Laminated bow limb timing?

[longrifle]

Can anyone tell me clearly what is timing and how do I do it.  Thanks

[Brock]

that is a compound term...no such thing though some make limbs equal distance...and others make the bottom limb slightly shorter.

explain what you are talking about to make sure I am not just jumping to conclusions....put it in context for me.

[Crooked Stic]

I think what you are referring to is that when the string is dropped that both limbs get back to brace at the very same time. When this is accomplished it cuts down on vibration and more energy goes to the arrow.
The way you check it is pull the limbs thru the draw cycle and make sure they are bending the same every inch. This can be checked by tracing a profile of the bend at each in. then fold the tracing in the center and compare.Sand the glass in the strong parts and check again. Most times if the glass is consistant and you have a good grind job on your lams it wont be too bad. I am not sure how many guys actually check this unless they have unless they have above normal vibration.

[Sixby]

Ron its just as important in a stick bow as it is in a compound bow; Timing means that the limbs return at a rate that brings them to brace at exactly the same time; This eliminates a lot of vibration and lost energy as the arrow absorbs more of the energy from the string as it is being evenly applied  to the nock. It is getting the same power from each limb. Everything works in harmony. Some bowyers graph the bow limb out like Mike said.
After you have built a lot of bows and know your glass and stacks and tapers and the build of the bow you can pretty much tell simply by thumping the string and knowing what it sounds like when timed.
A lot depends on the accuracy of your grinds and stack , closeness of the strength of the lams ect. Once in a while you will get exact stack on each limb and for some weird reason the entire tiller will be off . If its too much I usually build another set of limbs. The only thing I have figured that could cause this is a weakness I did not detect in the materials somewhere; That bow would be hard to time as you would have to dress so much more weight off of one limb to get it into tiller that the weight alone would throw the timing off. However it can be done. Just does not look real great .

God Bless you all, Steve

[Brock]

Thanks for explanation Sixby...  never heard timing used in traditional bows.  Am very familiar with tiller on selfbows and figured the same type of process is used on glass backed as well to ensure they are bending evenly and where you want the working part of the limb.

Thanks for explanation.....only heard it referenced to having both wheels/cams of a compound rotating so they both come to the max weight and let-off at same time.

[Sixby]

Ron, You are most welcome,

it is something that is neglected [mostly due to just not understanding it] in a lot of trad circles but when you shoot a bow that is timed and tillered to perfection it is the smoothest bow you ever shot and if the entire design is good it is also extremely fast and quiet; It does take a bit of extra time and a bit of understanding of the process on the bowyers side to do it though. That is one thing that is really improving the quality of custom bows today , I believe.
God bless you, Steve

[Al Dean]

I would logically think that if you can bare shaft at 30+ yds your timing and tiller are excellent.  Of course my logic my be way off.

[Roy from Pa]

Can someone explain to me why a bow with a string tied on each end of it, pulled at the center from a stationary brace height, won't have the limbs return to the same brace height at the same time when the string is left go? You pull it with the string and the limbs bend so far together, you let go of the string and they return to their natural starting point every time.

[BenBow]

The only time the limbs will react the same is when the point of pressure on the bow riser and the string are both centered and since we physically can't do that without shooting through our hand we have to work with the way limbs bend to get them to react the same.
Unless the low spot of the grip is below center and the rest is at the center the string is never pulled from the center. This causes the limbs to bend differently and react differently. And as long as the pressure point on the riser is different than the pulling point on the string limbs have to be tuned to get the most out of a bow.

[Bowjunkie]

Roy, we don't pull them from the center, but regardless of where we pull them from, they will only return in unison if they're tillered to do so with the fulcum points that are used when actually shot. It's why you try to replicate your holds on the bow and string while placing it on the tillering tree.

There are even reasons besides poor tillering that can cause limbs to return out of sync.

Tillering it to completion on the tree by pulling from the handle center, but then shooting from 2" higher, because the handle center and shelf cannot be at the same place, will cause a bow's limbs to return at different times... or more precisely, differently than they did on the tree.

Altering the grip on the bow, pushing down on the heel of the hand for instance, will cause limbs to return differently... as will string walking, etc.

I often put my glass bows on my tillering tree to check their tiller just like I do wooden bows. Sometimes adjustments are needed.

As Sixby said, it's something that is often overlooked and/or misunderstood.

[Swissbow]

Because the arrow shelf is located above the center of the bow therefore the lower limb is longer than the upper one and must be slightly stronger to work in perfect synchrony. The difficult thing is that the lower limb, although stronger, should have the same mass as the upper one. If not, vibration can be caused during release.
If you're doing a good sanding job on the limbs, you're almost there. Sometimes all you need are a few strokes with the sanding paper at the  right spot to to make a good bow into a fine bow. But sometimes it takes a lot of experience and patience to get the job done...

----------
Andy

[BenBow]

X2

[longrifle]

Thanks for the replies guys, but I am still confused. If I build my Hill style longbows with the geographic center of the bow in the middle of my grip, and my bottom limb is 1 1/4'' shorter than my top limb, and my bottom limb stronger for a 1/4'' tiller than how can both limbs bend evenly throughout the draw and release? It would seem that in order to get both limbs bending evenly everything would have to be exactly the same length, and thickness. Right!!! or not.

[Roy from Pa]

I think yunzs all put too much thought into these stickbows:) If ya tiller both limbs for a smooth equal bend, then they are gonna shoot fine. Longer top limb, shorter bottom limb, equal limbs, pos tiller, negative tiller. Just like pulling a gum band between your fingers, it snaps back to where it started.

Show me data, show me diagrams, show me pictures, show me videos, then I might believe it.

[Brock]

i think I will stick with just making sure the limbs are in good tiller....I want to get simpler not more confusing.  

[jsweka]

Originally posted by Brock:
i think I will stick with just making sure the limbs are in good tiller....I want to get simpler not more confusing.    

Me too.

[Bowjunkie]

The theory may SOUND confusing (hence misunderstanding and bows, and bowyers, not realizing their potentials) but the PRACTICE of expert tillering is no more difficult to accomplish than anyhing less.

[Roy from Pa]

That's what I do, Jeff. And with a good tiller my bows shoot nice so in effect it may be limb timing I am achieving.

[Brock]

yeah but tillering is getting a smooth and balanced bend in the limbs....Sixby's explanation sounded like this is much more than just tillering.  It ensures the limbs go from full draw to brace height with the limb tips in mirrored positions through the stroke.  That is not tillering-- though good tillering may make timing an unintended byproduct....

I would like someone that has actually done it to let me know how you measure and then modify limbs for timing where they both move at same speed and arrive at same time at brace height?  High speed photography, intricate timing devices attached to limb tips on each end, etc?

[Bowjunkie]

Neither limbs, nor limb tips, need to be in mirrored positions to achieve pefect limb timing. In fact, in order that some bows be properly syncronized, the limbs must NOT be in mirrored positions. There are ways to evaluate without high tech imaging or timing sensors.