Arrow Spine Rating
The spine of an arrow is an indication of its stiffness and is calculated by measuring the amount of deflection, bending, that occurs when a 2 lb weight is hung from its centre of the shaft whilst it is being supported at two points 26" apart. This deflection can be turned into an approximate draw weight of the bow it is suitable for. In general spine meters, used to measure spine, are configured in 5lb increments and hence when you buy you shafts they will generally be rates 50-55lb, 55-60lb, 60-65lb, etc.
Bow Weight and Arrow Spine
As a rule of thumb these draw weights are a good measure if you are shooting a bow that draws through the handle; by this I mean something similar to a recurve of a flatbow. If on the other hand you are shooting an English Longbow, or a bow that shoots around the handle, you will need to choose an arrow shaft that is spined less than your bow. Their seem to be a number of rules of thumb on how you determine the correct spine for your bow but the only correct way to do this is to make and try out a number of arrows; then once you are happy put your best arrow on a spine tester and record its spine.
Personally I tend to spine my arrows at about 10lb less than my bows draw weight, then using my 65lb bow but often have to drop lower than this when making arrows for my 90lb warbow (it's can be difficult getting heavy spined shafts). Needless to say if I can stick to my rule of thumb I will and it works for me.
Archers Paradox
As a Longbow Archer, or an archer who shoots around the handle, you will be affected by the Archers Paradox. If you consider the nocked arrow resting in the drawn position (I do need a picture for this) it does not define a straight line from the string through the handle to the target instead it is pointing off to the left (I am assuming a Right handed archer here). As you release the Arrow it flick off the fingers (assuming the traditional three finger loose) and will push the front of the arrow against the side of the bow. This causes the arrow to bend in towards the centre line until it reaches its maximum bend As the arrow travels forward the string begins to move back to the centre line whilst the arrow, based on its resonance frequency bends the other way. As the string continues forward the natural movement and flexibility of the shaft will cause it to move back. This continues for a short period after the arrow has left the bow until it finally straightens itself.Incorrectly Spined Shafts
Shafts that are to stiff, overspined, will fly left whilst a shaft that is to flexible, whippy, will tend to leave the bow and fly right. This assumes a Right handed archer for left handed archers the directions are reversed.Fletching - Size Really Does Matters
The size of fletching you choose will have an effect on the cast and accuracy of your shooting and in general, if you plan to shoot varying styles, you will need a number of arrows. Personally I have three sets of arrows with 3", 4" and 5.5" fletching although I am currently in the process of making some with 7" fletchings for indoor (but that will be covered in another blog entry). As mentioned previous I shoot a 90lb warbow for outdoor target archery and a 65lb longbow for indoor and field archery. Therefore this should be taken into account for the fletching sizing below and if you shoot a lighter bow you may need slightly smaller fletching.
In general though the larger the fletching the more accurate you arrow whilst the smaller the fletching the less drag you have and hence the further it will fly. The size of the fletching will also play a part in how quickly the arrow straightens after leaving the bow.
Again in many ways the exact fletching size you require can only be identified by trial and error (but making arrows is fun) and as such what you see below should be taken as a starting point.
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