Limb timing.

[Buemaker]

Some discussions about this on another site. This is what was posted. Any thoughts on this?



Is Limb Timing an Issue?
« on: Today at 10:02:21 am »
People were talking about limb timing on a recent thread.
I find it hard to see how the limbs can return at different times, after all the limb tips are connected by the string!
They are balanced at brace, and (unless the grip is somehow clamped in an unbalanced position) the force is in balance at every point from brace to full draw, and thus presumably during the return as the arrow is loosed.
The only imbalance I can see is if someone is string walking (a hideous practice for a wooden bow)

They are not "individual" limbs, the whole bow is effectively one continuous spring. Even a very asymmetric bow like a Yumi remains in balance throughout the draw.
Is there any video evidence of limbs returning out of synch'? I can see it happening with a compound (spits on floor) if the cams don't match.
Anyone got any explanation, comments thoughts?
I'm happy to be shown to be wrong and have my understanding (or lack of it) enhanced.

[Longcruise]

Roy has covered a lot on limb timing here and I'm definitely a "believer".

I started paying close attention when I saw a series of high speed photos of a bow part way through From release to brace on the PowWow (with an arrow).  I can't say exactly where in the forward travel the arrow/string was but in this photo one limb was a blur and the other appeared to be practically standing still.

Apparently that didn't arouse any interest amongst the OP and topic followers because nobody but myself addressed the oddity.  I recall posting "what's going on with that upper limb".  Never saw any follow-up comments but to me it was obviously a matter of limb timing.

[Kirkll]

A better description would be "Limb Balance" rather than "limb timing", and very few bowyers using glass and carbon backing pay much attention to limb balance because their limbs are typically coming out if the same form, and are typically pretty darn close to the same by the time they get the tiller adjusted.

 A bow that is out of balance has the limbs bending differently from top limb to bottom limb caused by a wedge shifting or not using identical core laminations. Or it is way out of tiller. it's more commonly seen in one piece bows than TD's. To check this you can "Map" your limbs by just tracinging the limb shape on butcher paper, then flipping the bow over 180 degrees. A balanced set of limbs should be the same shape at brace height both top and bottom limb.

For example.... Some bows have a slight buzz to them without string silencers that can typically be quieted down by adjusting brace height. but if you raise the brace height to high, you are killing your performance.

Often times a slight buzz at optimum brace height can be eliminated by balancing the limbs by just sanding glass and tinkering with the tiller a bit.  It can end up positive or negative tiller measurement 1/8"  too to get it balanced perfectly.  Most bowyers don't mess with it though...


BTW.... a bow that has a stronger limb top or bottom will definitely have a timing issue. the stronger limb will return to brace height faster than the weaker limb with less limb travel. Basic physics....


Kirk

[Even]

I've always found this very interesting in regards to the Japanese Yumi mentioned above.   Building those has to be interesting, with one limb way longer than the other.   Yet they work extremely well.

 It must take some very interesting balancing of length versus strength in the limbs to make it drive equally. 

OR, if you are just driving the arrow from one point on the string, does it really matter?   Do you just tune the limbs for feel/vibration, and let the limbs sort it out?   

Its interesting, and I imagine it has a LOT to do with a particular bow's apparent "smoothness", between designs.

[Stagmitis]

Bur I’m with you- the string is connected to both limbs- I build asymmetrical limbs and went crazy trying to figure out the difference between what the top limb and lower limb should scale at in a horizontal plane- maybe I do what Roy and bowjunkie have figured out on their tiller tree- I know exactly how my hill bows need to be held exerting pressure into the grip. I look for the top limb and bottom limb stopping at the identical vertical plane- watch videos of guys shooting their bows. Sometimes the top limb tips forward or the bottom limb kicks out- when my bows are balanced both limbs stop together on a “vertical” plane. Two possibilities : either the archer places the grip pressure where it needs to be or they “heel” too much or high wrist too much . If they hold it correctly then it’s a tiller issue from the bowyer

[Stagmitis]

Just one thing to add- I balance the tiller as I shoot the bow to get the vertical stop- maybe I’ll try JunkiRoys tiller tree in the future:)

[Stagmitis]

Old age- it’s a tiller issue if they don’t stop dead nuts on a verticle plane:)

[Crooked Stic]

What if you had an ILF RISER and put a 35 LB. limb on one and 40 on the other and bottom them out timing may be an issue------

[buckeyebowhunter]

Has always seemed to me that adjusting the nock point, and like Kirk said, the brace height usually sorts out any tiller issue. I've shot bows with positive and even tiller and notice no difference once my nock point is adjusted. That being said every bow I've ever shot seems quieter and more stable shooting split finger, but I prefer 3 under.

[Kirkll]

What if you had an ILF RISER and put a 35 LB. limb on one and 40 on the other and bottom them out timing may be an issue------

Why would anyone do that?

[Stagmitis]

Buckeye, because if you Need an excessively high nock point to correct the issue your arrow nosedives robbing trajectory- in reverse the the arrow does the same thing by ticking the shelf on the way out

[buckeyebowhunter]

I understand, although in my experience I've never had to use an excessively high or low nock point to correct any issues, if anything I'd say that most of my bows look like they have the nock point too low. But for whatever reason 99/100 , times when I bare shaft I get some nock high. Doesn't seem to effect anything once feathers are on the arrow.

[Kirkll]

I understand, although in my experience I've never had to use an excessively high or low nock point to correct any issues, if anything I'd say that most of my bows look like they have the nock point too low. But for whatever reason 99/100 , times when I bare shaft I get some nock high. Doesn't seem to effect anything once feathers are on the arrow.

Sounds like your arrow is most likely hitting the rest and you are getting a false high nock reading to me…. But…. Bare shaft tuning is highly over rated and can be frustrating if you haven’t taken the time to spine match your arrows. Some carbon shafts are incredibly different just rotating them 90 degrees…. 

[buckeyebowhunter]

Agreed with ya there Kirk, I just use bare shaft to get into the ball park.

I think you're right, I think I do get some bounce of the shelf, but the strange thing is that on every bow I have ever shot I get that nock high. It's infuriating. Even with an elevated rest I've never been able to completely eliminate it. I think it has to be some sort of quirk in my form. My accuracy has never really suffered from it so I basically just ignore it anymore.

[Longcruise]

Might be your grip on the string.  I've observed some shooters torqueing their grip enough to bow the arrow at full draw.

[buckeyebowhunter]

I shoot 3 under.

[Stagmitis]

Buckeye, slight nock high with Bs is normal.

[Kirkll]

I don’t think I’d get all bogged down with it myself… I think I’d be more inclined to try some different type fletching and orientation. Sometimes going to a low profile feather and rotating them with the cock feather in can make a world of difference.

Set up a video camera behind you and watch your arrow flight. Try different spine arrows and different types of fletching until you get a good recovery and decent flight.

I went from a 4” parabolic to a 3” LP shield cut feather and got much better clearance and arrow flight.    Food for thought.