Winter project - Yew Recurve bow

[Gordon]

Scott, I'm sorry but I do not understand your question.

[Bryce]

This might be a dumb question but. I was always taught that if your going to sinew back a yew bow to remove all the sapwood. And do 2-3 layers of sinew.... Why did you leave the sapwood on? So you didn't have to put more sinew?

[mikekeswick]

This might be a dumb question but. I was always taught that if your going to sinew back a yew bow to remove all the sapwood. And do 2-3 layers of sinew.... Why did you leave the sapwood on? So you didn't have to put more sinew?

The sapwood is doing nothing other than acting as a spacer in this bow. Sapwood has a lower sg than heartwood so the limbs will work out a little lighter. It's a neat 'trick'.
Gordon - I'm sure this buildalong will help a lot of folks.

[nativenoobowyer86]

There are no dumb questions Bryce, if i had asked the same question or if gordon would have posted a month earlier i wouldnt have removed the majority of the sapwood on my recurve......and whats worse, i decrowned the thing!  When i started the project, it really made sense to me that i should decrown it.  sapwood is strong in tension strength but i thought i had the sinew to do the tension work so the sapwood was not needed.  That what i wanted was the compression strong heartwood.  Buut now that i have worked the wood and recieved some helpful advice i see that the sapwood serves to push the sinew further from the neutral plane and the sapwood underneath the sinew is not doing much.  A crowned back works the same way, making the sinew at the tip of the crown work extra.  Yew is amazing and can handle nearly any and all compression tasks.  also im used to workin marginal bow woods where caution is needed at evry turn to succeed, so i left flat spots for knots and imperfections.  I noticed that gordon has a knot right on the belly edge of one of the limbs and pays little attention to it, i left a flat spot to reduce the local strain on the edge knot :S so the rest of the bending area is more strained than it should be, causing more set :S    *sigh* read and learn i suppose

Gordon - thanks so much for this build-a-long!  I am going to take what you have "taught" me and try a second attempt at one of these.  My first worked out and shoots very well but my understanding has changed and i want to compare the old to the new   also, if my understanding is still twisted please let me know haha

[Bryce]

Iam no stranger to yew. But why not just add more sinew to raise the nuetral plane? To where the wood does the compressing and tue sinew works out the tension?

[Onebowonder]

Iam no stranger to yew. But why not just add more sinew to raise the nuetral plane? To where the wood does the compressing and tue sinew works out the tension?

Just guessing here, ...but I'd think the answer would be something along the lines of, ...because the sapwood is already there, capable of doing the job, performs identically, costs nothing more in either effort or money, and saves both the effort and money that would be spent to remove the sap wood and add the additional sinew.

[Gordon]

First let me be clear to all who are following this thread - I am not an expert at sinew backed yew bows. In fact, this is my first sinew backed yew bow. Regarding the question of the sapwood - my research was inconclusive on this point. I do, however, have the benefit of having an example of a well known bowyer's work in my possession. The bow was broken when the owner over-drew it (the bow is 48" and was pulled to 30"). Because the bow is broken I've been able to deconstruct it to learn something of how it was made. On this bow the bowyer left a very thin layer of sapwood under what appear to be 2 courses of sinew. I let this inform my decision to leave the sapwood on.

I also want to clear up any confusion as to how many courses of sinew I applied to this bow. I applied 2 1/2 courses of sinew, but I applied all the courses on the same day. I saw no particular advantage in waiting for the sinew to cure between courses, and evaluating the result now, I still don't.

I don't believe the edge knot will cause me any problem based on prior experience with similar knots, but if it does start to act up, I am prepared to wrap it.

It remains to be seen if these decisions are wise and I expect I will have my answers soon as I begin the tillering process.

Thank you all for your comments and for following this thread.

[Bryce]

Iam no stranger to yew. But why not just add more sinew to raise the nuetral plane? To where the wood does the compressing and tue sinew works out the tension?

Just guessing here, ...but I'd think the answer would be something along the lines of, ...because the sapwood is already there, capable of doing the job, performs identically, costs nothing more in either effort or money, and saves both the effort and money that would be spent to remove the sap wood and add the additional sinew.

I disagree. Sinew and yew sapwood are not the same. Sinews shinks 4% and stretches 10X farther than wood storing more energy. As far as time and effort. That's what being a bowyers is all about. If you dont want to put out time and effort into your bows just go buy one or string up a pvc pipe or something idk. Sinew is beyond cheap and 90% of the time free whether you harvest it yourself or someone on PA will gladly throw some your way.

So let me rephrase. Is there any performance advantages to leaving the sapwood on and sinew over the back?
Compared to just heartwood and sinew. Because that's how I was told to do it......

All of the bows that I have seen that had sinew backing in local museums had no sapwood.
and I apologize if I came off jerkish that's not my intent.

Oh boy wheres Jim hamm when yah need him.

[Keenan]

Bryce,
 Often people take things as a dogma or  "The only way to do something". Not saying you are doing that, just saying sometimes we get in a mindset.  I have also read Jim's an many other great bowyers books as well as having allot of hours on yew. If fact More yew experience then any other type woods.  On some wood types the sapwood is worthless. I think there are some crossover thoughts to that as well, that may be a factor.  Yet on yew it simply is the opposite. Yew sapwood is one of the most versatile and forgiving sapwoods that there is in. The tension strength is fantastic and it will hold the sinew very well. Probably better then the heart wood.  I have not done side by side comparisons but that would be interesting.
  My thoughts are that with the yew sapwood being left on there is double protection. Sapwood + Sinew for tension strength instead of just the sinew for tension.

[Gordon]

Is there any performance advantages to leaving the sapwood on and sinew over the back?
Compared to just heartwood and sinew. Because that's how I was told to do it

Bryce,

I really have no idea as I do not have sufficient experience with such bows to weigh in on your question. Frankly, for my first effort I'll be delighted if I simply end up with a decent build-a-long and a shootable bow.

[Onebowonder]

Perhaps I am misunderstanding the whole question.  What does "the neutral plane" mean?  Isn't it largely like a core in a tri-lam?  Meaning it does much less or no work and therefore does not have to have the same high end material characteristics as the working portions of the limb.  That's how I had envisioned the question.  Hope that helps.  If not I guess I'll have to go back to a clothes line and a PVC pipe...  :embarassed:

[Prarie Bowyer]

I mean the radius of the flipped tip.

[Keenan]

Onebowonder,
                   The neutral plain of a bow is an imaginary line or better stated " A place" where the wood is not in compression or tension. It is not a measurable amount but rather a place where everything above (towards the back) is under tension and everything below (towards the belly of the bow) is under compression.  The mear shape or the limb can change where that point is. Example Imagine if the limb had the shape of a triangle, with the point being the top or back of the bow. The neutral point would be very close to the bottom because of greater surface area.  If inverted. with the flat as the back of the bow and the point at the bottom The neutral plain would sit much higher and sure overpower and crush the bottom.  If the limb profile is that of a rectangle the forces would be closer to the center and better distributed. Hope that makes sense.

Gordon. Sorry to clutter up this great buildalong. However it is great discussion for our learning.

[Bryce]

I know the reason why I do things. So am I correct when saying gordons sinew backing is more for protection? Very beautiful bow by the way Gordon. Like always

[Gordon]

Yes, protection - definitely.