Sinewed Ocean Spray

[willie]

If DC doesn't mind the side discussion, I will try to offer an explanation. One source of confusion in these kind of discussions is the different ways folks often use the same word to mean different things.

The term strain is usually understood in science as a linear measurement. For  example, if a rubber band 12" long is stretched to 13",  by hanging a weight on it, then the strain is said to be....      1 inch per foot.

I hope  Onebow does not mind me reforming his statement to what I think he meant.

then both the backing AND the belly are going to be subjected to 65 pounds of strain force, the back in tension and the belly in compression

 With a given force, how much the sinew or wood stretches on the back of the bow depends on its "stiffness",and how much it can stretch before it breaks, is its elasticity.

Sinew of course is not as stiff as wood so it wants to stretch more than a wood back, and does so without breaking, because it can. The tension and compression forces on the back and belly are still equal.

[bradsmith2010]

 

[PatM]

You have to account for the properties of the wood as well. Sinew is essentially all equal. Wood is not.

[Marc St Louis]

By adding an elastic backing to the bow then the belly will not endure as much compression force.  Essentially what is happening is the neutral plane has shifted towards the belly of the limbs making for more stretch on the back and less compressing of the belly

[Badger]

  Think about it like this, the belly is under about the same amount of strain as it would be under if the bow weight was measured without the sinew. By adding the sinew you up the draw weight without really adding much strain to the belly because the sinew is stretching.

[DC]

One thing that confuses me is that you can bend a sinewed bow so much farther. Do you think that a selfbow would bend that far if the back would hold out?
  Another thought is that for a sinewed and unsinewed bow of the same weight the wood on the sinewed one will likely be thinner so it will bend farther.

[Onebowonder]

OK - Sorry it took so long, ...but I think I am seeing my way through this little puzzle a bit.  It helped me to realize that the Compression vs. Tension ratio was still balanced and how that could be explained by the elasticity of the sinew.  Basically, the sinew on the back of the bow is not starting at zero.  Rather, it is starting from a negative value for it's compression force of 5 - 15 pounds of draw weight due to it's elastic properties.  Before the compression force on the belly is loaded up at all, the tension side has already contributed a few pounds of draw weight.  I realize that is mental rambling, but I can kinda make sense of it as long as I don't stare at it too long!

Thanx for all of the help...

OneBow

[bjrogg]

I've read that bow building will drive accountants crazy.

That's funny Ed. I'm not a accountant but I do like to understand how things work.
 
I'm wondering, because of its elasticity is the sinew " opposing compression force" being transferred to the original back of the bow instead of the belly? I could understand how this might work. The original back would have less tension force therefore the belly would have less compression force.

I also was thinking like DC in that with all that extra bend, if all the compression force was transferred to the belly like a plain selfbow it would seem to add more stress on belly
Bjrogg

[bushboy]

That thing is awesome dc!

[BowEd]

It was a tough build DC on account of the wood and it's shape.Not many options were left for corrections with heat to get the bow in line besides cold hand twisting and the string to correct and settle it in the way I see it.
They are'nt a lying when they say it takes twice the time to make these type bows compared to self bows,but everyone ought to try it at least once and determine if it's worth it.It can get easier but seems there is always just a slight bit of alignment that needs to be done.Sometimes not.
The farther back the recurve & reflex in the limbs the more finicky it gets.That's why grabbing an almost perfect piece of wood or making it almost perfect before recurves are put on it for these type bows makes the least trouble.
Kuddos for sticking it out DC.You took the rough road on this one for success.Glad it shoots so well for ya.

[DC]

Thanks Ed   Here's a bit of what I went through. I had to bend it a bit to get the string in line. I didn't want to heat the limbs any more than I had so I heated the handle. I wrapped it with tin foil and opened up the belly side of the foil. I clamped the foil to the sides of the handle and folded it out to keep the heat from going around the back. I opened the drawer and put a hair dryer in there blowing cold air on the back to try to keep it cool. Then I aimed the heat gun at the handle. It worked. I got enough bend. What, me worry Rube Goldberg's got nuthin' on me

[BowEd]

I see.Thanks for posting.Glad it worked.
Having some character on them makes them even more special.

[Onebowonder]

Extra points for creativity of tool usage DC!   - OneBow