Author Topic: Mechanical Properties of Woods for Arrows  (Read 2861 times)

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Offline pnwarcher

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Mechanical Properties of Woods for Arrows
« on: December 13, 2017, 01:02:19 pm »
Hi PA Community!
I compiled some data on wood properties for making bows and arrows and started a thread over in the bows section. See original thread here if interested:
http://www.primitivearcher.com/smf/index.php/topic,61920.0.html

While I looked at more data for bow-specific properties, I thought I'd share here what I explored for arrow woods. See attached PDF for the data, with notes explaining the properties. Of course, the big caveat with all this is the wide variation possible within a given species -- so take the raw numbers with a grain of salt.
I have limited experience making flight arrows, but it seems the best materials for the job are those that are stiff (high modulus of elasticity) and also low density. I've been thinking about something I'm calling the "ballistic index" of a wood, which is a measure of how light and how stiff the wood is (relative to POC as a reference). Lower density, higher stiffness woods get a better score. Low density is good because it helps decrease overall arrow weight, increasing potential cast. High stiffness is good because it lets you achieve the required spine with a skinnier, more aerodynamic shaft. The tricky bit is in the efficiency of the specific bow and arrow combination, which depends on a lot of variables, and might dictate stiffness or mass or both being the limiting factor in performance.

Not surprisingly, many of the mainstream shafting woods (POC, sitka spruce, doug fir, ramin, bamboo) are good performers. Purpleheart and ipe are good if you want something very stiff and widely available. One standout candidate I haven't tried is greenheart. A 1/4" greenheart shaft should spine similar to a 5/16" POC. Anyone made a greenheart arrow?

Unfortunately there's not a lot of data available for non-commercial arrow woods, such as viburnum, hazel, ocean spray, and river cane. Maybe I'll get around to making some measurements one of these days.

Offline jeffp51

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Re: Mechanical Properties of Woods for Arrows
« Reply #1 on: December 13, 2017, 02:23:47 pm »
add red osier dogwood to your list of testing materials when you do it.

Offline DC

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Re: Mechanical Properties of Woods for Arrows
« Reply #2 on: December 13, 2017, 02:26:05 pm »
Thank you for this. I've been trying to make light arrows for the last week or so and was wishing that there was a chart like this. I've made a 35# bow to help correct my form and wanted to keep to 10gpp so I need 350 grain arrows. The bow seems to need around 45# static spine even with 50 grain tips. I had to sort though all my bamboo shafts to find 5 that would work. So in hindsight I was already using the wood that is at the top of the list.

Offline willie

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Re: Mechanical Properties of Woods for Arrows
« Reply #3 on: December 13, 2017, 03:53:58 pm »
Stephen
Thanks for posting. What makes for a good arrow wood is not as simple as it appears at first glance. I also have been testing some of the relative properties of different wood for use with arrows, and appreciate the new perspectives.

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Offline DC

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Re: Mechanical Properties of Woods for Arrows
« Reply #4 on: December 13, 2017, 05:00:02 pm »
I was looking at a bunch of arrow making sites and one of them mentioned arrows chrysaling. I have never heard of this before. Apparently the chrysals happen just behind the tip because he repaired them by footing the arrows. Has anyone heard of this. How low does your spine have to be so that the arrow bends far enough to chrysal? Or have I got this all wrong?