Post Mortem Help Please

[Steve Kendrot]

I was working on a BBO for my wife and it was coming along nicely. Drawing 40#@26" with decent bend on both limbs. Sorry no pictures. I wasn't sure of her exact draw length and wt so I stopped tillering until I could check her stats. I was exercising the bow, shooting a short draw around 26#. I may have pulled it back to 27 one time. It was shooting very nicely and I was pretty excited when BAM. The top limb snapped. I have no idea what caused this failure and would like some feedback from those who have broken more bows than I have ( this is the 2nd so far). Here are some pics:

Break at mid upper limb
 

A little closer
 

Belly View
 

Side View
 

Back View
 

End Grain
 

I was liking this one!
 

It was a pretty clean piece of osage. No knots. No obvious problems with glue lines. Took me a while to get there but the tiller was pretty even according to my gizmo.

I did not shoot the bow more than six times before this break-in session (pun intended). I'm wondering if I should have exercised it more regularly at shorter draws throughout the process. Can you rush it? My other thought is maybe I overdried the wood, but it sat at ambient conditions for a couple weeks after glue up. What are your thoughts folks. I have another one in the works that I will probably have some questions on too.

[Eric Krewson]

Looks like a bad piece of bamboo to me. I made a bow out of bamboo that had been stored in a basement and was a little moldy when I put it in my drying box prior to making a bow. It failed the same way yours did,with a very clean break, during the tillering process.

[John Sturtevant]

Agree it looks like bad BB.

Had 3 bows pop in a row last winter, same clean break.   All at full draw.  

First one I thought was a fluke.
Second one I got a bit suspicious.
Third one really got my attention.
 
Had kept all three and could tell the BB all came from the same pole.  Had a couple other pieces I hadn't used yet and started testing.   You could put it in a vise and bend it, and it would pop like glass.
If you have any more of the same BB I'd pitch it.

[Steve Kendrot]

Now that I hadn't considered.... Got the Boo from a reputable source and at $20/pop, not real keen on pitching it.

[Art B]

Hey John, did all yours fail on the upper part of the boo (top of the stalk)?

Of all the boo backed bows I've had fail they ALL failed on the upper limb. I orient my boo as it stands in the stalk as per Torges' advise. I don't think this is a coincidence. Just like my bows, I build them as they stand in the tree and 95% broke in the top limb. That's not a coincidence either. Natural materials just appear to be stronger on their trunk end.

Steve, your bow failed partly because of those bias cut growth rings IMO. Was your boo overly dry? Was your osage slat cut from a larger dia tree? You see a lots of the swirling bias ring from larger trees. Look for light and dark areas in you osage wood next time. This is an indication of soft and hard areas in the wood and should be avoided. Scraping the rind off can violate the power fibers also. Sorry it didn't work out for you. That was going to be a nice looking bow.

ART B

[John Sturtevant]

Art, I don’t recall….the last one had both limbs break at the some time.   One BANG, three pieces.  
I’ve busted my share of bows, but that was a bit unusual.  

Steve, I might have been a bit harsh when I said “pitch it”.
Certainly I can’t say for sure it was the BB’s fault..it’s just that when BB let’s go it’s normally not that clean of a break...and it looks just the same as the failure’s I recently had.

When I finaly got around to thinking it was the BB I started testing different types from different sources I had.
The ONLY bamboo that broke cleanly…no splintering...no tell-tale popping before it let go was the material I had split from the same pole.   When it broke it went all at once. Appeared to be very brittle.

Please do some testing with your remaining material before you us any more.

Agree the grain orientation on the belly was not the best, but I’m still suspecting a BB issue

[wingnut]

After looking at the belly wood, it has a awful roll to the grain and is basically running straight across at the break point.  Not bamboo is going to hold that together.  Try and select the belly wood to have straight running grain either 1/4 sawn, rift sawn or plain sawn.  But when the grain runs across the bow, most will let go.

Mike

[Aeronut]

I agree with Mike.  It broke right on the grain.

Dennis

[Eric Krewson]

If it was a problem with the osage the bamboo would have splintered but probably still held together somewhat. Bamboo that breaks clean has a flaw.

I no longer buy bamboo from Franks because of past failures. All I have bought from Wingnut is still doing well in the BBOs I have built, no problems.

[KENDALL TECHAU]

I agree with Wingnut.The break follows where the grain runs across the belly,once that snapped the boo had to go.

[Steve Kendrot]

Thanks for the feedback everyone. I had some doubts about that bias cut board, but was hopeful that a light weight bow could be teased out of it. I would have thought the backing would have held it together. After all self bows are all "bias cut" in a sense. It almost seems it slid apart along the growth ring. My wife would have never shot again if that baby had smacked her on the forehead! Now I'm worried about the new bow I'm making. Its got some serious runouts in the first third of one limb, although there are some rings that follow the length of the limb.

I'm not hearing too much concern about tillering too quickly. At what point in the tillering process (draw length) should you start shooting the bow? Can it hurt to take a bow from glue up to fully tillered in one evening?

[bigcountry]

Well, if it makes you feel better, you taught me a thing or two on this thread.  One, it can happen with bamboo.  Never thought bamboo could have tension failures so easily.  Two, I thought you could use any type of core belly grain with BBO.  Learned that is not so.

[Eric Krewson]

I have made 40 or more BBOs with every type of grain configuration from edge to cutting through a 45 degree propeller with no osage failures.

Here is my moldy bamboo break.

 

It still has stringers in spite of the break.

[John Sturtevant]

Hey Mike….
Hope you, Jason and your lovely wife are doing well.
I’ll miss seeing you guys at Mojam this year.


Steve, these guys are right...the grain is a bit squirrelly.    It’s impossible for anyone to know if that is where the problem started or ended, but it’s best to avoid.

 I do know the BB break does not “appear” to be normal...and looks just like the bad stuff I had.  
You can do what you want...if it was me I’d want to know more, and the best place to learn is in your shop.
I would band saw part of the backing off, sand the rough sawn surface and put it in a vise and see how it breaks.   It should not pop clean across.
Do the same with some other BB you have and compare.
At least then you’ll know if one of the problems could have been the bamboo.  You'll also find out if the rest of your bamboo is OK....and it may save you some “character building” experiences in the future.
 
Mike sells the best BB I’ve used.  I ran out this winter and got a “deal” on some poles.   Some deal, huh?  

[bigcountry]

Originally posted by Eric Krewson:
I have made 40 or more BBOs with every type of grain configuration from edge to cutting through a 45 degree propeller with no osage failures.

Here is my moldy bamboo break.

 

It still has stringers in spite of the break.

Oh, that looks heart breaking.

[Eric Krewson]

Here is the same bow after a liberal application of Urac in the cracks and a new strip of bamboo. Still shooting a bunch of years later.

 

[Steve Kendrot]

I think I might have my terminology screwed up. I understand quarter sawn and plain sawn. I think Rift sawn is between the two, but what is bias cut? Is that where a growth ring starts on one side of the board and exits on the other side? Can someone straighten me out here?

[Art B]

Rift/bias, same thing (diagonal cut).

ART B