I've got the bamboo backing blues

[Gordon]

Chris, I've never had a problem with bamboo backed bows until recently. But I agree that a well made self-bow is a very dependable weapon.

Art, I cannot tell which end of the bamboo failed as I am cutting the backing from bamboo planks.

Rich, I do not think lack of moisture is an issue as it is quite humid in the Pacific NW in winter. I have, however, been making the backing strips quite thin lately - almost like a knife at the edges. It looks really good, but I think maybe that's not such a good idea.

I'm not sure what to think about the rind issue. I learned to remove the rind and smooth the nodes from John Strunk - and he's built lots of boo backed bows. I don't know...

[mullet]

 I quit removeing the rind after James Parker told me about a string of failures he had. I haven't had a problem with it since then. And I don't sand the Nodes anymore, either.

[Marc St Louis]

The rind on Bamboo does nothing to keep the Bamboo together.  It scrapes off much the same as the early wood on Osage.  The only reason it would fail from that is if it was removed too aggressively and the back nicked.  When I remove the rind I am not too picky about it and leave small amounts on the Bamboo.   It's the same with the nodes.  They have no power fibers in them until you go down to a certain point then you can see where the 2 sides begin to interlock.

[kayakfisher]

I always file the nodes down smooth and never had a problem. The last laminated bow that I had explode that section got to close to the fire and scorched it or severely dried it out, when put on tillering tree and really started getting into tillering you guessed it. Right in that spot started splintering and ka pow . If you have a moisture meter take a reading and see what the mc is.
                                                                      Dennis

[huntinoly]

I feel your pain Gordon, I am sure you will figure it out. See ya next Boyer's meeting. Greg

[artcher1]

You shouldn't have any problem in reading the orientation of the backing Gordon. Nodes are closer together at the trunk end and further apart at it's top. Looking at it's butt ends you'll notice the difference in power fiber thickness also. Thicker and tighter power fibers at the trunk end. The catch lip at the top of the node is another indicator. That shows the direction in which it grew. ART

[Gordon]

Art,

If the nodes are closer together at the trunk then the trunk is always on the bottom limb. That's because I make the lower limb shorter than the upper limb. Interestingly enough, in all 3 cases it was the upper limb that failed.

[Gordon]

That said, the last bow was made by splicing the two remaining good limbs from the previous failures so they were both trunk pieces. But it was sweet, 70 lbs at 27", curves perfectly aligned, tiller just where I wanted it. I put about 50 arrows through it and it was fast and smooth as silk - I thought I had it made. Then I put it on the tree to begin my "torture" routine, and it failed. These bows will sometimes just break your heart...

[artcher1]

Same here Gordon.  I've lost probably a dozen bamboo backed bows where the upper limb lifted a splinter. Never a bottom limb. And as I said before, I build everything as it stands. Any patterns that emerge are easy to identify this way. I'll bet that others with failures like this, their problem occurs on the upper end of the stalk/plank no matter how they orient the boo to their bow.

As I mentioned before, I think you'll have better odds using two lower ends of the bow plank and splicing in the handle area. ART

PS After reading your last post I'm going to chalk this one up to just bad boo .

[Jesse]

I stopped removing the rind as well due to advice from David and others. Not because of failures but because it stains and seals just fine with just a little fine sandpaper. Saves a lot of unnecessary work and has no impact on performance I noticed. I too heard that it makes a bow more durable long term and I can see why. If you scrape right down to the fibers then it only takes a little nick to cut through. If the rind is left it can take a bit more abuse. I would think its also a good extra moisture barrier.  Not saying thats why your bows broke. Rich is right also that if it gets too dry it becomes brittle.

[Rich Saffold]

Gordon,
It's pretty easy to tell which end is up on bamboo by the smooth outward curve on a node is from the bottom of the pole and you can see the bamboo grows  from the inside out as you look at a node from the side. Having cut  well over 100 poles of many different species this node shape remains the same.

I also think there are so many variables in using bamboo that the common trend I read here is using bamboo that is too thin, and removing the rind which allows the back to get too dry.  In the right climate with good bamboo thinning the rind and smoothing the nodes on bamboos like Giant Yellow timbers isn't a problem when its thick enough. It's that "right climate " part that is a tough variable to master unless you live in a slightly humid region year round.

These  factors got me more than once we well, and why 3/16" is about as thin as I like in the crown and no less than 1/8" on the sides. Heck most of the backings on my Ipe long bows  are around 35-55% of the limb thickness. Of course this won't bend around a power lam, but it can be thinned a bit to fit this curve.

Rich

[Ryano]

Bad bamboo Gordon....It happens. My brother had a bad batch a couple of years ago and every bow he made from that batch broke eventually. Some while tillering, some 1000's of shots later. It did the samething, it was splintering for apparently no reason.

[Marc St Louis]

Gordon,
I also think there are so many variables in using bamboo that the common trend I read here is using bamboo that is too thin, and removing the rind which allows the back to get too dry.  In the right climate with good bamboo thinning the rind and smoothing the nodes on bamboos like Giant Yellow timbers isn't a problem when its thick enough. It's that "right climate " part that is a tough variable to master unless you live in a slightly humid region year round.

Rich

Richard
I don't think the rind would make any difference in how dry the back gets especially once the bow is sealed.  Once the bow is sealed then its moisture content should fluctuate as one unit

[Tom Leemans]

I just knock the rough stuff off the nodes, and I always sand the rind, instead of scraping it. Scraping tends to leave ridges that have to be sanded anyway.

[artcher1]

Perhaps a less stressful design such as a d/r out of the handle would be better suited for a boo backing? Would up the odds for a successful bow build I would think.  ART