get it to a more exact measure, there are 2 steps to getting there. Firstly you need your otherwise untouched shafts, tapered as cleanly as possible, a good grain scale and a sharp taper tool.
Once your raw shafts have been brought down to the same low weight mark, you need to:
Ok, now that you have your shafts all measured and you are happy in how they match, you need to test them to make sure they all fly the same. This is the pesky bit I hate to tell people who cheaped out and only bought a dozen shafts. You have to make up a bunch of arrows and shoot them to see where they each go.
I seldom make arrows in groups of less than 24 and I do not recommend you do less if you would be accounted a good archer.
Have them hand you each arrow in order and then record high, low, dead on or wild for each shot, the actual score matters not.
At this point you should have a pretty good idea of where your arrows hit in relation to one another so now go see what you can do on the range.
Back To The DIY Page
|© 1999 Renny-James Bachner. All rights reserved. suggestions and submissions|