Science

[joachimM]

in yew, the juvenile wood has the best compression strength properties (have a look at this post I wrote earlier: http://paleoplanet69529.yuku.com/topic/61477/Mechanical-properties-of-European-Yew#.VU02YvntlBc), possibly because of its higher lignin content.

Heat treating the belly reduced the hygroscopic nature of the belly wood but not of the back. I posted a thread some time ago on the physical properties of heat-treated wood: http://www.primitivearcher.com/smf/index.php/topic,51962.msg703208.html#msg703208
Cheers
Joachim

[E. Jensen]

I guess I was a part of that second chat and didn't even recall!  Could you PM me a link to the paper in the first chat?  There is evidence that heat treatment increases compression strength independent of just lower MC, but its a small window. 

[E. Jensen]

I found one by Bjurhager, is that the one?

[joachimM]

Right, the Bjurhager paper deals with the properties of juvenile versus mature wood for bow-making (in yew and common juniper).
I made a temporary link to it here on my google drive, for those interested in the paper: https://drive.google.com/open?id=0B3YYA3Sr_3gqeVQ3Sk1yd21wc3M

cheers
Joachim

[E. Jensen]

It is asking permission to ask your drive.  I have requested the paper through my university anyhow.  If you come across any other similar readings, let me know.  Surprisingly, wood science people don't care as much about bows as you'd think, considering bow making is the working epitome of every aspect of wood science.

[joachimM]

OK, permissions for the google drive pdf changed, so it should be available to anyone now.

[willie]

E.Jensen or joachimM

hope the more knowledgeable might comment on a question that has been in the back of my mind for a while.

Most all the local hardwoods nearby are considered ring diffuse porus. I have found examples of different densities between staves I have collected, but as yet do not understand what causes these differences. What would you look for when searching for dense staves?

age?
protected vs exposed location?
elevation?
something else?

thanks
willie

[E. Jensen]

The rule of thumb for ring porous is the thicker the rings, the denser it is.  Think about it, earlywood is another way of saying lots of vessels.  Vessels are empty space, air.  The more empty space, the less dense.  The more rings, the more earlywood, the more empty space.  As someone else commented, there could be exceptions like white oak.  I wonder if that has something to do with tyloses, which is basically the clogging of those vessels in the heartwood.  Which is very important, and why whiskey barrels are made from white oak, and not red oak which does not have the clogged vessels.  Basically, all your beer would leak out!!!

[E. Jensen]

Paper is printed and I look forward to reading it.  It has already led me to a few others and I'm sure I'll find more in the references.

[willie]

E jensen

my bad, I meant to say diffuse porus

looking at easy to see rings makes early/latewood  judgements easier for sure

willie

[joachimM]

with the very limited experience I have, my feeling is that in diffuse-porous woods, slow growth gives denser wood, just like in softwoods. Hazel, for example, can grow very fast. When well-watered, well fed and with plenty of light it can give 3" staves in 3-4 years. Such a stave I got lately only had SG 0.36... I've had staves from below a canopy in the shade of an oak forest closer to 0.55. These 3" staves are sometimes 30-40 years old. These are the ones I'm after lately.

In ring-porous wood, there seem to be quite some exceptions to the rule of thumb that the thicker the rings, the denser the wood. I have had black locust with rings of 1.5 cm that was less dense than other trees with >5 rings per cm. In many oaks, you will find that the density of the older branch wood, which is typically very fine-ringed, is very high.

So really, what you should look for is density or specific gravity, how much the wood weighs (dry) for its volume.

[E. Jensen]

Beats me

[Springbuck]

  I can add this to what Joachin said, but can't vouch.

  I cut hazel from a landscaped yard once, two staves that grew in a row of others in the sun along a fence, and twio that grew from a round cluster along a fence.  The sunny ones were younger and less dense.  The shaded ones were older, more dense, and had only a few sparse leaves.  The staves were equally straight, but the shaded THICKET on average had straighter trunks and fewer knots, of course.

[PlanB]

  Something I would like to see done and would be fairly low tech and easy to establish would be a rating system designed specifically for bow woods.

     Example take a piece of wood that you might expect to come out mid range. Cut it 1/4"thick, 1' wide  and maybe 24" long. Cut into a pyramid shape. Clamp the wide end and then progressively bend it to correspond with a 1" incremental measure board that would accommodate the shape of the arc we are using. 1" back up, 2" back up. 3" return etc, measuring the weight each time, monitor at what point it first registered a weight loss due to set and continue until it has taken 1/4" set. The mark on the measure board would be the rating for elasticity.

    Each sample would be thickness ground not to match the test piece in thickness but to match it in weight at say the 6" mark. The thickness measure would express the stiffness. Some designs look more for stiffness and some more for elasticity. This would help to identify better woods for various designs.

Badger, this pair of Australian threads was pretty interesting reading re. testing bow woods and rating, though not quite the same as your suggestion

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=13765

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=5450

[Springbuck]

Lot of my Botany classes are coming back to me.....