Extreme Reflex sinew backed Juniper Bow

[pierce_schmeichel]

Hey Guys I am trying out an extreme reflexed sinew backed juniper bow. I want to test out the full capabilities of juniper and sinew. I want to see how strong juniper can be in compression and make the limbs as light as possible for faster arrow speeds. I used a greenwood juniper stave that I got from a dense branch to get that substantial reflex into it. I will be sinew backing it either tonight or tomorrow night and then its just going to be a waiting game. This is mostly just an experiment. I do not know if it will crysal under extreme amounts of compression like this. I know the sinew isn't going to give on me and if anything does give it will be the juniper.


Also that stick that I had tied to one of the limbs was because I had a hinge there and I didn't want it to end up snaping on me as I put it into backset. I didn't want to remove material from the rest of the bow just quite yet because I wanted to wait until it fully dried out. Since it wasn't dry yet i didn't really know how it was going to warp and harden in different areas.

[Bob Barnes]

Very cool...I hope it works out for you and will be watching your posts.  I have never had much luck with juniper heartwood on the belly.  It is beautiful, but the sapwood seems to be much stronger in compression for me.  Thanks!   

[Pat B]

That should be fun to brace. 

[superdav95]

Wow.  That’s a lot of reflex.   Should be a cool experiment for sure.  I’ll be watching this one. 

[willie]

I want to see how strong juniper can be in compression..... I used a greenwood juniper stave that I got from a dense branch to get that substantial reflex into it. ........This is mostly just an experiment. I do not know if it will crysal under extreme amounts of compression like this.........  Since it wasn't dry yet i didn't really know how it was going to warp and harden in different areas.

interesting experiment!

juniper is actually poor in compression compared to most bow woods. in a sinew backed design tho, its strong enough to put much of the bending stress into the sinew back. 

if you force the juniper to dry in extreme reflex, wouldnt this cause more stress on the juniper when drawn?

sinew and juniper seem to "balance" each other well, although you have hit on a way to tip the balance some.

branchwood can be diffucult to work with.  Did the stave come from the top or bottom or side of the branch?

[pierce_schmeichel]

It came from the top of the branch. Also I found on a site that the compression strength of juniper is about 6340psi and comparatively osages compression strength is 9380psi

But where juniper has an advantage is in its specific gravity which is about .44 and osages is about .75
That's a pretty significant difference. Now I don't know if the loss in specific gravity compensates enough in speed or not though, but I have seen and made some sinew backed juniper bows that are proportionally more efficient than that of osage.

[willie]

from topside  seems traditional if I remember correctly an old study.  the bottom side has the "compressionwood" which can cause the drying problems, and as far as I can tell with other conifir bow woods, offers no performance advantage except durability.

good luck!

[pierce_schmeichel]

As I understand it the sinew does not take any of the compression off of the belly it just shifts where the tension is. It takes the tension off of the wood putting it into more compression. But as the bow is bending into reflex it does take the compression off of the belly in the reflexed position but as the bow bends forward its going to be under the same if not more amount of compression as if you didn't reflex it at all.

So the goal behind the extreme reflexing with the sinew is to put that sinew under more tension, taking advantage of the elasticity of the sinew more.

But yeah idk about that sapwood being better under compression. I have heard from others that the heartwood is better and in my experience the heartwood has been better in compression because it's a little more rigid, conversely, the sapwood is better in tension. Although I have noticed that the heartwood shrinks much more than the sapwood as it dries.

[Gordon]

Good luck tillering that thing.

[RyanY]

Looks kind of narrow. Good luck!

[pierce_schmeichel]

I just finished sinew backing it

And I wrapped it with rolled gauzeto make it pretty...just a waiting game now hahaha

I will post more once it dries and I'm on the tillering process