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Author Topic: Bow Broke..:-( Help me understand what went wrong
arachnid
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Hi Guys.

I finished a KennyM 60" longbow, came out 46#@28".
I had a 18" long riser, 20" long powerlam and 8" ling tip wedges.
Took it out today for some test shots it shot very well. Until I draw it and as I reached full draw- BOOM.... the top limb broke. No warning.
No the thing is, it seems like the back glass peeled of and remained intact. I don`t have a clue as to what went wrong and I`d like to know so I won`t make the same mistakes again. Here are some pics... Please tell me what you think.

Thanks.

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Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
arachnid
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If more pics are needed, let me know
Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
Wolftrail
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Looks like a De-lam failure to me. I hate it when they BREAK..! As long as ya dont get hurt.
[scared]

Posts: 694 | From: BC, Canada | Registered: Mar 2014  |  IP: Logged | Report this post to a Moderator
arachnid
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quote:
Originally posted by Wolftrail:
Looks like a De-lam failure to me. I hate it when they BREAK..! As long as ya dont get hurt.
[scared]

What can be the cause of it? And do I avoid it?
Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
arachnid
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Is it salvageable?
Can I make a new limb?

Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
Pat B
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Looks to me like the core wood gave loose for some reason. Curly woods are violated when sawn but I would have thought the glass and glue would have held it together. You can see how the wood separated along the grain. Whether it was material failure or manufacturer failure I can't say.

--------------------
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wood carver 2
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The glue around the fade had bonded. Everywhere else, it just let go. It's like the wood was contaminated with oil or wax. Was the epoxy from a fresh can? Is it possible that the glass had mold release on it?
Those are some possibilities that come to mind.
Sorry to see that. It was a nice bow.
Dave.

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" Vegetarian" a Native American term for bad hunter.

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arachnid
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quote:
Originally posted by wood carver 2:
The glue around the fade had bonded. Everywhere else, it just let go. It's like the wood was contaminated with oil or wax. Was the epoxy from a fresh can? Is it possible that the glass had mold release on it?
Those are some possibilities that come to mind.
Sorry to see that. It was a nice bow.
Dave.

The glass was all good. The glue wasn't a new can, it was actually the end of a can... I didn't measure the amounts, I just eyeballed it, can that be the reason?

About the oilly wood- I didn't wipe it with aceton (I've read the it releses more oils) , I sanded it and then made grooves with a hacksaw blade to give it more gluing surface.

Don't know why it gave....

Well, is there a way to make a new limb and salvage this bow?

Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
kennym
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Hey Dor, hate that for you.

It is really hard to say what caused it, once the delam starts, there are a lot of things that happen that might have held forever til the stresses get changed by the thing that started the prob showed up. Hope that made sense!

To me it looks like the glass started coming loose at the tip and then tore the wood lams toward the riser.

Can't really say tho.

As far as making another limb and putting it on this bow, there were some guys at one time doing a half form and doing one limb at a time on one pieces, but I never tried it.

How many lams in there between the glass?

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Stay sharp, Kenny.

https://www.kennysarchery.com/

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arachnid
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Kenny, I had 2 lams- one parallel and one tapered. Does the number of lams really matter?

I took another look at the fades, and I noticed something on the lower fade (the one that didn`t break). Eventhough I had a pretty good glue line, once I bend the limb, it the lams rise. So something wasn`t going well...

That`s the lower fade when the limb is not bent
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That`s the fade when the the limb is bent. | gap appears between the powerlam and the core lam
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Don`t know if that caused the bow to fail or if it`s a result of the bow faliure...

Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
arachnid
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Can the reason be a too short fade-out?
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mwosborn
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Sorry to see that! Gaps between lams are not good. What kind of epoxy? Did you use a hose on your form?

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Enjoy the hunt! - Mitch

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Shredd
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As a general rule I think the the fade should be about 1/16" at 1" from the end...

How many pounds did you air the hose up to?? I am not a big fan of going over 40 lbs... Did you have enough resin on there and get plenty of squeeze out??
The time you waste fixing that one, you could build a new one... Maybe give it to a guy with one arm... [Smile]

I know it did not fail there, But IMHO I would stay away from glue joints in the fades... I like a solid piece of wood there... It is a very high stress area...

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Stagmitis
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It looks like you may have issues with your form and clamping pressures. I see another gap up the Belly ramp... Did you make the Lams yourself, if so what grit paper..Did you use compressed air or a brass brush to clean the lams well after using a hacksaw blade? Check for moisture in the wood? Did you use smooth-on?

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Stagmitis

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arachnid
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quote:
Originally posted by Stagmitis:
It looks like you may have issues with your form and clamping pressures. I see another gap up the Belly ramp... Did you make the Lams yourself, if so what grit paper..Did you use compressed air or a brass brush to clean the lams well after using a hacksaw blade? Check for moisture in the wood? Did you use smooth-on?

I don`t have a air hose, I use clamps. I make dry runs and check the glue lines (especially the fades) before I glue it up.
I make the lams myself with an attachment to my oscillating spindle sander, using an 80 grit sanding sleeve (I can`t find a lower grit). After I use the hacksaw blade I sand and clean the lams so theres no chips and dust.
I use smooth on.

A german guy on facebook (bowyer`s corner group) said the problem was my fade outs being too short. Possible?

Posts: 210 | From: Israel | Registered: Jul 2016  |  IP: Logged | Report this post to a Moderator
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