Primitive Archer
Main Discussion Area => HowTo's and Build-a-longs => Topic started by: Skeaterbait on December 19, 2006, 04:19:07 pm
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What are the affects of thicker and thinner growth rings and which is more desirable?
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Lonnie,
I'm no expert but here's my take on it. I don't look at the ring thickness as much as I look at the ring density. Thin dense rings are very good where as thick rings that are not makes for flabby cast an more mass. That being said...a thicker ring is easier to work. I had some thin ringed Osage that was red in color and very dense. It was a pain to get a back on but made smokin' bows.
Hope this helps...
R
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I agree with Roger but I'll throw in a few more observations.
First, I often find that thinner growth rings often have a worse ratio of summer to spring growth, simply becuase the spring ring is going to be about the same thickness while the summer growth can vary considerably. Also, older trees tend to slow down in growth rate it seems. I generally find thinner rings on the outer parts of bigger diameter trees, and you can see more vigorous growth in the tree's younger years. Might be that it is simply using up some of the nutrients avaialbe in the soil. Maybe a tree has a set lifespan like humans. Who knows. And of course there are exceptions, and they are worth looking for for the following reason.
Second, when you make a bow belly you are tapering thickness, and whenever you get to s pring ring you are at a bit of a step in terms of strength. That bit of spring ring that is exposed on the surface of the belly, is weaker than the surrounding summer wood, however slightly. I think maybe the spring growth mashes down to the density of the surrounding wood, but that takes just a bit of set for this to happen. For this reason, several thin growth rings would lead to several smaller steps, and a more gradual transition along the belly. At least when the total spring/summer ratio is the same as a corresponding thicker ringed piece of wood.
One more observation. It seems that sometimes within a summer ring you will find somewhat more of a porous nature, more of the light colored dots that are the spring-type vessels. These hollow vessels are not as strong as the deep yellow wood. So in evaluating your wood, don't just limit yourself to measuring (by eyeball) the spring/summer ratio. Look more closely.
Thats all assuming you're standing in front of a pile of already-split staves, trying to select a few of the best. If you've cut a tree and split it, whatever you got is going to make a bow. No need to be super picky after you've done all that work.
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See this is why this site helps so much. Ive been trying to find thick ringed mullberry, and elm, because i thought that it made better bows.
the elm stave i chopped down the other day is somewhat in between. but the hickory i cut was pretty thin.
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I too look more for the early/latewood ratio than thickness, but all else considered, I'd rather have some good thick rings if they're dense and solid. I've never dealt with yew, but apparantly with it, the thinner and tighter the rings the better, opposite of what most of us look for in hardwoods. Bootboy, it's really hard to find hickory with thicker rings unless it is a small, young tree. Thin-ringed hickory still usually makes good bows. It's common to find mulberry with very thick rings, though.
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Two cents worth:
Large trees put on mass faster than small trees because they have larger systems to take in more nutrition. A 1/32" growth ring on a 4' diameter tree 200' tall represents much more actual mass than a 1/2 growth ring on a 4" tree that's 20' tall. Logging companies cut their trees while they are still young, not because they grow too slowly when they are mature, but because the interest on their investment maxes out at about 30-40 years.
Yew is often judged loosely on its ring count because tight ring count is sometimes a clue to its density. Soil nutrition, genetics, availability of sunlight, and a dozen other things contribute to a woods density. Yew (and other woods) can be dense at 10 rings per inch and light and flimsy at 150 rings per inch.
J. D. Duff
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Tom Thumb, you sure do alot of observing?:)
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So how do you tell the difference in summer and spring rings?
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On Osage the darker rings are the latewood which are transformed each year from the lighter spring growth in the sapwood...The thin yellow rings are the spongy earlywood rings.
(http://i6.photobucket.com/albums/y215/Sparky59/DSCF0016.jpg)
R
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Boy Roger, I would take a ratio like that any time. If you get wood with thin early rings like that you cant go wrong. With hardwoods like Osage and Mulberry I also look at the darkness of the late wood. If you see the real dark color like in Rogers sample it is good. Sometimes you will get some that looks bleached out, it usually sucks. That is the reason why nothing is better than experience. Even with my limited experience I can see the difference. I can only imagine what you guys that know what you are doing can see. Justin
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On this one you can see what Justin is talking about. The color seems a little washed out and not as dark...this is still good but not as good....Look at the second thick ring from the outside.
(http://i6.photobucket.com/albums/y215/Sparky59/Picture009.jpg)
R
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I am a visual person, the pics were great and really put all this info in to perspective. Thanks all.
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that's about as good as osage gets!!
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The osage ELB I won BOM last Feb has very thin rings(would be perfect yew) and the early/late ratio was about equil. This bow took a little set but nothing excessiuve and that could be the design ...or me. I have a few more staves with those same rings that I will try some differant designs with and see how they come out.
The first Pic Roger posted is ideal as far as I am concerned. It's hard to find sage like that around here.
There is also a consideration about ring defused and ring porous woods. I have a hard time explaining the differances but the early rings seen to blend in more with the late rings and the wood is more uniform through out in ring diffused wood(is that right), so woods like black walnut, cherry, have early and late woods blending together and woods like osage, mulberry, locust and ash have very differant early and late woods.
Do the same principals come into play with both types of wood, ie ring porous and ring defused ? Pat
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Yep I'm very observant. Doesn't seem to have got me anywhere though.
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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
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Thanks Tuukka. Good explaination. Pat
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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
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ttt
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Sure it did, Tom Sawyer. It got you here for which we are grateful. :) Jawge
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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?
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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
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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.
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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.