Bow fail diagnosis request

[Hamish]

Diagnosis: Broke across the belly first, because of short grain. Glue line not optimal adhesion, is apparent, but the trouble did not start there. 40 grit sanding or toothing plane grooves as have been mentioned earlier, would increase chances of success, as would a pre glue wipe down with acetone.

A poor glue line can delaminate one entire limb, and the underlying belly wood won't break if the grain is reasonably straight. It will also happen early in the tillering process, during floor tiller to low braced string work.
 
I  had a similar break in the past, with an elb with  short grain across the belly lam. Deep rounded belly and narrow limbs are the riskiest combination with short grain, but apparently it happens on flat bows too.

[scp]

The guy who glued it up is responsible.   My purpose is to stop people from trying to rectify mistakes made b.y others.

 And to stop noobs from rushing into business before they have even mastered the simple side of things.

I never pretended to be an expert. But for the last ten years on and off I read almost a dozen books on "primitive" bow making and made more than 50 bows. I even made almost a dozen bamboo backed bows without even realizing doing so. And I basically ask questions here and say what I would do as a hobbyist if I am in the position of other posters who are asking questions.

As I review your reply here, first it was tectonics. Then it was the bad glue-up. Then it was not the original poster's fault. Nobody ever accused anyone for the failure. It was either the ipe's grain runoff or the careless glue-up. Someone suggest the glue itself. But more likely the glue has gone bad or the gluing surfaces was not properly prepared or too much pressure was used.

I'm more interested in the question of whether a bamboo backing can overpower a weak belly wood. The wood can be too weak because either it has bad grain run-off or it is relatively too thin. I don't think this issue has been resolved here. There are almost limitless case by case questions to be answered if we sincerely pursue this hobby. Better not presume to know the answer without investigating the details.

[PatM]

The belly wood suffered from plate tectonics due to the grain running practically diagonally through the limb and the poorly applied backing allowed that movement to pry the bow apart.

 You can clearly see that at spots the bamboo was a cable backing  relatively.

 Someone else glued up the bow, not the OP.

[Marc St Louis]

I have to say I wouldn't try and repair that

[scp]

The belly wood suffered from plate tectonics due to the grain running practically diagonally through the limb and the poorly applied backing allowed that movement to pry the bow apart.

 You can clearly see that at spots the bamboo was a cable backing  relatively.

 Someone else glued up the bow, not the OP.

We are not disagreeing much. The bow failed because the glue-up was not good AND/OR the belly grain run-off was terrible. Many people here were satisfied with just one simple answer or answering the question from the perspective of their own expertise in how bamboo backed bows normally fail.

The failure might not have happened if the belly ipe was at least as thick as the bamboo backing, or the glue had not gone bad, or the glue-up was well prepared and done right, or if the bamboo back was thinner, or who knows what else. Way too many variables and that's often what fascinates us in making "primitive" bows. I'm often quite relentless in questioning, probably because of my training.

Does the relative thickness of the bamboo backing and the belly wood matter at all? In this case, it probably did not matter at all. But someone here thinks the thickness of bamboo backings does not matter at all. However the consensus is probably that the bamboo backing needs to be rather thinner than thicker relative to the belly wood in most cases. Case by case always?

[scp]

I have to say I wouldn't try and repair that

I would rather try to get the bamboo backing off with heat and reuse it. But it appears today I have too much time on my hands to think about all kinds of learning possibilities. Sorry.

[Eric Krewson]

I got a run of bad bamboo one time, it all popped splinters. I replaced the bamboo on several bows before I trashed the rest of the 25 piece bundle of bamboo slats. I would grind the bamboo off with a 36 grit belt to just above the glue line, I didn't take all of the bamboo off, I left about 1/16" and glued my new bamboo to this. I never had one of these repairs fail.

I never replaced the belly wood because I never had any fail, I have replaced a limb on several osage bows just to see if I could save an otherwise good bow, never on a bamboo backed one. I guess one couple salvage the bamboo from the aforementioned bow but bamboo is cheap and readily available, I would trash everything and start over.

[scp]

I guess I have been watching too many forensic pathologist movies lately. I still like to organize the possible causes of the failure in the order of plausibility, in the form of simple questions. This is just a guesswork of a hobbyist.

1. How old was the epoxy? Gone bad?
2. Was the bow glued up pre-stressed?
3. Was the Ipe belly bend tested at all? Grain runoff checked?
4. Was the Ipe belly well prepared? Cleaned with acetone and/or sanded just before glue-up?
5. Was the glue line good enough?
6. How was the bow clamped in the glue-up? Too much or too little pressure?
7. What was the temperature of the place?
8. How thick was the belly wood? Too thin compared to the bamboo backing?

Is anyone still interested in answering these questions or any other ones?
Is any of the question, especially #8, irrelevant?
How many negative answers will constitute the sufficient cause?
Just about any one of them? Several of them combined?

I guess it's time to get back to the movies.
Be safe, stay at home as much as possible.

[PatM]

All of the key points have been addressed and make the others redundant.

[scp]

All of the key points have been addressed and make the others redundant.

In what combination? So far, I'm the only one who is asking the questions #1 and #2. Are they irrelevant?

[PatM]

  Yes.

[scp]

  Yes.

I once tested a several years old epoxy. It mixed well and was tacky enough soon. Don't remember how warm it got. I glued some wood strips to test. It never cured completely. It was just very tacky indefinitely. It was turned into a "sticky note" epoxy. It can be very useful in many ways, but not for bow making.

More questions: How long ago was the bow glued up? Was this question answered? Does the cured epoxy last indefinitely? What if it has been frozen and thawed?

[PatM]

You do see those clear spots across the bow width, no?   Those would be gaps a light would shine through.    Glue only matters if it's actually gluing something together.

 Those areas are unsupported in shear which this bow is already going to struggle with if glued up perfectly.

[Hilongbow]

I'm pretty late to the party here but if I could offer my 2 cents, I think grain run out was the biggest factor. If you look closely you can see that the grain not only crosses the belly lam from left to right at about 45 degrees, it also crosses from back to belly at about 45 degrees. It looks like the fibers on that lam are only about 1/2" long. The board must have been cut from a seriously crooked log. Cut a 4x4 post at 45 degrees, move up an inch, and make the same cut again. The thin slat you end up with should have pretty similar grain to this, and will be very fragile.

It looks to me like the glue stuck to the bamboo for the most part. The brown coloration on the glue side of the bamboo is bits of ipe fibers stuck to the bamboo. My guess is that the shiny parts on the ipe are where there were air bubbles in the glue up. This makes me think glue was spread on the ipe but not the bamboo, because I don't see any shine on the bamboo (though that could just be the picture). So, maybe not the best glue job? But with those short fibers on the belly I think the best glue would have still allowed this failure.

[Marc St Louis]

If you look at the pictures you'll see exactly where the failure started, right where there is a void in the glue.  This was not a failure due to bad core wood.  As I said before, it was due to bad glue-up.