Bamboo backed ipe bow failure, question

[Hilongbow]

Very sad... I really liked this one. Oh well, when it happens a lot you get used to it!



(this bow http://www.primitivearcher.com/smf/index.php?topic=65047.0)

Seems like a glue failure (smooth on). It delaminated along the glue line with glue on both sides on the split. Very unceremoniously, too. I started pulling back for the shot, and it just sort of collapsed at the beginning of the draw. Didn't even really make any noise. Think it's worth keeping either the back or the belly if I can get them separated? Or maybe worth repairing somehow? Since there was some perry reflex glued in at the beginning, the belly has a bit more of a bend now that its separated from the backing.

Side note: I've had a similar break before, where it almost looks like the string loop was putting some pressure on the backing and caused it to shear towards the center. Since then, I've always been super careful about cutting in the nocks to distribute stress evenly, but maybe it wasn't enough. I had about 4 dry fires with this bow with some loose nocks, maybe they played into it a little too.

[Del the cat]

4 dry fires  errr, that's not going to help.
Have you ever watched a slo mo of a bow shooting? Even with an arrow there is a huge amount of flex and vibration in the limb. A dry fire must flex the hell out of it.
As Oscar Wild once said  .
One dry fire is unfortunate two is careless. (Dunno what he thought of four  ).
My money is on the dry fires causing the tip to start delaminating.
I always take extra care of glue up at the tips, I generally allow an extra inch, which is then sawn off , as it's hard to get good even pressure at the end of a stave.
If there is glue on both faces, then maybe not enough pressure on glue up causing a thick glue line? Glue past it'shelf life? Poor prep'?
Incorrect incantations or phase of moon?

This isn't a dry fire, it's a 260gn arrow from a 50# ELB flight bow. It shows some of the limb vibration.
Bear in mind that 260 grains accelerating at that rate has an inertia equivalent to about 11# of inertia. It shows why a dry fire is soooo bad.
https://www.youtube.com/watch?v=_pWBvcecdwM
Del
PS, Split off the back with a V thin blade, clean it all up and try again... it might even give some clues about what happened. Worst case it will be you penance for 4 dry fires

[Hilongbow]

Yeah, I'm not happy about the dry fires. I normally shoot 3 under with a tab, but I tillered this bow for split so I used a glove for the first few days instead. My glove was pulling the arrows off the string while drawing causing the dry fires. I made up a split finger tab and it never happened again. Lesson learned.

I actually filmed this one high speed and it was very interesting to watch the vibrations. It looked like a wave traveled from each tip towards the center, with the crest of the wave on the back of the bow. I started to hypothesize that controlling where these crests meet might help control hand shock and vibrations. Testing that is a job for someone with more time and materials than me though, unfortunately.

I too do the glue ups extra long and then saw off the last inch or two on each end as I get close to final tiller. I try to make sure I have even, appropriate pressure along the portion of the "stave" that will be used for the bow. The epoxy was just ordered recently from a reputable supplier so I think the condition was good. It could be that my surfaces are too smooth for the epoxy, especially with shock from dry fires. I try to rough everything up with course sandpaper, blow it off with compressed air, and wipe it down with denatured alcohol then let fry for at least 15 minutes.

Thanks for the advice and insight! I thought it would last quite a while, those dry fires were very early on and I've put several hundred shots through since then. Oh well, I have already been thinking about what I would have done differently from the beginning and plan to do just that on the next one. It was a great learning experience. I'll try and recycle the backing, but might toss the belly in the fire because it has already taken some set.

[Del the cat]

Let's see the slo mo then... post it on Youtube! 
Del

[Dances with squirrels]

I'd say the dry fires definitely had something to do with it, but just for insurance... are you mixing the two parts of Smooth On adequately?

I have never had such a failure after many bamboo backed bows with Smooth On. Not one.

I prep the bamboo's gluing surface with a toothing plane blade, run lengthwise down the piece, leaving noticeable grooves behind. And then my wood piece is ground in a thickness sander with 40 grit paper on the drum. So both are quite rough, making it virtually impossible to starve the joint. I'm not saying that was a cause for you... just some things to think about.

Oh yeah, clamping pressure is another factor to consider, especially if the surfaces are smooth.

[ohma2]

I too used alot of smooth on ,but its been a while back i was at the wood store where i do business and i was buying some more smooth on and the owner gave me some numbers to check on my supply i had at home and told me to throw it away at advice from his supplier.was supposed to be a bad run or something .never had trouble with the new stuff.

[Badger]

  I think about the best glue for ipe is tightbond original. Not water proof but I have never had a moisture problem with it. Takes a lot of water to cause a problem.

[Hilongbow]

Del, I've been wanting to post the video but the only method I have for seeing the vibrations is by scrolling frame by frame with my fat fingers on my phone screen. If I can find a way to get the video to play really slow frame by frame I will be happy to share. I wish I had an ultra high speed high res camera. Would be really useful for tuning too haha

Squirrels, I mix my smooth on for 2-3 minutes at least, so my guess is maybe surface prep combined with the dry fires. I use 50 grit on my belt sander, then before gluing I take some 60 grit and sand in random directions along the length of the gluing surface to make lots of little grooves. I clamped this one by wrapping with inner tube strips and small spring clamps every few inches. Should that be adequate under normal circumstances?

[Hilongbow]

 Badger, I have read that before (probably from you) and have considered it, but where I live we get about 130" of rain a year at the lower elevations and even more up high where I live and hunt. I'd say at least half of the time I'm shooting, it's raining. When I'm hunting, I've sat in the pouring rain for 4 hours plus, and that's not abnormal. Im not sure it would handle that! Any thoughts? I usually just do an oil finish but maybe with a urethane or something instead?

[Bayou Ben]

"I've done my two D/R trilams like this, using c clamps to get adequate pressure in critical areas (only tight enough to close the gap, but theoretically not tight enough to squeeze out all of the epoxy), and spring clamps and inner tubes for the gentler portions. But yes, you are right that it seems like something in my glue up process is causing me all of these failures. In my other recent post about my BBI delamination, it separated perfectly along the glue line. In the case of the FG bow mentioned in the original post of this thread, it delaminated perfectly along the glue line. In this bow, all of the separations in the riser/fade area were along the glue lines. None of the wood ever cracked or splintered in these bows. It looks like there is epoxy residue on both sides of the split.

This is kind of drifting from the original purpose of the thread, but does this system appropriate? Do you think that it is a surface prep issue or something? Since I am using epoxy, I use rough grit sand paper, and clean with compressed air or denatured alcohol, sometimes both. I cure for at least 24 hours at 90F-100F"



That's more clamps than I imagined you were using.  I don't think that's your problem. 
Your surface prep seems ok too.  I use 40 - 60 grit, then just vacuum clean. 
Are all these failures from the same epoxy?  If so I would suspect you got a bad batch like was mentioned, and I would ditch what you got left.  I use Uni bond 800 and it is forgiving as far as mixture rates and cure time/temps.  I haven't used smooth on, but from everything I hear, it's better than Unibond. 
The last thing I could think of is making sure each lam is at relative moisture content. 
I hope you are able to figure out what's going on.  I'm frustrated for you. 

[Bayou Ben]

Just thinking some more, how do your glue lines look right after it's cured and cleaned up?  The glue lines should be small, uniform in thickness, and barely noticeable.  If they aren't, then there's a clamping issue. 

[Del the cat]

This video about testing various glue joint preparations and clamping pressures is really interesting. There are obvious points where it's not the same as gluing up bow lams, but still interesting.
https://www.youtube.com/watch?v=14Mkc63EpMQ
Del

[Hilongbow]

This bow is from a different, newer batch of smooth on than the trilam and FG mentioned in the other post.

As for glue lines, I always do several dry runs and check the fit of all the parts to make sure they mate well. For my power lams, the last half inch or so is so thin it's translucent, and the ends of the lam are so thin it's basically just single wood fibers and it starts to fray. When clamped dry, I use a flashlight to ensure no light is coming through. Any spots that won't sit flush against the mating surface with a little bit of pressure gets attention until it fits.

After cleaning off the excess glue, the lines are clean and so thin you can't really even see glue. But, I know it's there because there is epoxy on both inside faces of the delaminated area, along with very very tiny splinters of wood from the opposite face, indicating that the glue stuck.

If my prep and glue method seems solid, maybe in this case it really was the dry fires causing too much shock and rippling down the glue line, eventually leading to failure.

I'm almost certain the trilam handle came apart because the power lam was too thin and too short, causing noticable flex in the fades early on in the tillering. That's why I brought the weight down so low. I think the FG bow was a case of poorly mixed glue as the residue left behind looks like sugar crystals instead of cured epoxy.

Not sure on the moisture content, but with over 130" of rain a year in my area, it's always quite humid. Not much I can do about that.

Del, that's a great video. I'm definitely not using as much pressure as the ones with 4 clamps on one joint. I just turn until it stops, and then after it warms up and settles I tighten it a tiny bit more

Wordy posts, thank you all for taking the time to read and respond

[DC]

You're not doing something dumb, are you? Like a 2:1 mix when it should be 5:1. Or two hardeners when it should be two resins. Have you read over the instructions? Go ahead, wait til she's not looking and then read them, we won't tell. I can't tell you how many times I've done something wrong so I thought I'd ask

[Woodely]

Like I say.......
"Doing bad work is an exercise in futility, but honestly making mistakes is trying your best."  eventually doing things your way that way your methods of work, your own ideas, your style and design are your own.      I mixed some Plastic Resin one day on the weak side and the bow flew apart, luckily it happened before I shaped it so I was able to save most of the lamination's.
Having said that so many on here have built Thousands of bows there is no lack of information and tips.