What do you think caused this failure.

[razorback]

I have an idea but would like to hear what you guys think caused this failure.
This is a hickory bow with glued on tips as seen in 4est's board bow build. These are actually the second set. First set were walnut and failed along a grain swirl. I put a new set on of straight grained hickory. Areas were sanded smooth and then scored with saw blade. Glue was unibond 800 and clamped over night. When I strung it up this end popped off before it was even strung.

Intact end.

 

popped end.

 

 

 

[bornofmud]

Looks like the glue joint failed. Maybe try smooth on?  Or wrapping the joint probably would have helped.  Soak some sinew or rawhide in glue and wrap it around the whole splice.

[DVSHUNTER]

Id say there is too much stress there.  Its kinda like a big teter toter with the tip being that far past.

[Bowjunkie]

That doesn't look like "straight grained" hickory to me.

But it does seem the glue joint failed. Get yourself a toothing plane iron.... just the blade is all ya need. I got a spare blade on e****. Groove both pieces the full depth of the blade's teeth, and glue up with Smooth On and a blanket covered shop light for a heated cure. Not a guarantee, that's an iffy task, but it would better your odds. If you had done it that way, that piece of hickory would have likely failed across the growth ring runout before your glue joint.

[George Tsoukalas]

It broke along grain lines because the lines are not straight tip to tip.

If the grain runs out more than in 2 places per limb...forget about it. Leave it in the stacks. It will look much better on someone's wall.

Looks like the board choice is really bad, razorback. Info on my site.
 http://georgeandjoni.home.comcast.net/~georgeandjoni/index.html

Jawge

[scars]

I see a starved glue line, and with a scarf joint 4" long  and you have another 4" beyond the scarf. 3" to the string nock the very tips on one side broke. Looks like one side lifted as it was pulled back, like a fulcrum pivot point. maybe a fishtail joint would work better.
I may not know much about bows but I do know joints.
Joe

[LittleBen]

Too much leverage. The glue on tip portion extends too far beyond the scarf joint.

It clearly broke at the glue line so something there is not working right whether the glue is old or you clamped too tight or something. Perhaps it was cold and didn't fully cure overnight. For some reactions temperature has an exponential effect, for example smooth on, at 170F it cures in 4 hours, and at 70F it cures in 24 hours. I'd venture to guess that at 55F it takes 48 hours. See what I'm saying? I don;'t know what the cure time for unibond is.

[PEARL DRUMS]

Try wrapping it with silk thread next time, bet she stays put.

[Roy from Pa]

What Ben said. You are expecting that glue joint to hold the weight of the bow at full draw. Your string grooves should be in the bow limb, not way out on the end of a glued on tip over lay.

 

[PEARL DRUMS]

Tim Baker did the same exact thing, check out the recurve section TTB2. It worked fine.

[4est trekker]

Pearl is correct.  That's where I stole that idea from.  (In fact, this technique is a VERY tamed down version of the siyahs found on many Asiatic bows.)  This part of the bow won't bend (or barely at all) because the lamination created by the glue joint yields stronger stock per identical dimensions than unglued stock.  That having been said, hickory LOVES to soak up moisture, and glue is no exception.  I would try sizing each surface before applying your glue.  That'll keep the glue from being sucked away from the joint.  I truly believe that's the culprit here.  

Also, I've found TitebondIII to be the easier for gluing handle riser and tip laminations on boards.  It requires smooth mating surfaces, and the factory surface of most lumber is perfect.  

And, as Pearl said, a wrap will provide some great insurance, as will a longer/less severely angled joint.

Hope that helps!  

[Roy from Pa]

Tim and you guys can do it but I wouldn't:)

[PEARL DRUMS]

Sissy....

[LittleBen]

I'm familiar with the image showin in TBB, I think there's way more overhang and less glue surface on this one here.

Can someone confirm if the glue line failed or if it cracked along the grain?

As George had said, that is not a straight grained piece of hickory ... I wouldn't be suprised if it broke along the grain even if the glue line held.

You gotta walk before you run. How long is the stave? do you need the extra length?

[PEARL DRUMS]

Looks dry to me Ben. A small stitch of wood stayed behind, the rest was a clean split away. That's 4" of glue joint, seems ample to me? It appears to be about 3" overhang. If you figure it was a 50# +/- bow, tahts only 25# per limb. That glue should easily hold that in my opinion.

[razorback]

As Pearly said, it failed along the glue line. I was worried that this tip might be a bit long but also thought that it works on siyahs so was hoping it would work. The glue was new unibond and the temp in the workshop was within the recommended range, don't remember exact temp. the glue was dry and powdery. I think it may have been starved of glue.
My worry is, if I glue this one back on, will the other one fail next. The piece of hickory has straighter grain than it looks. Well it did before I cut it to shape, not sure how to fix that problem.

[Roy from Pa]

I wouldn't trust Pearly Girl any further than I could throw him... He doesn't glue up bows..    

Unibond should not be dry and powdery. Ya sure you mixed it right? Glue it up again and keep your fingers crossed..

[fujimo]

i glued on some hickory recurve tips(ala- 4est tracker) on an ipe bow- its still going strong. that grain runout , from when you cut it out, shouldnt present too much of a problem right at the tips.
i say...re face the surfaces. score it well and reglue it. i mix mine using the grain scale- so it is exact!

[scars]

A good bond with unibond 800 is going to be a neutral tan or if you have the dark harder dark brown. I did not see that I see a clear glue joint with the grain of the limb visible. So I called it a starved joint. When you enlarge the picture you can see the sanding marks through what is left of the glue. Archemedes said he could move the world with a lever.

[fujimo]

good point scarman!