Bamboo back Sapele core and bamboo belly

[Msturm]

I really want to build a bamboo bow to hunt with. I'm hoping to get 50 -55 lbs out of it.  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 Roy uses in his posts. 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? 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

[KenH]

I make bamboo self bows from 25"-50# from "fence slats".  See my recent post:  http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=014623

and under this discussion:  http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=014621

Burning the outside of the culm for the belly is not wise.  The strength of bamboo comes from keeping the skin of the culm untouched, and you've destroyed that integrity. If you want a black belly, use black liquid shoepolish or paint.

If you had used bamboo that was much thicker walled (1/2" or more), and much larger diameter (say 6") that would have been much better -- the thickness of the wall is like the thickness of a stack in a 'glass bow -- where the most of the strength comes from.

Gluing two thin-walled pieces of bamboo together (even with a center lam) will not make it much stiffer.  You'd be better off building a Bhutanese style "bundle bow" from several thin sections and just binding them together in a "loose laminate stack".  The Chinese built bows like that over 3000 years ago.

As you can see, I use the outside of the culm as the belly, and the sanded inside as the back.  

For a 50# bow I want a wall thickness of at least 1/2" to start.

Rasping to flatten is IMHO a waste of time.  You can go to a tool rental place and rent a handheld belt sander for a few bucks.  Turn it upside down and you've got decent flattening sander.  

This kind of bow is, IMHO better as a 'bendy handle' flatbow design.  With two rounded surfaces, trying to bend and glue recurve into the tips is going to be very difficult at best, if not impossible.  Better (but still hard) would be to glue reflex into the whole bow...

[Msturm]

Thanks for the scoop KenH. I had seen your bamboo self bow before. I thought about it but I do not have the bamboo for it.   This is just an experiment really to maybe get something out of some scrap material.

I have read alot about burning the belly lam of a bamboo bow as it helps in compression... Is this untrue? I have enough leftover to make another couple lams if need be.


Thanks again!

MSturm

[KenH]

Not burning --- toasting.  Sometimes toasting will help with compression.  But not always, and not by much -- not 25% better for example... maybe 2-5% if you're lucky.

Try making a loose laminate bow?  Say three or four lams of different lengths -- maybe 64", 56", 48" and perhaps 30".  Longest culm at the back, shortest at the belly.  Only taper the ends of the longest culm to make the nocks.  Bind the centers together pretty tightly with perhaps paracord to make the handle, with the outside of the culms to be the belly side.  Then bind (but not tightly) the ends of each lam about 3" in from the ends.  On my loose laminate crossbw prod I use black shrink wrap at the lam ends.  You're just trying to keep them lined up with each other.

The result will look vaguely like an old fashioned car/truck leaf-spring...

[wood carver 2]

I have built several bamboo/wood/bamboo trilams and I always toast the belly lam. I learned how to build them here on Trad Gang.
 
The bow above is a straight limbed longbow with a padauk core. I don't remember the exact thicness of the core, but it's about 1/4 inch.It also has a very thin power lam that is 4 inches longer than the riser. It draws around 55 pounds and is 66 or 68 inches long. Sorry I don't have exact measurements, I gave it to a friend a few years ago.
I plane my back lam flat on the concave side, then I taper it so that it is 1/8" thick in the middle and 1/16" at the tips. I also narrow this lam from 1 1/4" at the fades to 1/2" at the tips. After the glue has set up, I'll use this as a guide to narrow the bow blank. Next, I plane the belly lam flat, then I burn the outside of it with a propane torch. You will notice that the flattened face has become convex after you burn it, so I take it back to the planer and get it flat again. I also will taper this lam to the tips. I cut this lam in two so that I can bend each piece up the fades.
The core gets tapered from 1/4" to 1/8" at each end.
Ok, I dug up a bow I built two years ago. It is 65" NTN and draws 63# @ 28". The riser is 18" long and it has a 1/8" power lam that is 22" long and a hickory core.
 
This was my moose hunting bow and it was fast and almost silent. Unfortunately, the backing failed last spring when it popped a splinter. One weekend, I'll grind off the back and glue on a new one. This bow was a favorite of mine and had a couple of thousand arrows through it.
You can't build this on a regular form. What I do is use a straight beam. I clamp the riser blank with the back, the power lam and the core to the beam. Place the belly lams under all of this. The tips rest on blocks to get the reflex and I get the deflex by pulling the mid limbs down to the beam with big clamps. Then I go nuts with lots of spring clamps all along the limbs. I use about 50 clamps in all. Titebond 3 does a great job on these bows and it's easy to clean up the clamps afterwards.
I hope this helps.
Dave.

[Msturm]

Dave you are the MAN!  that is exactly what I am looking for!.

Do you think I over did my burning of the belly? I used a torch too.  I burned it before I flattened it. I thought the heat might change the flat side too. got lucky with that guess.  So right now I have everything at about 1/8in.  If I taper all the lams from 1/8 at the center to 1/16 at the tip, Won't I get a whip tillered bow?

I will work on making a riser tomorrow.
Thanks a bunch. You have been most helpful!

Msturm

[Roy from Pa]

David that is nice.

[Msturm]

Dave, can you tell me a bit more about the power lam?

what is it made of ? how much of it is tapered?  Could I make one from sapele or should I try and use a thinned out piece of bamboo or another wood?

Thanks.

Msturm

[wood carver 2]

I don't remember what I used for the power lam on the first bow. On the second one I used walnut. I just use a wood that looks good with what I'm building. Walnut makes good lams. I have no experience with sapele , but If it's strong and flexible, why not? I taper the power lam from the center out to nothing.
I don't think you overdid the burning. It looks like mine do after I burn them. I use a fine grit sandpaper to get rid of the soot and wipe it off with a rag so it doesn't turn everything black. I forgot to mention, I usually add tip wedges to bolster the tips. I make them 8" long and about 1/16" thick. I took a closer look at the second bow and realized that the belly lam is more than 1/16" at the tips. I do my tapers by eye using my stationary belt sander. I measure after every few passes and they turn out pretty good.
Thanks Roy. I learned a lot of what I know from you.      
Dave.

[wood carver 2]

When you test fit the parts you may find that the belly lams don't want to bend up the ramps. Don't force them or the bamboo will split. Use a gradual curve for the ramps and what I do sometimes is sand the lams a bit where they need to bend.
Dave.

[Pat B]

I've watched James Parker absolutely burn boo belly lams with a propane rosebud torch for his Bamboo Dragons and his high performance Asiatic "Horn" bow style all wood bows. I thought he had ruined the piece but he was pleased with it.

[LittleBen]

I won't pretend to know about burning bamboo, but I will say that wood glue is a much better choice than cheap epoxy.

Titebond II or III, or probably any water resistant yellow glue. I've used TBIII a lot, but I think I prefer TBII, cheaper, works well.

[Mad Max]

I have one of James Parker's BBB with the burned belly.
Very nice bow.

[Msturm]

I hear ya. about the cheap epoxy... My primary concern is I don't have a planer to get the bamboo PERFECTLY flat. I do have a belt sander now. well it's borrowed but same difference.  But I wanted something that will fill a gap just as added insurance... I also have some westsystems epoxy I use for spearguns. I have used it to back BBi bows successfully. That may be a better option.

Thanks again for all of your input!

Msturm

[turmoiler]

I can't see wood carver's pictures, this photbucket issue is really annoying  :(

[wood carver 2]

I used the fix for getting my pictures back, but it looks like it stopped working.
Dave.

[Msturm]

If the total bow is 64 in. will a 15 in riser be too much? I mocked everything up and it seems like it will leave me with very little working limb. Should I make this riser significantly shorter?  (keep in mind the profile is going to come down quite a lot.

 

[wood carver 2]

It will probably work. I like a longer riser so I can make long, gradual ramps. It's easier to get the bamboo belly to curve around longer ramps. If I have trouble bending the belly lam up the ramps, I will sand the part that will glue to the ramp a little bit thinner.
Make sure you do a dry fit before you commit to a glue up to sort out any problems while you can.
Dave.