Bow limb broke. Help!

[WilltheArcher]

I usually use an overlay on the attachment area to help to distribute the stress that full size washer might do the trick

Bubby you have any pictures of that? Might try to glue an overlay on to this new pair of limbs I'm cutting out. How thick is it?

   Did you rough sand the ipe, if you put it through a planer it might not be pourous enough.

I sanded it to rough it up then wiped it off with acetone to make sure it wasn't oily, but maybe I didn't rough it up enough.

[bubby]

I'll have to take a look see if i have a pic

[WilltheArcher]

Bubby I think I get the idea from this thread you linked me to a while back:
http://www.primitivearcher.com/smf/index.php/topic,24354.30.html

That brown diamond shaped piece at the riser ends of the limbs right, looks to do about 1/8 inch thk? Do you think that and Del's washer plate would be too much?

Del - machined two of these today. Going to round the corners tomorrow.

[Del the cat]

That looks much better
What material is the plate made of ?...
Oh , I see you said steel...
Yeah 1/8 steel should do it... I just said 3/16 to err on the side of caution
Still use a decent thick washer (especially on the lower bolt to spread a good clamp action across the whole lower edge of the limb)
Looking at the pic of the break again, I can see it's actually pulled the limb away from the end stop in the riser. So it's effectively just split out that narrow strip the width of the bolt.
Maybe a thin rubber sheet between the faces (increase the friction/grip and spread the load evenly onto the wood fibres?)... dunno?
What do they do on commercial bows?
If you glue the plate to the limb you can call it an 'overlay' like Bubby suggested  
Del

[WilltheArcher]

That looks much better
What material is the plate made of ?...
Oh , I see you said steel...
Yeah 1/8 steel should do it... I just said 3/16 to err on the side of caution
Still use a decent thick washer (especially on the lower bolt to spread a good clamp action across the whole lower edge of the limb)
Looking at the pic of the break again, I can see it's actually pulled the limb away from the end stop in the riser. So it's effectively just split out that narrow strip the width of the bolt.
Maybe a thin rubber sheet between the faces (increase the friction/grip and spread the load evenly onto the wood fibres?)... dunno?
What do they do on commercial bows?
If you glue the plate to the limb you can call it an 'overlay' like Bubby suggested  
Del

Glad to hear it. The rubber sheet to spread the load out sounds like a good idea. And I'll remember to still use a washer.

Del, the funny thing is the ipe didn't break, just the ash lam. I'm using that same piece of ipe and gluing a new piece of ash lam on top. Once it's finished drying I'll sand it to match and make sure it's the same thickness as the other limb. I still don't know whether it was the stress concentration at the bolt that did it or whether it delaminated. I'm hoping it's the stress concentration. If it was the lam, I don't know what to do

Ok I'm not gonna do the wood overlay for now. Tomorrow I'm going to remake that limb once its finished drying, then remount it with the plate washer and some 1/16 rubber sheet underneath. I'll warm it up, do some light tillering, and hope for the best. Speaking of tillering I took a few photos yesterday and wonder what you guys recommend.

[Del the cat]

The failure was due to the bolt!... else why did it happen exactly there?
Occams razor... the obvious is the most likely.
Del

[WilltheArcher]

The failure was due to the bolt!... else why did it happen exactly there?
Occams razor... the obvious is the most likely.
Del

A cat that knows of Occam's Razor...the wonders never cease

Hoping you're right!

[Del the cat]

S'pose if I was being picky, I'd probably do an overlay on the belly (underlay?) with a fade incorporated so there isn't a hard transition where it meets the riser.
Del

[PatM]

The failure was due to the bolt!... else why did it happen exactly there?
Occams razor... the obvious is the most likely.
Del

Why would it delam after the limb was no longer supported? I still think it was the delam first. The rubber gasket is not a good idea. A soft surface in a structure that you're trying to make rigid is a poor recipe.

[Del the cat]

The failure was due to the bolt!... else why did it happen exactly there?
Occams razor... the obvious is the most likely.
Del

Why would it delam after the limb was no longer supported? I still think it was the delam first. The rubber gasket is not a good idea. A soft surface in a structure that you're trying to make rigid is a poor recipe.

It would delam because the spilt has then allowed the part which is still held by the bolts to bend on a tight radius and delaminate... once it starts to delaminate it continues along the limb.
I'd suggest if the delamination started mid limb, the limb would loose all it's rigidity and no longer have the strength to cause the split.

There is no actual way of telling which came first.
I'm quite happy to be wrong, I'm just saying what I'd do*.
Note I said thin rubber. I agree you don't want it to be able to move, but on the other hand you don't want it flexing up against a sharp edge.
Is any part of any bow is ever trully rigid...? (Answers of 500 words to "philosophy and bow design" department WPB... Del the Cat, Harlow UK.... )
Del

*As the old Irish joke goes:-
A driver pulls up at the road side to ask an old guy the way to Balally...
The old Irish guy looks at him, strokes his chin and replies.
"Ah, to be sure, If I was you I would start from here... "

[mikekeswick]

For it to delam like that you had a shoddy bond. Fact 
The best way to prepare surfaces for TB3 is with a drum sander. Failing a drum sander then a planer thicknesser will work but you must roughen the surfaces up for a good bond. Planer thicknessers will compress the fibers and TB is a water based glue that won't get 'into' the ipe. They also leave the surface washboarded (if you look closely enough!).
The best glue is probably Smooth On EA40 expensive but it real is very good. Cure it with heat for a better bond.
Your design is in my eyes destined to failure...maybe not today, maybe not tomorrow but someday! Look at Fiddler's thread the advice there is solid and you should follow it. After all why do 'normal' bows have fades and why is it critical to get them right.
Also your bow is on the edge of hinging at the inner limbs. You need to remove more material on the mid to outer limbs - this will also help to stop it failing where it did again.
Good luck and don't try to rush it 

[DavidV]

So many wooden takedowns have this problem, you need a wedge where the limbs and riser meet! Every laminated takedown has wedges or they'd blow out at the bolts too. compounded by the grain structure of wood it makes it even more important.

[WilltheArcher]

First of all guys thanks a ton for taking the time to help me troubleshoot, really appreciate it.

So many wooden takedowns have this problem, you need a wedge where the limbs and riser meet! Every laminated takedown has wedges or they'd blow out at the bolts too. compounded by the grain structure of wood it makes it even more important.

David, this is really useful. I have another pair of limbs and I'm going to try to make wedges like this for them today and glue them on. Can you help me out with dimensions and materials? Looks like it's flat along the riser bed then slopes in for about an inch or two? Maybe quarter inch thick? What kind of wood should I make it from?

For it to delam like that you had a shoddy bond. Fact 
The best way to prepare surfaces for TB3 is with a drum sander. Failing a drum sander then a planer thicknesser will work but you must roughen the surfaces up for a good bond. Planer thicknessers will compress the fibers and TB is a water based glue that won't get 'into' the ipe. They also leave the surface washboarded (if you look closely enough!).
The best glue is probably Smooth On EA40 expensive but it real is very good. Cure it with heat for a better bond.
Your design is in my eyes destined to failure...maybe not today, maybe not tomorrow but someday! Look at Fiddler's thread the advice there is solid and you should follow it. After all why do 'normal' bows have fades and why is it critical to get them right.
Also your bow is on the edge of hinging at the inner limbs. You need to remove more material on the mid to outer limbs - this will also help to stop it failing where it did again.
Good luck and don't try to rush it 

Good advice. I hate to rush but sometimes you don't have much of a choice. School project and the woodshop closes end of day Thursday so I'm workin' round the clock. I'm not sure I'll be able to get my hands on smooth on in time - can you buy it in a store (not online)? If not - is there an epoxy that's better than TBIII that I can get at an Ace Hardware/Home Depot? If I can, I'll try to get that and some more Ipe/Ash and do a better laminate. I don't have a drum sander but I roughed up the Ipe pretty good with some 80 grit sandpaper so I was pretty surprised with the delam.

There is no actual way of telling which came first.
I'm quite happy to be wrong, I'm just saying what I'd do*.
Note I said thin rubber. I agree you don't want it to be able to move, but on the other hand you don't want it flexing up against a sharp edge.
Is any part of any bow is ever trully rigid...? (Answers of 500 words to "philosophy and bow design" department WPB... Del the Cat, Harlow UK.... )
Del

Del, you're right it's hard to say. I actually woke up this morning thinking what PatM about why it would delam after the bolt failure. But at least I have some ways to troubleshoot. The rubber sheet I have is only 1/16 thk so I'll go with it for now. That and the plate washer and the bolt shouldn't fail. If it delams again at least I'll know it's the lam and not the bolt. Hurray troubleshooting haha!

One thing though - do you think that rubber sheet should go between the riser bed and the limb, or between the washer plate and the limb?

[Del the cat]

Q. Rubber sheet between bed limb or plate and limb?
A. Either neither or both.
I'd actually be tempted to epoxy the plate onto the back of the limb* and then have rubber between riser and limb.
Other opinions my vary. Contestants must be 18 years or over. Terms and conditions apply 
Del
*This is good on several counts.
1. It helps make the root of the limb more rigid.
2. The epoxy will fill any imperfections.
3. It will prevent any movement between plate and limb due to vibration, slight flexing etc.
4. You won't loose the plate.

[WilltheArcher]

I think my problem now is there are so many possibilities I don't know what order to try them in.

1. Plate washer/rubber sheet like you (Del) say.
2. Wedge like David says.
3. Try to relaminate.

Number three is hard because the guy I bought the Ipe from hasn't gotten back to me, and I don't think I can get my hands on the Smooth On epoxy in time.

I'm tempted to try the plate washer, rubber sheet, and David's wedge. But the fact that Bubby and even the guy in Fiddler's post made takedown longbows without wedges that lasted 1000+ shots without incident makes me think that it's not the critical problem right now (though it'd definitely make the bow better in the long run).

think once the new ash lam is done drying on the broken limb I'll try those with the plate washer/rubber. I'd epoxy it on like you said but it'd be hell to get it off if the limbs end up breaking again, and it takes a while to machine em on the mill.

if I can figure out dimensions on the wedge I'll try to make that and glue em on to my second pair of limbs.