Using Info From "The Wood Database"

[huisme]

These number dont make me question why Osage is considered the best all you have to do is make a bow from Osage and you'll know it's the best no matter what numbers on the internet say

That's debatable though; while I love my few Osage bows and enjoyed making or receiving them I still haven't used one that tops locust for performance. Might be design, I make mollegabets more often than not, and it might have just been luck on the locust's part to perform so well, or bad luck on osage's part, but locust is still my favorite wood.

Doesn't mean I'm not buying another piece of gold when I get back to Washington, of course

I don't think it wise to disregard quantified observation on such matters. Better testing on properly cured Osage and yew sapwood would make everything better-- whether the numbers show Osage is magic or not. It might not be important to bowyery to prove that a magnificent wood like Osage is or isn't the best, but discouraging thought and the gathering of information is dangerous to any community.

In the mean time, has anyone tried greenheart?

[Joec123able]

These number dont make me question why Osage is considered the best all you have to do is make a bow from Osage and you'll know it's the best no matter what numbers on the internet say

That's debatable though; while I love my few Osage bows and enjoyed making or receiving them I still haven't used one that tops locust for performance. Might be design, I make mollegabets more often than not, and it might have just been luck on the locust's part to perform so well, or bad luck on osage's part, but locust is still my favorite wood.

Doesn't mean I'm not buying another piece of gold when I get back to Washington, of course

I don't think it wise to disregard quantified observation on such matters. Better testing on properly cured Osage and yew sapwood would make everything better-- whether the numbers show Osage is magic or not. It might not be important to bowyery to prove that a magnificent wood like Osage is or isn't the best, but discouraging thought and the gathering of information is dangerous to any community.

In the mean time, has anyone tried greenheart?

I guess it is debatable but personally I've never worked a wood as good. It hardly takes strongfollow even after horrible stress put on it. it's snappy, beautiful after thousands of shot my Osage bows show NO signs of wear or weakinging so that's why I personally consider it the best. But you are right it's an opinionated thing

[Badger]

   I have never had any luck with using wood data base tables. Possibly because I don't know what I am looking for. That being said, black locust and a number of other woods that tend to chrysal are also very fast woods. Testing different wood for hystrisis it seeemed to show a pattern that woods that chrysal are also low in hystrisis. Which tend to give them good speed.

[huisme]

Well since I agree that seems to be the case my next question is why. Like, exactly why. Not necessarily to make me a better bowyer, I'm already good with my locust, but because I want to know.

And I really do wonder about greenheart. That stuff sounds like it'd make a real zinger.

[Aussie Yeoman]

The short answer to the OP is: you can use the numbers, as long as you know what to look for, and know how to use them. Failing that, just try woods, or ask around.

DavidV,

The Modulus of Rupture is not the tension strength. It is the bending force required to cause the wood cells to rupture. Some woods will collapse on the belly before the back breaks. A wood that chrysals badly before the back comes apart has ruptured.

One reason many of the published numbers on woods are less than useful is because the tests the wood scientists conduct measure figures at failure, and not a sub-maximal loads such as we (almost always) make our bows to.

I've done a whole bunch of bend testing. Quite like Tim Baker's bend test but with more formulae that generate MoE/MoR/bend stress/strain etc. A few years ago I made a generalised statement that a bow made from a wood with 60% of the MoR as the bending stress would be close to correct. I sort of stand by that still, but there're heaps of exceptions. As a matter of fact, Elmer came to a similar conclusion early last century.

The reason Osage and Yew make such spectacular bows is not their stiffness or their MoR, but the amount of strain those woods can take before taking set. Osage and Yew can often withstand about 1% strain before taking an unreasonable amount of set. Some woods I've tested (and made wuite good bows from) tested as only being able to withstand 0.78% strain before taking set.

By the by, strain is the percentage of elongation or compression at the surface of a bent beam.

Why is this ability to withstand strain good? If a wood can withstand more strain, it can be made thicker without taking excessive set. And/or can be bent further for the same sized limb. This makes for a more efficient use of wood, and is quite independent of the stiffness, and is also quite independent from MoR and crushing strength. It's fascinating that two different species might have exactly the same MoR and crushing strength, but have wildly different allowable strain values.

Now, some people rightly point out that all these numbers aren't important for making bows. To a very large extent they're correct. But working with the wood's numbers is something I enjoy quite a bit, and I've written a bit about it here:
http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=13765

DavidV, it might be that bit that you find yourself disagreeing with.

Dave

[KS51]

Dave,

I'm of the understanding that wood has actually 6 poison ratios and I am curious if your research for the allowable strain rate takes this into account.  I ask, because I've become convinced that the diference in allowable strain on the compression side and tension side can be partially compensated by trapping the cross-section and shifting the centroid towards the surface.

Ken

[Aussie Yeoman]

Well, a peculiarity of wood (or rather, different wood species) is that their relative tension/compression strengths are not uniform.

Some woods like some samples of Spotted Gum will crack on the back before the belly frets or takes excessive set. A wood like this would benefit from having a narrower belly. A wood like Hickory or Elm will take horrendous set before the back fails, and so these woods would certainly benefit from having a narrower back.

It's difficult to quantify this trait as a number. It's more of an experience/observation thing.

I've never heard of the '6 poison ratios' of wood. Can you elaborate on it/them?

[KS51]

The wood engineering handbook indicates that wood will strain different amounts based upon the stress orientation to the wood.  They use a cylindrical coordinate system to describe this, so you have parallel, radial, and tangential. You also have either a tension or compression force acting in these directions.  Thus you get 6 different poisson's ratios and subsequently 6 MOE's due to the relationship of MOE and the poisson ratio.

2 of these poisson ratios don't appear to be of much effect to bow builders. (Parallel to grain) .  The other 4 would appear to be potentially important, with 2 being critical for selfbow evaluation ("flat-sawn" equivalent) and the other 2 being possibly important for laminated bows with wood in a "quarter-sawn" condition.

Ken

[PatM]

Well since I agree that seems to be the case my next question is why. Like, exactly why. Not necessarily to make me a better bowyer, I'm already good with my locust, but because I want to know.

And I really do wonder about greenheart. That stuff sounds like it'd make a real zinger.

 Chris Boyton makes his record setting laminated bows with a Greenheart belly. It is great stuff by all accounts.

[bow101]

You have to consider the moisture and relative humidity in the area you are as these will affect the performance.
I a dry climate where I live I would warn against backings for laminate bows that are not hickory. Beware of maple and ash.
Cores are easier to match up and I favor maple and jatoba for those.
In dry climates hickory is king but not in wet climates.
SG should be .5 or greater on all woods used for bow making.

Beware of maple and ash...?   Can you be more specific