Sinew question

[DuBois]

"Dubois

He is not saying that 78%  of the work resides at a depth that is  20% of the way to the neutral axis.
He is saying that 78% of the work is done between a 20% depth and the surface the middle third of thickness is pretty close to doing nothing."

Thanks Willie, this makes sense to me now.

I agree with SB and Beadman on hands on experience over theory. I peek at theory and then jump in and make my own observations and mistakes. And these mistakes are a lot of fun even if they do hurt once in a while.

experience/experiment  I don't speak Latin or any of that fancy stuff but there must be a reason these are so similar in sound.

[DuBois]

I forgot Explossion

[willie]

LOL

News update: another OOPS

experiment results in explosion, and Dubois experiences an extra 30 days added to his banishment in the garage

[DuBois]

Hey, I'm kinda enjoying the garage

[BowEd]

I think research is a very good thing.Don't get me wrong,but a person can't be afraid of a bow breaking in this hobby.It's gonna happen.Seems even when a person gets to know a wood after making enough out of it a person tries to push the envelope at times and that takes planning etc. too.Does'nt have to be that way.It's just an individual thing I guess.

[joachimM]

Getting a bit off-topic, but still:

the relative strength of back and belly (including sinew backs) tremendously depends on relative humidity, and on how different woods react in tension and compression forces to such changes.
Note the below graph from the wood handbook:

A: tension strength of wood peaks at 12% MC, and decreases at lower MC and higher MC
C: Compression strength of wood increases with decreasing MC.
The 1/3 2/3 rule of thumb (rule of thumb, not the absolute truth) holds for regular 12% MC, no heat-treated bellies. Some woods are stronger in compression, there it will be closer to 40-60 at 12% MC, and it may shift to 50-50 at lower MC, and even 60-40 at very low MC.
That's why bows gain poundage at lower MC, and break at very low MC: the belly overpowers the back.
Most of the time, the back overpowers the belly, and we get set. A bow with set is still a bow. In reverse, a belly can only overpower the back once...

Sinew, however, will behave in tension like wood in compression: its MOE (stiffness) decreases with MC.

Sinewing a bow is like trapping the back, but in a safe way: you make the back surface weaker, hence the belly is working less. In a trapped back, the neutral plane moves towards the belly, relative to an untrapped back. It's safe because it's darn difficult to break sinew. If, however, the sinew layer is too thin, you'll still break the back when the wood fibers underneath the sinew are overstretched.

If you sinew an existing bow, the neutral plane will shift a bit towards the back. But not as much as it would for a same draw weight all-wood bow to which you would add a wood backing. The reason is that nowpart of the draw weight comes from overcoming the shrinkage of the sinew which put the belly under tension. This is similar in theory to a one-sided perry-reflex. (not that this clarified anything  )

If you really want to know how things work the way they do, walk the walk: perform predictions on how something's supposed to work, make bows (or test samples) to test these predictions (not one of each kind, but at least three), and see if the predictions worked out.

[bradsmith2010]

wow nice,, I am learning a little at a time as my old brain will obsorb,,its nice to know some of the whys,,thank guys,,

[Stick Bender]

I think reserch is great also ,one of my favorite things to do when I cant work in the shop but Im just saying when there is a contreversal subject I will take the boots on the ground advice over theory !

[BowEd]

To most osage is the best balanced type wood that is out there.Getting bored making the same thing over and over from the same wood stiffels my enthusiasm really so investigating and trying different type woods with different types qualities and designs helps to make a better bowyer far as I'm concerned.Usually other woods besides osage are a bit more touchy and not as forgiving.Sinew can make less forgiving woods up to the standards of osage I feel.Osage is such a forgiving type wood of mistakes but.....it will break yet if certain rules are not heeded.
Hope this is'nt off the track too much of the subject but it all makes a difference.

[willie]

To most osage is the best balanced type wood that is out there

and I suppose yew is right up there somewhere, too.

With these proven woods, are the exceptional qualities on account of the balance between tension and compression?

Or could it be a matter of the tension qualities being exceptional, or is it the compression qualities?

I guess if osage and yew perform well as a belly wood, with a variety of different stiffness backs, then the quality could be said to be in the compression side.

Don't see many folks trying yew sapwood or osage for backing different belly combos, like you do with sinew, but you never know until you try!

"boots on the ground"  experiments that break bows are certainly the best teacher, some of us just want to understand why, after the explosion or slug gets consigned to the kindling pile.

[DC]

Del has done at least one with a yew sapwood backing. I seem to remember it working well. I think "good wood" is a serendipity thing. There is every combination of features in the wood of the world. A few of them have to work out good for bows. Osage and yew just happen to top the list. I don't think it's just tension or compression, it's the combination that makes it work.

[PatM]

I think quite a few other woods are also balanced woods relative to their own strength. Or they can be readily balanced with heat.

[BowEd]

To most osage is the best balanced type wood that is out there

and I suppose yew is right up there somewhere, too.

With these proven woods, are the exceptional qualities on account of the balance between tension and compression?

Or could it be a matter of the tension qualities being exceptional, or is it the compression qualities?

I guess if osage and yew perform well as a belly wood, with a variety of different stiffness backs, then the quality could be said to be in the compression side.

Don't see many folks trying yew sapwood or osage for backing different belly combos, like you do with sinew, but you never know until you try!

"boots on the ground"  experiments that break bows are certainly the best teacher, some of us just want to understand why, after the explosion or slug gets consigned to the kindling pile.

Yes willie it's the balance of tension to compression in the wood itself on their own.Pat M's right too that balance can be played with on most tension strong whitewoods.

[BowEd]

I've personally never seen the need to heat treat a hickory that's going to be sinewed anyway though,but on their own without sinew yes.Many fellas can make a good hickory bow just by trapping the back too.Again balancing out those 2 forces of tension and compression.

[willie]

I guess it makes sense to see if one can make a stiffer belly by heat treating on a known tension strong wood, that can take the extra strain.

But what about applying sinew. Are there any basic rules of thumb about how thick it needs to be?

getting a good balance with juniper might be a lot different from getting a good balance with hickory.