bend test

[stuckinthemud]

So, I am building a billet bow out of a pair of very characterful billets, before I commit to splicing them I am roughing them out and bend-testing them.  My hypothetical question is this, suppose each billet bends, for argument's sake to 25" at 25 lbs, would that be a 50lb bow - 2 times 25??

[Bob Barnes]

seems like the opposite would be true...?  If you break a stick in two, it takes twice as much to break each half...?   

[goomba]

I don't think so, if' that were the case, let's say one limb pulled 25# at 25" and the other
pulled 15 # at 25 , that would give you a 40# bow.

I could be wrong though.

[DC]

I think so. I've been meaning to test it and never got it done. You can do do it for us.

[Bayou Ben]

In theory each limb holds half the draw weight (symmetrical bow with even tiller, held and pulled from the center).  It would get you in the ball park.

I would like to see how you plan to conduct this experiment. You would have to pull this 25 lbs from the same direction as if it were drawn by hand 25".   

[goomba]

I would think a bow is only as strong as
its weakest limb. If one limb pulls 25# at 25"
and the other pulls 22# at 25" you end up with
a 22# bow at 25". The stronger limb bending less.

[stuckinthemud]

Fascinating isn't it  when I posted the question I was working the limb in my afternoon break and a long way from a bow, just wondered if anybody knew; I'll strap a few bows to my bench and put a scales on each limb as soon as I get chance, I'll report back

[DC]

I would think a bow is only as strong as
its weakest limb. If one limb pulls 25# at 25"
and the other pulls 22# at 25" you end up with
a 22# bow at 25". The stronger limb bending less.

The weak limb would bend more and the strong limb would bend less. They have to reach equilibrium because they are tied together. I'm assuming the bow would be free to rock.So if the weak one  would bend as if it went to 26" and the strong only went to what would be 24" I'm thinking you would get approx 23.5 per limb which would be 47#

[SLIMBOB]

If the stronger limb bent less, then the weaker limb bent farther to get to your draw length, or so I would argue.  So the weaker limb would be drawn farther than intended and the stronger limb drawn shorter.  The math is more than I am capable of doing, but practically, the draw weight I would think, would be somewhere between the target weight of each limb.  I think.
Cross posted with DC, but it looks like we agree.

[DC]

That's what I was trying to say

[Badger]

  It has more to do with string angle than the amount of effort it takes to bend the bow. Your length would have to be set up at exactly 1/2 and you would have to have exactly the same string angle you would have on the finished bow to have any accuracy at all.

[goomba]

If each limb pulls 25# at 25" you end up
with a bow that pulls 25# at 25"... correct?

[DC]

Nope, 50#

[goomba]

Ok I got it.

[Bayou Ben]

Yeah you can’t just hang 25 lbs from the tip and compare it to another bow. 
Like Badger mentions, it would have to be setup exactly like you would have the bow on your tiller tree.  The only way I can see it done is clamp the billet on your tree cradle, setup a channel where your pulley is only allowed to pull vertical, and pull out to 25” like it was a complete bow. That would put the angle the same