Spining arrows
Thu 02 December 2010
The archers paradox best explained by this youtube video Picture speak a thousand words.. but anyhow the basic thing is this nock you arrow in your bow and depending how much of centre the bow is (how thick it is at the arrow rest) the more to the left or right your arrow is pointing. However the arrow if correctly spined for the bow will fly straight as if short form the centre, this is the paradox. When you draw the string of your bow and release it push’s from the back of the arrow causing it to bend inwards then it straightens out and bends the other way it continues vibrating until it stabilises. This effect causes the arrow to bend around the bow and shoots as though it comes from the centre line. If the spine of your arrow doest match your bow then some interesting effects can happen a stiff arrow could fly to one side instead of straightening up. I to low spine can shatter as it is being push beyond its bend radius. The standard way of measuring the deflection of arrows comes form the USA and is specifically designed for american flatbows. It uses a 2lb weight a scale and an arrow suspended 26” from each other. I built my own here very roughly The arrow is suspended between the 26inch gap and the arm is placed on to the arrow making sure you get the orientation correct you should nock across the grain so the strain from the string goes across the grain make sure the grain runs horizontal when you do this test ;) I created a very crude scale notice the use of duct tape my trade mark. the scale here is measured from the centre point using the piece of wood marked with .25” spaces between 0 and 1inch from the resting centre point of the pointer arm The centre point here being the x on the rawlplug. The scales used are the american standards for a 2lb weight between 26” and are used for american flat bows it is recommended that you spin arrows roughly the poundage of your bow at 28 inch draw. But for a longbow it is recorded that this be 2/3 of the total weight of your bow. I think the best way is to make up a few shafts of differing spine weights around the poundage of your bow and shot them with piles but no feathers. Check which ones shoot well and choose that as your spine rating for that particular bow..