Bamboo backed hickory delaminated

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Bamboo backed hickory delaminated

jtester
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jtester
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Joined: December 26th, 2014, 5:15 pm

December 27th, 2017, 6:12 pm #1

I was building my first bamboo backed bow, a hickory board with a planed bamboo backing.  It delaminated at the junction of the bamboo and the tip overlay when I first put it on my tillering board.  I had rasped the bamboo off the hickory at the overlay so I would have a overlay/hickory joint and that's where the failure started.  Right at the joint, the glue let go of the bamboo, but an inch or so towards the handle, the glue held and the hickory split.  I used Unibond 800 epoxy.  Should I have done the overlays differently, or maybe left them off entirely?  I'm pretty disappointed, I had a lot of hope for this bow.
Any ideas or suggestions would be appreciated.
Thanks
Jim
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jtester
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jtester
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Joined: December 26th, 2014, 5:15 pm

December 29th, 2017, 12:53 pm #2

I've studied this thing for two days.  At first I thought my mistake was removing all the bamboo where I applied the tip overlay.  Now I'm not so sure.  I watched a couple you tube videos and they indicate that the glue joint should be stronger than the wood itself.  If that's true, butting the overlay up to the bamboo instead of gluing it over the bamboo wasn't the problem, or at least not all of it.  As I mentioned, the bamboo separated from the glue and hickory right at the tip overlay.  It looks like the glue joint was faulty.  I'm going to try another backed bow and see if my theory is correct.  If I could post pictures I would, but so far I haven't had any luck.
Jim
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Quest for fire
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Quest for fire
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Joined: March 22nd, 2007, 6:19 am

December 29th, 2017, 8:45 pm #3

I admire your aplomb.
If I were to break such a bow when almost finished there would be a lot of unmentionable words in my thread.😣
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jtester
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jtester
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Joined: December 26th, 2014, 5:15 pm

December 30th, 2017, 12:31 am #4

It's not my first bow blow up, but I was disappointed.  
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burnbarrel
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burnbarrel
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Joined: September 11th, 2008, 7:02 pm

December 30th, 2017, 3:37 pm #5

Following. Thanks for posting. I'm getting ready to start my first bamboo backed bow.
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jtester
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jtester
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January 14th, 2018, 2:32 pm #6

Sorry for the delay in posting, a friends daughter wanted to learn to build a bow so I took two weekends helping her.  I'm sure my problem with the first bow was a bad glue joint.  When I use wood glue, I apply it to both surfaces being glued, but when using epoxy, I heard I only needed to apply it to one surface.  That was the cause of the first blow up.  The glue didn't adhere to the bamboo completely.  This time I put glue on both surfaces and it was apparent that the bamboo resisted the glue a bit.  I put lots of glue on and things came out perfect.  The bow pulls about 45# at 27".  I shot about 50 arrows yesterday and it's sweet.  I'll try to figure out how to post pics again and post some when I get the finish on.
Jim
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French Crow
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French Crow
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Joined: May 25th, 2006, 5:31 pm

February 11th, 2018, 11:46 am #7

Glad you found what was wrong. Too much pressure can also weaken the glue joint.
Bruno
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jtester
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jtester
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February 11th, 2018, 5:59 pm #8

Thanks French Crow.  I have built two bamboo backed bows since the one that blew up.  The first was backed to hickory and as I mentioned, it came out nice.  The second is bamboo backed to a Brazilian hardwood, Goncalo Alves.  It's also really nice.  66" ntn, about 50# at 27".  I haven't figured out how to post pics yet, I'll keep trying.
Jim
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Robson Valley
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Robson Valley
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Joined: April 24th, 2015, 12:27 am

February 22nd, 2018, 1:55 am #9

Are you pulling against the tangential resistance or the radial resistance of the wood?
Or maybe some quarter-sawn intermediate.?
Wood anatomy mechanical properties offer a profound difference here.
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jtester
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jtester
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February 22nd, 2018, 6:57 am #10

I really don't know the difference.  Could you explain?  I purchased the hickory from a reputable supplier so I'd be surprised if it was the wood.
Jim
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hixton
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Joined: December 23rd, 2017, 2:30 pm

February 25th, 2018, 6:00 pm #11

jtester wrote:I really don't know the difference.  Could you explain?  I purchased the hickory from a reputable supplier so I'd be surprised if it was the wood.
Jim
I can't answer grain orientation questions but I have laminate a bow using
titebond I I I. It's good for all conditions. Epoxy is good but it might be too hard.

https://www.walmart.com/ip/TITEBOND-141 ... 3=&veh=sem



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jtester
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jtester
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February 25th, 2018, 6:37 pm #12

Hixton
I'm familiar with the Titebond family, I have both II and III.  I chose the Unibond800 because it is specifically for wood to wood bonding without a hot box.  I got it from a reputable bow material supplier.  As I mentioned, the two that I built after the one that blew up work great.  I'm going to try Titebond 3 next.
Thanks for the thoughts
Jim
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