Thought about set

[Badger]

  Any of us who have made a few bows know what set is. We also have seen where when we first unbrace a bow it may have say 1 1/2" but gradually over an hour so go back to maybe 1/2" or so. If you were able to look at bow limbs under super high speed photography you might see that a bow with 1 1/2" set has maybe 4" of set for maybe 1/10 of a second and maybe 3" for 1 second and by the time we get the string off maybe 1 1/2". I just made those numbers up but to me it doesn't sound unreasonable and when testing performance in some bows this is about how they might act in a typical situation just based on how they shoot. The heavier the arrow the slower the limbs retun so the less they suffer from this, very light arrows exagertate this same effect.

[DC]

Do you think that may be the last bit of hysteresis working itself out (for lack of a better way of saying it). I like to think of hysteresis like a shock absorber or the friction between leaves in a leaf spring. I think of permanent set as damage to the wood. It may be the tension forces and the compressive forces evening out.

[Badger]

  Not sure DC, I do know that very fresh wood has very little hystrisis, once it goes past a tipping point bending it starts increasing even with almost 0 visible set.

[scp]

Interesting idea. I read that the set that matters is the one immediately after the bow is unstrung. Now you are talking about the hidden set immediately after shooting an arrow but still stringed. I have no idea how to measure such a thing. Does the hysteresis of a bow change during shooting?

[Badger]

  Once a bow is broken in it seems to stay pretty much the same shot after shot on a dry bow. I was trying to figure out a way to identify hysterisis a few years ago because I wasn't satisified wit the test we were doing. Without going into a bunch of detail as I recall, I noticed a bigger differential in the virtual mass on a bows as arrows got lighter. All bows are more efficient with heavier arrows but the virtual mass will stay pretty consistent regardless of arrow weight unless histeris is present that can only be measured in micro seconds. ( spelling hystrisis wrong I think) I never could spell it.

  I had always thought in the past that the internal friction was happening throughout the stroke but now I am thnking it is mainly present just in the last few inches. Not sure how to prove this. I do know if you build a bow with no set it is almost non existent and the virtual mass stays a lot more consistent.

[DC]

Do we know what causes hysteresis (correct spelling-I checked )? Friction between cells?  Why do some have more, or do they?

[Badger]

     The testing I have done indicates that very little hysterisis exists when you first start bending the wood, the more you bend it the more it build up. I am pretty sure it just the stuff in the wood that holds everything together breaking down and when it breaks down it starts moving around durring the shot. Internal friction I think would be the best way to describe it.

[redhawk55]

Hey, my favourite topic!
I' ve read a lot of posts all around the internet focused on hysterisis in wood. It is definitely a destruction of the wood itself caused by strain, compression...........etc., even driving a nail into wood is causing hysterisis. Moisture content is forcing hysterisis.
Since about 15 years hysterisis is a main topic of the research, you'll find a lot of posts like this: http://web.byv.kth.se/bphys/reykjavik/pdf/art_032.pdf

That sounds very interesting.

Michael

[PatM]

One thing I never see addressed is if a broken in bow outperforms a bow only drawn up to the point where it does not break down.
 Shoot a bow at 23-24 inches and then shoot it beyond the breaking down point.
 I had a sinew backed bow that I pulled until it was mushy at 33 inches and it far outperformed it's shorter drawn fresh version.
 The performance at the shorter fresh draw length of course plunged but that is irrelevant to ultimate performance.

[redhawk55]

Interesting observation, PatM, even it means a broken down bow (ultimate performance).

The discussion above and some facts I' ve read about hysterisis made me think of modifying heat- treating.
What about heat- treating a roughly tillered bow step by step. At every step drawn  a bit more till about 2/3 of full draw and than(when the bow is still hot) fixing it with clamps into the shape you want( straight, reflex....etc.), for to squeeze out every moisture and any open space within the wood?

Michael

[Badger]

  Pat, thats not hard to believe. Most of the time we are talking about 28" or so. Can you imagine how fast it would have shot at 33" had it not taken any set?

  Redhawk, I have noticed and others here might confirm this that some bows seem to heal up a little from the intitial build if put aside and allowed to season for a while. Sometimes it is hard to tell if a bow just dried out a bit or if it actually healed itself. I am convinced that a little bit of healing takes place in the wood. Like a lot of other things I babble about I can't confim this. I have a stack of semi finished bows, tillered but not to exact weight. Around flight time each year I get into the stack and play with some of them looking for potential. It never fails that I find a good one amoung a stack of regulars. It tested regular when I set it down and now it is testing in the good bracket.

[PatM]

Steve, That's where saving it all for one shot would count. Test the bow at shorter draw length and get everything balanced and then try to make a perfect shot on that first long draw. Don't tiptoe up to it a lose something with each gradual extension.
 Certainly worth it if it means setting a record.

[mullet]

Steve;
Remember the bow I posted a few years ago Bamboo backed Ipe, highly reflexed/deflexed? It was 68#@ 28" I had never shot it but twice at 28" and it hit 194 and 193, through the Chrono and everyone called BS. I was using a Flight release, pulling back and releasing fast. Then the third shot I was going to pull it as far or break it and see what it would do and it was a 209.9.

 It never took more then a half inch of set. During tillering I never stressed it on the pulley or the tree, just long enough to get a good look at the tiller.

I gave it away during the bow trade and recommended  taking the noisy, FastFlight string off before it was used for Elk season. As far as I no it still lives.

[Badger]

  Eddie, I rememeber that bow, if they don't take any set and have reasonable demensions they will be fast. Pat, I often do that. Tiller ot to about 21" and use my best arrow for the first shot. I keep grabbing what I think is my best arrow, one day I will get it right.

[bradsmith2010]

ok I understand that part,, the bow may perform great on that first long draw,, but if the arrow is not matched then it may not translate to a new record