Physical balance

[DC]

I'm working on a Yew R/D. When I put it on the tree I have to put it an inch off center to get it to sit level. I'm not"too" concerned but it got me wondering if this will affect limb timing etc. I've double checked all the measurements and if anything the heavy end is the smallest. Is this physical imbalance going to affect the "dynamic balance"?

[RBLusthaus]

I am sure some others will chime in here, but I think the actual timing of the limbs is more important than the actual balance point of the entire bow - but that said - the balance point at the mid handle makes it easy to carry the bow (not tippy in the hand) and - although maybe not a direct correlation, but I think the physical balance point is a good indicator of the amount of mass on either side of the balance point (of course - definition of balance) and thus a good indicator of the limb timing you may expect to see.   On my tiller tree, the block that the  bow rests on, is radiused - so - only bows that are "balanced" will sit level on the tree when pulled - - this aids in my tillering -  as I am shooting for a bow that pulls even and sits level when pulled on my tree. 

Not sure I explained that well.  I hope you get my gist. 

Russ

[FilipT]

Interesting question. I think it has more to do with internal composition of the wood (coarser grain, knots), rather than actual dimensions. I have found also that almost perfectly symmetrical limbs don't necessary make bow be in balance on their supposed center mark.
My new hazel warbow is one of the examples. But I don't worry about it, its not even on tiller tree yet.

I made my new super reinforced tiller with double pulley system so that I pull the string 1" to the right of the center of the bow. Surprisingly that barely made hazel bow I made yesterday rocking on the tiller. That is also first bow on my new setup so I don't know how other hazel or future bows will behave.

[jaxenro]

Wet wood is heavier. Is it possible one end is drier than the other? Not sure how this could even happen but theoretically I suppose depending on how it was stored when drying it could

[Badger]

        I don't think it is possible to make two limbs not return at the same time. They are connected so always have exact same tension on them even if the tiller is way off. One limb may keep moving longer or go further past brace once it releases the arrow if the limbs are off.

[Dances with squirrels]

Badger, I disagree. Limbs of different strengths have the same tension on their tips at brace because they directly oppose one another in a straight line, but once we grab the handle and string, draw it, and load the limbs by hand from a third direction, the tensions measured between the string hand fulcrum and limbs tips differ relative to the degree of dynamic imbalance.

[DC]

Sorry guys, I didn't mean to start the "balance thing" again but it was an honest question

[PatM]

You could always add weights if you think things can be fine-tuned that way.

[Badger]

Badger, I disagree. Limbs of different strengths have the same tension on their tips at brace because they directly oppose one another in a straight line, but once we grab the handle and string, draw it, and load the limbs by hand from a third direction, the tensions measured between the string hand fulcrum and limbs tips differ relative to the degree of dynamic imbalance.

  I agree, but most of us tend to let go of the string when we shoot the arrow.

[mikekeswick]

If one limb is thicker than the other it will have a faster return time to brace. I know what you are saying Badger but just because the tips are essentially tied together they have to move together to some degree doesn't mean that they are moving in union. If one was thicker it would be 'pulling along' the thinner limb to a degree.
Think about tuning forks, why do they make different sounds? Different thicknesses produce the different notes/vibrations. Thicker vibrates faster. Same with bow limbs.

[Dances with squirrels]

"I agree but most of us tend to let go of the string when we shoot an arrow."

Of course. And loaded springs of different strengths tend to travel different distances in different amounts of time.

[Pappy]

I am in Steve's camp on this one.
 Pappy

[PEARL DRUMS]

When I start my initial tillering I always sit the bow on center and pull from center until the limbs are dead even (and heavy) and the bow sits perfectly still when drawn 12-15". Once I get it balanced I shift the bow to sit in the same place my hand will, that almost always makes my bottom limb tilt downward, so I start on that limb and balance it out again. I start out on center because its easier for the initial tiller. If it doesn't balance on your tree it cant balance in hand without you shifting your hand, and that's no good. It makes for a loud, inaccurate bow that thumps your hand.

[Tuomo]

Physical imbalance is not a problem.

Please see these two videos:
youtube.com/watch?v=oAXSMKogHgI
youtube.com/watch?v=8pYVmrWzTP8

As long as the nocking point is right, the bow is behaving well. The heavier limb tips are, the more handshock, as is well known. "Timing" is not a problem because there is no such a think like "limb timing" you could affect.

Please, test it - take any bow and grip it middle of the upper or lower limb, put a nocking point at right place (+10 mm of square, as usually) and shoot it. What happens? The bow and arrow are behaving well, the bow is fully shootable.

See this video (starting from 0:50 s.:
youtube.com/watch?v=ir5GKAQG14g

It is interesting to see yumi bow in slow motion, although you can not see the full bow. But you can see the same thing than you see from my videos. Although limbs are moving different distance and different speed, they are in unison - they stops at the same time.

One more thing - how would a bow shoot, which had one normal limb and one fully stiff limb, so one limbed bow? Please try, it is easy to test. How it differs from normal bow? What is efficiency of this kind of bow? If there is some differencies, is the reason limb mass or "limb timing"?

Tiller tree geometry is totally different thing. You have two contact points - hand pressure point at the handle and drawing point at the string. Using these, you will get what you see. But, the problem is that using symmetrical tillering tree geometry and these two points, the bow are tilting at the tillering tree, so you have to "read" the bending of the bow correctly.

[Marc St Louis]

I'm in Steve's camp as well.  The only possible way the limbs can be "out of time" is if their outer limb mass is grossly different and you would have to be a pretty poor bowyer for that.  Small changes in this mass-difference will not affect the way they return substantially, they will contribute to that hand-shock though