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Hysterisis and performance

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DC:
If a particular species has more hysteresis than others wouldn't it have gained a reputation as sluggish by now, at least in the flight bow world?

PatM:

--- Quote from: Badger on October 22, 2014, 11:41:15 am ---     Pat, I have seen bows with amost no set be loaded with broken wood cells and bows with 2" of set feel fresh as a daisy. You can feel it by pushing backward on some bows. On a real badly broken down bow I suspect that the tension wood is just pulling it back into shape. Not all set is the same.

--- End quote ---
I know that but why do  people espouse a no-set tillering method if it doesn't give a reliable indication of what is going on within the stave?
 I know you measure weight but many people go by visual indications of set.

Badger:
     DC, in the flightbow world hickory, osage and yew are about all I see. Hickory excels in a dry climate. One of the reasons I came up with the posted formula was to help myself identify woods that had better flight potential. ost woods are a lot more similar than they are different if properly dried and seasoned. Cherry and black locust are two woods that should excel if designed properly. A lot of woods that tend to chrysal are also low in hysterisis.

     Pat, The no set tillering method is fairly reliable it tends to err on the side of caution. Some woods can take set and still be relatively low in hysterisis, other woods can take very little and the hysterisis will go through the roof. No set tillering will not seperate between these two if you don't apply a sense of feel to floor tillering along with it. I would say it is about 80% reliable though if I just took a stab at the odds.

Matthias Wiltschko:
Steve,
I dodged the hysterisis bullet for some years now but this topic is great fun.
Back when I was on the university studying wood and natural fiber technologies I ran some tests on 127 different yew heartwood samples to check out their quality for bowmaking. I used European mountain Yew and Pacific yew from Orting Washington.
I was searching for signs of the perfect bow wood and how to separate the good from the bad and the worst. I took X-Ray pictures, tested them for their mechanical properties and examined them under the microscope.

Hysterisis was the last thing on my mind but as I was reading this post of yours, the gears in my head started moving.

Some bow woods have a predetermined amount of hysterisis or better called inner friction due to their cellular structure; even zero set tillering can’t change it, but will reduce the amount of inner friction, for some time. The more you shoot the bow the higher the inner friction will become. For example Black Locust has great potential but will be worn out after some time.

Ash and Elm work great at temperatures below freezing and in very dry conditions but will also have higher inner friction due to their cellular structure and low compression strength.

Osage, Hickory and Yew have one thing in common, great cellular structure for saving and releasing energy, while having great compression strength.
What I learned from checking out all the different yew samples is that looks can be deceiving. Even the best looking yew samples with tight rings where not the best for making bows. Most of them showed more inner friction than anticipated.
The density of those samples, the ratio of early wood and late wood and even the color could have fooled any bowyer.
My goal was to clearly say which stave is good for making great flight bows and which staves are good for normal hunting bows. But in this point I clearly failed. Only one out of 50 different yew staves really had the potential of having an outstanding bow hidden inside. But only from the looks of it, there was no way I would have known.

As I was writing on the start of the post, some bow woods have predetermined inner friction but what I learned from the yew samples was that the differences between samples from the same species could be even greater than the interspecies differences.

At first I was really disappointed with my results. Before making the tests I already knew how good bow wood looks like and after the tests I was none the wiser. But now after some years I am really satisfied with the outcome of my studies. I wanted to find some kind of rule to go after when choosing wood for different tasks but found out that there are still some surprises Mother Nature has for us when making a bow.

Steve, you are trying to prove the influence of hysterisis and inner friction on the performance of wood bows which is in my eyes a very important task. If you have bows that are out of the ordinary, extra fast or for their design and wood quality too slow you want to know the reasons for their performance. Was it exceptional craftsmanship? The best bow wood? The particular design? In some cases the questions are still unanswered and this is where your hysterisis measuring method comes to use.

Badger:
   Mat, those were some great insights. I was particularly interested in you rcomments about yew and they agree with my personnal experience. I have some beautiful yew bows at home which came out nearly perfect but just don't perform at the level I would have suspected they would. In all honesty and not being humble I cannot attribute any exceptional results I may stumble on to now and then on my exceptional craftsmanship. I don't rate myself very high in craftsmanship. I try to stick to certain rules I have found that tend to give me better performance.

   I find a certain amount of hysterisis is ineveitable but it is much lower than we have previously thought and more avoidable. Strong evidence suggests it increases as the wood fatigues and this process starts much earlier in the bending process than I had previously expected. Testing hysterisis by bending the wood over a radius as opposed to just bending the wood with no protection will give a good insight in to how quickly it can start to set in. Decreasing the size of the radius we bend the wood over durring a test I feel is a good way to measure.

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