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Alan Case's flight arrows - learning how to make them!

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mikekeswick:
Yes the 28 inch arrows are a bit long!
I am now working on making a siper and learning how to use it.
I'm looking forward to getting some better quality cane and making some dedicated shorties.
To get the weight down on these arrows I had to go silly thin on the walls...so much so that I don't have much confidence in the lightest arrows strength. Obviously going shorter will help but I was wondering if you had made any of these arrows with narrower (width) sections to give thicker walls but smaller overall diameter. I think I will try that on my next ones. Greater sectional density should help. My lightest arrow has plenty of 'space' inside!

avcase:
The stiffness of the arrow is primarily driven by the outer diameter. The stiffness of a solid section increases 8 times if the diameter is doubled, so just a small difference in diameter makes a large difference in stiffness.

Thicker walls for a hollow arrow doesn't make as large difference to stiffness, but it does add a lot of mass.

For example:
Arrow 1, solid Tonkin arrow shaft, 28" long and .25" outer diameter:
Mass = 412gr , spine = 38.8#

Arrow 2, 28" long, .25" outer diameter and .125" hollow inner diameter:
Mass = 309gr, spine = 36.4#

Arrow 3, 28" long .25" outer diameter and .177" hollow inner diameter:
Mass = 205gr, spine = 29.1#

Arrow 4, 28" long, .267" outer diameter and .186" hollow inner diameter:
Mass = 242gr, spine = 38.6#



Alan

joachimM:
Once you have the properties of the materials you're working with (a baseline diameter and spine is enough) you can calculate the expected spine of thicker or thinner arrows (with same wall thickness), at least in principle. I do this for bow thickness and draw weight, and it works pretty well for me.

You can use the excel sheet below (bow thickness tab, but should work as well for arrows).
With or without the hollow 0.125" diameter on a 0.25" thick arrow would only make a spine difference of c. 3.5#

mikekeswick:
Thanks for those numbers Alan. :) That has saved me quite some time testing. When you think about it it makes sense.
It might be a week or so before I can get started on my next 'batch' of arrows but i'm looking forward to getting some new ones made. I'll make some of those candycanes you mentioned before as well. I have some suitable pieces of purpleheart and hornbeam :)
In the mean time I think i'm going to cut a few inches off the front of the arrows I've already made, both to stiffen/lighten them and give me a bit more room to make better points. I have a friend who will turn me some brass points on his lathe.

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