Crack on glue seam?

[mps989]

Hey everyone,

I'm attempting to build my first laminated bow, and while on the final stages of tillering I noticed some cracks or gaps in the glue seams. My first thought was that the bow is going to delaminate and I'll lose it, but now I'm hoping it's nothing too bad, or that I may be able to fill them with some superglue. The gap shown seems to "continue" on the other side of the bow too, though smaller there, and this is the one that worries me the most. Have you ran into similar gaps? Thanks in advance!



The glue used is a grey super strong, 2h hardening epoxy (resin and hardener amounts eyeballed), the woods from back to belly are bamboo, "North American" (dont know which) maple, and Ipe.

And while here, this is what the bow looks like on the tiller, any comments or criticism welcome here too.

[tattoo dave]

No way to know for sure until it breaks...if it breaks. Super glue might work, or it may just delay the breakage. If that bow was mine, I'd fill with super glue and some really fine dust, but never let anyone else shoot it. Can't trust it 100%.

Tattoo Dave

[Bayou Ben]

Nice bow.  I've had many gaps like that show up from not enough even clamping pressure.  I use a thin steel flatbar now to even out the clamping force and I haven't had those problems since. 
The one difference though on the gaps that I experienced is that they were only on one side.  The fact that it goes all the way through has me a little nervous.  Like Dave mentions, super glue is your best bet at getting into that small gap and hopefully it holds up.  I personally think it will if the surrounding glue is sound.
Can you post an unbraced pic?  Looks like a good amount of deflex with isn't necessarily a bad thing.   

[mps989]

Thanks for the insight, I'll try the superglue tomorrow. What bothers me now is that it's supposed to be a gift, unsure if I'll have to build another one or if I could wrap some cord around the weak spot to secure it.. It's only going to be 20-25 pounds heavy, wondering if it akes it easier on the glue joints too. It's fairly narrow though, so I guess it brings the stress levels back up..

Anyway, here's the unbraced picture. The tips were pretty much on line with the back of the grip, but it's taken about 1 inch string follow on both limbs.

[Del the cat]

Been there done that, planed off the back and re-did it properly.
The pic in this blog entry shows the size of the hidden dry area in the join... 
https://bowyersdiary.blogspot.com/2013/08/haporth-of-tar.html
Only way you'll ever be really happy.
It doesn't take that long once you decide to go for it...it's character forming, and you'll never do a poor glue up again 
Del

[mps989]

Would it work woth a bow on this stage though? It's been bent, and I'm not sure how I'd plane a curvy piece of wood like that.
Another issue is that 2 of the 4 gaps aren't under the back lam, but one is next to the belly, and one between teh core and the power lam. I think I'll just have to fill the gaps with glue, and start another similar bow to give as a gift

[Bayou Ben]

That's a good plan.  I didn't know this was for someone else.  If you have that many gaps then I would say you don't have enough clamping pressure. 
On the next one I would go less on the deflex and make sure your limbs are balanced.  That one limb has taken a good bit more set than the other. 
This is what I do to tiller for equal limb timing: Draw a vertical line on your tree where you intend to pull your string from.  Set your pull hook there.  Figure where your center of pressure will be on your bow hand.  The pressure on the tree cradle should be centered there.  Once you know those 2 points make the hook tote the vertical line.  If it sways to one limb, that limb is too strong.  When it totes the vertical line your bow is balanced for how you intend to hold and draw the bow.

I learned this method from "Dances with Squirrels".  I believe that's his name on here.     
 


 

[bushboy]

If you guys are taking about ca glue (crazy glue) I personally think it great in tensile but not so great in shear!I found that the little cheap brass wire wheels and a drill to clean up the joint in order to remove the excess crap and then apply a good quality expoxy pushing in with a fine edge while stabbing it much like concrete vibrators do and tapping it on soild surface to remove any air bubbles.make small batches of expoxy so time is not a concern.just my .2cents.

[mps989]

Thanks for the new ideas! Both limbs were stressed about evenly, it looks uneven because I took the picture with the bow leaning against the door frame (thus the gap to keep it balanced) and then flipped it horizontal

[Stick Bender]

Like was said if there showing up on both sides you probably have a void , maybe if you have room to narrow a bit and re glue the area ,there's guys around here that use pet syringes to glue in voids , with any laminate glue up good even presure is your friend , what system did you use to clamp ? If Im using c clamps I sandwich rubber strips between thin metal presure strips , I have never used them but there are guys here  that wrap there limbs with inter tube strips , or if you have a set design you can build a form with pegs in it to wrap the bands around for solid even presure similar to the pic.

[Eric Krewson]

back before I made my clamp pads out of bamboo and had a limited number of C clamps I got voids in my glue lines. I filled them with superglue and forgot them, I never had a failure.

The bamboo clamp pads have just the right curvature to provide a good glue joint. Of course I only use these pads on a BBO glue-up.

[Stick Bender]

Here is a simple form and clamping system with the rubber strips and lams sandwiched in between 2 presure strip the rubber conforms around the bamboo nodes and using the small clamps help from applying to much pressure !

[mps989]

The system I used is shown here



The only difference being that I wrapped some tyre strips around it too, but I suspect I didn't tighten them up properly, or didn't use enough glue (I misjudged the amount of glue needed and had to use thinner layers).

The bamboo clamp pads sound like something I might try on my next attempt. The metal and rubber setup looks safe, if I had the material I'd give it a shot too. I'll probably just use a lot of epoxy and wrap the rubber as tight as I dare, adding some of the few clamps I have available to secure spots like the handle and bending the lams. Thanks again for the help everyone!

[bubby]

Ditch those clamps and get some bike innertubes. If there's a bike shop around they will give you old tubes if you ask nice😉. You get a nice even pressure with the tubes and will have sweet glue lines

[Del the cat]

The system I used is shown here



The only difference being that I wrapped some tyre strips around it too, but I suspect I didn't tighten them up properly, or didn't use enough glue (I misjudged the amount of glue needed and had to use thinner layers).

The bamboo clamp pads sound like something I might try on my next attempt. The metal and rubber setup looks safe, if I had the material I'd give it a shot too. I'll probably just use a lot of epoxy and wrap the rubber as tight as I dare, adding some of the few clamps I have available to secure spots like the handle and bending the lams. Thanks again for the help everyone!

You didn't just use that many clamps???
Clamps need to be about an inch apart, (maybe 2" at a push), any more than that is asking for trouble.
If you are using rubber strapping you need to keep it tensioned as tight as you can... when you've wrapped it you should feel like you've had a damn good work out... minimum 2 layers of wrapping, no gaps visible.
Del