Limb Timing

[mwosborn]

....exact rules of physics dont really apply ....

  "Rules of physics always apply."     I know what you are saying - I just couldn't resist replying as my college physics professor would say!   

[Dances with squirrels]

Bingo George.

Marc you said, "Making a bow, to me, is getting the limbs balanced with uniform tips so that they are very close to the same and bending smoothly so that it neither rocks back or forth when drawn.  I call that proper tillering of a bow.  Some may just call it timing a bow."

I'm partly of the same thought process, but don't need the tips to be uniform, the same distance in front of or behind the handle, coming down the same distance on the tree, etc. One can be straight and the other reflexed, or whatever. It can be a really weird, unique thing, and can still be timed/tillerd/sync'd correctly to the archer's holds. It may look bizarre to many folks at brace, but I don't much care so long as the limbs' relative strength allow the arrow nock to come straight back and leave straight ahead... she's good.... she'll feel like an equally well tillered/timed straight bow... and she's gonna do exactly what she was meant to do... with the good attributes we claim to value... and in the end, the braced profile simply is what it is.

I used to heat straighten stuff more than I do now. I understand now that it was more just to please my eye cuz like most folks, I grew accustomed to symmetry, now I usually only heat and bend if I have to.

I concur though that when making bows for the 'uninformed' I will do more heat correcting than I would for myself.

To me, 'correct tillering' encompasses much... and high on the list of importance are limbs that are synchronized such that neither overpowers the other when drawn as the archer will. Due to their inherent irregularities, in order for wooden bows, especially selfbows, to accomplish this, for any given archer's holds, their braced profiles may vary considerably. Many folks however, use the same predetermined brace height measurements as their beacon and ultimate goal throughout the process on ALL their bows. This is a mistake IMO.

Dragonman, I'm not trying to apply direct laws of physics to my bows, at least not with blinders on... quite the contrary. I do whatever needs done to get the bow to do best what it is meant to do... shoot an arrow straight away with purpose... not porpoise :^) while treating itself, the archer, and the arrow most kindly. Two bows that LOOK the same unstrung, may act and look different later in the draw due to invisible inherent differences. Tillering/synchronizing the limbs the way I do makes neither more difficult, may make them look different at brace and/or full draw, yet function and feel the same.

Conversely, it could be viewed that those who are 'trying to apply direct laws of physics' to their bows and tillering are those who tiller to specific predetermined brace height measurements and 'expect' their wooden bows to behave a certain way... which they always don't... those who do what they're told whether best for them and their own bows or not.

Talk about making assumptions :^)

If someone looks at one of my bows and tells me the "tiller's off" because it's negatively tillered, or not what they'd otherwise 'expect'... "I need all my bows tillered 1/4" positive"... or some such... I'm going to have to assume they're making too many assumptions :^)

[dragonman]

DWs. I  agree with what you say....I think it is just the word timing that confused me

mwosborn.....I agree with you too,......rules of physics do always apply......but in nature there is no symetry untill you get down towards a molecular level, a bow may appear to be unbalanced,  but stilll be perfect, like a flower that isnt symetricaly perfect, but still created out of perect underlying symetry...so is still a perfect expression of creative force.....a like to see bows like this.....nothing is perfectly in balance in this world....or else it would cease to exist....not to say we shouldnt try to acheive it

[4dog]

dang...yall think too much...scrape scrape...bend bend....lol

[George Tsoukalas]

One last thing...my last osage bow with the different limb entry points does not have a brace or full draw tiller pleasing to the eye but it is well tillered.
Jawge

[Marc St Louis]

DWS
Actually you only think you are in partial agreement.  You were assuming that I meant that the tips were bending uniformly to the same point but that is not what I meant, possibly if you re-read what I wrote you will see this.  What I meant was that the tips need to be uniform in mass/size.  Unbalanced tip mass contribute to hand-shock as does the tiller.  Now if you really want to be able to tell if your bow is well tillered/"timed" try shooting 4 or 5 GPP arrows out of her.  She'll let you know quickly if you've done a good job or not

P.S. You may like symmetry more than you think you do.

[PatM]

Or actually don't hold onto the bow at all on release. The distance the bow travels tells you how much hand shock you actually cope with and call "dead in the hand".
 Whether the bow leaps strait forward or cartwheels end over end will tell you something as well.

[Dances with squirrels]

Marc, ok, gotcha.

I really need to get out there and do some more spraying. Ain't gettin no bows made in here :^)

[Marc St Louis]

Please, see this video:

http://www.youtube.com/watch?v=8pYVmrWzTP8

Very unbalanced bow, and 1500 grains weight in upper limb. As you can see, limbs are "timed", of course, but the bow is rotating in my hand. Same is happening if you cut the string but more pronounced.

There is videos where the weight is in lower limb and with no weight.

Very interesting video.  I can almost swear I see the lower limb reach brace a split second before the top limb

[Tuomo]

Who remember this one:

http://www.youtube.com/watch?v=GuvGkApgsm4

I will get the high speed camera for one week again, so I can film, what is happening when I dry release & not gripping a very unbalanced bow, or bow with different weight limbs. The camera is real high speed camera, so all the phenomena you see will be true.

So, what do you think, will happen? Will the bow jump just forward, regardless of the tiller, like the in the video here? Or, if limb timing is different, will the bow rotate in air (it should)? Ok, you do not need a high speed camera to see that, but hopefully there is something else to see with high speed camera.  If you have ideas, how to film tiller/limb timing issues, please tell!

[Tuomo]

Marc - I can analyze the full resolution video to see, if that is true. Lets suppose, that the bow is in brace, when the string is straight - which means, that neither limb can move forward...

How do you define "brace" because the bow is rotating? The lighter limb of the bow is moving faster but still the both limbs are at brace same time.

[Pappy]

Still at it I see. Interesting discussion for sure ,but I do know one thing,I ant dry firing one or shooting one open handed to find out if it rotates on the ground on goes straight out in front of me.   If it happens to do just what is is supposed to,what ever that is you still are taking a good chance on having a broken bow,so whats the point.   I agree Jawges on a character bow it is all about the feel, I do heat/steam bend a lot to get the worst out on most bows but on some you can't get it all out and you have to go by the feel and a lot of looking.Then it is all about how it shoots/how it feels in the hand and how it feels when it hits home.
   Pappy

[Buckeye Guy]

Don't recall ever having a bow do any spinning when shot from an open hand
Unless you are talking the string following the arrow around ,non center shot bows will do that and typically hit your hand then bounce back the other way and the top limb will move forward more from being shot from above your hand ( since it is the pivot point )
Maybe I am just fortunate to get this timing thing right without even knowing it!
Have fun
Guy

[Marc St Louis]

Marc - I can analyze the full resolution video to see, if that is true. Lets suppose, that the bow is in brace, when the string is straight - which means, that neither limb can move forward...

How do you define "brace" because the bow is rotating? The lighter limb of the bow is moving faster but still the both limbs are at brace same time.

I guess it would be pretty difficult to tell when one tip gets to it's original resting place.  The archer is probably the only one that can tell and that would be by feel.

[Slackbunny]

Here's my take.

It all comes down to how much the string stretches throughout the process. If there is zero stretch, then the limbs are geometrically constrained and the limbs would be perfectly timed. This is because they would have no other option due to the string being of a specific and constant length. Given a consistent grip and finger positioning, they would need to arrive at the same corresponding points at the same times, every time. If the limbs are improperly tillered they will have different stress cycles, which may cause unwanted stress peaks at certain times, but the limbs will have perfect timing.

But if we have a dynamic string then that can change. Now one limb can gain on the other temporarily until the string reacts to equalize the situation. But this will only happen if one limb is stronger than the other, or if one limb has more mass to move than the other, both of which proper tiller and design should take care of.

In order to have perfect timing with a dynamic string you must have limbs that are balanced in both strength and mass. That doesn't mean that the mass or the strength are equal for both limbs, but that the strength/mass ratios are the same.
On a symetrical bow with relatively homogeneous characteristics, this kind of balance would show itself to us as a nice even bend across the entire length. But for asymetrical bows or character bows, a perfectly even bend isn't always ideal.

I'd guess that timing becomes less and less meaningful as we upgrade to strings with less and less stretch.

These are all just my intuitive thoughts based on what I know so feel free to comment or critique them.

Since we can't judge timing by eye very well, we focus on all the components that lead us to it that we can readily see and feel like proper tiller, and symmetry. I think we're all striving for the same final result, we're just looking at different related characteristics to get there.