Post For Tim Baker ( Sinew)

[loefflerchuck]

Hmmm? Cool idea to get the sinew working a little more. Seems to me a wider flat sinew back would work better than just a crown when the arrow is released. More working area.  One thing I have found with sinew tension in horn/sinew bows 50/50 ratio. After 6 months of seasoning the bow will have 13" of reflex or so from sinew curing. Using heat on the horn to reduce that reflex to 7" or so to make it more stable does not seem to change the early draw weight much. Like the sinew with the decreased reflex is just constantly already strained even with the bow unstrung. Horn is about the heaviest thing you can make a bow out of though so it will never be the fastest. Just need to find something like it that weighs a fraction of it. Use your same ratio 50/25/25. Back  "X"  with sinew until it cures to a large reflex and do the Perry reflex to attach it to the wood.

[Tim Baker]

BowEd:
When sinew is placed that far above the NP it's made to stretch several %, but flax can only stretch 1 %, so it would break before a reflexed bow was braced. It also doesn't spring back well when stretched so can't return much stored energy. Likely why they never used flax on Asiatic composites.

Marc:

" Just mound the sinew in a high crown down the center of the limb..."  That works to some extent, but since most of the mass of the sinew is then much lower than the top of the crown it's doing far less work yet adding considerable mass. The crown top is also a relatively small amount of sinew so can't store the needed energy for high draw weight increase. The geometry used here raised draw weight not by just the typical few % points but by several times. Less than half the mass increase bought four times the draw weight. -- Tim

[Tim Baker]

Mark: 

Thanks for the posting clue. 

DC: 

" ... I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly."

Yes, a little sinew spaced away from the belly would make it stretch more and store more energy per mass. That's the base idea here, just enlarged a bit: A little sinew can only store a little energy, raising draw weight just a little, so put a lot of sinew spaced away from the belly and store a lot of energy. The 2 ounces of elevated sinew in this test bow caused it to store 4 times the energy of the 5.5 ounce bow alone. 

Tim

[PatM]

Aren't you mostly just seeing the effect of increased thickness of the bow?  Twice as wide is twice as strong, twice as thick is 8 times as strong.

  What is the thickness measurement of the final stack of material?    We've all glued two pretty flimsy feeling pieces of Ipe and Bamboo together and had a railroad tie when the glue sets.

  I always use the sinew backed strip of  wood glued up separately in extreme reflex and then glue that down to my belly material now for  several reasons.   I think that's what Chuck was suggesting.

[BowEd]

BowEd:
When sinew is placed that far above the NP it's made to stretch several %, but flax can only stretch 1 %, so it would break before a reflexed bow was braced. It also doesn't spring back well when stretched so can't return much stored energy. Likely why they never used flax on Asiatic composites.


I see your point.I was concentrating too much about the mass weight factor I suppose.Never seen cotton used on the Asiatics either though and would think cotton has a breaking point too.Cotton has no spring back properties either I would think.
The difference of the distance of raised sinew on the back and difference of mass weight by replacement with cotton to all sinew would be interesting to see.2 bows the exact same length/width/and thickness made would reveal the difference.
One of the concerns too I would have is the core staying in robust good working shape to keep that high energy storage.

[PatM]

Cotton is more elastic than hemp of flax but I'm pretty sure its density is as high or even higher than theirs.   That would still make it heavier than wood when saturated with glue.

[Marc St Louis]

Cotton is more elastic than hemp of flax but I'm pretty sure its density is as high or even higher than theirs.   That would still make it heavier than wood when saturated with glue.

Maybe a strip of Balsa instead?

[PatM]

I think you'd still need a bit more "fiber" to the ridged portion.  Even typical core woods are about half the mass of cotton or other plant fibers.

  I would dabble with something like willow or alder before Balsa..

[DC]

Don, you are from yew country, is there something special about yew sapwood?

I don't have a lot of experience with other woods. Let's just say that it wouldn't surprise me if Yew sapwood stretched a bit more than average.

[George Tsoukalas]

How is this different from a cable bow with the sinew being twisted as the Eskimos did? Jawge

[willie]

interesting question George. considering that sinew is supposed to stretch much more than wood, you would think that the Eskimo bows would use some sort of fret or trestle to elevate the sinew cord off the back, yet many examples did not. I don't know much about the qualities of whale sinew, however

[sleek]

I like this udea and think a cooked bamboo belly with a cork core, make one of my short bows i like, tlsinewed, would be fun. Gonna start this weekend.

[gfugal]

Has anyone ever had sinew break in tension? How about without breaking the bow? I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly.

Sinew can stretch like 5% whereas wood can only stretch about 1%. If he had a bow that broke the sinew you would be getting some out of this world bends. It's possible that it breaks when the wood breaks underneath it because then that sinew is subject to all that force and stretches it beyond that 5%, but it's not because of the bend that it broke.

[gfugal]

How is this different from a cable bow with the sinew being twisted as the Eskimos did? Jawge

I was wondering the same thing. Tim, didn't you do a silk cable bow with raised nodes from bamboo?  Why not go that direction some more, or were you looking to also gain the protective layer that helps keep fibers down too?

[DC]

Do you think cork will stand the shear forces? I can see it ripping apart.