Primitive Archer
Main Discussion Area => Bows => Topic started by: Gordon on December 22, 2009, 05:30:50 pm
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Well, I just broke my 3rd bow in a row due to a backing failure. I'm not sure if there is a problem, or I'm just on an extraordinary run of bad luck. At any rate, this is starting to get old...
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i think you need a good pick me up... of vine maple..john
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Got pics?
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Gordon,
Lemme guess 4+month old Urac, and/or the work shop is around 60 degrees... Or sometimes batches of bamboos aren't what they seem to be quality wise..
I feel your pain, and when you have your skills this only amplifies it.. I know it can be figured out. I get a fair amount of phone calls with folks in a similar funk and can usually get them straightened out in a laminating kind of way..
Rich
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Rich,
The Urac glue is new and I've sucessfully made several bows from the same batch of bamboo. But my workshop is probably around 60 degrees. I didn't think that would make a difference if you cured the glue-up in a warm place though. Is that an issue?
Gordon
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Why do you think it's backing failure? The only reason I'm asking is the only failures I've had, when it comes to bamboo, have been because the boo crushed the belly...something that actually happened to me this very day.
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Why do you think it's backing failure?
The last two failures had a large splinter lift up from the bamboo backing. I did not see any evidence of compression stress on the belly (both of which were Ipe).
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Did it lift at a node or a damaged area? Not calling your bluff...I just never had splinters lift on bamboo myself.
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You've got my sympathies. I've read enough of your posts to believe that you're probably a better bowyer, so I won't even try to guess what's going wrong. Ron
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Maaaaan Gordon, really sorry to hear that!
Do you do any tempering on your bamboo before glueing??
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The first failure I believe was due to an improperly implemented powerlam and the limb broke between nodes. The second failure was a splinter that lifed about 1/2 inch from a node - I think I may have made the bamboo too thin in that spot to withstand the high draw weight. The final failure, and the most heart-breaking, was a splinter that started very close to a node. Perhaps I got too agressive when I took off the rind and smoothed off the node, I don't know...
Frank, I did not temper any of the bamboo.
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I have had failures exactly like yours, with all kinds of bamboo, ie Franks in Ca., Bamboo and Ratan works east coast, and the tonkin bamboo from Dryad Bows. Dean has ways of patching splinters with silk, and has alluded to selfbows being more dependable in some of his writings. I trust bamboo backed bows for extended hunts in remote areas only if I can take a spare selfbow. If I can take only one bow it is a selfbow or sinew backed. I know this will not be everyones opinion but most will agree a well made selfbow is simply the most dependable.
hope this helps
Chris
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It's just a run of bad luck I think Gordon. Unless you harvest the stuff yourself you're at the mercy of those that do. I've found hickory backing to be the same.
I've had many boo backings fail to no fault of my own. Curious thing though, they all failed on the upper portion of the stalk/upper limb. I build everything as it "stands on it own" and 99.9% of the time it's always the upper limb that fails. Whether backed boos or staves.
If I ever do build anymore boo backed bows it'll be with two lower sections of the stalk/backing and spliced 'em in the handle.
Can you tell us at which end of the backing is failing (as it stands in the stalk)? ART
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Gordon,
The splinters lifting might be from the bamboo getting a little too dry somewhere between the field and the bow. Often heaters run during cold weather will cause splinters to lift. This I have learned from sending bows to the cold regions where the heaters get the mc% in the house too low for what bamboo can handle..
They may have been helped by getting it a little thin and removing the rind..I stopped removing rinds because of the problems its caused even though I like how it looks.
Since bamboo is really a "grass" its not as tough in this sense as one might think..
If you were getting separation on the glue line then it might be a glue issue, but I think you are fine there..
I hope this helps, and trying bows with thicker bamboo backings was influenced by my desire to get as consistent on these as possible.
Rich
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For what its worth, I have never removed the rind, and have never had one break, but I've only done a half a dozen or so. I also leave the nodes proud.
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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...
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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.
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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.
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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
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I feel your pain Gordon, I am sure you will figure it out. See ya next Boyer's meeting. Greg
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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
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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.
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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...
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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 :(.
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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.
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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
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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.
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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
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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.
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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
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These all natural bows are fickle lak wimmen, and occasionally will torment you just to make sure you remember why this game is so interesting.
That said, I do stay off the nodes when finishing boo. But I've had it fail with the rind and nodes still untouched. I'd chalk it up to bad luck, natural variation in the material, and perhaps a bit of treading too close to the edge.
I've used URAC as old as 2 years or more Rich. But I keep it sealed in the fridge and only take out small quantities at a time to work from. Be mindful of how old the product may have been before it found it's way to your hands.
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David, I couldn't agree more, nothing is ever a guarantee with these bows, and it does keep things interesting. If we were all afraid of failure we would just make pipe straight selfbows with a hide backing ;)
Marc, I have plenty of bows out there with the rinds scraped and sanded off. I don't take rind removal as an absolute cause at all, but as you can read here many others have experienced the same problem. I don't think these problems arise from the back fibers being violated as much as just getting exposed, and this may be fine for some bamboos and not for others. Which is what I found. So I just don't bother with it, and most of what I get to cut has enough markings to make it a unique bow. I have seen more than one thoughly sealed bow get very dry in the desert so I never view any finish as a remedy to the conditions it may encounter. Like the super dry air in the cabin of a jet going halfway around the planet :o.
Getting bad bamboo is the worst scenario since nothing can be done to rectify this, and why I cut poles from as many locations as I can just to avoid this situation.
Rich-"midnight bamboo supply" ;D
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Gordon, you said you used bamboo planks, I'm interested what are these? Also , was the bamboo extremely dry (low moisture content) ? this might account for it?? I beleive its best to leave rind and nodes alone , the rind gives added protection and the nodes look good, why risk it just for looks??
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I'm a noob and know zero about bamboo, but I think I'm seeing something here, possibly. If it's always the upper limb that splinters, and the bottom of the bamboo is on the lower limb of the bow, and I'm going out on a limb here, but I'm guessing the splinters always point in the same direction? This would suggest to me that the bamboo should always be spliced with the bottom end of each piece at the nocks. Does that make sense to anybody? Like the bamboo is stronger if the bottom is pulled towards the top rather than vice versa.
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Dragonman,
The planks are actually called Bamboo Slats. The ones that I purchase are made of large diameter Moso bamboo and are milled flat on 3 sides so they can be screwed or nailed onto a surface such as a ceiling, bar, or counter top. I don't believe lack of moisture is an issue because it is quite humid where I live in the winter and bamboo readily absorbs moisture.
Zenmonkeyman,
The splinters were all in the same direction, but I do not know if that is just a coincidence. I think your theory is worth testing though.
BTW, I am attempting to repair the latest splinter. My plan is to super-glue the splinter down and wrap the area with a sheer silk strap that is saturated in TB3. I will then glue a thin patch of rawhide over the end of the splinter that rose and wrap that with serving thread. I'll make a matching wrap on the other limb for looks. I don't know if this will work, but I have nothing to lose.
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The repair seems to be working. I had to retiller the bow and lost 5#, but it's holding together. I can't say I care much for the look of the patch, but at least I salvaged the bow. I'll probably paint this one all black to obscure the patch and use it as a field bow.
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Well, the patch is holding fine, but now the bamboo on the other limb lifted a splinter. I give up...
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You know, Gordon... I feel your pain. I went throught the same thing with bamboo about a year ago, and as a result, I just don't use it anymore. Lifting splinters, cracking, checking, blah, blah, blah... it's just too dry here for it, and it cracks into bits. I even had a tri-lam ELB with bamboo as the core material, and it cracked and checked too!
I've been using ash, maple, hickory, elm, rawhide and sinew as backing material, with no issues. No more bamboo for me... it's too frustrating, and too labour intensive ta boot. Blaaagh :P
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I'd pop the backing off and back it with a slat of Ipe about 3/16th's-1/4" thick, and get it shooting again.. Gordon I hope you try it because it was this same bamboo scenario which made me try it the first time, and it was an epiphany of sorts from how easy it was to how the bow performed.. And shaping the backing to fit is kinda enjoyable as well.
Rich-
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adb,
I'm about ready to chuck my stash of bamboo into the dumpster - I would have never guessed that bamboo could be so fragile.
Rich,
That's a really good idea - no sense wasting a perfectly good core and belly.
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adb,
I'm about ready to chuck my stash of bamboo into the dumpster - I would have never guessed that bamboo could be so fragile.
Well, I gave it up. I'm not saying you should, but it doesn't work for me.
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I'm not going to give it up entirely - I have too much yew lumber in my garage to do that. But I am going to discard my current cache of bamboo. I don't trust it anymore.
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Gordon I was wondering if there is any way you can do a bend test on your remaing boo slats to compare one slat from another batch? Dean
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It is worth pointing out that Moso is notorious for being the weakest bamboo, particularly at the nodes. This is the same thing that Dean Torges described before he switched to superior types of bamboo.
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It is worth pointing out that Moso is notorious for being the weakest bamboo, particularly at the nodes.
It's interesting to note that only one out of the 4 failures that I experienced actually happened on a node. This last one is particularly vexing. The splinter started midway between two nodes, there were no obvious nicks on the back and the backing was not particularly thin at that point. And it happened after previoulsy putting at least 100 arrows through the bow. I'm beginning to wonder if these failures might be related to the method I am employing to heat cure. With this last bow I put on a thin coat of Tru-Oil directly on the wood to seal it not realizing that the oils in Ipe would inhibit the finish from drying properly. So I kept the bow in front of my fireplace for the better part of a day until eventually the finish cured enough to handle. The backing failed promptly after that.
I had one more bow in the queue so I glued it up this morning and carefully wrapped it in plastic film to prevent moisture from escaping as I cure it in front of the fire. I hope that's it because if I wreak one more bow I think I'm going to break down and cry :'(
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That's been the entire problem with me and bamboo... too dry.