Where do they break?

[Del the cat]

Nothing inconsistent in what I said Del. From my experience the trunk wood is the strongest part of the tree vs it's upper section. You build a bow as it "stands in the tree" (and most of us do whether we realize it or not) and more than not the upper limb will be the one most likely to break. Not a theory, or an assertion, just common sense..............Art

You obviously haven't read what you actually wrote....

Trunk end of the tree will be denser, stronger and have fewer defects. As you move up the tree the reverse is true.

Can't you see the inconsistency created by the second sentence?


And as for the 'most of us do it, whether we realize it or not' is arrant nonsense. I quite often will reverse a bow in the process of making it, or even after it's virtually finished.  Oh I get it! You'll now say I'm switching it to trunk end down subcosciously and thus proving your point .
Tell you what, You sit and have a cup of coffee, I'll do your arguing for you......

ok... never mind... I can't be bothered.

I wish people would be more careful with their words and and manage to have a concise logical discussion, asking and answering points in an ordered manner.
Just ain't going to happen.

The interesting thing for me in this thread is how a few people have experssed doubt about the received wisdom of positive tiller. I've always been sceptical myself and only started using it when I had a lower limb go weak on an Ash flatbow.
Del

[mikekeswick]

Positive tiller is essential in my eyes. How much is the point. The lower limb needs to be stronger to stand upto the strains of shooting. It's simple physics 
If you make a bow with exactly the same strength limbs when you come to shoot it that lower WILL come round more.
These things aren't set in stone measurement-wise but the idea should be!
The amount of positive tiller needed is linked to how you shoot/hold the bow. Less is needed with split finger and craddling the bow between thumb and 1st finger. People who use the heel of their hand against the grip will need more and those who shoot 3 fingers under need yet more.
My guess for limbs breaking is uneven forces at full draw. Afterall what else could it be? Unless somebody is going round and putting nicks in the backs of all these upper limbs!

[Del the cat]

Positive tiller is essential in my eyes. How much is the point ...

Exactly, I just wonder if maybe we over do it sometimes to the detriment of durability?
Del

[SLIMBOB]

That's kinda where I come down Del.  As has been said, I will shoot for a bit of positive tiller, I also will put the less sound limb on top.  That seems to me to at least offer a reasonable explanation.  My question now is, is this the right call?  Mark suggested that the top limb is more strained.  At least anecdotally, folks are putting the weak limbs on top and then shooting for positive tiller, then the top limb is more stressed, and top limbs break more often.  There you go.

[artcher1]

Wow! First time I've been called an elitist. Man, I apologize to you all if I came across like that.

Del, I take your point. I could have been more concise in my meaning. Looking forward to see where this discussion leads. Best of luck guys...........Art

[PEARL DRUMS]

If your breaking enough bows to cause a personal epidemic, you have bigger fish to fry.

[WillS]

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.

[adb]

The comment about newbies using boards IS out of order. Smacks of ignorance and arrogance. But, that's the subject for a different thread.

[SLIMBOB]

True PD, but that posts title would be "Why Do They All Break" and the replies could be even more colorful and entertaining than those offered here.

[artcher1]

The comment about newbies using boards IS out of order. Smacks of ignorance and arrogance. But, that's the subject for a different thread.

Man, my reply sure doesn't read that way to me. Sorry if you're offended by it. Surely I'm ignorant on many things, but never arrogant I think. Again, my apology...........Art

[Marc St Louis]

You should never tiller just to have a positive tiller when working with wood.  You should tiller so the bow has a smooth draw without any pivoting in the hand.  That is what will tell you if your limbs are balanced and stressed evenly not a positive tiller

[PEARL DRUMS]

You should never tiller just to have a positive tiller when working with wood.  You should tiller so the bow has a smooth draw without any pivoting in the hand.  That is what will tell you if your limbs are balanced and stressed evenly not a positive tiller

Marc it cant be that simple can it?.....

[mikekeswick]

For my bows at least I have to make the lower limb a little stronger or else the bow will pivot.
When you pull a bow with your fingers above measured center of the string you aren't pulling both limbs with an even force

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? 

That's where i'm coming from too.
No you want both limbs to be equally stressed at full draw. To do that you have to take into account the unequal forces being applied to the limbs during the draw.....making the limbs different strengths is how to achieve this. How much the lower limb is stiffer is the question. Setting out with a goal of making the bow have say 1/4inch positive tiller without regard to what happens along the way would not be a good idea. Watching how the wood is responding to what you are asking from it will tell you what you need to know.
Let look at this another way if you have two guys arm wrestling which one will win?

[artcher1]

You should never tiller just to have a positive tiller when working with wood.  You should tiller so the bow has a smooth draw without any pivoting in the hand.  That is what will tell you if your limbs are balanced and stressed evenly not a positive tiller

I would have to agree. That's how I determine my finished tiller. On average, mine turn out 1/16" positive tillered..........Art.

[adb]

The comment about newbies using boards IS out of order. Smacks of ignorance and arrogance. But, that's the subject for a different thread.

Man, my reply sure doesn't read that way to me. Sorry if you're offended by it. Surely I'm ignorant on many things, but never arrogant I think. Again, my apology...........Art

Apology accepted. I've been making bows for 10 years (the last 3 as my living), the majority of which are laminates made from dimensional lumber. I'm not a newbie, and they're not simple bows. I certainly make selfbows as well, but I don't limit myself. Blanket statements about boards being for newbies is an offense to some, as you've realised. It's certainly a good place for newbies to start, but not only that. But, like I said, apology accepted.