Saturday, 28 March 2015

A Shot In the Arm

I've been tinkering about with my lathe tuning it up a bit and making another point for one of my flight arrow. It had an antler tip and it's centre of gravity or  'point of balance' (POB) was aft of centre whereas it's generally reckoned that slightly front of centre is best.
This is slightly contentious as I believe some Turkish flight arrows were POB aft of centre and some claim it's possible to actually generate lift with a slightly nose up attitude. I can't really comment as I have neither the experience nor the aerodynamic credentials. However the antler tipped version didn't go as far as the others.

Anyhow, having made the new point I went off to the flood plain to try 'em.
As I walked across the field to recover my arrows I put up a Lapwing which made a startled call as it flew off low to the ground. I'd also taken a larger target for the laser range finder (an old steel shelf) which was much better.
I walked right up to one arrow, but couldn't seem to see the other... after much walking in circles and a bit of swearing I suddenly saw it ten paces past the first... no idea how I'd missed it!
The distances were 230 and 242 yards, a bit further than last time, possibly due to the slight tail wind rather head wind.
I walked back to try the arrows again, shooting them in reverse order. First arrow cleanly away, taking care to try for a good 45 degrees a full draw and a crisp loose.
Second arrow I tried to snatch the fingers back rather than letting them creep forward as I loosed.....
BANG! The point of the arrow had slipped onto the belly of the bow and the arrow exploded!
I've never done this before, but I have seen it happen a couple of times at roving shoots where people have been striving for extra distance.
the arrow can normally stand the huge acceleration of the string but simply can't take 40# of compressive force on it's rather long flexible shaft. It simply buckles and shatters, bruising one's arm (or worse. Hence the title of this post). The string flew off too, but the bow seems OK.

I'm still tinkering with flight arrows and made up this shaft reducing cutter, inspired by various YouTube clips I'd seen. You can see I tried it on a scrap of bamboo shaft.
It's made by drilling a 6mm hole in a piece of scrap steel opening one face slightly with a 'cone cutter', a tapered cutter (see pic), a corner is then sawn out to give a cutting edge.
I've since found it blunted rather quickly, needs to be hardened, or of a better design, plenty of stuff on YouTube. I've got a bamboo shaft nicely barrelled, but possibly too thin and weak spine. I'll have to test it (with suitable arm and eye protection!)

I'm using some bamboo shaft I have that are spined at 40-45# I've heard some say that bamboo is no good for flight arrows, but they offered no explanation. That's exactly the sort of advice I ignore.
The bamboo has some waggles at the nodes, but some work with a file and carefully spinning the shaft with one end in the electric drill while pressing the shaft onto the belt sander soon got it much straighter (I had a thick gardening glove on and the sander belt wasn't too aggressive).
The point of all this is to get the diameter down as wind resistance or drag is proportional to the frontal area (cross sectional area) so a 6mm shaft should be much better than an 8mm shaft as it's cross sectional area is only 0.56 that of the 8mm shaft. There are many other factors of course, but skinny with small fights is a good start point!


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