Bamboo tension failure

[Kidder]

Just had a boo backed hickory bow at full tiller and that was nicely tillered have a tension failure. You don’t hear about this very often. Glue line wasn’t perfect but it also wasn’t terrible. What gives?

[Pat B]

How did you handle the the boo backing as far as scraping and sanding. The power fibers are right under the rind so aggressive sanding or scraping can break into or through these power fibers causing a tension side failure.

[Marc St Louis]

Looks to me like you were too aggressive taking the rind off the back. 

I have never had a Bamboo backing fail...

[Eric Krewson]

I have had that happen several times, I bought a bundle of 25 slats of bamboo from Frank's, every piece I used from that bundle for backed bows failed like that, bad bamboo.

I am pretty sure the next time it happened I was much too agressive scraping the rind off. Now I don't remove all the rind and use a little scraping and mostly sanding. I like the way a little rind stains darker than a bare bamboo back.

You can see the dark streaks in the stained back, often bamboo will have indentions in the back. Previously i would scrap down and level the back, I had to get into the adjacent power fibers doing so. I leave a lot of rind at the nodes as well.

[Dances with squirrels]

I don't know fellas, kinda looks to me like the rind is still on it, except maybe on the very edge where he rounded it off a little.

[Pat B]

To me, it looks too dull for the rind to still be on.

[Kidder]

The rind is still on. I hadn’t even sanded the back yet. I did round the edges slightly trapping the back. I did this because the last one I tried I managed to fret up and down, but in hindsight that was likely from other reasons but I didn’t want to take my chances. There were no recognizable signs of decay or streaking in this bamboo. I had thinned it to 0.1 inches plus or minus 0.01 between the nodes. This was bamboo I had purchased from a well recognized supplier for bowyers.

Frustrating as that was literally the simplest build I’d ever had and had just finished tillering it which went without any hitch. I literally had 3 trips to the tiller tree on the long string, braced it, unbraced it and adjusted for limb balance, restrung it and made three more trips to the tiller tree and was at 45lbs at 29 inches (68 inches ttt so I know it wasn’t working too hard).

[Onehair]

I have experienced a few failures myself. What I have found is that under the rind is a hard shell. Looking at the end you will see some slats have a very thin shell others thicker. The thicker shells fail often. So far never an issue with the thinner .

[Kidder]

I have experienced a few failures myself. What I have found is that under the rind is a hard shell. Looking at the end you will see some slats have a very thin shell others thicker. The thicker shells fail often. So far never an issue with the thinner .

That actually makes sense as the whole thing didn’t fail - just the outer 1/3 or so.

[scp]

Tension failures at the outer 1/3 limb that wide must be rare. How thick is the hickory belly there?

[Kidder]

Tension failures at the outer 1/3 limb that wide must be rare. How thick is the hickory belly there?

Outer 1/3 thickness of the boo.

[bownarra]

I'd contact the supplier send them a picture and see what happenes. Most suppliers will send you another strip.

[silent sniper]

I’ve had my fair share of bamboo tension splinters over the years. It is really aggravating to say the least!  I have tried both thin bamboo backing as well as thicker backings in hopes that one would hold up better then the other. I have also tried leaving the rind on vs scraping it off. I believe the quality of the bamboo makes the biggest difference, but unfortunately you won’t know the quality until you use it.