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Main Boards => The Bowyer's Bench => Topic started by: pditto613 on June 26, 2019, 05:37:51 PM

Title: Limb failure
Post by: pditto613 on June 26, 2019, 05:37:51 PM



This is a youth bow, first off the form.  48” ntn.   15# at 24”.     Since it was the first prototype I decided to over draw it to see what the tolerances were.   It was on the scale at the time.  The first two pictures are the break that happen on the scale.  The last pic is where I clamped the riser in my vise and forced it fail.  The limb broke at 28” of draw.   Should I be concerned with it breaking at 4” of over draw and the way it broke so clean.  The failure that I forced is more in line with what I have seen before, with the glass intact and the wood shearing. Not a break like the other one
Title: Re: Limb failure
Post by: pditto613 on June 26, 2019, 05:43:47 PM
Sorry, pics posted out of order. First and third are the same break.   Second is the failure I forced
Title: Re: Limb failure
Post by: Buemaker on June 26, 2019, 05:50:03 PM
If you go about one inch and two inches in from the tip of the fade out it looks far to thick I think.
Title: Re: Limb failure
Post by: Crooked Stic on June 26, 2019, 08:23:37 PM
Yeah fades look thick. 48 seems short for even 24 in. unless the riser is short.
Title: Re: Limb failure
Post by: Mad Max on June 26, 2019, 10:43:49 PM
This 50" one can be drawn to 30"
Fades need to be longer.
Who's design ?
any pictures braced, unbraced?
http://peteward.com/2007%20new%20pages/test.sheepeater.html
Title: Re: Limb failure
Post by: Crooked Stic on June 27, 2019, 06:51:18 AM
Design csn determine how far a bow can be drawn. This one seems to have a problem in design or build.
Title: Re: Limb failure
Post by: pditto613 on June 27, 2019, 08:52:15 AM
The bow is my design.  Youth longbow, shallow r/d, 12” riser.   Every consideration is given to make lay up and build simple and quick.   The goal is to keep labor low to get a sale price low as possible. But not at the cost of safety.   I would like to have seen it draw further before failure, but for a bow this short 28” isn’t bad.   Thinning and extending the fades is good advice.  But what really concerns me is how clean that one break is.  Has anyone seen that before? Cause?
Title: Re: Limb failure
Post by: Mad Max on June 27, 2019, 09:23:20 AM
See how thin the fades are
https://tradtalk.com/forums/showthread.php?t=43658
Title: Re: Limb failure
Post by: Crooked Stic on June 27, 2019, 10:15:18 AM
Most times .250 2 in. back will work and thinner dont hurt.
Title: Re: Limb failure
Post by: jess stuart on June 27, 2019, 11:30:30 AM
I would agree fades need to be thinner.  I always try to be less tha .250 three inches in.  Thats hard to do on a 12" riser.  There is more room than you think, the kids have small hands.  I struggle with not making the grip area to large thus robbing from the fade out area. 
If the fades are to thick it concentrates all the pressure in a small area, a recipe for failure.  Believe me I have had the same thing happen.  It is probably impossible to make your fades to thin and flexible.  At least that is my thinking
Title: Re: Limb failure
Post by: bigbob2 on June 27, 2019, 08:30:33 PM
my first FhLB did almost the same clean break across glass and stack near fades. I believe it had a similar problem, fades just a little too abrupt away from end. Made the second with more progressive taper and has had hundreds of shots with zero problems. It is a very high stress area at end of fades and and anomaly will soon show up.
Title: Re: Limb failure
Post by: Forwardhandle on June 29, 2019, 06:12:47 AM
I had one limb failure and it made me rethink my riser tapers I now keep a smooth taper back in the riser to the point where the lams and glass keep it from flexing seems to work good for me I think by doing the thinner longer tapers it probably acts performance wise as a shorter riser giving a little bit more working limb all guessing on my part !

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Title: Re: Limb failure
Post by: Crooked Stic on June 29, 2019, 09:17:07 AM
Although Ihave a top name longbow here 58 in. With a max draw of 33 in. And the fades are not thin at all. But riser is short.

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Title: Re: Limb failure
Post by: Forwardhandle on June 29, 2019, 09:26:20 AM
Its weird Mike some designs work with almost non smallish fades & some will blow I think carbon limbed ones help to ,maybe thicker PL on some to ,who knows but I know Kennys FH likes the elongated fades , interesting topic !
Title: Re: Limb failure
Post by: Roy from Pa on June 29, 2019, 09:59:48 AM
Quote
Although Ihave a top name lingbow here 58 in.

Who makes the lingbow?

Never heard of it.
Title: Re: Limb failure
Post by: Forwardhandle on June 29, 2019, 11:52:03 AM
Mike you got a pic of the lingbow fades ? :biglaugh:
Title: Re: Limb failure
Post by: kennym on June 29, 2019, 01:13:46 PM
Quote from: Roy from Pa on June 29, 2019, 09:59:48 AM
Quote
Although Ihave a top name lingbow here 58 in.

Who makes the lingbow?

Never heard of it.

Prob from China.  Hop Sing make lingbow … :)
Title: Re: Limb failure
Post by: Forwardhandle on June 29, 2019, 01:25:01 PM
 :goldtooth:
Title: Re: Limb failure
Post by: Mad Max on June 29, 2019, 01:27:50 PM
Limb taper, width and thickness have a lot to do with how much the fades need to work.
Title: Re: Limb failure
Post by: kennym on June 29, 2019, 01:47:32 PM
Quote from: Mad Max on June 29, 2019, 01:27:50 PM
Limb taper, width and thickness have a lot to do with how much the fades need to work.

Yup and I’d add length to that list
Title: Re: Limb failure
Post by: Roy from Pa on June 29, 2019, 03:08:30 PM
Hop Sing Archery CEO....

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Title: Re: Limb failure
Post by: Forwardhandle on June 29, 2019, 04:24:14 PM
Length & taper & design all play a huge roll on the lowers I suspect ,wedged tips also ,in my case wedged tips short working limb .001 taper & long draw force me to go long fades all though the power lam part of the super lam exstends the fades aprox 3" but a higher taper rate & PL you could probably get away with abbreviated fades !
Title: Re: Limb failure
Post by: Crooked Stic on June 29, 2019, 06:32:14 PM
Okay that does I am getting a stylus for my new phone cause my fingers are too fat. Bunch of Smarty pants guys on here   :biglaugh:
Title: Re: Limb failure
Post by: Roy from Pa on June 29, 2019, 07:50:06 PM
Like who?

 :wavey:
Title: Re: Limb failure
Post by: Crooked Stic on June 29, 2019, 08:18:51 PM
Roy you da main one. Lol

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