Where do they break?

[lostarrow]

I have to admit total ignorance here - I thought positive tiller was used in order to make both limbs appear equal at full draw despite the bow not actually being held and shot dead center... Is that wrong?  Surely the goal isn't to have the bottom limb appear stronger at full draw is it? 

With only 1/4" positive tiller seeming to be the norm, is that enough to cause the top limb to fail completely?

Edit:  Didn't mean to call you elitist - that came out wrong.  I just felt the comment about only newbies using boards seemed a bit out of order.  I actually think staves are easier to work, as I can imagine it's bloody awkward tillering a long flat plank.

 I find board bows much easier and quicker to build. Almost cookie cutter. The tiller is exceptionally easy to judge when you look at a straight line . The layout is all done with a straight edge. Waste removal is done with a bandsaw in a mater of minutes , and after a bit of cleanup to the sawcuts, your bow is nearly tillered if your design was good in the first place.   It almost makes you feel a little dirty like you're cheating somehow

 As for this thread , I'm on both sides of the argument here I guess.   Wood from right at the stump is far more dense than even 2' up . After  you get past the buttresses it all evens out (or not. It's a tree. It's organic ,and it follows it's own genetic code for survival, and is primarily influenced by it's environment) . It builds up extra cells around spots that need reinforcing , like a branch or knot. Wider rings don't always mean weaker wood. 
  Having said that ,I would think the reason for any breakage( other than damage or abuse) , would be an overlooked design/tillering flaw  . It may not present itself in the first 300 shots, but a change in humidity , shooting style , etc.  could be the start of one tiny little change ,which will eventually  spiral exponentially to become a failure. Not always that it was tillered poorly , because it may have been tillered perfectly for the characteristics of the wood at the time. But I think all would agree , the piece of wood is not the same as it was when you cut the tree, or when you dried it ,or when you roughed it out , or when you made a bow.
   My suspicion would be that most in Dell's  shooting circle of friends would be shooting longbows(?) traditionally made with a positive tiller(?)   Common thinking and tradition dictates putting the stronger limb on the bottom. Maybe it's time to revisit this "Theory ". I know I've  decreased to 1/16 - 1/8" max, and am still not entirely convinced of  the merits, so I'm going with Marc and PD on the fact that it should be balanced first and foremost.
   

[WillS]

Thanks Mike - makes a lot of sense!  I'll confess, positive tiller is not something I've ever thought about.  I don't think I've made enough bows yet to add that to the equation.  If there are no hinges or stiff spots I'm happy - but then my bows seem to take a lot of set, so perhaps that's why?  Dunno.

[Dances with squirrels]

Incorrect tiller relevant to the archer's holds on bow and string should at least bear scrutiny here. That's also why bows tip in the hand at full draw. Tillering, training, and timing the bow limbs to bend in harmony on the tillering tree while drawn from the center of the handle when it will never be shot that way is a bad idea, IMO. Then when it IS shot, the top limb, which many make weaker by default regardless of what the bow needs, realizes more strain than it was trained to deal with. I would also be interested to know how many of our broken bows are symmetrical vs. asymmetrical in design... since symmetrical bows are pulled farther above center and require a greater shift during the draw between the static balance and dynamic full draw balance points.. I'll bet it's a combination of things.

I've had one bow break on me when drawn by hand, and it was an arborvitae shrub I cut in the yard.... not exactly what most bowyers would deem bow wood :^)

Two others, osage selfbows let go at major knots, one a hole through the upper limb broke when I let someone else draw her on a winter day that was very cold... single digits... it just went "tick" and lifted a splinter at the edge of the knot hole.... but that's it in 15 years of selfbow, backed bow, and composite bow making :^)

[Jodocus]

I know I put more strain in the top limb while stringing, cause I grip it below the tip.

[half eye]

Hey Dell,
      Being as how I make little, short elfin bows maybe don't have any say in this discussion. I tiller my bows by hand and feel, not on a tiller tree. had them called everything from polished turds to well.....you get the idea. Anyway, all the bows are shot without a designated "top" limb, and are expected to produce the same profile regardless of which end is up, also as others have said the bow should not rock in the hand, just a smooth even draw to loose. Doesn't make any difference if it's lumber I milled, or a stave I cut, all the same to me.
      I've made a few that were NOT even in their bend and shot them both ways (up and down) to see what the bow had to say about it, and they seemed to shoot better with the stiffer of the two limbs upward.....but that experience is very limited so may not be worth much.

Sorry for the limited input but that's my experience, and the advantage to the even bend (in my opinion) is that you can "feel" what's going on with the bow all the way from start to full draw.
rich

[Mo_coon-catcher]

So far my failures have been glue releasing the sinew from the back and lower limbs. The glue failure was because I used a penetrating oil finish without thinking. One was a black locust molle that had a slight hing that got worse, so I quit shooting it when it started fretting. The other that exploded was a white ash molle that had a knot on the back. I had shot it a few hundred times, then when I showed it to someone it decided to go and blew apart into 3 chunks, with the break starting at the knot. I'm thinking it held up for a while because I had made and shot it in the early fall when it was still humid. Then it broke in the winter after I hadn't shot it for a few weeks and it had been very dry in the room.

Kyle