Winter project - Yew Recurve bow

[PatM]

The thought in the past seemed to be that the shrinking sinew had the potential to separate the sapwood from the heartwood. Don't know how often that actually happened.
 While the backing Grodon is putting on will add protection it does have performance enhancing potential if the bow is drawn far enough to access it.

[Bryce]

Gordon i was thinking last night while reading a book on Asiatic bows. would i be correct in assuming your bow is similar to a composite bow?

(composite)    (Gordon)         (Reference to)
sinew  =  sinew     =    tension
-------     ------------      ----------------
wood  =  sapwood =  neutral plane
-------    ------------       --------------
Horn   = Yew heart = Compression

[DarkSoul]

Technically, Gordons bow IS a composite; it is composed of wood and sinew - two different materials.

The principles are the same, but the used material is not. The belly resists compression very well, while the back resists tension very well. But that's where the comparison ends. Horn is MUCH better in compression than yew heartwood. You really can't compare an Asian horn/sinew composite to a sinewed yew recurve, IMO. Both are good bows - just not comparable.

Gordon; excellent build along. Very clear way of describing the process, nice photo's and outstanding craftmanship. It's inspiring to see an experienced bowyer at work.

[toomanyknots]

nice photo's.

I gotta commend your photography skills too!

[Bryce]

i know that horn and yew cannot be comparable, as far a the amount of compression. as to they play a similar role in the construction.

[juniper junkie]

this bow that Gordon is building is way different than a horn composite bow. this bow would probably function fine without the sinew, but in this case the sinew is adding to the tension strength as well as adding some security. it will offset the amount of set that the heartwood take because of the increase in tension as the sinew cures. you can analize and disect it all you want, but this is really just about watching Gordon build a fantastic bow that will be a reliable and incredible work of art that we can all learn from. thank you Gordon again for this build a long.

[Bryce]

I agree. But for someone like me whos built only a certain type of bow for years without any other outside refferences other than the guy next door. Iam new to PA and am seeing bows I've never seen built so I'm gonna ask questions and learn. Last post on the subject.

[Keenan]

Bryce, The neutral plane is not a measureable substance in any way. It is simply the point at witch it goes from tension wood to compresion.  An imaginary line that is to thin to even compare to a hair!

[Bryce]

Si senior

[Gordon]

Dave is correct, this bow could certainly function without backing but the sinew should allow it to safely hold more reflex and thus store more energy. That said, sinew is heavier than wood so you will lose more energy when loosing an arrow. My hope is that I'll gain more than I lose and come out ahead. We'll see...

Good discussion!

[StanM]

Great project, Gordon.  Beautiful work as always, and the information in this thread is invaluable.  Much to be learned.  Thanks for taking the time to post.

[Bryce]

gordon dont be modest this thing is gonna be a missile shooter

[Jude]

Can't believe I missed this until today!  Great build-along Gordon; got me wanting to order up a yew stave now. 

From what I understand on sinew, considering a yew bow with a thin sapwood layer needs none, is that the sinew is even more stretchy than the sapwood, and so will take some of the compression off the belly and helping the bow to retain more reflex.  This point has already been mentioned in the thread.  Another point mentioned, is that sinew is heavier than wood.  Removing all the sapwood and filling the gap with extra courses of sinew would place some of the sinew well below the working plane, where it wouldn't be doing much work.  It would also raise the mass of the limbs, robbing them of performance.  I'm not sure what it might be, but there must be an optimum thickness for sinew on yew, that you could use regardless of the presence of sapwood.  If it is truly necessary to remove the sapwood due to delamination issues, it would make more sense to make up the thickness with more heartwood, rather than more sinew.  I honestly don't see much difference between two and a half courses or three courses.

[Gordon]

Even three courses of sinew is a pretty thin when cured (relative to sapwood) so I think it is probably all working. I don't honestly know if I opened myself up to delaminations issues by keeping a thin layer of sapwood. The curing sinew has definitely pulled the bow into a more reflexed shape and I don't see any evidence of a problem yet. I expect I will find out this weekend when I tiller it. Performance wise, there probably isn't much difference between 2 1/2 courses and 3. I did it this way because I wanted to create a bit more of a crown on the back which made smoothing the sinew surface somewhat easier.

[Gordon]

I’ve let the sinew backing cure for a couple of weeks and it is looking good.  So today I am going to tiller the bow. The bow feels a little heavy so I take about 20 even scraps off of each limb using a card scraper. It’s now ready to be braced for the first time.

For the first brace I like to keep the brace height fairly low. I don’t want to unnecessarily stress the limbs in case the tiller is off.  The lower limb is a bit strong, and one of the tips is slightly out of alignment – not bad for the first brace.



I fix the alignment problem by clamping the bow in my vice and gently heating the problem area while hanging some weights off of the tip.  You don’t want to get the limb too hot or you may end up with a delamination. I keep the heat gun on the lowest setting and sweep it evenly across the belly from a safe distance. This ensures that the core will heat gradually and settle into the desired position.  When I am done, I let the bow cool for about one hour before I string the bow again. I got lucky and the procedure worked as intended – the tips align perfectly.