Marc St Louis
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Marc St Louis
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January 22nd, 2006, 12:35 pm #21

I would list the best to worst of those species I have tried as such. Elm, HHB, BL, Osage, White Ash, Red OakMarc
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ragiwarmbear
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January 22nd, 2006, 4:30 pm #22

ya know marc if you list ash and red oak as worst and they are so hugely improved by my tempering efforts I wonder what elm of HHB would be like. I really dont have access to any of the others but would love too.Ragi warmbear

(if it is tourist season why cant we hunt them)

www.brokenaxe.ca
Live long, Drop dead.
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Simo Hankaniemi
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January 23rd, 2006, 8:55 am #23

I had in the winter of 1975-76 a juniper self bow, which I kept in the woods, often without any protecting cover, just pushed into snow. When I happened to roam the area I took this bow, built a fire and warmed the bow (belly side against the fire) before bracing. The bow was usually quite frozen so I had to give it much heat. This bow did not follow the string as much as similar bows usually do after use. I have often wondered why this bow remained quite straight, without being able to find any theory. Only some time ago I got the idea that perhaps my primitive "heat treating" of the bow belly had something to do with this.
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OzPrimitive
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January 23rd, 2006, 11:48 am #24

Thanks Simo, this was a very interesting post. It is quite possible that people of the past used the same technique to dry and strengthen their bows.
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Woodsman
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January 23rd, 2006, 7:11 pm #25

Hello,

About how hot do you have to get the belly to heattreat it?

Do you have to get it to that "thermoplastic" state described above?

thanks
Brian
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Marc St Louis
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January 24th, 2006, 1:06 am #26

Brian
I was doing a bow a couple years ago and I thought I would put my candy thermometer on the wood as I was heating it. The temp climbed to about 400 degrees F.Marc
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badger5149
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January 24th, 2006, 5:17 am #27

Ragi, maybe I need to get my red oak a little hotter deeper, I have never had much luck with red oak as I have other white woods, I guess if the oak is working in compression deeper this might explain why my method didnt work here. Or for that matter it might be doing most of the stretching in tension and in this case wouldnt have much effect either I guess, so confusing!! Steve
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bowman79
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January 24th, 2006, 5:24 am #28

This is a very interesting thread going on here. I saw some people have had success using this method on ash, elm, and hhb. I have a sugar maple bow in progress that is coming in a little light. I was wondering has anybody tried tempering sugar maple? Also was wondering would it work on beech, black birch, and black locust? When is the best time to temper? Thanks in advance.
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badger5149
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January 24th, 2006, 5:51 am #29

I would really like to see how it works on the locust, it will likely raise the weight on yiour maple bow, if I were going to treat a locust bow I would go slowly and heat it deeply. Steve
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Richard Saffold
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January 24th, 2006, 6:38 am #30

My first try at tempering the guava bow I'm working on sure stiffened it up..
GoodlandArchery.com
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OzPrimitive
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January 24th, 2006, 11:09 am #31

Just thinking, how is it that kiln drying at elevated temperatures can weaken the wood and yet heat treating at even higher temperature strengthens it? Anyone with explanation?
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Marc St Louis
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January 24th, 2006, 11:58 am #32

Black Locust tempers very well. It is an odd wood that bends like butter with dry heat and seems to take less heating time for the wood to react to the heat, much like Osage. I haven't found a best time to temper, I usually do it any time of the day . I heat treat the wood after floor tillering

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Could be because kiln drying is done when the wood is still wet. Heat treating has to be done when the wood is dry. My guess anywayMarc
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OzPrimitive
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January 24th, 2006, 12:48 pm #33

Thanks Marc, has to be this.
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Fundin
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January 24th, 2006, 3:27 pm #34

Simo, this is perhaps not totally the same thing, It might be so that the Juniper had a higf MC, but as you heated the belly the moist went to the back of the bow, making MC uneven. This would lead to a juniper that is both strong in tension (as juniper is with high MC, 12% beeing optimum) and in compression as compressionstrength risas as MC goes down...

A really neat trick, I have been thinking about the possibility of having different MC in belly and back, and you have a possible sollution, that is so neat.
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Tim Baker
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January 24th, 2006, 11:57 pm #35

Fundin: That's an interesting line of thought. Linen is stronger in tension when wet, so maybe many other cellulose materials are also. Possibly it would be good to wet the backs of selfbows before shooting in low RH conditins. That would be a worthwhile test to do. Tim
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Fundin
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January 25th, 2006, 9:18 am #36

Wood is strongest in tension at something like 9-12%, but its strongest in compression at 0%, I have tried to achieve this by wetting the back, but that doesnt make a difference since the hummidity doesnt penetrate if its dry, think that the bow MC is 9%, you heat the belly and the moisture moves away (thats how its described) this would lead to a very dry belly and an intact back. Easy to try with a bow with a little high mc that is heat treated without inducing a reflex and then shot emmediately, perhaps something for the flight shooters, crank up a bow 15# keeping the weight of the limbs, its not a equlibrium state, but that doesnt matter if you just use it in one competition like badger.
I Guess I will have to try and heat treat a bow and see the immediate effects if it holds together.
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Tim Baker
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January 25th, 2006, 9:56 am #37

Fundin: Speaking of tension strength alone, I can't find figures for varying strength at varying MC. Any idea if such exists? After some thought, it shouldn't necessarily follow that wood would be stronger when wet as is true for linen. Linen is essentially pure cellulose fibers. Wood has lignin and other ingredients affecting strength. It would be interesting to know the numbers though. Tim
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Marc St Louis
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January 25th, 2006, 11:47 am #38

Fundin
Sounds good on paper but it just doesn't work. First of all the surface wood on the back gets pretty dry from the belly wood being tempered. Secon what really happens is the moisture gets driven sideways following the cells and natural pores in the wood. If you try to heat treat wet wood you get an accumulation of water in front of the moving heat and the resulting pressure splits the woodMarc
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Fundin
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January 25th, 2006, 12:10 pm #39

Tim, I think it was sumptian who mentioned it. That was in a discussion about different woods different optimal MC (hickory-Juniper for example)

Mark, yes, when you say it I should have anticipated this, after all i have studied plant and tree physiology...

However, Is it possible to achieve different MC in back and belly? Putting wet cloth on the back of an extremely dry bow for some time for example. would that make the bow as strong as it would be completely dry without failing in tesion from beeing brittle? This would make the bow stronger per unit of weight, and therefoer faster and more efficient.
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sumpitan
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January 25th, 2006, 2:04 pm #40

Tim % Fundin,

The effect of wood's MC on it's various strength properties is published in a very thorough book about wood science by a Finnish professor (in Finnish only). Wood's tension strength is at it's greatest at between 6-12%MC, but stiffness and compression strength hit their peak at 0% (actually, the author states that "most strength properties are at their greatest in 0%MC"). I translate this to mean that as wood gets drier and drier, even extremely so, a bow's draw weight and resistance to compression increase (and mass decreases, all good stuff), but the tension strength is "left behind" and fails, leading to a broken bow.

There's a ton of other interesting stuff I haven't found anywhere else in the aforementioned book, like the effect of continous freezing/thawing on wood's strength (not good), or how wood's basic S.G. (not just green S.G.) inside a living tree varies surprisingly much with the seasons, due to various substances in the green parts being sucked into /out of the wood.

Tuukka
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