Author Topic: ??? on growth rings  (Read 14216 times)

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Offline sumpitan

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Re: ??? on growth rings
« Reply #15 on: December 20, 2006, 12:08:51 pm »
A whole bunch of scientific studies have been conducted on the effects of growth rate on wood strength. Some solid rules of thumb have emerged (most of these center around commercially important species, which excludes most classic bow woods).  On ring porous woods (ash, elm and oak among common woods, plus osage, mulberry, black locust, laburnum etc.), ring thickness largely correlates with density. In other words, wood grown fast is denser and stronger than wood grown slowly. The early wood layer of a ring porous wood's yearly growth is weak mush: slow-grown ring porous wood has lots of this and little else, since the strong latewood part of the rings is thin. Very quickly grown wood, with very wide rings may be less dense (and even looks like that) than somewhat more slowly grown wood - there probably are species-specific optimal ring widths. And a high S.G. wood can of course objectively be dense and strong even when thin-ringed (lilac is the densest and strongest wood here, ring-porous, and always grows slowly).

In conifers, the situation is reversed: slow growth and thin rings equal dense, strong wood. Countless studies on dozens of conifer species confirm this. The thinner the rings, the more dense, strong latewood in comparison to earlywood a piece of coniferous wood contains. But ring-count is not the sole answer, since, as others have pointed out, the density increase is not a constant but subject to differences in genetics, growth conditions etc. In yew, for instance, a relatively coarse-ringed specimen from one location may have equal density to another from somewhere else with a higher ring count. And two pieces with equal ring count can have measurably different density, each following their own genetically(?) determined range. But I'd sure like to see J.D.'s  150rings/inch yew that's light and flimsy (unless disease or decay are at play)! Take 1000 yew samples of various growth rates and measure their density: a definite trend emerges. The few exceptions don't change the trend.

In diffuse-porous woods (maple, beech, birch etc.) ring thickness does not correlate with density: they can be dense with either wide or thin rings. Many trees that seem diffuse-porous are in fact semi-diffuse porous; walnut, cherries, rowans and many other trees in the Rose family, for instance. In these the difference between early and late wood is not as pronounced as with ring porous woods, but is still there if one looks closely. Specimens with little porous early growth and thick, dense late growth are dense and strong.

The thing is, trees are too complex beings to fit into simple equations. But the basic rules of strength-growth correlation still apply most of the time, and are a good starting point for evaluating most bowstaves.

Tuukka
« Last Edit: December 20, 2006, 12:13:20 pm by sumpitan »

Offline Pat B

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Re: ??? on growth rings
« Reply #16 on: December 20, 2006, 01:08:34 pm »
Thanks Tuukka. Good explaination.   Pat
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

duffontap

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Re: ??? on growth rings
« Reply #17 on: December 21, 2006, 04:37:08 pm »
Hey Tuukka,

I agree with you for the most part.  When I'm cutting Yew, there is no question that I gravitate toward the tightest rings I can get.  But, I don't throw coarse Yew out like they may have when it was more disposable.  One of the best treatments of Yew wood was done years ago in TBM in an interview with Gerald Welch.  I suppose everyone has read it.  He lists some of the traditional criteria for selecting good, dense, high-performance Yew, and then clearly states that there are very surprising exceptions. 

The thing I was trying to communicate was that there are too many exceptions to prove a hard-and-fast criteria for choosing Yew staves.  John Strunk, who has cut more Cascade-grown Yew than most people recently told me that he doesn't even judge by growth rings anymore, and Pip Bickerstaffe, who has made war bows out of Yew sourced all over the world wrote me recently and told me that he prefers Yew that is wide-ringed and dense.  You may remember that Ascham wrote in Toxophilius that the tighter-ringed Yew was more brittle (granted--he wasn't a bowyer) and Ford wrote in Theory and Practice that the tighter-ringed wood was 'probably' a little better.  So even in England in the past 500 years there was less tight-ringed dogma than there is now.

As far as other conifers go, I have quite a bit of experience cutting, milling and making arrows from old-growth doug fir and there is a definite trend that develops there.  I and others I have talked to in the area agree that higher-spined arrows come from mildly-courser grain.  If I want low spines, I reach for the tightest grain I've got.  That way I can get spines down to 25#.  If I'm pushing for 100#, I'll reach for course, 10-ring-per-inch bolts.  So this raises another point:  Good bow wood is not just dense.  Good Yew needs to be elastic, have high bend strength, etc.  And while those qualities often haunt tight-ringed, dense samples, they are by no means guaranteed. 

Of course I don't have a sample of 'flimsy' 150-per-inch Yew.  I just said it could be flimsy at 150 rings to make a point.  Strunk and others have told me of staves with outstanding ring counts and appearances that yielded floppy bows.  I have a yew bow in my collection that has a course billet joined to a fine-grained billet and the course billet is better by far. 

All that being said, I agree that your proposed 1,000 samples test would produce results in the favor of very tight-ringed Yew, but I would add that those who have access to course-ringed yew would be pleasantly surprised at the many, many exceptions.

                  J. D. Duff

Offline DanaM

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Re: ??? on growth rings
« Reply #18 on: December 18, 2007, 12:25:16 pm »
ttt
"Prosperity is a way of living and thinking, and not just money or things. Poverty is a way of living and thinking, and not just a lack of money or things."

Manistique, MI

Offline George Tsoukalas

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Re: ??? on growth rings
« Reply #19 on: December 18, 2007, 12:35:24 pm »
Sure it did, Tom Sawyer. It got you here for which we are grateful. :) Jawge
Set Happens!
If you ain't breakin' you ain't makin!

Offline robbsbass

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Re: ??? on growth rings
« Reply #20 on: March 18, 2008, 11:32:09 pm »
Ok I don't want to aooear to be to stupid but alot of you know by now that I have a few injurys, so here is my question. If I understand right the sap wood is on the outside and that is the lighter coloured wood, and that is the wood that you do not want to use, Is that correct?
live each day the best you can

wvfknapper

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Re: ??? on growth rings
« Reply #21 on: March 19, 2008, 04:37:24 am »
Here is some good reading on the subject http://en.wikipedia.org/wiki/Wood

I cut some ash and the rings are very tight, almost like yew and you cant hardly tell the difference between early and late wood.

wvflintknapper

Offline DanaM

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Re: ??? on growth rings
« Reply #22 on: March 19, 2008, 06:08:56 am »
Ok I don't want to aooear to be to stupid but alot of you know by now that I have a few injurys, so here is my question. If I understand right the sap wood is on the outside and that is the lighter coloured wood, and that is the wood that you do not want to use, Is that correct?

robb for osage, black locust and some others you typically remove the sapwood, the outer lighter colored wood.
For white woods ash, hickory, maple, elm etc you peel the bark off and thats the back of the bow.
"Prosperity is a way of living and thinking, and not just money or things. Poverty is a way of living and thinking, and not just a lack of money or things."

Manistique, MI

Offline robbsbass

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Re: ??? on growth rings
« Reply #23 on: April 16, 2008, 07:49:22 pm »
Just wanted to thank you guys for all your help , it is sure appreciated by this guy. The bow is coming slowly ,I only hope that I can do a good job on it.
live each day the best you can