Backpack Bow Challenge!

[ricktrojanowski]

David ifin ya would have made this a six pack challenge I would most likely be on board

I'll hide a six pack easy.  In my gut no one will ever know. 
Kegan- 2yrs of highschool and don't forget 4+years of college depending on how much fun you're having.   

[D. Tiller]

So does this bow have to be under 40" when strung? Because I'm thinking nice long static tips could make this work, but then again I'm no good at short drawing.
Heck, maybe I just need to get working on it and call it done. It's gonna be Ipe with either Hickory or Bamboo backing, with perhaps some ears bent in.
      Cheers,
           Grant

Sorry, 40" Total so you can hide it away strung or unstrung. I really want to see how good you guys are! 

[Far East Archer]

Ok, update on whats going on over here:

First bow 33" long, 1" wide 45#@22". Raw bamboo back and belly with 3" siyahs. The bow had a C shape unbraced profile and so when strung the handle was set back and the outer limbs reflexed. At full draw it looked like a Korean horn bow (what I designed it after) and was super fast!  ;DThen out of now where the glue failed in the fade area and the bamboo kinked.  :PI failed the bow since it wasn't safe to use anymore but I can show pics later.

Second bow, still working on the design but I think its gonna be same as the first except Im going for an extreme reflex/deflex design. This one might be a little longer though. Cant wait to see what you guys come up with!


Alex

[grantmac]

Ok, update on whats going on over here:

First bow 33" long, 1" wide 45#@22". Raw bamboo back and belly with 3" siyahs. The bow had a C shape unbraced profile and so when strung the handle was set back and the outer limbs reflexed. At full draw it looked like a Korean horn bow (what I designed it after) and was super fast!  ;DThen out of now where the glue failed in the fade area and the bamboo kinked.  :PI failed the bow since it wasn't safe to use anymore but I can show pics later.

Second bow, still working on the design but I think its gonna be same as the first except Im going for an extreme reflex/deflex design. This one might be a little longer though. Cant wait to see what you guys come up with!


Alex

Thats the sort of design I was thinking about. Did you use a bending handle or fit a center lamination? What sort of wood for the Siyahs? What sort of glue did you use? And finally, did you saw, bend or laminate the siyahs?
I'm personally thinking a thin Ipe belly with bamboo backing at about 1" wide should do the trick, as long as the Ipe can take that much curvature. On the other hand I do have a fair amount of scrap bamboo, so I may use that.
Good to know that someone else has had some success with the design I think will work. It's either this or else something cable backed.
     Cheers,
             Grant

[Far East Archer]

The handle was set back, but did nott have a center lamination so it was free to bend at full draw.
The siyahs were just some scrap wood I had, very light, close to pine in weight.
I used titebond, I think I just got a bad bottle of it as I have been having some failures with it recently.
Usually it hold up just fine....
The siyahs were just some quickly thing I did after I found out my recurves were too thin to remain static,
so I cut the recurves off and then sawed out the siyahs at 60 degree angles or so, notched the bottom and
tied them onto the limb tips. Its very easy to do and If I made it more permanent you would not be able to take
them off, very solid and it never came off even at full draw.. I think I will do this on the next one as well.

The only reason I have not used ipe is because I do not have it. I think if you put in less reflex than mine it will perform
better for the ipe. The only reason I induce so much reflex with bamboo is because I usually loose 25-50% of what ever I put
into it. This changes however if a core lamination is added. Good luck!

Alex

[grantmac]

How far off from being static were the recurves when just glued in? I'm thinking that perhaps adding a core just in the siyahs might do the trick, I've seen some Korean bows with fairly wide but think tips.
So you just tied the siyahs onto the tips of the bow with sinew? No glue or anything? Thats a very interesting way of giving them a try, I think I'm just found a way to use all that scrap Douglas Fir 2x4 I've got kicking about.
I've had limited success getting bamboo to bend with the power fibers on the inside of the curve, do you find it works much better when it's thinned right down?
Thanks for the tips, you've got a heck of a lot my bamboo experience then I do.
       Cheers,
              Grant

[Far East Archer]

Well lets just say they were not recurves anymore after the first bend 
Yes, I was thinking of adding a core just in this area like you say, it would have
saved it, no doubt.
I am making Korean bows at the moment and yes the tips are quite wide, about
1"-- 3/4" wide and in the center it has a spine which is 1/2" thick but the shoulders
are about 1/4". This makes the tip very light but strong at the same time.

Yes, no glue, just tied on. Also, I did not even use real sinew, just artificial sinew! It worked
better than I thought it would, but real sinew would be more solid.
When you say you have not had success, was it because it became too stiff? I usually make
the backing thinner than the belly but yes,the belly is also quite thin as well, maybe 3/16"

Alex

[grantmac]

Well I was just experimenting with steaming boo. I tried dry heat but it just seemed to open cracks. I only had it thinned down to 1/4" though so still quite thick. The pieces that were bent with the power fibers on the outside of the bend did quite well considering I did a 90 degree bend with perhaps a 2" radius, the ones with the power fibers on the inside seemed to delaminate the core fibers but leave the power fibers completely intact.
More experimentation seems to be required. I will be back in my shed next week and try a few things with thinner bamboo, glued-in bends only and larger radius'. I will also heat tember the belly after glue-up.
Cheers,
       Grant

[Far East Archer]

Ahh ok, ok I see what you say now. Yes, bending bamboo like that is tough,
this is why I always either thin the backing a lot for small radius bends or heat bend
it with dry heat and oil from the skin side on larger radius curves.
This way I can keep the backing thicker.
I never steam bamboo into shape, I think it bends better with dry heat and had
the same experience as you with steam and boiling.

Bamboo does not have to be very thick to hold its shape. If you make the backing
maybe 1/8" thick and the belly full thickness, this should be about 3/8" thick or a little
more. This thickness is plenty to hold a static recurve on bows up to 65# or more depending
how long the recurve is. (maybe 6" or so, shorter is better)
Mine was only 3/16" thick total because I was expecting to get a lot of weight....

BTW, I would be cautious about heat tempering the belly after glue ups unless the glue you use
is heat resistant.(epoxies might be ok for this, so Ive heard) My experience with titebond is it will
de-laminate while you heat it. I suggest you do any heat tempering before the glue up though,
just in case.

Alex

[grantmac]

Precisely the information I was wondering about.
So even just glued-in recurves with no stiffener should be good to go as long as the backing is 1/8 and the belly is 3/16? That makes the whole project seem much less difficult.
I've heard bamboo looses a lot of reflex, should I start with around 12" or so then? reverse stringing it during the drying?
I tried heat-treating after glue-up and I had the same experience as you did.
I may still use the Ipe in a very thin lamination, experimentation is the name of the game here.
       Cheers,
               Grant

[D. Tiller]

Wow!You guys really are pushing the material limitations. I just love it! Show your successes and failures. We can all learn a lot from wins and losses.

David T

[Kegan]

This is all getting so good ! Sounds like it'd also be a cool article for PA.

Once the deflex sets and my dad is done working on the car for the night, I'll back the bow and start on the arrows. Kyle and I are now debating some footed poplar shafts for these. This is fun .

[D. Tiller]

Wow! You two go fast.

[Kegan]

Wow! You two go fast.

Twenty minutes of scraping and shaping a night. With little bows, it goes a long way . Arrow might take longer though, I think they might be more wood on them than the bows .

[Keenan]

Heck I'm still thinkin bout this un Thanks Tiller as if my brain dosen't go in enough circles, And you have to go do some experiment on us. thanks Bro.