Primitive Archer
Main Discussion Area => Bows => Topic started by: youngbowyer on February 05, 2011, 09:04:36 pm
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Hi,
i recently got 5 yew limbs. i dont want to risk splitting and end up with propller twisted staves. i have a couple of options. bandsaw them in half or axe half of the wood away. for some of the smaller limbs this is the only option. Also, how well does yew respond to dry heat, i have several staves with deflex and using the dry heat is a heck of a lot easier than using steam. http://s415.photobucket.com/albums/pp235/tombowyer/yew/?albumview=slideshow
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Young, yew responds to dry heat very well if dried. Don't use dry heat on green wood or it will check. I would bandsaw as yew has a tendency to tear out chunks when green if using hand tools. Shape out the bow,debark as it will peel off easy when fresh cut, and wrap it very well in Saran wrap and that will control the drying., Store in cool place and wait. ::)
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Bandsaw or chop away the back half of smaller branches is fine. I tend to leave the bark on, paint the ends with pva and leave 'em for 6-12months, then de-bark, leav'em a bit longer, rough 'em out leave 'em a bit longer etc.
Yew takes steam or dry heat bending fine, I tend to use steam as I find it quicker and more controllable.
Del
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I'm not very familiar with working with yew or drying it but shouldn't Youngbowyer consider the difference in tension and compression wood, especially with limb wood before cutting out his stave?
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Pat is right and good point. You want to use the top of the limb. If you look at the end, the center of the heart wood will be closer to one edge. That is the top of the limb. This is a pic of the Juniper limb that I used on the December BOM. You can see that the top of the limb is about at 2:00 if looking at a clock. Good input Pat.
(http://i30.photobucket.com/albums/c326/bornagainprimitve/IMG_0067.jpg)
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so the compression wood should be chopped away? if you look at the pictures of my yew the center is offset as well.
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Yes, In the fourth pic the top would be at 10:00 Be very carefull chopping, yew can tear out a huge splinter very easy.
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i had no problem with splinters, took me about 10 minutes to chop away with my fiskars hatchet, it's a real nice axe
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can the core of the wood be in the final bow?
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I had to respectfully disagree with a fellow on paleo planet about yew having tension and compression wood, he posted info he got of a encyclopedia webpage or something saying that conifers dont have tension wood and that its all compression wood in conifers? what are your thoughts on this?, im not sure I agree with that especialy in limbs. The best way I have found to dry and season yew is to cut it in half with a bandsaw or chainsaw and peel the bark off and seal the back. This is how John Strunk showed me after I discovered that most limbs have good proppeler twist in the grain. The picture here shows if I hadnt marked the tension wood on these it would have been harder to tell where it was by looking at the end cut lol. o and the big log is old growth fir ;D
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Would someone mind explaining the benefits and weakness of the difference between tension wood and compression wood? Danny
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Danny, I'd like to hear a response to this too. My assumption is that since the back of a bow is the tension side and the belly is the compression side you need to make your stave in line with the tension and compression side of the limb.
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The theory is that a horizontally growing branch has it's top side in constant tension due to the weight of the branch hanging down and thus it will make a good bow as the upper sapwood surface has been used to tension all it's life.
Conversely the sapwood on the underside of the limb has been in compression all it's life due to the weight of the branch and theoretically might not be so good in tension.
I tend to just look at the growth rings myself as I've found hugely assymetric rings in vertically growing limbs as well as horizontally. Add in the fact that the underside of a branch is far more likely to be clear of small branches and hence knots, and your choice isn't so straight forward anymore!
So I take the view of listen to all the advice, then do what you want and re-appraise the results afterwards. :)
If your findings agree with the received wisdom them take it on board, but if your results are good then go your own sweet way.
With natural materials it's difficult to make hard and fast rules. Maybe the underside of a branch of 'good' Yew could be better than the top side of a poor piece.
It's like all the 'armchair experts' I've hear telling me "You can't make a longbow from English Yew"... I've had some beautiful English Yew, I've also had some not so good, but it's all made shootable bows.
So that's cleared that up ;)
Del
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Very good explanation Del, I would agree. ;) Not all wood is the same and you need to "read" the wood. My very first self bow was Poplar, if someone had told me it was the worst possible wood and wouldn't work then I might not have succeeded. ::)
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is there like a sort of neutral wood in compression branches? like wood that is neither compression nor tension wood, maybe the wood that is off too the side with medium sized growth rings? ill try to illustrate what i mean in a picture later.
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(http://i415.photobucket.com/albums/pp235/tombowyer/DSCN2876-1.jpg)
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Young, Intresting thoughts, Here is my take on the situation.
Just like in a bow there is no "real" neutral line, but rather an imaginary line at witch point the wood is not under tension but is being compressed. That Invisible hair line neutral zone can change depending on shape and structure of the back of the bow or even the shape of the sides. For example if a bow were to be shaped like a triangle for "Exaggeration purpose" and the wide part was the bottom and the point at the top. Then the neutral plane would sit lower and near the bottom and the most extreme tension on the very top point. We know that if bent it would certainly break from tension failure because of the extreme small defined area for tension strength. And if we invert the situation and made the wide part of the triangle the back of the bow, then the belly would surely crush from being over powered by the wide tension surface. Yes these are extremes for example. Now if we consider that tree branches very in uniform structure as well and also in the angle toward the gravitational pull. That "Neutral zone" would also fluctuate slightly. So certainly there is going to be some natural tension strengths built in as well as compression strengths in other areas.
All those factors are fairly mute because the real challenge that I see, is that on one side your rings are likely to be tighter and denser and on the other side of the stave, they will be more open and less dense. This will likely cause the stave to warp when drying and have a weaker side. If it's a smaller stave like what you show in the pic. If much larger you could certainly get a stave from the side that is more uniform in density. as you look at your pic you can see that the bottom if fairly consistant as well as the Tension side of the limb. but the sides show a slight difference. Would it be noticeable? Maybe not as tight as those rings are..
Dose your head hurt as much as mine now? ::)