Bamboo back/Belly/ sepele center. Help?

[Msturm]

I really want to build a bamboo bow to hunt with. I'm hoping to get 50 -55 lbs out of it. I have built a bunch of successful self bows and board bows but this is new territory!!  I did as much reading on here as I could, but many of the pictures are down due to photobucket being the devil.

So right now I have some supplies and a bunch of questions....

Both bamboo lams are cut to 64 in.  The sepele center lam is 66.

Here is what has happened so far: cut bamboo a year ago. its really dry now so I split off a  1.5 in section. burnt the hell out of it for the belly lam then flattened it the best I could with a rasp. ( I don't have access to power tools). I split out a section a bit wider and rasped it flat as well. I had a piece of sapele I used for making spearguns laying around already cut to about 1/8th inch and decided I would use that as a core lam trying to get a few extra pounds out of it. Nothing has been tapered both bamboo pieces are about 1/8 in (roughly).

Questions:
I have some 2 ton epoxy and a bunch of inner tubes I plan on using for the glue up. looking to put in some reflex at the tips using a form like the one on poorfolkbows. anyone see any problems with this idea?

I cannot figure out how to get a handle on this thing... should I cut one and laminate it in there? If I do this do I have to cut the belly lam in half?  should I keep it bendy in the handle and not worry about a "handle"?

I am worried about not getting enough power out of it for a hunting weight bow. I have done some floor flexing of the stack and its real bendy... I have read that the epoxy will make it much stiffer, so I am banking on that. Anyone with experience in these things have any input?

I really like the looks of bamboo back and belly bows, I have wanted to make one for a long time and I hope I can pull this off But I don't know what im doing so I am going to hold off until I get some input. Thanks everyone!!

Pics:
Materials 

Size of lams 

Compressed stack of lams 

The rest of the bamboo I cut a year ago just to give you an idea of the diameter. 

Belly after toasting real good.  .

Thanks in advance for your input and help!

Msturm

[Badger]

  We have a few guys on here who build those, I have built tons of bows but would not even attempt what you are doing. The guys that do it pretty much know the exact dimensions they will need when they end up, they build the tapers into the laminations etc. The only advice I have is work your way up to a build like this, it may not work on your first shot at it. Most the ones I have seen are reflex deflex designs with a riser laminated between the belly and back, this presents a whole new set of challenges getting your boo to lay flat on the riser. Entirely different skill sets than building self bows.

[Del the cat]

+1
The following is all guesswork, but I have done boo back and belly crossbow prod etc.
I'd guess you pretty much have to get the core tapered right to give the right tiller before glue up. The boo can be thickness tapered too, but it's gotta be about right. Final tiller tweaks would be on the width, especially near the outer ends if you've used a linear taper elsewhere.
If I was trying it I'd go for a 2mm reduction in thickness every 6".
I'd probably build up the belly side of the core lam for a gradual increase in thickness (maybe just 1/4 - 1.2") and maybe thin the belly lam a tad in the centre so that it will flex enough to clamp down tight onto the thickened grip.

This post will self destruct in 30 seconds... 
Del

[mikekeswick]

Yes these aren't really the bows for beginners.....;~)
First you need around 0.005 taper per running inch and mate that to a parallel to half limb, taper to tips width taper. Best to get it professionally ground.
As Badger says you need to make a riser the same way most glass bow risers are made. They go in-between the stack with feather edged fadeouts. Cutting the belly lam in half and making sure it is thin enough to conform to the belly ramps.
chances are when you start making these you will need to make 3 bows to go the stack info you need to glue-up bow with the correct thickness for your desired weight.
It is not epoxy that stiffens the lams. It is simply the thickness of the total stack.
epoxy will work and the innertube method is good.

[bushboy]

May be message Dragonman, he is the only guy that I've seen post such a bow.hard maple may be a better choice for a core from what I've read.

[bubby]

First this is a hard build, ditch the 2ton epoxy and get some smooth on or some unibond. You need to match the nodes up belly to back as well, even if you have to cut and splice the belly, but joints will work

[bubby]

Join tradgang, there is a build a long for one by dutch warbow i think is his user name, i will see if i can find it

[Pat B]

Bamboo back/belly bows are pre-engineered. Once glued up you are limited how much tillering you can do, and that is from the sides. Your belly lam looks to be well tempered. If you can't get Unibond or Smooth-on use TBIII. Don't use 2-ton epoxy. The riser on this type of bow goes between the 2 bamboo lams or cut the belly in half and  bring them up the fades.
James Parker has been building these types of bows for years and does an excellent job of them. I have a highly reflexed/deflexed variety that David Knight gave me a few years ago.

[Msturm]

Hey guys thanks for the input! 
Badger: its just a bunch of scrap Im trying to make something useful out of.  If it goes bang It will be a learning opportunity. I don't have much invested in it. If it works out Great!

Del: I think I am just going to do a gradual taper of the center lam. I have some work to do on the bamboo as well there are low spots on bamboo near the nodes. more sanding!

Mike: Thanks that is the kindof stuff I need! Good info. I am going to try to "professionally grind" my lam with a sanding block. lol.
Bubby: Im on the gang. just digging up as much info as possible. That is a great build along. and I am basing my experiment off of what I have read on that build along.

Pat B: Thanks for pointing me in the right direction. I also have some west systems marine grade epoxy that I have used to make BBi bows with (also used for making spear guns). Think that would work?

Thanks guys for all the info!

Msturm

[Pat B]

I've never used West System but I believe others have successfully.

[mikekeswick]

It is do'able by hand but be as accurate as you possibly. If you are going to do it by hand glass sheets and blocks are cheap and very useful for lam grinders aka sanding blocks!
I've made a few of these bows over the years and when you get them right they are great performers..

[leonwood]

I have no idea how well that sapele works in compression but you can try to do it in stages:

First glue on the backing and the handle, then tiller it to fulldraw or a few inches less. Basically using your core as a temporary belly so your core is tapered for equal bending limbs.

Then cut you bamboo slat in half,  plane your bamboo belly really thin and glue it in to the belly. If you make the belly slat really thin it won't need any more tillering. If you leave the limbs a bit wide from mid limb to tips you can adjust the tiller from the sides if needed after the belly glue up.


Below is a 70 pound boo/ipe/boo bow I did the same way. I only use hand tools as well and I have never had problems with glue ups even using non-gap filling glue like titebond. Just take your time to make sure your glue surfaces match.

[Msturm]

Leonwood: That is a stunning looking bow! how thick is your Ipe Lam? I have 2 pieces of Ipe already about 3/16 that I have not used for anything as they have knots. Might be able to splice them if they are going to be center lams. Thoughts?

[leonwood]

Thanks! This was actually just an experiment if I could do a bamboo belly on an existing bow. Did not even temper the bamboo. The bow is really narrow and the bamboo still holds up fine.
The ipe core tapers from about 7mm to 4mm at the tips. It was actually tillered and shot before I added the bamboo. On this bow the bamboo belly was too thick and added about 30 pounds to the draw weight so make sure the belly lams are as thin as possible or make the core really thin

[darinputman]

One of the best shooting I've made was a bamboo backed osage that came in under weight once tillered. I flattened the belly, ground a couple of belly lams one for top and bottom then glued them on. As much as I would have loved the look of nodes on the belly it was now too heavy, so I just tillered the bamboo the same as I would osage. It took a bit of scraping before poundage started to fall but fell quickly into place once it did. With the help of a Eric Krewsons tillering gizmo it made a fine shooting bow. I was making it for a left handed friend and really hated to glue that shelf on as I really liked that bow.  But my belly lams had not been tempered. It was a gift so I asked him to keep me updated on how the bow holds up due to belly tillering bamboo, I work with him and am sure he doesn't shoot it as often as  we shoot them but says it shoots great still and really impresses all who see it shoot.  The hardest part was working the lams up the fades for me nut next time I will try the same as leonwood as his fade transition looks nice.