Bow exploded - Critiques please

[bubbles]

Hi there, had my first violent bow explosion today.  Trying to make a bow for my buddy with a long draw - 30 inches, and had the bow explode at 29.5. It was 68" ntn, 2" wide from the fades to 1" past mid limb were it tapered to 1/2" at the nock area. I had it braced at 5 1/2" and it had about 2" of string follow when it blew. I heat treated it (first) and backed after I had it bending 20"@ 1" brace, waited a week for re-hydration.     Maple board backed with linen canvas, the grain wasn't perfect, but it was pretty good, in fact the break happened where the grain was straightest. The stiff handle including fades was 10" long. I realized after I had roughed it out that I should have probably made it 2-4 inches longer for such a long draw. 

[Red Tailed Hawk]

Looks like both limbs right out of the fades could have been bending more. A liitle extra length would have helped. Sorry about your bow, now you get to have more fun trying again.

[Del the cat]

I mostly dissagree with Red Tailed Hawk, but I can see a tad more bend right out from the fade would help ... BUT
IMO the outer half of each limb isn't doing much work which is overstressing the inner 1/2 - 1/3
Did the limb have any thickness taper?
It's what I call a slightly 'square' tiller e.g As a vastly exagerated explanation of what I mean. Flat in the middle third, then a right angle bend and the last third of each limb coming straight back.
Obviously it's not that square, but if you hold  CD or something circular up the the picture you can see the tips are not working as hard.
Del

[Del the cat]

This pic illustrates what I mean...
Even if we allow for the stiff handle (2nd pic) and just look at the curve of the upper limb and fit an ellips it shows a bit too much bend near the centre and not much in the outer third.
... let's hear from everyone else.
Del

[bubbles]

Ahh,  I should start drawing ellipses on my tillering pics from now on.   

There was thickness taper about to the point that the width taper started taking over, but it may have been too slight.  The poundage was #45, I forgot to mention that.  I think I left the outer part of the limbs a little stiff as I didn't want the bow to stack when I got way out to 30", maybe I left them too stiff.
I was also going by the "tiller should agree with limb shape" in that I should have been putting most of my bend in the wider sections of limb that can handle it more. 

[bubby]

I think del nailed it, for a 30" draw go with an elb style, that's what i'd do, or a bendy eastern woodland, I just finished one from a hard maple BOARD and it would easy make 30", 59 1/4" ntn

[SLIMBOB]

I think everyone has a point here.  You could have made it longer, I would not have.  It could start working closer in to the fades AND the outer 1/3.  Most of your bend is in the middle with little happening elsewhere.  All of these would have relieved the stress midlimb where it broke.

[bubby]

I wouldn't have made it any longer, but i'd go elb style for that draw, bub

[Hrothgar]

I think I have to echo what Del said, something more needed to be bending. If your fades are 2" and mid limb has already tapered to 1", that's pretty drastic, even for a mollegabet design. I bet it would have blistered an  arrow.

[Squirrelslayer]

hmm the pic looking at the inside of the break looks similar to my hickory bow that broke at a chrysal. but what do i know. good luck on your next bow. SS

[Ifrit617]

I think everyone has a point here.  You could have made it longer, I would not have.  It could start working closer in to the fades AND the outer 1/3.  Most of your bend is in the middle with little happening elsewhere.  All of these would have relieved the stress midlimb where it broke.

+1

Jon

[bubbles]

I think I have to echo what Del said, something more needed to be bending. If your fades are 2" and mid limb has already tapered to 1", that's pretty drastic,

Sorry, let me clarify,  It was 2" wide from fades to past midlimb (sides parallel).  The width taper began 1" past midlimb, the to 1/2" at the tips.

[ionicmuffin]

i knew what you were saying bubbles, its a nice attempt. so tell me, what was the weight on this bad boy before it blew? i would always use a scale, granted the limbs were over-stressed, but the limbs could be pulling more than you wanted in the first place, so the may have exploded partly because of that! weighing helps you to avoid over-stressing past target weight. but of course if the bow was bending too much mid limb and not enough fades and tips it could have blown anyway. several factors can be critical in determining weather or not your bow will turn out or not.

[bubby]

that's all good muffin, don't know if he has a scale but sometimes ya just gotta make do with what ya got, not saying your wrong, heck all I still have for a scraper is a 6" lockback knife

[bubbles]

Are we talking a scale to measure poundage of the bow?  I used to use one and I didn't like it.  I just have a bag filled with weights that i fill to the desired poundage, with three caribiners that simulate fingers. I pull the bow with a tape measure hanging from the handle to get the draw at that poundage. Then I have an arrow with and elastic band that is my draw check and I shoot a video of me drawing the bow to that length.   This one was 45# @ 29.5 when it blew.  Never drew it past 45#