Sinew question

[bradsmith2010]

Wille thats a great question about the thickness,,,
most people will say,, well about so many layers,, but a layer can vary in thickness dramaticly,,
there is just not a very good rule of thumb that I know of,, hope someone can chime in,
I think I read somewhere,, not to exceed 25% or the thickness of the wood,, its really hard to judge,, cause when you put it on ,, it looks soooo thick, and then shrinks to almost nothing,,
I started weighing the dry sinew before I put it on ,, just so I have a general idea how much is going on there,,
I usually start about 1000 grains on a bow that is 55 ish,,
and you could easlily go more,, but then there is a point of diminish return where the sinew would be to heavy to increase your performance,, I dont know where that is, I plan on doing some bows with too much sinew just to see what happens,,

[BowEd]

Yes that could be true willie.I personally hav'nt worked juniper.Many do on here though.As for hickory alone 2 to 2.5 ounces on 1 and 3/8" wide parallel limbs to midlimb on a 48" long stretch including handle and fades reflexed to 6" will give you 4" most times of held reflex with good tillering and tapering.At least 1/8" thick dried cured sinew.A 1/16" thick layer of sinew does'nt do much but protect the back from breaking and will give too much in set for this design to hold all that much reflex.That's on a 60 to 64 inch bow.I don't sinew the tips last 8".It'll give you upwards of almost 20 pounds.So you can factor that into making a bow of 25 to 30 pounds[tiller it to brace and then to a 20" pull to get a good reading on how strong the bow is.Put your sinew on.Reverse brace it and let it cure a good 2 months and end up with finished bow of around 45 to 55 pounds.The hickory will more than likely take a slight set while pulling to 20" but that will be negated after the sinew cures.You can heat treat the belly before sinew too but then your poundage will go up from heat treatment on hickory a few pounds.Many ways to go but it makes a terrific bow.Think you could do it with hackberry too.These numbers can be adjusted too to suit your needs.

[PatM]

willie and gfugal, have you guys done a sinew backed bow yet?

[willie]

Thanks Ed
your approach seems to have a lot of merit,  if I understand you correctly. Enough sinew to prevent set,  (can I also assume that any more than whats needed to do that job, would be heading towards too much?)

Taking that for a guide, would one think that the amount of sinew needed to prevent set, (can that be the" balance point"?) would be less for a belly wood that was not as stiff and had a MOE closer to the stiffness of sinew?

[Stick Bender]

I have only made 2 sinew bows one a thin D type bow that I only used 750 grain which in hind site probably to little & the other was a wide maple bow & used around 1100 grains which seemed about right, on my current build which is a 57 in. bendy that is going to have about 5 in of reflex  I'm planing on using 1000 to 1100 grains  only because that seems to be the comon denominator  with the guys that keep track of there sinew weight & bows posted here , I find it interesting that the guys that have made a lot of sinew bows always state sinew used between 1000 to 1100 grains 2 ex samples in posts above.

[BowEd]

Set is still gonna happen but to a lesser degree with enough sinew.Look at it this way.Point being with sinew is you want to make it work more to it's abilitys.If you put more on reflex it more.Otherwise your carrying dead weight that is'nt working enough.If a person puts a strong 1/8" thick cured as a starting point to see some benefits from it it'll handle the reflex previously talked about.Putting more on goes in stride with more reflex.Make it work!!!

[gfugal]

willie and gfugal, have you guys done a sinew backed bow yet?

I've made two. The first picture is the very first bow I made. It's working limb juniper branch, thats 37 inches long or so. It wasn't a big branch so it had a high crown, so I was suprised that i got it as far as I did. It's at a 23 inch draw in this pictureI sinew backed with on layer and surprisingly it had little set. I wasn't satisfied with the draw weight though, so I put another layer of sinew on to increase it. It did make it stronger but unfortunately it altered the tiller and I didn't think to check before I brought back to full draw. It broke.

The second is a douglas fir that I put two layers of sinew on. I actually, put a bowstring sized cable on the back made from polyester, and seccured it down with thread and the second layer of sinew. You can see in the third picture if you look closely the outline of the cable underneath the sinew in the closest recurve. I got it pulling to 27 inches despite being 43 inches long. It has bad string angle though so it stacks, as well as quite a bit of set.

As you can see I've really been testing the limits on how far these bows can bend. Mainly because I didn't know any better at the time, secondly because I like short bows, and thirdly I have a long draw of about 31" so If I could get these shorter bows to draw that far then In the future hypothetically I should be able to get an average length bow as far as 31-or-32 inches. I didn't know as much about string angle then so I've learned that they need to be much longer, or have large siyahs. But I've also learned that sinew can really protect the back of a bow and allow the design to be much more stressful.

[PatM]

So just get going on a slightly longer bow with siyahs. I posted a picture of exactly what you are looking for.  You may be overanalyzing things now.

[BowEd]

Amazing over draw your getting.Looked like good tiller too.Sorry it broke for ya.Could of maybe helped for it to be a wider bow to help carry the load,but we work with what we got I guess.Ishi made some powerful sinewed juniper bows with a lot of reflex.
The tips flipped back help yes for smoother draw and less stack towards the end.Here's a pic of a current bow in progress curing.It will look a lot like your full draw picture when done.It's 58" long.Hickory/horn/and sinew so I expect it to hold a lot of the reflex as one's like it in the past I've done.A little more sinew and refllex I expect to put on this one yet.

[willie]

Ed

I don't know why people refer to a "balance point" when matching a backing with belly, perhaps it goes back to the Baker "see-saw" analogy. possibly implying something inherent in the back or belly properties need to be matched. I like the idea of....     it's not too much, if you are bending it enough   

Hmm...    sounds kind of condescending to my ears, Pat. Why do you think Greg is over-anylazing?  that's often said when work gets stalled, but I don't see any indication of that happening.

As for my self, Not yet.
Is that the answer you are looking for?

[Stick Bender]

Ed that looks like a supper model setting in that chair  Bow porn....lol nice pic I know I have over thinked stuff in the past but have under thought & paid the price too ,while where on this topic does any body have a preference for a certan sinew preferance elk,moose,horse,white tail etc ?

[BowEd]

StickBender....It's not got a string on it yet and can't be called  bow....lol.Personally I like the longer 6" to 16" long strands from my elk legs.Sometimes longer.Moose too.I use my shorter strands of deer leg to fill in a lot.It's all good really.Gotta try horse sometime.Heard it's pretty good.Backstraps' good too but I have a hard time during the presoak to get it soft enough but when a person does Pat M's method of wrapping and heating that usually softens it up pretty good for a nice smooth clean job.Like the length of backstrap though.
willie...The whole balancing thing of back to belly in forces is to get away from too much set and just plain good tillering and design.

[PatM]

 Not at all but it's the answer I expected.     I would say he's over-analyzing the theory without pursuing the basic execution. Those two bows were a while go.

[BowEd]

gfugal......On your other bow the polyester cable you put on underneath while probably in your mind gave you some sort of security or poundage hike actually I think took set and did not come back as sinew will.Best to leave synthetics out of the equation and just go with sinew alone.
Linen string backed bows will take set too just like wood.Any fibrous type back will but it can increase poundage and make them practically unbreakable.

[gfugal]

Not at all but it's the answer I expected.     I would say he's over-analyzing the theory without pursuing the basic execution. Those two bows were a while go.

I'm pretty new to bow building, but I did research a lot before I started. Sure I don't have as much experiance as others, but of the four i've built all have been backed with 2:4 ratio for sinew. That's more experience on this subject than most beginners, or even some veteran bowyers who've never backed a bow. It's not near the experience you have, but I don't think you need a lot of experience to theorize.

There's two ways to learn. The hard way through experience, and the fast way through research. Ideally you need both to really get going places. Research alone won't translate to a bow, you actually have to make them. On the other-side, making without researching is just wasting your time in my opinion. You can spend hours on hours making something, not to mention the materials, only to have it break and learn a lesson you might have found out with some research. I don't prefer that, to me it's almost like pounding your head into a rock. As long as your not halting your work to learn what harm is it doing?

Needless to say I'm not stalled. Since I finished my first bow I've immediately moved on to the next. Again I go to work and school full time. I was able to push out a bow in the month of December because of Christmas break. I don't have that time now. What I do have is down-time at work and I, fortunately, am allowed on here to research, so I might as well utilize that time. My execution will get better, but do you feel it was subpar in someway? Is there something I said that makes you think I don't know what I'm talking about? If so let me know and I can examine it, don't attack my experience.