Steam bending bamboo recurve?

[DC]

I'm trying this with a scrap of bamboo to see what luck I have. Mine is about 3/8" thick and maybe 3/4" wide. I've got a caul that looks much like yours. I'll steam it and dry heat it to see if I have the same results.

[DC]

OK It went fine. It was a very dry piece of boo. I didn't soak it. I steamed it for 1/2 hour and clamped it to the caul. Let it cool/dry for a couple of hours and then heat treated it still on the caul to a light brown. Left it for another couple of hours and then did the other limb the same way but I heat treated to a dark brown. I didn't take a lot of care so the treating is a little uneven. It had 5 3/8" reflex when I f took it off the caul. Put it in the vice and grabbed a tip in each hand and pulled a half dozen times. The limb that didn't get as much heating straightened a bit. Lost about 1" of reflex total and I believe that most of that was in the middle where it was too thin and didn't get heat treated. It feels very springy. I may try this with a better piece of boo Did this sound like what you did?

[nabiul]

Yeah that's pretty much what I did, but the fibers pulled apart before I could get to even a light brown toast. Did you scrape away the hard crust on the inside of the bamboo like I did?

I wish it was that easy for me. Other than the bending and scraping away the hard crust on the inside, bamboo seems to be pretty much the ideal bow material.... for a beginner anyways.

[DC]

I sanded the inside with my belt sander until it was all a uniform thickness.

[DC]

How far away are you holding the heat gun? Is the boo still on the caul when you're heating it?

[nabiul]

I hold it maybe 3-4 inches away and move it back and forth, it was still cool enough for me to be able to touch it without any worry of burns when it cracked. It was on the caul, maybe my caul design is the problem; the limb comes under a great deal of tension once it cools from the steaming and springs back by a large amount once I loosen the rope.

Well other than being ugly, it should still work right since the belly is under compression only? I'm going to move ahead and see what happens.

[DC]

All I can think of is maybe try a different steaming method. The wet T-shirt in the oven doesn't sound like it's working. When you unwrap it is the shirt still wet and really hot? Maybe steam it longer. It has to reach boiling point for the full half hour or more.

[nabiul]

Yeah steam comes off the shirt for a while after you open it. I had no trouble bending it on the caul, it was really compliant, but like I said the reflex on the long part of the limb doesn't take which causes the recurve to come under great tension when it cools.

I will say that the appearance of the bamboo is different after my soak and steam, the fibers seem to have swelled and lifted up on the areas not covered by the smooth rind. On the next one I will try a long steam without a presoak.

Are you sure there are no tiny cracks in yours on the belly side?

[DC]

No cracks. How thick is your limb?

[nabiul]

A little over 2/8ths around the tip/crack area going down to much skinnier near the handle. Actually my raw material itself isn't that thick to begin with, I used the upper portion of the bamboo stalk which is thinner but has much longer spacing between nodes.

[nabiul]

Should I keep long fades or is it better to have more working limb? I originally planned for fades to end right at the nodes, but then I got worried about a hinge forming from steep fades or the handle and glue joint not being strong enough if I made the fades both short and shallow. I also want to avoid a situation where the forces in the power fibers make it to where the limbs end in the middle of the handle; I did a bending test on one of my previous failures against my shin and the rind and power fibers 'delaminated' from the softer bamboo.

I feel like I don't have enough working limb for a decent brace height and a long draw.

[bassman]

Go to Dave Mead,s website.

[nabiul]

Actually I saw his videos on youtube originally and that's what got me to try making a bow out of bamboo, but I've done a few things differently which makes me uncertain on my design.

Well any ways it doesn't matter now. This was an absolute disaster, the handle is too round for my clamps to grip onto and I spent too long dicking around with the alignment while the TB3 was tacking. I'm going to wrap the fades with something when it's dry and CA the crap out of it.

[nabiul]

Is having a hinge bad even if I intend the bow to bend there? The right limb has a natural deflex right after the fade and then a hinge where the material is about 0.5mm thinner than the left limb. But as I understand it, this is the main working part of the limb anyways for a bow of this type right? I'm tempted to thin out the left limb in the same area to have it bend in the same profile because it looks appealing to me, bad idea? Also how do I approach the tillering process since bamboo is only so thick and already bendy to begin with, it's not like you can floor tiller it. It feels like I should have it braced already.

[nabiul]

Well I've wasted my life. I took it out to full draw and the bow has literally no weight, like 15# at 32". Is there a rule of thumb for shortening bows? It doesn't have to gain by much, I normally shoot a 30# olympic so a 30-35# trad bow would be ideal for me to start with.